m w 31 ET). m u&. Won ,' 1.1888“ Seismicity of the United States, 1568—1989 (Revised) By CARL W. STOVER andJERRY L. COFFMAN U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1527 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1993 U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Published in the Central Region, Denver, Colorado Manuscript approved for publication February 20, 1992 Edited by Richard W. Scott, Jr. Graphics prepared by Wayne Hawkins; extensive use made of author-drafied material Type composed by Shelly A. Fields Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Library of Congress Cataloging-in-Publication Data Stover, Carl W. Seismicity of the United States, 1568—1989 / by Carl W. Stover and Jerry L. Coffman. — Rev. p. cm. — (U.S. Geological Survey professional paper ; 1527) Includes bibliographical references. Supt. of Docs. no.: 119.16: P1527 1. Earthquakes—United States. I. Coffman, Jerry L. 11. Title. III. Series QE535.2.U6$77 1993 92—26509 55 1 .2’2’0973—dc20 CIP For sale by the Book and Open-File Report Sales U.S. Geological Survey Federal Center, Box 25286 Denver, CO 80225 CONTENTS Abstract ........................................................................................ 1 Seismicity maps ............................................................................. 4 Introduction ................................ 1 Damage summaries ....................................................................... 4 Acknowledgments 2 Explanation of tables ..................................... 5 Magnitudes ................................................ 2 Modified Mercalli intensity scale of 1931 .................................... 6 Intensity, felt area, and isoseismal maps .................................... 3 References cited ............................................................................. 14 STATE CHAPTERS Alabama .......................................................................................... 15 Nebraska ........................................................................................ 279 Alaska ...... 19 Nevada ................. 283 Arizona ........... 61 New Hampshire ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 301 Arkansas ......................................................................................... 65 New Jersey __________ 305 California... 71 New Mexico ................................................................................... 307 Colorado --------------------------------------------------------------- 187 New York ....................................................................................... 313 Connecticut. ......................................................... 193 North Carolina 321 Ddaware ----- 195 North Dakota ................................................................................. 325 Florida ----- 197 Ohio .................. 327 Georgia 199 Oklahoma ................................................................................ 333 Hawaii ..... 201 Ore on 337 ho ..... 215 g ............................................................................. Illinois 223 Pennsylvania 343 Indiana 231 Rhode Island .................................................................................. 345 Kansas ........ 235 :out: gaiohna .............................................................................. 347 out a ota ..................................... 355 5:312:33 :3; Tennessee ........................................... 357 Maine ................. 245 Texas ---------- 361 Massachusetts... 249 Utah ............................................................................................... 365 Michigan ............................. 253 Vermont .......................................................................................... 373 Minnesota ........................... 257 Virginia ----------- - 375 Mississippi.. 259 Washington ...... 379 Missouri ......................................................................... 261 West Virginia-u 391 Montana .......................................................................................... 267 Wyoming ---------------------------------------------------------------------------------------- 393 ILLUSTRATIONS FIGURE 1—2. Locations of magnitude 2 4.5 or damaging earthquakes in the conterminous: 1. Western United States, 1769—1989 .............................................................................................................................. 8 2. Eastern United States, 1568—1989 ............................................................................................................................... 9 3—6. Locations of earthquakes causing damage (MMI 2 VI) in: 3. The conterminous Western United States, 1769—1989 ............................................................................................... 10 4. The conterminous Eastern United States, 1568—1989 ............................................................................................... 11 5. Alaska, 1786—1989 .......................................................... 12 6. Hawaii, 1834—1989 ........................................................................................................................................................ 13 7—64. Isoseismal map for the: 7. Alabama earthquake of October 18, 1916 .................................................................................................................... 17 III CONTENTS Yakutat Bay, Alaska, earthquake of September 10, 1899 ........................................................................................... 51 Southeast Alaska earthquake of July 10, 1958 .......................... . 56 Prince William Sound, Alaska, earthquake of March 28, 1964 ..... 59 Sonora, Mexico, earthquake of May 3, 1887 ............................... 64 Arkansas earthquake of December 16, 1811 .................. 67 Fort Tejon, California, earthquake of January 9, 1857 ........ 103 Owens Valley, California, earthquake of March 26, 1872.... . 107 San Francisco, California, earthquake of April 18, 1906 ...................................... 119 Long Beach, California, earthquake of March 11, 1933 ........................................ 133 Kern County, California, earthquake of March 15, 1946 .................. 139 San Bemardino County, California, earthquake of April 10, 1947 ............................................................................ 140 Riverside County, California, earthquake of December 4, 1948 ................................................................................. 142 Kern County, California, earthquake of July 21, 1952 .................. 147 Borrego Mountain, California, earthquake of April 9, 1968 ....................................................................................... 155 San Fernando, California, earthquake of February 9, 1971 ....................................................................................... 160 Coalinga, California, earthquake of May 2, 1983 ......................................................... 174 Santa Cruz Mountains (Loma Prieta), California, earthquake of October 18, 1989 ................................................ 186 Colorado earthquake of November 8, 1882 .................................................................................................................. 189 Southwest Idaho earthquake of July 12, 1944 .............. 218 Borah Peak, Idaho, earthquake of October 28, 1983 .................................................................................................. 219 Southern Illinois earthquake of September 27, 1891 .................................................................................................. 226 Southern Illinois earthquake of April 9, 1917 ............... 227 Southern Illinois earthquake of November 9, 1968 .................................................................................................... 230 Wabash River valley, Indiana, earthquake of September 27, 1909 ............................................................................ 233 Northern Kentucky earthquake of July 27, 1980 .............................. 239 Southern Michigan earthquake of August 10, 1947 .................................................................................................... 255 Charleston, Missouri, earthquake of October 31, 1895 ............................................................................................... 263 Southeast Missouri earthquake of March 3, 1963 ............ 265 Gallatin County, Montana, earthquake of June 28, 1925.... .............. 271 Southwest Montana earthquake of November 23, 1947 .................... 273 Hebgen Lake, Montana, earthquake of August 18, 1959 275 Northwest Nebraska earthquake of March 28, 1964 ....... 281 Pleasant Valley, Nevada, earthquake of October 3, 1915 .......... 292 Cedar Mountain, Nevada, earthquake of December 21, 1932... 293 Fallon-Stillwater, Nevada, earthquake of July 6, 1954 .......... 296 Fallon-Stillwater, Nevada, earthquake of August 24, 1954 ........................ 297 Dixie Valley—Fairview Peak, Nevada, earthquake of December 16, 1954. 299 New Hampshire earthquake of December 20, 1940 ................ 303 New York City, New York, earthquake of August 10, 1884 315 Attica, New York, earthquake of August 12, 1929 .................. 317 Massena, New York, earthquake of September 5, 1944 .................... 318 Blue Mountain Lake, New York, earthquake of October 7, 1983 319 Waynesville, North Carolina, earthquake of February 21, 1916 ...... 323 Lima, Ohio, earthquake of September 19, 1884 ..... 329 Northeast Ohio earthquakes of January 31, 1986 . 331 El Reno, Oklahoma, earthquake of April 9, 1952 ............................................................ 335 Milton-Freewater, Oregon, earthquake of July 16, 1936 ................................................ 340 Charleston, South Carolina, earthquake of September 1, 1886 352 'Ilexas Panhandle earthquake of July 30, 1925 ............................................................................................................ 363 Valentine, Texas, earthquake of August 16, 1931 ....................................................................................................... 364 Kosmo (Hansel Valley), Utah, earthquake of March 12, 1934.. 369 Cache Valley, Utah, earthquake of August 30, 1962 ................................................................................................... 371 Giles County, Virginia, earthquake of May 31, 1897 .................................................................................................. 378 Central Washington earthquake of December 15, 1872 ...... 383 Northwest Washington earthquake of November 13, 1939 ........................................................................................ 386 Puget Sound, Washington, earthquake of April 13, 1949 ........................................................................................... 387 Eastern Wyoming earthquake of October 18, 1984 ..................................................................................................... 396 CONTENTS TABLES TABLE 1. Hypocenter and intensity references .. 2. Magnitude references ............................................ 3. Deaths from earthquakes in the United States .............................................................................................................................. 418 3 ..1;51..§22. : . ,. 1 / , . . , _ ._ . . _ . » ._ r ‘ x \ ‘ _ \ , . w a , ‘ . A ‘ ‘ V \ . L SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) By CARL W. STOVER andJERRY L. COFFMAN ABSTRACT Macroseismic effects of the principal earthquakes occurring in the United States from 1568 through 1989 are described. Princi- pal earthquakes are defined as those of Modified Mercalli intensity 2 VI or Richter magnitude 2 4.5. Exceptions are the State of Alaska and the offshore areas of California, Oregon, and Washing- ton, where the magnitude cutoff is 2 5.5. A tabular list of earth- quake data giving date, location, magnitude, intensity, and reference information for each earthquake is provided for 47 States (earthquakes in the categories described above were not reported in Iowa, Maryland, Wisconsin, or the District of Colum- bia). Following each table is a brief narrative of the damaging effects of each earthquake of intensity 2 VI. The narrative includes, where reported, a description of property damage and geologic effects as well as an estimate of the total area over which the shaking was sensibly felt by humans. Isoseismal maps, depict- ing the areal distribution of effects, and photographs of property damage and geologic effects complement the narratives of selected earthquakes. INTRODUCTION This publication is a history of the principal earth- quakes in the United States from 1568 through 1989. It contains all pertinent information on the date, location, size, and effects of these historical events. We have included only those earthquakes of Modified Mercalli intensity (“MM intensity” or “MMI”) 2 VI and magnitude 2 4.5. Exceptions are the State of Alaska and offshore areas of California, Oregon, and Washington, where the magnitude range was increased to 2 5.5 because of the high seismicity of those regions. This publication supersedes the com— pilation by Coffman and others (1982), published jointly by the US. Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA). This publication differs from the publication by Coffman and others (1982) “Earthquake History of the United States,” as listed below: 1. It is organized by State and has many new or revised isoseismal maps. 2. Epicentral locations were evaluated, and some were revised. 3. Many more earthquakes were added, making the data more complete. 4. All maximum intensities were reevaluated, and a uniform criteria for intensity assignment was used, thereby changing some of the intensities previously published. 5. Magnitudes are listed by type and source and are completely referenced. The summaries of earthquake damage and other effects enumerated in this publication have been compiled from many sources (see table 1). Selection of information to be included for each earthquake was based on the authors’ experience in evaluating and publishing earthquake data as well as on a review of the type of data most often requested from the USGS National Earthquake Information Center by scientists and laymen. The earthquakes described herein are listed alpha- betically by State name and chronologically by date of occurrence (1568 through 1989). Further, earth- quakes in Canada and Mexico that caused damage in the United States are included in the chapter for the State in which the damage occurred. Each State chapter includes the following: a map showing the distribution of earthquakes; a tabular listing of loca- tion, magnitude, maximum intensity, and references; brief summaries of damage caused by earthquakes of MMI 2 VI; isoseismal maps showing felt areas for selected earthquakes; and photographs of damage and geologic changes induced by destructive earth- quakes. Intensity and damage summaries for earthquakes that occurred in 1987—89 have been compiled from unpublished USGS data and are supplemented by data published in journal articles for the most dam- aging events. Thus, the summaries for 1987—89 reflect the data available at the time of compilation. 2 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) ACKNOWLEDGMENTS The isoseismal maps were drafted by EW. Baldwin; L.R. Brewer prepared the tables and text for publica— tion; and B.G. Reagor did the programming to format the tables. G.A. Bollinger, Virginia Polytechnic and State University, provided many discussions on the data and critically reviewed the final manuscript. T.R. Toppazada, California Division of Mines and Geology, reviewed the data for California and Nevada. R.L. Street, University of Kentucky, provided data for his- torical earthquakes in the Eastern and Central United States. Many of the photographs in this report were provided by the NOAA National Geophysical Data Center, Earthquake Hazards Photograph Library, Boulder, Colorado. After 32 years of providing earth- quake information to the public, Carl W. Stover retired from government service on January 3, 1993. MAGNITUDES Magnitude, a logarithmic measure of the “size” of an earthquake, is related to the energy released as seismic waves at the focus of an earthquake. Although the magnitude scale has neither “top” nor “bottom” values, the highest magnitude known to have been calculated was about 9.5, the lowest about —3.0. On this logarithmic scale, a magnitude 6.0 shallow-focus earthquake represents elastic-wave energy about 30 times larger than that generated by a magnitude 5.0 earthquake, 900 times (30x30) larger than that of a magnitude 4.0 shock, and so forth. Many factors influence the determination of earthquake magnitude, including focal depth, dis- tance between earthquake focus and observing sta- tion, frequency content of the sampled energy, and earthquake radiation pattern (variation of vibrational amplitude with azimuth). Magnitude values calcu- lated by the USGS are based on the following six formulas: Surface-Wave Magnitude: Ms=log (A/T)+1.66(log D)+3.3, (1) as adopted by the International Association of Seis- mology and Physics of the Earth’s Interior (Bath, 1966, p. 153), where A is the maximum vertical sur- face-wave ground amplitude in micrometers; T is the period in seconds, and 18STS22; and D is the dis— tance in geocentric degrees (station to hypocenter), and 20.<_Dsl60°. No depth correction is made for depths less than 50 km, and, generally, Ms magni- tudes are not computed for depths greater than 50 km. Body—Wave Magnitude: mb=log (A/T)+Q(D,h), (2) as defined by Gutenberg and Richter (1956), except that T, the period in seconds, is restricted to 0.1ST33.0, and A, the ground amplitude in microme- ters, is not necessarily the maximum of the P—wave group. Q is a function of distance (D) and depth (h), as published by Gutenberg and Richter (1956), where D25°. Local Magnitude (Western United States): ML=lOg A—log A0, (3) as defined by Richter (1958, p. 340), where A is the maximum trace amplitude in millimeters, written by a Wood-Anderson torsion seismometer, and log A0 is a standard value as a function of distance, where the distance is < 600 km. Values of ML are also calculat- ed from other seismometers by converting recorded ground motion to the expected response of the torsion seismometer. ML magnitudes are listed for events with depths less than 70 km. ML is the only true “Richter magnitude” (originally defined for Califor- nia only), but general usage has extended that de- scription to include other areas and types of magnitude as well. There is a potential for misuse in this practice, however. When technical or scientific applications are to be made, it is essential to specify the type of magnitude being used and not to resort to a generic “Richter magnitude.” Local and Regional Magnitude (Eastern United States): Mn=3.75+0.90 (log D) + log (A/T) 0.5TEDS4.0° Mn=3.30+1.66(log D)+log (A/T) 4.0°SDSB0.0°, as proposed by Nuttli (1973) for North America east of the Rocky Mountains, where A/T is expressed in micrometers per second, calculated from the vertical- component 1-second Lg waves, and D is the distance in geocentric degrees. The designator MbLg often is used in place of Mn. (4) (5) Moment Magnitude: M=2/3(log Mo)—10.7, (6) as defined by Hanks and Kanamori (1979), where the seismic moment (Mo—commonly expressed in dyne- cm but may be expressed in Newton-meters; 1 New- ton—meter = 107 dyne-cm) is equal to the product of the area of the earthquake fault, multiplied by the av- erage fault slip over that area and by the shear mod- ulus of the fault rocks; seismic moment may also be determined from the long-period body- and mantle- wave moment tensor inversion method of Dziewonski and others (1981); or, in California, seismic moment is estimated from measurements on Wood-Anderson seismograms (Bolt and Herraiz, 1983). INTENSITY, FELT AREA, AND ISOSEISMAL MAPS 3 Other Magnitudes: Variations of Ms, mb, and Mn magnitudes have been designed by seismologists for local seismo- graphic networks or for particular geographic regions so that the results are compatible with the magni- tude values derived from the standard formulas above. These variations are defined below. MD designates magnitude estimates derived from the duration or coda length of earthquake vibrations. MD is commonly computed from the difference, in seconds, between Pn- or Pg-wave arrival times and the time the final coda amplitude decreases to the pre-event background-noise amplitude. Duration or coda-length magnitude scales normally are adjusted to agree with ML or Mn estimates, so that resulting magnitudes can be accepted as compatible. Thus, the MD formulas vary for different geographic regions and for different seismograph systems. Mfa is a body-wave (mb) magnitude commonly com- puted from the felt area for earthquakes occurring before seismic instruments were in general use. The computations are based on isoseismal maps or defined felt areas using either the intensity-attenua- tion method of Nuttli (1973), the magnitude—felt area relation of Nuttli and Zollweg (1974), or the inten- sity—felt area relation of Sibol and others (1987). MLa is a local magnitude (comparable to ML) com- puted for earthquakes in California and adjacent areas and Hawaii. The computation is based on the area of perceptibility shown on isoseismal maps or on the area enclosed within a particular intensity level as defined by Toppozada (1975). MSn is a surface-wave (Ms) magnitude that is based on the source parameters for mid-plate earth- quakes as defined by Nuttli (1983). Some seismograph network operators determine a magnitude formula for their specific network by com- paring their computed magnitude values with magni- tudes published by other sources, such as the USGS mb, ML, or MH magnitudes. In this publication, those types of magnitudes will be designated mX for body- wave magnitudes (mb) and Mx for local magnitudes (ML or Mn). ML applies west of the Rocky Moun- tains, Mn east of the Rocky Mountains. MR magnitude represents the average of MS mag- nitudes computed by different seismograph stations or taken from other seismic networks after standard- ization as defined and published by Rothé (1969). A magnitude labeled as “Ukn” means that the com- putational method was unknown and could not be determined from the published sources. The published sources for the “Other” and Moment (M) magnitudes are shown by an alphabetic code. These codes are defined in table 2. INTENSITY, FELT AREA, AND ISOSEISMAL MAPS The term “intensity,” as applied to earthquakes, represents a number assigned to the effects on people (number affected, frightened, etc.), manmade struc- tures (toppled chimneys, collapsed walls, etc.), and the Earth's surface (landslides, faulting, etc.). The intensities listed in this publication were assigned according to the effects outlined in the Modified Mer- calli intensity scale of 1931 (Wood and Neumann, 1931), which has 12 discrete steps (see scale on p. 6). Modifications applied by the authors to this scale are described below. The single intensity value listed as a size parameter for each earthquake is the value assigned to the maximum reported effects of that particular earthquake. The maximum intensity is based on documented effects or damage at a place (usually a city or town) and are not necessarily the same as epicentral intensity (Io), which is the esti- mated intensity at the location of the earthquake. Some of the maximum intensities in this publica- tion have been changed from previously published values (namely in Coffman and others, 1982), mainly owing to new sources of information, or reevaluation of existing information, or both. Interestingly, many of those changes have resulted in the downgrading of intensities from MM intensity VI to V. This action has eliminated many earthquakes from this compila- tion if their associated magnitude was less than 4.5 (< 5.5 for Alaska and offshore California, Oregon, and Washington). All Rossi-Forel intensities gleaned from earlier publications were converted to MMI val- ues using table 4 from Barosh (1969). The Modified Mercalli intensity scale of 1931 has been further modified by the authors for assigning intensity values. These modifications were made for several reasons: The recent changes the USGS has made in the format of the questionnaire used to col- lect earthquake information have improved both the qualitative and quantitative data on the effects of shaking; the field experience of the authors (includ- ing personal observation of damage) has provided insight for more accurate intensity evaluation; and the subjective effects on people described in the MM intensity scale are not reliable considerations for assigning values above the intensity IV level. These modifications to the MM intensity scale of 1931 are described in more detail below: IV—Felt by many to all. Trees and bushes were shaken slightly. Buildings shook moderately to strongly. Walls creaked loudly. Observer de- scribed the shaking as “strong.” V—Felt, frightened, and awakened effects were not used at this or higher intensity levels. Hanging 4 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) pictures fell. Spilled liquid effects were not used to assign any intensity. Trees and bushes were shaken moderately to strongly. People had diffi- culty standing or walking. Felt moderately by people in moving vehicles. VI—At this level, there must be reports of physical damage to man-made structures as described in the MM intensity scale. The only exception is that intensity V1 is still assigned if many small objects fell from shelves and (or) many glass- ware items or dishes were broken. VII—Only damage to buildings or other man-made structures (as described in the MMI scale) is con— sidered. VIII—XII—The MM intensity scale is used as written, except that neither landslides nor effects on peo- ple were used for assigning an intensity. Geolog- ic effects were used only if the earthquake occurred in an isolated area having no nearby structures that could be damaged. The “felt areas” listed in the tables were taken from different published sources or were estimated by the authors from previously published or newly drawn isoseismal or intensity maps; the felt areas are listed to the nearest 1,000 km2. When an earth- quake occurred in a State bordering an ocean, Can- ada, or Mexico, the total felt area sometimes could not be estimated precisely. In those instances, the felt area was estimated only for the land area in the United States. Isoseismal maps depict the extent of the felt area of an earthquake and separate the effects into areas of different levels of intensity. The outer isoseismal line defines the total, or projected, contiguous geo- graphical area over which the earthquake was sensi- bly felt by people. The isoseismal maps that illustrate this compilation either are modified ver- sions of previously published maps or are new maps prepared by the authors (see figs. 7—64). New isoseismal maps also have been compiled from MMI values assigned by the authors after reevaluat— ing original sources of data. These intensity values were assigned only to the effects of shaking; geologic effects alone were not considered unless the area was uninhabited and there were no structures to damage. However, maximum MM intensities assigned by other researchers to geologic effects in remote areas (mainly in Nevada) have not been changed. The isoseismal maps contained in this publication were mostly selected to represent geographic cover- age. If States had a number of damaging earth- quakes, only the isoseismal maps for the most damaging events were included. SEISMICITY MAPS The seismicity and intensity maps for the United States, Alaska, Hawaii (figs. 1—6), and those at the beginning of each State chapter, show the areal dis- tribution of earthquakes of magnitude 4.5 or larger. Those earthquakes are depicted by open symbols that increase in size with increase in magnitude or intensity. To depict the earthquakes by magnitude on the maps, we assigned arbitrary magnitudes to events that had no computed magnitudes. This was accom- plished by correlating the maximum intensity with the average magnitude of earthquakes in four geo- graphical areas (Western U.S., Eastern US, Hawaii, and Alaska) that had both magnitudes and intensi- ties. The results for four areas are listed below: Western United States MMI Magnitude V < 5.0 V1 5.0 VII 5.5 VIII 6.0 IX 6.5 X—XII 7.0 Eastern United States MMI Mag nitude VI < 5.0 VII 5 .0 VIII 5.5 IX 6.0 X—XII 6.5 Hawaii M Mi Magnitude V < 5 .5 V1 5.5 VII 6.0 VIII 6.5 IX 7.0 X—XII 7.5 Alaska M Ml Magnitude V < 6.0 VI 6.0 VII 6.5 VIII 7.0 IX 7.5 X-XII 8.0 DAMAGE SUMMARIES The effects of all earthquakes of MI VI or higher are summarized for each State, and descriptive EXPLANATION OF TABLES 5 information that substantiates the maximum inten- sity assigned to each earthquake is listed. The data sources used to compile the effects (see table 1) are listed by source—reference numbers in parentheses at the end of each earthquake description. For example, “(Ref 1, 2, 250)” means that those three references were used to compile that particular summary, including the epicenter. Earthquakes are listed chronologically by date and time of occurrence (in Universal Coordinated Time— UTC). When the UTC date differs from the local date (i.e., the date/time of the earthquake at its epi- center), the local date is given in parentheses follow- ing the UTC date. When more than one earthquake occurred on the same date, origin times are repeated after the date to prevent ambiguity (HST, Hawaii- Aleutian standard time; AST, Alaska standard time; PST, Pacific standard time; MST, Mountain standard time; CST, Central standard time; EST; Eastern standard time). All published magnitude values cannot be listed in the tables because of lack of space or other reasons. However, those available values that are not listed are included at the end of the earthquake summaries, e.g., Magnitude 7.0 MS GR—GR refers to a magnitude ref- erence code; these codes are listed in table 2. Dollar estimates of property damage are available for most destructive earthquakes. These estimates, where quoted, use the dollar value for the year in which the earthquake occurred. Table 3 lists the numbers of deaths caused by destructive U.S. earth- quakes. Information on the effects of many large earth- quakes in Alaska's Aleutian Islands is not commonly available because of the remoteness of that region and the sparseness of its population. Therefore, the summaries for many large-magnitude earthquakes in Alaska give only date, region of occurrence, and magnitude. EXPLANATION OF TABLES Each State chapter includes a table that lists the basic parameters of the principal earthquakes in that State. Dates and origin times for each earthquake have been converted to the date and time of the Greenwich meridian and labeled as Universal Coor- dinated Time (UTC). The origin times for some earthquakes may differ from that given in the source reference. If so, the listed origin time was estimated using more accurate sources of data, such as seismograms, earthquake phase data, US. Weather Service reports, or other data sources. Latitude and longitude values are listed in decimal degrees. The number of digits following the decimal point does not indicate the level of accuracy, however: it only duplicates the value published in the original source reference. More than one location has been published for many earthquakes in the United States. We, there- fore, have selected for this publication the epicenter/ hypocenter that, in our judgment, most accurately represents the location of each earthquake. Some of these epicenters either have been revised from those previously published or have been assigned new, pre- viously unpublished epicenters, based on felt-area descriptions and locations of damage. All epicenters/ hypocenters included in the tables have been given a reference number (see table 1). Only in recent years has the depth of' an earth- quake in the United States been reliably computed. Therefore, the State tables do not give depth values for most pre-1930 earthquakes. Magnitudes are listed for all earthquakes that had a published value. Some erroneous mb magnitudes computed and published in the Preliminary Determi- nation of Epicenters during the 1960's have been eliminated. Published magnitudes that were based on maximum MM intensity, however, are not included. Many original magnitudes have been recomputed on the basis of recent research and new computational techniques. Consequently, magnitudes selected to be listed in the State chapters are values that the authors believe most accurately represent the “size” of the earthquake. The Mfa magnitudes, identified by the code “SC” in the tables for States east of the Rocky Mountains, were computed by the authors using the intensity—felt area relation of Sibol and others (1987). When magnitudes were published as a range (i.e., 6—61/4), the average of this range is the value listed in the tables. Additional magnitudes are listed in parentheses at the end of the summary of effects for many earthquakes. The alphabetic codes associated with the magni- tudes represent the source reference for that magni- tude. These alphabetic codes are defined in table 2. West of longitude 126 W. (offshore from California, Oregon, and Washington) only earthquakes with magnitudes 2 5.5 were included. The MMI values given in the State tables repre- sent the maximum intensity observed for those earthquakes listed. However, for a few earthquakes in Canada or Mexico that caused damage in the United States, the maximum intensity given is that observed nearest the epicenter. If that maximum intensity is not known, the maximum intensity observed in the United States is then listed (see the State chapter for details). A “Felt” in the MM inten- sity column indicates that insufficient information was available to assign an intensity value. The 6 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) source references for intensity are listed by number in the State tables and defined in table 1. The felt area given in the tables should be consid- ered only as an estimate because the limit of percep- tibility of shaking requires detailed reports that are unavailable for many earthquakes. MODIFIED MERCALLI INTENSITY SCALE OF 1931 (From Wood and Neumann, 1931) I Not felt—or, except rarely under especially favorable circumstances. Under certain conditions, at and outside the boundary of the area in which a great shock is felt: sometimes birds, animals, re- ported uneasy or disturbed; sometimes diz- ziness or nausea experienced; sometimes trees, structures, liquids, bodies of water, may sway—doors may swing very slowly. II Felt indoors by few, especially on upper floors, or by sensitive, or nervous persons. Also, as in grade I, but often more noticeably: sometimes hanging objects may swing, especially when delicately suspended; sometimes trees, structures, liquids, bodies of water may sway; doors may swing very slowly; sometimes birds, animals reported uneasy or disturbed; sometimes dizziness or nausea experienced. III Felt indoors by several, motion usually rapid vibration. Sometimes not recognized to be an earth- quake at first. Duration estimated in some cases. Vibration like that due to passing of light, or lightly loaded trucks, or heavy trucks some distance away. Hang- ing objects may swing slightly. Move- ments may be appreciable on upper levels of tall structures. Rocked standing motor cars slightly. IV Felt indoors by many, outdoors by few. Awakened few, especially light sleepers. Frightened no one, unless apprehensive from previous experience. Vibration like that due to passing of heavy or heavily loaded trucks. Sensation like heavy body striking building or falling of heavy objects inside. Rattling of dishes, windows, doors; glassware and crockery clink and clash. Creaking of walls, frame, especially in the upper range of this grade. Hanging objects swung, in numerous in- stances. Disturbed liquids in open vessels slightly. Rocked standing motor cars no- ticeably. V Felt indoors by practically all, outdoors by many or most: outdoors direction esti- mated. Awakened many, or most. Frightened few~slight excitement, a few ran out— doors. Buildings trembled throughout. Broke dishes, glassware, to some extent. Cracked windows—in some cases, but not generally. Overturned vases, small or unstable objects, in many instances, with occasional fall. Hanging objects, doors, swing generally or considerably. Knocked pictures against walls, or swung them out of place. Opened, or closed, doors, shutters, abruptly. Pendulum clocks stopped, started or ran fast, or slow. Moved small objects, furnish- ings, the latter to slight extent. Spilled liquids in small amounts from well-filled open containers. Trees, bushes, shaken slightly. VI Felt by all, indoors and outdoors. Frightened many, excitement general, some alarm, many ran outdoors. Awakened all. Persons made to move unsteadily. Trees, bushes, shaken slightly to mod- erately. Liquid set in strong motion. Small bells rang—church, chapel, school, etc. Damage slight in poorly built build- ings. Fall of plaster in small amount. Cracked plaster somewhat, especially fine cracks in chimneys in some instances. Broke dishes, glassware, in considerable quantity, also some windows. Fall of knickknacks, books, pictures. Over- turned furniture in many instances. Moved furnishings of moderately heavy kind. VII Frightened all—general alarm, all ran out- doors. Some, or many, found it difficult to stand. Noticed by persons driving motor cars. Trees and bushes shaken moderately to strongly. Waves on ponds, lakes, and running water. Water turbid from mud stirred up. Incaving to some extent of sand or gravel stream banks. Rang large church MODIFIED MERCALLI INTENSITY SCALE OF 1931 7 bells, etc. Suspended objects made to quiv- er. Damage negligible in buildings of good design and construction, slight to moderate in well-built ordinary buildings, considerable in poorly built or badly de- signed buildings, adobe houses, old walls (especially where laid up without mortar), spires, etc. Cracked chimneys to consid- erable extent, walls to some extent. Fall of plaster in considerable to large amount, also some stucco. Broke numer- ous Windows, furniture to some extent. Shook down loosened brickwork and tiles. Broke weak chimneys at the roofline (sometimes damaging roofs). Fall of cor- nices from towers and high buildings. Dis- lodged bricks and stones. Overturned heavy furniture, with damage from breaking. Damage considerable to con- crete irrigation ditches. VIII Fright general—alarm approaches panic. Disturbed persons driving motor cars. Trees shaken strongly—branches, trunks, broken off, especially palm trees. Ejected sand and mud in small amounts. Changes: temporary, permanent; in flow of springs and wells; dry wells renewed flow; in temperature of spring and well wa- ters. Damage slight in structures (brick) built especially to withstand earthquakes. Considerable in ordinary substantial buildings, partial collapse: racked, tum- bled down, wooden houses in some cases; threw out panel walls in frame structures, broke off decayed piling. Fall of walls. Cracked, broke, solid stone walls seri- ously. Wet ground to some extent, also ground on steep slopes. Twisting, fall, of chimneys, columns, monuments, also factory stacks, towers. Moved conspicu- ously, overturned, very heavy furni- ture. IX Panic general. Cracked grOund conspicuously. Damage considerable in (masonry) structures built especially to withstand earthquakes: threw out of plumb some wood-frame hous- es built especially to withstand earth- quakes; great in substantial (masonry) buildings, some collapse in large part; or wholly shifted frame buildings off founda- tions, racked frames; serious to reservoirs; underground pipes sometimes broken. X Cracked ground, especially where loose and wet, up to widths of several inches; fis- sures up to a yard in width ran parallel to canal and stream banks. Landslides considerable from river banks and steep coasts. Shifted sand and mud horizontally on beaches and flat land. Changed level of water in wells. Threw water on banks of canals, lakes, rivers, etc. Damage serious to dams, dikes, em- bankments. Severe to well-built wooden structures and bridges, some destroyed. Developed dangerous cracks in excellent brick walls. Destroyed most masonry and frame structures, also their foundations. Bent railroad rails slightly. Tore apart, or crushed endvvise, pipelines buried in earth. Open cracks and broad wavy folds in cement pavements and asphalt road surfaces. XI Disturbances in ground many and widespread varying with ground material. Broad fissures, earth slumps, and land slips in soft, wet ground. Ejected water in large amounts charged with sand and mud. Caused sea waves (“tidal” waves) of signifi- cant magnitude. Damage severe to wood- frame structures, especially near shock centers. Great to dams, dikes, embank- ments often for long distances. Few, if any (masonry) structures remained standing. Destroyed large well-built bridges by the wrecking of supporting piers, or pillars. Af- fected yielding wooden bridges less. Bent railroad rails greatly, and thrust them end- wise. ‘Put pipelines buried in earth com- pletely out of service. XII Damage total—practically all works of con- struction damaged greatly or destroyed. Disturbances in ground great and varied, nu- merous shearing cracks. Landslides, falls of rock of significant character, slumping of river banks, etc., numerous and exten- sive. Wrenched loose, tore off, large rock masses. Fault slips in firm rock, with no- table horizontal and vertical offset dis- placements. Water channels, surface and underground, disturbed and. modified greatly. Dammed lakes, produced water- falls, deflected rivers, etc. Waves seen on ground surfaces (actually seen, probably, in some cases). Distorted lines of sight. Threw objects upward into the air. 45° 40° 35° 30° 25° SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 130° 125° 120° 115° 110° 105° 100° EXPLANATION Magnitude ° 4.5-5.9 6.0-6.4 6.5-6.9 O O 7.0-7.4 O 7.5-7.9 500 KILOMETERS FIGURE 1,—Locations of magnitude 2 4.5 or damaging earthquakes in the conterminous Western United States, 1769—1989. SEISMICITY MAPS 1oo° 95° 90° 85° 80° 75° 70° 50° 0 O / ‘ O .- °° so o oo o o o o 0 45° . o O o oo o o o 0 0° 0 o 0 0° 0 ‘90 o O 0 ° ‘9 0 o 40 " V, 009 % ‘ ° ° 0 °o o 0 ° 0 9 o 0 00 o o o 0 ° 0 o 95 O o O 8> 00 g 0 35° 0 ° ° 0 5 ° EXPLANATION W» o Magnitude O 4.5-5.9 0 6.0-6.4 6.5-6.9 o o 7.0-7.4 0 30° 1 0 fl 0 500 KI OMETERS I L l I 25° 4. FIGURE 2.—Locations of magnitude 2 4.5 or damaging earthquakes in the conterminous Eastern United States, 1568—1989. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 10 130° 125° 120° 115° 110° 105° 100° 00 9. o 45" 0% 0° 5 ° w o 0 °°° A° °9 0 ° g o 0 ° ° *0 0 ° 0 40 0° 0 0 o 0 $0 0 03 o 90 % 0 O my 0 ° 6“" 0 0° 0 O °8 0 o $° ° 35° ° o0o o 0 o o A o o 0 0 °oe ° 0 8 o . 0 o 0 ° o° ° 0 °> 11 b 0 j 0 O 0 30° 0 o 0 EXPLANATION 0 Intensity [:l 0 VI 0 0 VII \ A VIII 0 0 1x 25° [:IX-xn 0 500 KILOMETERS FIGURE 3.—Locati0ns of earthquakes causing damage (MMI 2 VI) in the conterminous Western United States, 1769—1989. SEISMICITY MAPS 100° 95° 90° 85° 80° 75° 70° 50" l o 0 O o «3 I ° 80 o o O o o 45" A 1 9 . 0 o o 00 0 0° 0 ° 0 $0 .. J’ 0 40°‘ 0o0 co ° 6 ° ° 000 o o o O ° o o 6 6 8 0 Q 0 o o o oo 35° EXPLANATION 0 o ‘ Intensity ° VI 0 VII A VIII 0 OIX ,,_ ° Dx-xn 30° 0 fl 00 KILOMETERS , 25° FIGURE 4.——-Locations of earthquakes causing damage (MMI 2 VI) in the conterminous Eastern United States, 1568—1989. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 12 .mwmalwwz ,mxmmz 5 EV N 3):): own—hum. mama—Eu win—55.3w mo 3058316 @305 WIJIIJ wmmfizofi com o =x-xD x. O ___> < => Av _> o 35:35 ZO_H 4’0 O A 2m" 0 19° , c 0 20C KILOMETERS L_____1___I HAWAII 17" FIGURE 6.—-Locations of earthquakes causing damage (MMI 2 VI) in Hawaii, 1834-1989. 14 REFERENCES CITED Barosh, P.J., 1969, Use of seismic intensity data to predict the effects of earthquakes and underground nuclear explosions in various geologic settings: US. Geological Survey Bulletin 1279, 93 p. Bath, Markus, 1966, Earthquake energy and magnitude, in Phys- ics and Chemistry of the Earth, v. 7, New York, Pergamon Press, p. 115—165. Bolt, B.A., and Herraiz, Miguel, 1983, Simplified estimation of seismic moment from seismograms: Seismological Society of America Bulletin, v. 73, no. 3, p. 735—748. Coffman, J .L., von Hake, 0A., and Stover, C.W., 1982, Earthquake history of the United States: US. Department of Commerce,~ National Oceanic and Atmospheric Administration, and US. Department of the Interior, Geological Survey, Publication 41- 1, revised edition [through 1980], 258 p. Dziewonski, A.M., Chou, T.A., and Woodhouse, J.H., 1981, Deter- mination of earthquake parameters from waveform data for studies of global and regional seismicity: Journal of Geophysi- cal Research, v. 86, no. B4, p. 2825—2852. Gutenberg, Beno, and Richter, CF, 1956, Magnitude and energy of earthquakes: Annali di Geofisica, v. 9, no. 1, p. 1—15. Hanks, T.C., and Kanamori, Hiroo, 1979, A moment magnitude scale: Journal of Geophysical Research, v. 84, no. B5, p. 2348—2350. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Nuttli, O.W., 1973, Seismic-wave attenuation and magnitude rela- tions for eastern North America: Journal of Geophysical Research, v. 78, no. 5, p. 876—885. 1983, Average seismic source-parameter relations for mid— plate earthquakes: Seismological Society of America Bulletin, v. 73; no. 2, p. 519-535. Nuttli, C.W., and Zollweg, J.E., 1974, The relation between felt area and magnitude for Central United States earthquakes: Seismological Society of America Bulletin, v. 64, no. 1, p. 73—85. Rothé, J.P., 1969, The Seismicity of the Earth, 1953—1965: Paris, France, United Nations Educational, Scientific, and Cultural Organization [UNESCO], 336 p. Richter, CF, 1958, Elementary Seismology, San Francisco and London, W.H. Freeman and Company, 768 p. Sibol, M.S., Bollinger, G.A., and Birch, J.E., 1987, Estimation of magnitudes in central and eastern North America using intensity and felt area: Seismological Society of America Bul— letin, v. 77, no. 5, p. 1635—1654. Toppozada, TR, 1975, Earthquake magnitude as a function of intensity data in California and western Nevada: Seismologi- cal Society of America Bulletin, v. 65. no. 5, p. 1223—1238. Wood, H.O., and Neumann, Frank, 1931, Modified Mercalli inten- sity scale of 1931: Seismological Society of America Bulletin, V. 21, no. 4, p. 277—283. 88° ALABAMA 86° 34° 32° 30° TENNESSEE NC. 0 c3 EXPLANATION Huntsville Magnitude/Intensity O 3.8-4.4/Vl O 5.0-5.4/vu O 8 o H Birmingham 0 9.. E m m g GEORGIA E ALABAMA 0 Montgomery M0bi|e FLORIDA Q 100 KILOMETERS NV— Earthquakes in Alabama with magnitudes 2 4.5 or intensity 2 VI. 15 16 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) ALABAMA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 3 (°) (°) (km) ml, Ms M (1,000 km?) 1916 10 18 2204 33.5 N 86.5 W — 272 — — 5.10Mfa SC — VII 38 384 1931 05 05 1218 33.7 N 86.6 W —— 38 —— — 4.00Mfa SC - VI 38 17 1957 04 23 0923 39.0 33.770N 86.723W 005 349 -— —— 4.10Mf8| SC —- VI 30 28 1959 08 12 18 0601.4 34.789N 86.562W 005 349 —- —-— 3.80Mf8| SC — VI 32 7 1975 08 29 0422 52.1 33.659N 86.588W 004 349 3.5 -— 4.40Mx ILM — VI 48 25 1989 08 20 000317.8 34.736N 87.645W 010 74 — — 3.90Mn GS —— VI 579 6 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1916. Oct. 18. Irondale, Jefferson County, Ala. On the basis of the number of chimneys destroyed, this earthquake was more severe in Iron- dale than in any other town between Easonville and Birmingham. At Irondale, about 5 km north of Bir- mingham, 14 chimneys in a two-block area were partly destroyed, and six chimneys on a brick store were leveled almost to the roof. Many other chimneys either were leveled to the roofs or were cracked so badly that they had to be rebuilt. At Pell City, a few bricks were dislocated from one of the courthouse chimneys, and near Easonville, a few chimneys were damaged lightly. Poorly built chimneys on the east- ern edge of Birmingham were damaged heavily. A careful study of the Red Gap fault, which extends from near Gate City to beyond Irondale, did not reveal direct evidence of recent earth movement. The most significant geologic result was the effect of the earthquake on underground water, particularly in Irondale. Five wells in a one-block area of Irondale went dry immediately after the shock, and the water level in many others was lowered. At Pell City, the shock lowered the water level in one well about 50 cm. Several small aftershocks occurred through Oct. 28. Also felt in Georgia, Indiana, Kentucky, Missis- sippi, North Carolina, South Carolina, and Tennessee (see fig. 7). (Ref. 38, 105, 272, 508.) 1931. May 5. Near Birmingham, Jefferson County, Ala. This earthquake knocked bricks from a chimney at Birmingham, and shook objects from walls of a blacksmith shop at Cullman. Also felt in Georgia and possibly in 105, 508.) 1957. Apr. 23. Near Birmingham, Jefferson County, Ala. Several chimneys sustained minor damage at Birmingham; concrete steps were cracked and several small cracks formed on interior walls. Items on tables tumbled to the floor. Also felt in Georgia and Tennessee. Magnitude 4.2 Mfa BAR, 4.2 Mfa DG. (Ref. 30, 349, 508.) 1959. Aug. 12. Hazel Green, Madison County, Ala. This earthquake was strongest in Madison County in northern Alabama. North of Huntsville, at Hazel Green, bricks toppled from chimneys and alarmed residents ran from their houses. One chim- ney and a new concrete-block building were damaged at nearby Meridianville. Plaster cracked slightly at Huntsville, and merchandise was thrown from shelves. Also felt at several towns in Tennessee. Mag- nitude 3.8 Mn BAR, 3.8 Mfa DG. (Ref. 32, 349, 508.) 1975. Aug. 29 (Aug. 28). Palmerdale, Jeffer- son County, Ala. The earthquake cracked a sheet- rock ceiling and shifted lamps on tables at Palmerdale, north of Birmingham. It caused slight damage at Watson, where furniture was displaced slightly. Also felt in southern Tennessee. Magnitude 4.4 Mn SLM. (Ref. 48, 349.) 1989. Aug. 20 (Aug. 19). Near Littleville, Colbert County, Ala. A Colbert County official reported that, south of Florence between Littleville and Russellville, a basement wall collapsed beneath a house. Only slight damage was reported north of the epicenter at Florence, where windows were cracked and hairline cracks formed in plaster. Also felt in Lauderdale, Lawrence, and Morgan Counties in northwest Alabama and Lawrence County in south-central Tennessee. (Ref. 74, 579.) South Carolina. (Ref. 38, EARTHQUAKES IN ALABAMA 17 90° 88° 86° 84° 82° 80° \ Y E .’ Y ' ‘x. ! I l OH'O -./ 'a‘f-O’" \i /'( l Cincinnati 1" ' ‘u-x. ILL. '\. 'ND‘ PX. ,. .3 St. Louis -) P L \ u ; d I ."J .\ '~ -\ C W' VA' /' /. rm, \_f \_’.l L ’J ,‘\ . I). ’ -- .1 .\ .l J. \.J ./ /’ - l" O J f _ d _l Charleston ,‘ I- . )"L Louisville \ . I '1 '1}"‘\,/"\ u“ h (I l (I _/’ \" r ”J '\'/‘V" ( . ‘ A.’ —') l\ I”'\- ‘/ \./ .J' I _______ ./ —- _..._.._._._._.._. —- -' *‘x f)", ........... J I" ',l \5 .4 36° —\ 1.1. ’ 'r' ' ARK. (f N. o. . v ‘5. J .\ Memphis (i _ _._ — _ ._._._._U\' V ............. 1 ....... -. f; \.\. .’ \ QT.) 34° Columbia S. C. '\ .\ l.‘ Charleston Jackson . 32° i l —._ l j ! .r'_'_. ,__ ‘ .‘ | Mobile \' . .x. i, l \ ‘ ---------------- l LA. \ _ I ________ ‘ . . I > i I ‘ l. ‘ / ‘ FLA. ' 9 ‘. New Orleans Jacksonwlle 30° - '7 . l \\ ,,_ \ 0 150 KlLOMETERS EXPLANATION GULF OF MEX/CO * Epicenter \ \ ’ I V" Intensity 7 FIGURE 7.—Isoseismal map for the Alabama earthquake of October 18, 1916. Isoseismals are based on intensity estimates from data listed in reference 272 of table 1. 45 an,» n f. ~3le fiMEwfiAiTG. .3 15 . , v . 4 . ‘ ; V ‘ r d 4 . ‘ \ , . .m _ , ... _ , 7 . a , . t _ . _ ‘ ‘ _ , x w K a , ; y xv»; .C‘wh fr 19 .; N 36:35 .8 m.m N 835159: 515 «Mum—aw E mwxasufihwm _ _ _ O mam—PNEOJE com o o O O . O ‘ ”.o .. 1.5m. 0 . .‘ 1m..‘r,..’.”,: . O 0 3 , 0 .kva 3. M .on :o 1.. . . (a... u . .GLK...’ .ovw: O ”I 0 .0w 3 w 0 2-2 0 5212: O .5593 O _>\v.o-m.m o >=mc9c Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 kmz) 1982 01 25 05 29 33.5 53.222N 165.719W 060 74 6.1 —— 6.40m}, PAS 5.93HAV IV 350 ~— 1982 04 23 23 18 23.5 51.178N 179.844W 043 74 5.6 5.1 5.20Ms BRK 5.64HAV III 350 —— 1982 06 04 03 01 04.2 51.280N 177.154W 039 479 5.8 — 5.70Ms BRK 6.00HAV V 350 — 1982 07 01 07 41 53.2 51.426N 179.943W 047 74 6.3 5.5 5.40ML PMR 5.84HAV IV 350 — 1982 07 31 06 29 15.5 51.755N 176.137E 038 74 6.2 6.0 6.10Ms BRK 6.20HAV III 350 —- 1982 08 06 04 53 59.2 51.6(X)N 175.921W 043 479 5.4 -—- 5.50mb ISC 5.48HAV IV 350 — 1982 09 06 07 48 54.9 56.844N 151.588W 033 74 5.7 5.6 5.40Ms BRK 5.77HAV III 350 -— 1982 09 12 09 22 23.1 52.640N 166.941W 033 74 5.7 5.9 5.60M: PAS 6.23HAV — — — 1982 09 12 16 50 37.7 52.819N 167.053W 033 74 5.5 5.1 5.30ML PMR 5.64HAV — — 1982 10 04 07 46 53.1 51.421N 176.615W 036 479 5.5 5.0 5.20ML PMR 5.42HAV Felt 350 1982 12 02 09 43 53.4 51.883N 170.447W 033 74 5.5 4.8 5.50mb ISC — —- — — 1983 01 14 18 20 52.6 55.911N 154.154W 033 360 5.6 5.8 — 6.05HAV — — 1983 01 24 1302 37.2 51.381N 176.251E 033 360 5.4 5.7 -— 5.84HAV -— — 1983 02 14 03 20 03.7 54.809N 159.108W 016 360 5.9 6.3 6.50Ms BRK 6.52HAV V 360 — 1983 02 14 08 10 02.7 54.862N 158.875W 014 360 6.0 5 6 6.00M], PAL 5.95HAV V 360 — 1983 04 03 19 14 05.0 51.976N 179.259E 116 360 5.6 — 5.60m}, ISC 5.54HAV — — - 1983 06 09 18 46 02.7 51.249N 174.056W 023 479 6.2 5.8 5.80M, BRK 5.56HAV III 360 — 1983 06 28 03 25 17.6 60.182N 141.253W 012 360 6.0 5.4 5.90ML PMR 5.86HAV IV 360 —— 1983 07 12 15 1003.7 61.035N 147.185W 030 360 6.2 6.4 6.20Ms PAS 6.46HAV VI 360 675 1983 09 07 19 22 05.0 60.978N 147.320W 030 360 6.2 6.2 6.20Ms BRK 6.34HAV VI 360 230 1983 12 27 23 05 52.9 53.586N 164.376W 040 360 5.6 5.3 5.80ML PAL — V 360 — 1984 05 06 19 54 49.3 51.389N 176.621W 037 479 5.6 — 5.60ML PMR 5.58HAV V 370 1984 07 27 15 57 50.9 50.324N 176.870W 021 479 5.8 5.0 5.70ML PMR 5.57HAV IV 370 ~— 1984 08 14 01 02 08.4 61.857N 149.104W 019 74 5.7 5.2 5.70ML PMR 5.82HAV VI 370 74& 1984 09 20 04 17 24.4 60.322N 146.(X)IW 018 74 5.5 5.2 5.20ML PMR 5.47HAV IV 370 — 1984 09 23 17 06 36.3 53.577N 165.424W 033 74 5.7 5.5 5.90ML PMR 5.89HAV IV 370 — 1984 11 08 13 02 00.1 52.181N 170.999W 033 74 5.4 5.3 5.50M; PMR 5.90HAV — - — 1984 11 19 04 10 42.4 51.170N 179.096E 038 74 5.6 5.5 5.70ML PMR 5.87HAV II 370 -— 1984 11 19 12 06 37.9 51.580N 175.243W 039 479 5.6 — 5.50ML PMR 5.66HAV IV 370 — 1985 01 02 05 32 49.1 55.428N 157.835W 033 74 5.6 5.6 6.10M; PMR 5.95HAV III 371 —— 1985 01 09 19 28 21.2 60.289N 140.744W 014 74 5.7 5.1 5.40M; PMR — IV 371 — 1985 03 09 1408043 66.239N 150.029W 011 74 5.9 6.0 6.00ML PMR 6.14HAV V 371 —— 1985 03 10 13 30 29.5 66.136N 150.148W 010 74 5.2 4.9 5.60ML PMR 5.45HAV Felt 371 — 1985 05 09 19 05 21.5 51.465N 177.913E 033 74 5.7 6.0 6.20Ms BRK 6.25HAV IV 371 — 1985 05 09 19 14 07.7 51.302N 178.024E 033 74 5.4 6.0 5.90Ms BRK — H1 371 — 1985 05 24 22 04 45.4 51.193N 178.367W 033 479 5.8 5.8 5.80ML PMR 6.14HAV III 371 — 1985 07 17 19 31 29.5 51.443N 172.883W 016 479 5.5 5.9 5.70Ms BRK 6.05HAV III 371 — 1985 07 31 07 37 54.6 52.404N 173.487E 045 74 5.7 5.0 5.70mb ISC 5.61HAV IV 371 —- 1985 08 09 13 03 10.6 52.424N 173.648E 037 74 5.5 4.9 5.40ML PMR 5.38HAV IV 371 — 1985 08 30 17 31 11.9 53.097N 172.629E 033 74 5.1 5.0 5.60ML PMR — — — — 1985 09 15 01 28 16.7 59.102N 136.423W 001 74 5.4 5.9 5.10M], PMR 6.30HAV V 371 —— 1985 10 01 15 54 51.1 52.296N 168.856W 033 74 5.7 5.4 5.30ML PMR 5.67HAV III 371 — 1985 10 09 09 33 32.4 54.765N 159.613W 030 74 6.2 6.6 6.60Ms BRK 6.58HAV V 371 — 1985 10 25 02 09 04.3 52.072N 171.350W 033 74 5.6 5.5 5.60ML PMR 5.95HAV II 371 — 1985 10 26 15 59 36.0 54.838N 159.534W 033 74 5.6 — 5.30ML PMR 5.36HAV V 371 — 1985 10 30 19 05 37.5 51.801N 175.5331! 033 74 5.6 5.4 5.50ML PMR 5.82HAV II 371 1985 10 31 19 33 06.5 53.249N 166.936W 030 74 5.8 5.7 5.80Ms PAS 6.14HAV IV 371 —— 1985 11 14 22 17 44.5 54.756N 159.787W 033 74 5.5 5.7 5.70ML PIVIR 6.05HAV V 371 — 1985 12 28 07 44 38.2 56.580N 156.509W 058 74 5.3 — 5.70mb PAL — — — — 1985 12 30 12 41 02.7 61.541N 150.340W 062 74 5.5 —- 5.20ML PMR — V 371 -— EARTHQUAKES IN ALASKA 45 ALASKA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only. Leader (u) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m s (°) (°) (km) mb Ms M (1 .000 km?) 1986 01 18 0159009 51.387N 173.055W 016 562 1986 03 04 0847146 51.553N 166.943W 033 562 1986 03 09 13 49 28.2 54.256N 167.864W 033 562 5.3 5.00ML PMR 5.54HAV . 5.60ML PMR 5.42HAV 5.5 5-50Ms BRK 5.72HAV sap-s:- Mm“ b. O\ 562 "ri "fl Iléaz ?—.|| MUIUI ||$$$ 1986 04 ll 17 22 20.8 54.164N 167.883W 033 562 5.3 5.9 6.00Ms BRK 5.98I-IAV — 1986 05 07 2043 33.3 51.234N 174.741W 025 562 6.1 6.0 6.10ML PMR 6.24HAV ~— 1986 05 07 22 47 12.3 51.325N 174.751W 031 562 6.4 77 7.90M3 BRK 7.95HAV —- 1986 05 07 22 5505.0 51.500N 174.800W 033 562 5.6 — — — — 1986 05 07 22 57 47.6 51.575N 174.219W 015 562 5.7 — — — — 1986 05 07 2307410 51.317N 174.598W 020 562 5.5 —— — — — —— -- 1986 05 07 23 36 18.3 51.297N 174.132W 020 562 5.7 —— -—- —— — — — 1986 05 07 23 51 01.9 51.273N 174.836W 020 562 5.8 ' ——- —— — — — — 1986 05 07 23 52 20.5 52.3(X)N 174.423W 015 562 5.7 —- — — — —- -— 1986 05 08 0111021 50.960N 176.655W 020 562 5.9 — 5.90ML PMR — —— — — 1986 05 08 0115149 51.028N 176.778W 020 562 5.6 — —— — — — — 1986 05 08 0204002 51.002N 176.886W 020 562 5.5 — 5.50ML PMR -— — — — 1986 05 08 0403 49.7 50.971N 176.449W 020 562 5.8 5.5 5.70ML PMR — — — —- 1986 05 08 05 37 21.6 51.166N 175.329W 015 562 6.0 6.2 6.20ML PMR 6.42HAV — — -— 1986 05 09 0105 31.2 51.061N 176.902W 023 562 5.5 5.6 5.40ML PMR — III 562 — 1986 05 09 0108105 51.062N 176.856W 018 562 5.6 5.5 5.50ML PMR — IV 562 —- 1986 05 09 1904284 51.283N 174.200W 021 562 5.8 5.6 5.50Ms BRK 5.89HAV —- — —- 1986 05 09 1924420 51.268N 174.036W 020 562 5.3 5.8 —— ——- —- — —— 1986 05 11 1940307 51.359N 173.696W 018 562 5.6 5.2 4.90M], PMR 5.68HAV — — —- 1986 05 11 2248472 51.371N 174.616W 029 562 5.5 5.2 5.70ML PMR 5.65HAV IV 562 —- 1986 05 14 01 58 30.9 51.364N 173.437W 021 562 5.5 4.7 — 5.34HAV — — — 1986 05 15 0638 37.9 52.432N 174.719W 015 562 5.7 6.4 5.50ML PMR 6.38HAV VI 562 — 1986 05 17 16 20 24.3 52.443N 174.271W 015 562 5.8 6.6 6.50Ms BRK 6.40GS VI 562 —— 1986 06 03 23 05 28.8 51.256N 174.631W 020 562 5.4 5.1 5.80ML PMR — II 562 — 1986 06 04 1548208 65.636N 152.604W 010 562 5.2 4.7 5.70ML PMR — V 562 150 1986 06 09 02 17 38.2 54.142N 168.132W 033 562 5.0 4.7 5.60ML PMR 5.241-IAV — — — 1986 06 18 0805164 51.465N 176.833W 041 562 5.8 6.3 6.00ML PMR 6.46I-IAV IV 562 — 1986 06 19 0909092 56.331N 152.914W 017 562 6.0 6.3 5.40ML PMR 6.75HAV IV 562 — 1986 07 05 0301 32.6 51.248N 179.746W 033 562 5.6 5.2 5.20ML PMR 5.65HAV —— —- —_ 1986 07 19 043155.9 53.352N 165.882W 033 562 5.5 5.1 5.90ML PMR 5.58HAV IV 562 — 1986 07 19 0504082 53.339N 165.859W 033 562 5.1 4.5 5.60ML PMR 5.18HAV IV 562 -— 1986 07 19 0653178 53.6(X)N 167.171W 033 562 5.5 5.7 5.80ML PMR 5.95HAV IV 562 ~— 1986 07 19 22 32 36.0 53.521N 167.301W 033 562 5.6 5.6 5.60Ms BRK 5.98HAV V 562 — 1986 07 25 0901326 51.079N 176.137W 021 562 5.3 5.6 5.30ML PMR 5.81HAV IV 562 — 1986 07 25 0904163 51.056N 175.996W 020 562 5.4 5.6 — — Felt 562 — 1986 08 01 21 05 40.1 51.262N 174.224W 022 562 5.5 5.0 4.60ML PMR 5.40HAV IV 562 — 1986 08 03 1329104 51.026N 176.749W 022 562 5.4 5.6 5.60ML PMR 5.89HAV IV 562 —- 1986 09 12 23 57 15.6 56.201N 153.405W 031 562 6.1 6.3 6.00Ms BRK 6.51GS IV 562 1986 09 16 20 57 21.9 56.222N 153.600W 033 562 5.3 5.5 5.10ML PMR 5.87HAV III 562 1986 10 26 0443 27.4 53.758N 170.049W 214 562 5.4 — 5.90mb BRK 5.74HAV —— —— — 1986 ll 06 18 27 02.9 51.242N 176.631W 039 562 5.1 5.5 5.20ML PMR 5.90HAV IV 562 — 1986 ll 14 2142459 51.442N 173.845W 025 562 5.5 — 4.90ML PMR — —— — — 1987 01 05 121155.7 52.448N 169.381W 033 74 6.1 6.7 6.50Ms BRK 6.731-IAV V 577 — 1987 02 18 0000525 51.298N 179.279W 033 74 6.2 5.9 5.50ML PMR 6.23HAV V 577 — 1987 02 18 0528232 51.344N 179.298W 033 74 5.5 4.7 5.40ML PMR — III 577 — 1987 02 27 08 3154.4 53.470N 167.291W 010 74 6.2 6.7 6.80Ms BRK 6.89HAV V 577 — 1987 03 21 10 41 35.9 52.056N 177.547W 093 74 6.0 — 6.20M3 BRK 6.37HAV V 577 — 1987 03 22 02 49 15.9 51.594N 173.574W 020 74 5.9 6.0 5.80ML PMR 6.15HAV IV 577 — 1987 04 18 02 01 38.8 61.374N 150.656W 068 74 5.7 — 5.60M; BRK 5.31HAV V 577 — 1987 05 02 1921 29.6 54.801N 160.103W 033 74 5.1 4.6 5.80ML PMR 5.26HAV V 577 — 46 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) ALASKA—Continued [See table 1 for hypocenver and intensity references and table 2 for definitions of magnitude source codes. 8:, land area only. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo De h m 3 (°) (°) (km) mb Ms M (1,000 kmz) 1987 05 06 040614.1 51.272N 179.898W 020 74 6.3 6.4 6.10ML PMR 6.57HAV V 577 —-— 1987 05 10 0939 06.6 51.394N 179.820W 033 74 5.0 -- 5.50ML PMR — — — —— 1987 06 21 0546100 54.211N 162.601W 034 74 6.2 6.2 6.60ML PMR 6.50HAV V 577 — 1987 06 21 05 55 26.9 54.285N 162.597W 033 74 5.5 — 5.40ML PMR -- ]I[ 577 — 1987 07 05 0923 00.0 51.486N 174.660W 033 74 5.5 52 5.40ML PMR 5.63HAV II 74 -— 1987 07 06 0023 25.6 51.508N 174.721W 033 74 5.8 5.5 5.80ML PMR 5.89HAV IV 577 — 1987 07 24 0525105 56.231N 153.650W 033 74 5.5 5.3 5.70ML PMR 5.65HAV 111 577 -— 1987 08 14 17 39 32.2 53.416N 169.113W 118 74 5.7 — —— 5.98HAV IV 74 — 1987 08 22 0509144 52.164N 174.066E 033 74 5.5 4.8 5.20ML PMR 5.21HAV IV 577 — 1987 09 10 034844.8 51.931N 176.006W 049 74 5.1 — 5.50M; PMR — IV 74 — 1987 10 20 0923 36.2 52.577N 172.320E 033 74 5.5 5.6 5.50ML Pm 5.95HAV -— — —— 1987 11 17 0846533 58.586N 143.270W 010 74 6.6 6.9 7.00ML PMR 7.16HAV V 577 3758: 1987 11 17 0938123 58.608N 143.096W 010 74 5.5 — 5.20ML PMR -— —- — — 1987 11 18 13 01 55.2 58.642N 143.190W 010 74 5.2 5.6 5.60ML PMR 5.78HAV — — — 1987 ll 23 07 18 20.5 61.616N 141.323W 005 74 5.7 5.0 5.40ML PMR 5.50HAV IV 577 —— 1987 11 30 1923195 58.679N 142.786W 010 74 6.7 7.6 7.10ML PMR 7.86HAV VI 577 4708; 1987 11 30 1948 26.0 58.239N 142.742W 010 74 5.9 — 5.60ML PMR — Felt 74 — 1987 12 01 1203 59.7 57.953N 142.611W 010 74 5.4 5.7 5.60ML PMR 5.77HAV — — — 1988 01 13 0101502 51.309N 174.654W 033 74 5.6 5.2 —- 5.51HAV — — — 1988 01 23 02 45 35.7 51.400N 174.268W 048 74 5.5 4.7 — 5.02HAV — — —- 1988 02 07 0846586 60.296N 152.972W 138 74 5.6 —-— 5.60m], BRK 6.46HAV V 578 175 1988 02 07 18 15 05.6 50.785N 173.465E 033 74 6.2 6.0 5.90Ms PAS 6.30HAV III 578 —- 1988 02 13 23 56 58.7 50.636N 173.410E 033 74 5.2 55 — 5.21HAV — —- — 1988 02 13 23 57 45.6 52.296N 173.379W 054 74 5.7 -— — — II 74 — 1988 02 16 0422 36.1 51.564N 175.041E 033 74 5.9 5.7 5.60ML PMR 5.98HAV -— — — 1988 02 16 0544386 51.495N 175.054E 033 74 5.5 5.0 5.00ML PMR 5.54HAV -— -— — 1988 02 24 0254226 51.723N 176.797W 060 74 5.5 — — 5.34HAV III 74 — 1988 03 06 22 35 38.1 56.953N 143.032W 010 74 6.8 7.6 7.40ML PMR 7.74HAV V 578 5808: 1988 03 06 23 14 38.4 57.499N 142.803W 010 74 6.2 — 6.30ML PMR —— —— — — 1988 03 08 16 27 18.8 51.340N 17686213 033 74 5.5 5.5 5.50ML PMR 5.81HAV — — — 1988 03 25 2158205 54.776N 159.840W 033 74 5.4 4.6 5.90ML PMR — IV 74 —— 1988 03 29 08 3131.9 52.278N 168.182W 033 74 5.4 5.5 5.10ML PMR 5.79HAV — — — 1988 04 26 0147 35.0 57.534N 143.073W 010 74 5.4 5.6 5.90ML PMR 5.83HAV Felt 578 -— 1988 05 22 0939 55.9 53.619N 163.267W 033 74 5.7 5.7 5.70ML PMR 5.95HAV -— — —- 1988 05 25 14 05 17.6 50.549N 174.571W 040 74 5.7 4.9 5.30M3 BRK 5.58HAV — — — 1988 ll 06 08 2057.0 51.311N 178.148W 033 74 5.5 4.8 — —-— III 578 — 1988 11 15 08 41 42.3 52.109N 171.103W 023 74 5.9 5.4 5.50Ms BRK 5.91HAV Felt 74 — 1988 11 30 08 55 30.6 61.348N 152.270W 144 74 5.5 — — 5.73HAV V 578 90 1989 01 08 19 57 06.0 51.435N 174.880W 033 74 5.7 5.5 5.70Ms BRK 6.00HAV III 579 ~— 1989 01 08 2026251 51.432N 174.799W 033 74 5.1 5.6 5.70ML PMR 5.44HAV III 579 — 1989 01 08 22 37 30.9 51.393N 174.758W 033 74 5.6 5.4 5.80ML PMR 5.76HAV III 579 —- 1989 02 22 10 25 45.2 56.152N 153.642W 033 74 5.7 5.8 5.80M], PMR 5.95HAV — — — 1989 04 09 0507 50.6 51.510N 178.386W 033 74 5.2 4.7 5.70ML PMR 5.251-1AV III 579 — 1989 04 23 1921064 66.960N 156.289W 006 74 5.7 51 5.30ML PMR 5.45HAV IV 579 -— 1989 05 19 02 21 56.3 54.305N 165.574W 104 74 6.1 — 5.40Ms BRK 6.15HAV V 579 —- 1989 06 16 10 51 21.5 57.755N 153.992W 058 74 5.8 — — 5.67HAV V 579 -- 1989 07 03 1709558 51.617N 175.208W 033 74 5.7 5.7 5.70M; BRK 6.051-[AV IV 579 — 1989 09 04 13 14 58.2 55.543N 156.835W 011 74 6.5 6.9 6.90ML PMR 7.061-1AV V 579 —- 1989 09 20 13 19 31.9 51.184N 178.821E 033 74 5.5 5.8 5.80Ms BRK 6.22HAV Felt 74 ~— 1989 10 07 154829.0 51.314N 179.028W 020 74 6.1 6.7 — 6.79HAV IV 579 — 1989 10 07 16 42 30.7 51.188N 179.234W 033 74 5.7 5.9 5.70ML PMR 6.19HAV III 74 — 1989 10 07 17 42 36.4 51.137N 179.221W 033 74 5.6 5.7 — 5.44HAV — — ~— 1989 10 07 17 52 47.3 51.115N 179.241W 033 74 5.5 5.6 —- — — — — EARTHQUAKES IN ALASKA 47 ALASKA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &. land area only. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1989 10 07 18 5040.8 51.076N 179.306W 033 74 5.5 5.3 5.40ML PMR 5.68HAV III 74 — 1989 10 07 190634.7 51.173N 179.412W 033 74 4.9 — 5.50M], PMR — — —— —- 1989 10 09 1801073 51.780N 171.869E 026 74 6.0 5.3 5.40ML PMR 5.73HAV — — — 1989 12 01 0506121 51.631N 178.102W 043 74 5.6 5.0 5.70ML PMR 5.59HAV IV 74 — 1989 12 21 16 53 19.3 62.421N 155.620W 000 74 5.4 5.5 5.50ML PMR — IV 579 —— INTRODUCTION The Alaska table cannot be considered to be a com- Only those earthquakes of Modified Mercalli inten- sity 2 VI or magnitude 2 5.5 are listed in the Alaska table. Earthquakes without published magnitude or intensity values and those having intensities < VI were estimated to fall within the magnitude 2 5.5 range if they met the following criteria: 1. Pre-1913 earthquakes (the year instrumental ep- icenters were first published) had to be well doc- umented. It is believed that most shocks before 1913 would have to have a magnitude larger than 5.0 to generate sufficient interest for de- tailed information to be published; 2. The hypocenter had to be computed using a set of phase data comparable (in terms of reporting seismograph stations and distances recorded) to one published in the International Seismological Summary (ISS) or International Seismological Centre (180) bulletins with a computed magni- tude 2 5.5. The earthquake must have occurred within 3 years of the ISS or 180 event. The origin times in the Alaska table may not be identical to those shown in the source reference. If not, the listed origin times were estimated from more accurate sources, such as seismograms, earthquake phase data, US. Weather Service reports, and oth- ers. Some corrections in dates also were necessary because all sources did not list the same date. Many of the published origin times were given in "local time" (i.e., the time on the clock at the location reporting the earthquake). Most of these local times in the 1800's were local solar meridian time. We, therefore, converted all the local times to UTC. Other origin-time corrections resulted from differ- ences between local time and the time that the phase data were recorded on seismograms. In those instances, the arrival times published from phase data were used to compute new origin times. plete listing of magnitude 2 5.5 earthquakes. How- ever, it is as complete as possible on the basis of the selection criteria listed above and on the data avail- able to us. In the early days of seismology, the only earthquakes recorded were those having large mag- nitudes or those located near populated centers. Because of this, the list of earthquakes can be consid- ered complete only after about 1964, when the instal- lation of worldwide seismograph stations and the use of computers allowed the routine computation of hypocenters and magnitudes for smaller earth- quakes. [Reference (Ref.) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1786. Date unknown. Alaska Peninsula. Fol- lowing an eruption of Pavlof Volcano, and during a severe earthquake, the north crater of the volcano collapsed with a tremendous noise. (Ref. 38, 255, 426, 436, 520.) 1788. July 22. Shumagin Islands—Kodiak Island region, Alaska. Strong ground motion and landslides occurred on both Kodiak and Unga Islands. Land subsidence also was reported on Kodiak near the harbor. The earthquake is described as “a great shock that ruptured at least a 600-km segment of the plate boundary” (extending from Kodiak Island perhaps to Unga Island or beyond). A tsunami perhaps as high as 10 m inundated Three Saints Bay and caused extensive loss on Kodiak Island. Aftershocks on Kodiak Island lasted a month or longer. (Ref. 38, 426, 456, 520, 610.) 1788. Aug. 7. Unga Island, Alaska. A strong earthquake may have ruptured the plate boundary “from Unga to Sanak on Aug. 7. There was such a terrible flood on Unga Island that many Aleuts were 48 killed, and the water rose to 50 sazhens (about 91 m).” The tsunami was much smaller at Pavlof Bay (on the south coast of the Alaska Peninsula) and did not affect the north side of Unimak Island. There is some doubt that this is a second earthquake in 1788 (Ref. 456, 520.) 1792. Date unknown. Kodiak Island, Alaska. A strong earthquake occurred on Kodiak Island, “con- tinuing for 18 hours.” All cabins collapsed, and rocks slid down the hillsides. A vessel that was entering Three Saints Bay (Kodiak Island) at the time of the earthquake “encountered a strong agitation and suf- fered greatly from the unusual and highly anomalous wave patterns.” (Ref. 456.) 1796. May 20. Umnak Island, Alaska. An earthquake shook Umnak, and a new island (St. John Bogoslov) appeared in the Unalaska district. A rumble resembling shots from a cannon came from the mountains off the northeast point of Umnak. Rocks were thrown from the new island as far as Umnak Island. (Ref. 38, 436, 520.) 1802. Date unknown. Unalaska Island, Alaska. Makushin Volcano erupted “with great vio— lence,” and an earthquake destroyed “a considerable number of the earth huts.” (Ref. 38, 436, 520.) 1812. Date unknown. Atka Island, Alaska. Sarychef Volcano erupted, and a violent earthquake terrified residents on Atka. (Ref. 38, 255, 426, 436, 520.) 1817. Mar. 14. Umnak Island, Alaska. A vio— lent earthquake occurred. Yunaska Volcano erupted, sending ash as far as Unimak Island. (Ref. 38, 255, 436, 520.) 1818. Apr. Unalaska Island, Alaska. An earth- quake occurred following the strong rumbling of Makushin Volcano. To the residents on Unalaska, it seemed that the nearby island of Amakhnak had col- lapsed. (Ref. 38, 436, 520.) 1826. June. Unalaska Island, Alaska. TWO vio- lent earthquakes occurred, during which flames shot out of Makushin Volcano. (Ref. 38, 255, 436, 520.) 1836. Apr. 14. Pribilof Islands, Alaska. Shocks were so strong on St. Paul and St. George Islands that people could not remain standing. The first shocks collapsed many cliffs on the coast of St. George and caused others to settle. A barn collapsed on St. Paul. (Ref. 38, 255, 426, 520.) 1836. Aug. Pribilof Islands, Alaska. The earth- quake was less violent and the rumblings were more muted than the shocks and noises experienced in April 1836. (Ref. 38, 255, 426, 436, 520.) 1840. Apr. Alaska Peninsula. A strong earth- quake occurred at Nikolaev Redoubt in Kenai Bay SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) (Kenai Village, Cook Inlet). Stoves fell to pieces and chimneys collapsed. (Ref. 515, 520.) 1843. Dec. 17 (Dec. 16). Sitka, Alaska. At 4 pm. local time, a strong 3-second earthquake “rent houses” and moved trees back and forth. Cracking noises were heard. Two light foreshocks occurred on Dec. 15 and 16. (Ref. 38, 420, 515, 520.) 1844. Apr. 13. Kodiak Island, Alaska. A strong earthquake accompanied by a loud noise occurred at Pavlof (St. Paul) Harbor. The shock continued for more than 2 minutes and sent residents fleeing from their homes. Older residents reported this shock was the strongest in memory. The epicenter is uncertain. (Ref. 456, 515, 520.) 1847. Date unknown. Sitka, Alaska. This earthquake generally was felt along the Alaska coast and was severe at Sitka. The Governor's mansion was destroyed. Flame and ashes arose from the sum- mit of Mount St. Elias. The epicenter is uncertain (Ref. 38, 436, 520.) 1847. Apr. 16, 16 UTC. Chirikof Island, Alaska. A large earthquake on Ukamok (Chirikof Island) cracked the ground in many places and col- lapsed cliffs. On Unga Island, Alaska, a “fairly large” earthquake occurred early in the morning. At 10 am. (20 UTC), it “grew” to the point that it was impossi- ble to remain standing. At about the same time, a large earthquake was felt on the Alaska Peninsula. These two events, 4 hours and 320 km apart in time and space, are considered to describe one earthquake; however, the possibility exists that two earthquakes occurred. (Ref. 515, 456, 520.) 1848. Mar. 30. Sitka, Alaska. A large earthquake knocked down chimneys, damaged stoves, and cracked stones on many houses. The 15-second shock, which was accompanied by a muffled underground noise, terrified residents. The trembling continued almost without interruption until Apr. 27. (Ref. 515, 520.) 1848. June 30. Chirikof Island, Alaska. An earthquake on Ukamok (Chirikof Island) began about midnight. Several minutes later, the earth shook so hard that it was impossible to remain standing. It was accompanied by a wind-like noise and a rum- bling. (Ref. 456, 515, 520.) 1866. Sept. 6. Kodiak Island, Alaska. A violent earthquake struck Pavlof (St. Paul) Harbor. It “half destroyed” the landing on Woody Island and dam- aged many buildings, stoves, and chimneys. Huge rocks were thrown down the mountains. (Ref. 38, 426, 515, 520.) 1868. May 15. Shumagin Islands, Alaska. “During a slight earthquake the elevation is said to have amounted locally at Unga to over 20 feet.” (Ref. 38, 420, 610.) EARTHQUAKES IN ALASKA 49 1872. Aug. 23. Aleutian Islands region, between the Andreanof and Fox Islands, Alaska. It is suggested that, on Aug. 23, a tectonic displacement of the Aleutian continental shelf or slope was accompanied by an earthquake of large magnitude. A tsunami of 1.3 m was observed in Hilo harbor, lesser heights were observed at Hanalei, Honolulu, and Nawiliwili, Hawaii. It was also recorded at Honolulu, Hawaii; Astoria, Greg; and San Francisco and San Diego, Calif. From the reports of the arrival of the tsunami in Hawaii and mari- graphic evidence of its arrival in Oregon and Califor- nia, its source has been determined to be off the Aleutian Islands. (Ref. 516, 610.) 1878. Aug. 29. Unalaska Island, Alaska. The village of Makushin was destroyed by an earthquake. Major volcanic eruptions and earthquakes occurred on several Aleutian islands in late August and early September 1878. (Ref. 38, 426, 463, 520.) 1880. Sept. 29, 04 UTC (Sept. 28). Chirikof Island, Alaska. A major earthquake occurred, fol- lowed by three severe aftershocks at 07, 13, and 23 UTC. Many deep fissures 38—51 cm in width were observed on Chirikof after the shocks. In a one-story log cabin, shelves were thrown from walls, a brick stove was upset, flooring was twisted out of shape, and heavy barrels were pitched from one side of the room to the other. Outside, no one was able to remain standing owing to a violent jerking and rotary motion of the earth, which continued for at least 20 minutes. At low tide, the sea rose several times and traveled onshore about 55 m. On the south side of the island, a small, shallow creek widened about 2 m, and its depth increased. On the southwest shore of the island, heavy breakers were observed where they had not been seen previously. On the west side of the island, the tide did not rise as high as before the shocks. From the beginning of the earthquake series through Oct. 16, 1880, an uninterrupted trembling motion, interspersed with heavy subterranean rum- bling sounds, was observed. During these earthquakes, the northwest part of the island, bounded by a northeast-trending fault, tilted to the southeast. The fault on the southeast boundary displaced vertically about 1.8 m. Evidence of this faulting is still preserved in dammed streams and uplifted, wave-cut terraces. (Ref. 426, 463, 520.) 1880. Oct. 26. Sitka, Alaska. A severe earth- quake along with cracking and splitting earth noises occurred at Sitka, At the warm springs 32 km south- east of Sitka, the springs spouted like geysers. The shocks were severe at Whale Bay, about 58 km southeast, and a “tidal wave of huge dimensions ran into the bay.” The shock was violent on Tihiagreff Island (north of Baranof Island). At Hoonah village, people were thrown around “like chips in an eddy.” Aftershocks continued through Nov. 14. (Ref. 426, 463.) 1883. Oct. 6. Alaska Peninsula. Mount St. Augustine burst into volcanic activity. It was accom- panied by a severe earthquake and tsunami. A wave estimated at 7.6—9.1 m flooded Port Graham, fol- lowed by 2 waves of lesser height (Ref. 38, 426.) 1896. Late May. Prince William Sound region, Alaska. About 12 km north of Orca, this severe earthquake bent trees almost to the breaking point and made it difficult to remain standing. Waves appeared in the ground. Water in the creek splashed from one side to the other. (Ref. 38, 420, 426.) 1898. Aug. 1. Susitna Station, Alaska. Trees swayed violently. (Ref. 420.) 1899. July 11 or July 14. Cook Inlet, Alaska. A “severe” earthquake occurred at Tyonek. Possibly, there is a misprint in the date in ref. 420 (the table in ref. 420 lists earthquakes in chronological order, but the July 11 event is listed between two events on July 14), and the date should be July 14, 1899 (magnitude 7.2, epicenter at lat 60°N., long 150°W.). Tyonek is located at lat 61°N., long 151°W. (Ref. 38, 412, 420.) 1899. Sept. 4, 00 22 UTC (Sept. 3). Near Cape Yakataga, Alaska. During September, the Yakutat Bay region was shaken by a series of severe earthquakes. The first earthquake at 00 22 UTC was moderately strong at Yakutat but was extremely vio- lent at Cape Yakataga, about 160 km west. The shock broke off the tops of trees, generated land- slides, and raised the ocean beach about 1 m. Although no loss of life or property occurred in the region, reported effects include uplift of the coast, landslides, difficulty in standing upright, water waves on the bay, and shaking of houses. Faulting probably occurred at Cape Yakataga. The shock was felt at about 30 known locations, the most distant on the lower Yukon River, about 1,100 km from Yakutat Bay. Strong aftershocks were observed on Sept. 4. Magnitude of first shock, 8.3 MS CFR. (Ref. 38, 404, 412, 420, 424.) 1899. Sept. 10, 17 04 and 21 41 UTC. Yakutat Bay, Alaska. During September, the Yakutat Bay region was shaken by a series of major earthquakes, the most violent of which were felt at all settlements within a radius of 400 km. Several heavy shocks occurred on Sept. 4 and 10, but the main earthquake that caused great topographic changes occurred at 21 41 UTC, Sept. 10 (see fig. 8.) A US. Geological Survey team did not study the region until 6 years after the shocks, but the topo— graphic changes were obvious. Dead barnacles and 50 other shellfish were found everywhere, and several uplifted beaches were observed. A maximum uplift of 14.5 m occurred on the west coast of Disenchantment Bay, and changes of 5 m or more affected a large area. Subsidence of as much as 2 m was observed in a few areas. Phenomena observed included surface faulting, avalanches, fissures, spouting from sand craterlets, and slight damage to buildings. A destruc- tive tsunami 10.6 m in height occurred in Yakutat Bay, and tsunamis also were observed at other places along the Alaskan coast. The earthquake altered the regimen of glaciers in the area. The shattering of Muir Glacier started the rapid discharge of icebergs and the later retreat of this and other ice tongues in Glacier Bay. Avalanch- ing resulted in the later advance of at least nine gla— ciers in Yakutat Bay and perhaps many others in more remote regions. Some severely crevassed glacier fronts, which were found 6 years later, had taken several years for the fractured parts to reach the sea. The first earthquake on Sept. 10 lasted 90 seconds and was heavier at Yakutat than that of Sept. 4 (00 22 UTC). It was strong enough to throw people off their feet at Disenchantment Bay. The main earth- quake on Sept. 10 was felt over a largely unsettled region, and so the total felt area is unknown. Pros- pectors camped on Disenchantment Bay felt over 50 shocks on Sept. 10, two of which were strong. Residents at Yakutat Village also described as severe two of the many shocks observed on that day. Ten or more earthquakes were felt in the Coast and Geo- detic Survey camp near the Copper River delta, and several of them were violent. Several shocks were also felt on Sept. 10 in the Chugach Mountains near Prince William Sound; five were reported about 300 km to the northeast on the Yukon River; and several were felt to the southeast at Juneau and Skagway. Many large aftershocks occurred in September and the following months. Magnitude 7.8 Ms CFR (first shock), 8.6 Ms CFR (second shock). (Ref. 38, 404, 420, 426.) 1899. Sept. 16 (Sept. 15). Yakutat Bay, Alaska. Two strong earthquakes were felt at Yakutat village, each lasting as long as it took to run outdoors. At Skagway, this shock was more pronounced than those of Sept. 4 and 10. A section of one of the long piers at Skagway sank into the water. Several build- ings moved “a foot or two” on their foundations, and two small buildings toppled. (Ref. 420.) 1899. Sept. 23, 11 04 and 12 50 UTC. Near the Copper River delta, Alaska. Eight shocks were noted in the Coast and Geodetic Survey camp, one of which was strong enough to awaken everyone in the camp. A plumb bob vibrated through 25 cm from SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) northwest to southeast; the vibrations were distinct and slow. Possibly felt at Sitka. (Ref. 412, 420.) 1900. Oct. 9. Kodiak Island region, Alaska. The wharf at Woody Island was partly destroyed; chimneys, Windows, and crockery were destroyed in Kodiak. About 50 slight aftershocks continued through the next day. Felt along all of southern Alaska and probably to the west of Kodiak. Magni- tude 8.3 Ms CFR. (Ref. 420, 424, 477.) 1901. Dec. 30. Kenai, Alaska. A strong volcanic eruption occurred. The accompanying earthquake caused several tsunamis. This event is listed as “destructive” in Ref. 426. (Ref. 38, 426.) 1901. Dec. 31 (Dec. 30). Cook Inlet, Alaska. A strong volcanic eruption occurred. The accompanying earthquake caused several tsunamis. Magnitude 7 .8 Ms CFR. (Ref. 38, 477.) 1902. Jan. 1 (Dec. 31, 1901). Fox Islands, Aleutian Islands, Alaska. Magnitude 7.8 Ms CFR. (Ref. 404.) 1903. June 2. Southwest Alaska. Magnitude 8.3 Ms CFR. (Ref. 38, 477.) 1904. Aug. 27. Rampart, Alaska. Buildings swayed and cracked. Magnitude 8.3 Ms CFR, 7.7 Ms GR, 7.8 m1, ABE. (Ref. 38, 477.) 1905. Feb. 14 (Feb. 13). Andreanof Islands, Aleutian Islands, Alaska. Magnitude 7.9 Ms CFR, 7.7 Ms GR, 7.5 mb ABE. (Ref. 477.) 1906. Aug. 17 (Aug. 16). Rat Islands, Aleutian Islands, Alaska. Magnitude 8.3 Ms CFR, 8.0 Ms GR. (Ref. 477.) 1907. Sept. 2. Aleutian Islands, Alaska. Mag- nitude 7.4 MS GR, 7.3 mb ABE. (Ref. 477.) 1908. Feb. 14. Prince William Sound, Alaska. This earthquake was strong at Valdez, Where it upset bottles and vases and threw objects from shelves in all the stores. The Valdez-Sitka and Valdez-Seward submarine cables were broken close to Valdez, well inside Valdez Narrows. A ship approaching the Val- dez dock reported it “felt as though the ship struck on bottom.” Also felt at Cordova, Ellamar, Katalla, Landlock, and Latouche. (Ref. 38, 420.) 1908. May 15 (May 14). Southeast Alaska. At Katalla, the ceiling in one house was cracked, furni- ture was displaced, and dishes were knocked from shelves. Rockslides were reported at Cape Yakataga. Felt from Sitka to Seward. Magnitude 7.0 Ms GR, 7.1 mb ABE. (Ref. 38, 258, 420.) 1909. Feb. 16. Near Yakutat, Alaska. This earthquake was felt more strongly at Skagway and Yakutat than at Juneau, Seward, and Sitka. (Ref. 420.) 1910. Sept. 9 (Sept. 8). Rat Islands, Aleutian Islands, Alaska. The earthquake displaced furniture EARTHQUAKES IN ALASKA 156° 148° 51 132° 124° 66° 620 58° pACIFlC 300 KILOMETERS 54° EXPLANATION * Epicenter XI Intensity 11 oCEAN FIGURE 8.—-Isoseisma1 map for the Yakutat Bay, Alaska, earthquake of September 10, 1899. This map is a simplified version of figure 4 in reference 424 of table 1. in some houses. Magnitude 7.1 Ms GR, 7.1 mb ABE. (Ref. 38, 477.) 1911. Sept. 17 (Sept. 16). Rat Islands, Aleu- tian Islands, Alaska. Magnitude 7.0 mb ABE. (Ref. 412.) 1911. Sept. 22 (Sept. 21). Prince William Sound region, Alaska. This severe earthquake broke a submarine cable near Valdez, close to a point where the cable was broken in the earthquake of Feb. 14, 1908. Objects fell from shelves at Valdez. Large rockslides occurred at the head of the sound. At Golden, on the shores of Wells Bay in northern Prince William Sound, rockslides buried a gulch. One huge slide, carrying with it a part of a small glacier, “passed within a few hundred feet of the town.” The shock also was “heavy” in the mountains of Kenai Peninsula, which borders the western shore of Prince William Sound. An observer north of Kenai Lake reported that it was difficult to remain upright, trees swayed, and rocks rolled down the mountain slopes. Several aftershocks were observed in the area. (Ref. 38, 258, 420.) 1911. Nov. 13. Near Islands, Aleutian Islands, Alaska. Magnitude 7.0 mb ABE. (Ref. 428.) 1912. Jan. 4. Andreanof Islands, Aleutian Islands, Alaska. Magnitude 7.0 Ms GR, 7.0 mb ABE. (Ref. 258.) 52 1912. June 10. Cook Inlet, Alaska. Magnitude 7.0 MS GR, 7.3 mb ABE. (Ref. 258.) 1912. July 7 (July 6). Central Alaska. This earthquake was violent at Fairbanks and strong at Kennicott. The earth “heaved and rolled” at the north base of Mount McKinley, and the country was scarred with landslides. Magnitude 7.4 Ms GR, 7.3 mb ABE. (Ref. 38, 437.) 1919. Dec. 15 (Dec. 14). Juneau area, Alaska. Buildings were badly shaken by “one of the heaviest earthquakes experienced here in years.” (Ref. 38, 272.) 1923. May 4. Alaska Peninsula area, Alaska. Magnitude 7.0 mb ABE. (Ref. 432.) 1925. Feb. 23. Gulf of Alaska. Several chimneys were destroyed and walls were cracked at Anchorage and Seward. One bridgehead was cracked, and the submarine cable between Seward and Valdez was severed. Part of a dock collapsed at Valdez. Two shocks, the second of which was stronger, followed the first within a few seconds. Several aftershocks were observed to Feb. 28. (Ref. 38, 218, 265, 610.) 1926. Oct. 13, 19 08 UTC. Andreanof Islands, Aleutian Islands, Alaska. Magnitude 7.1 Ms GR, 7.1 mb ABE. (Ref. 432.) 1927. Oct. 24. Southeast Alaska. Submarine cables were broken between Petersburg and Wrangell and between Juneau and Skagway. At Sitka, cracks formed in buildings and people were thrown from their feet. Near Hoonah, water in Icy Straits was “churned and muddy,” and strong “tide rips” were reported on Cross Sound. A few windows were broken at Juneau, and several hundred were broken at Petersburg. At Seattle, Wash., small waves were observed on water in swimming pools. Felt through- out southeast Alaska, west to Cordova, and to the north of Fairbanks. Magnitude 7.1 MS GR, 7.1 mb ABE. (Ref. 38, 218, 432, 477.) 1928. June 21. Gulf of Alaska. Three distinct shocks were felt in the Cordova area, the second of which was the strongest. Men were thrown from their bunks 48 km north of Cordova; plaster cracked at Cordova; and landslides occurred at several places in the mountains. The earthquake was “heavy” at Valdez. Also felt at Anchorage, Chickaloon, Mata- nuska, and Seward. Magnitude 7.0 Ms GR, 7.3 mb ABE. (Ref. 1, 258, 477.) 1929. Jan. 21. Near Fairbanks, Alaska. The first earthquake was the most severe at Fairbanks, where it lasted several seconds. Windows were bro- ken, furniture was displaced, and many residents rushed into the streets. Heavy rumbling was heard. The shocks lasted about 4 hours and continued into the next day. (Ref. 2, 258.) SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 1929. Mar. 7, 01 34 UTC (Mar. 6). Fox Islands, Aleutian Islands, Alaska. This earthquake was felt onboard several ships at sea and severely at Dutch Harbor, Alaska. A small tsunami was recorded at Hilo, Hawaii. Magnitude 8.3 Ms CFR, 8.1 MS GR, 7.9 mb ABE. (Ref. 2, 432, 610.) 1929. July 5, l4 19 UTC. Andreanof Islands, Aleutian Islands, Alaska. Magnitude 7 .0 Ms GR, 6.9 mb ABE. (Ref. 432.) 1929. July 7. Andreanof Islands, Aleutian Islands, Alaska. Magnitude 7.3 Ms GR, 7.4 mb ABE. (Ref. 432.) 1929. Dec. 17, 10 58 UTC. Near Islands area, Aleutian Islands, Alaska. Magnitude 7.6 Ms GR, 7.4 mb ABE. (Ref. 432.) 1931. May 30, 11 34 UTC. Attu Island, Alaska. The earthquake broke dishes and overturned small objects on Attu. Almost all canned goods in a store were thrown to the floor. (Ref. 38, 265.) 1932. Mar. 25, 23 58 UTC. South-central Alaska. This earthquake was strongest at Seward, where it broke a water main; landslides occurred on the railroad to the north. (Ref. 5, 38, 258.) 1933. Jan. 4 (Jan. 3). Southern Alaska. Ground cracks formed in the streets of Seward and at several other points in Alaska. The valley leading north from Seward was noticeably disturbed; cracks formed in the Forestry Bureau road for a distance of about 32 km to Kenai Lake. Felt at several towns in the region. Magnitude 7.0 MS GR, 7 .1 mb ABE. (Ref. 6, 38, 258, 477.) 1933. Apr. 27 (Apr. 26). Near Anchorage, Alaska. Houses were shaken from their foundations at Old Tyonek, west of Anchorage across Cook Inlet. Plate—glass windows were broken in several stores in Anchorage, and merchandise tumbled from shelves. Telegraph lines were down for a distance of 80 km from Anchorage. The shock was felt strongly on Kodiak Island and along the Aleutian Islands. Many aftershocks occurred. Magnitude 7.0 Ms GR, 7.1 mb ABE. (Ref. 6, 38, 258.) 1934. May 4 (May 3). Southern Alaska. At Anchorage, windows were broken, stock in stores was jarred from shelves, and telephone lines were “knocked out of commission.” Felt at several towns in the region. (Ref. 7, 258.) 1934. May 14. Kodiak Island region, Alaska. Kodiak and Whale Islands were shaken severely. Plaster cracked at Kodiak and stock fell from shelves. A landslide occurred near Kodiak. The shock “probably was almost as severe” on Afognak and Whale Islands. (Ref. 7, 258.) 1935. Feb. 22. Near Islands, Aleutian Islands, Alaska. Magnitude 6.9 Ms GR, 6.7 mb ABE. (Ref. 258.) EARTHQUAKES IN ALASKA 53 1936. Oct. 23 (Oct. 22). Near Anchorage, Alaska. The earthquake was described as the stron— gest shock in three years at Anchorage, where property loss was estimated at $500. The shock was described as “heavy” at Seward and “strong” at Susitna. Many aftershocks occurred. (Ref. 9, 265.) 1937. July 22. Central Alaska. Only slight damage was caused by this major earthquake because the epicentral area was sparsely populated. Fairbanks sustained considerable minor damage, consisting mostly of broken windows and loss of mer- chandise in stores. Slight damage also was reported at Anchorage, about 580 km south of Fairbanks. At Salcha Bluff, southeast of Fairbanks, the highway was blocked for several meters by a landslide. Near there, mud boils appeared and cracks as wide as 38 cm formed. Water in the nearby slough rose consider- ably above its normal level and did not subside for several days. At mile 33 station of the Alaska Road Commission, a two-story log structure was knocked askew and several windows were broken. About 22 km from Fairbanks, small cracks formed in the road, and near the mile 18 roadhouse, silt and sand from many cracks covered the highway. The main earthquake was felt over most of central Alaska. Aftershocks occurred for several months. Magnitude 7.3 Ms GR. (Ref. 10, 265.) 1938. Nov. 10. Shumag‘in Islands region, Alaska. A major submarine earthquake, centered in a sparsely populated area, was felt strongly at False Pass, Unimak Island. It also was reported at Port Moller and Anchorage. The earthquake generated a small tsunami, which was recorded at Dutch Harbor, Seward, and Sitka, Alaska, and at Hilo and Hono- lulu, Hawaii. Magnitude 8.7 Ms CFR, 8.3 Ms GR, 8.2 mb ABE. (Ref. 11, 38, 432, 610.) 1938. Nov. 17 (Nov. 16). Alaska Peninsula area, Alaska. Magnitude 7.2 Ms GR, 7.2 mb ABE. (Ref. 432.) 1940. Apr. 16, 06 07 UTC (Apr. 15). Near Islands, Aleutian Islands, Alaska. Magnitude 7.1 Ms GR, 7.1 mb ABE. (Ref. 432.) 1940. Apr. 16, 06 43 UTC (Apr. 15). Near Islands, Aleutian Islands, Alaska. Magnitude 7 .2 Ms GR. (Ref. 432.) . 1940. July 19, 16 27 UTC. Kenai Peninsula area, Alaska. Slight damage occurred at Anchorage, Where walls were cracked and small objects were dis- placed. (Ref. 13, 38.) 1940. Aug. 22 (Aug. 21). Near Unalaska Island, Alaska. Magnitude 7.1 Ms GR, 7.2 mb ABE. (Ref. 258.) ‘ 1941. July 30 (July 29). Kenai Peninsula area, Alaska. At Anchorage, one building was shaken from its foundation and four “pipes” (prob- ably water pipes) were broken. Plaster fell, dishes broke, windows cracked, and stock toppled to the floor. Three aftershocks were observed. (Ref. 14, 38, 258.) 1943. Nov. 3. South-central Alaska. This earth- quake was felt at Anchorage, where an abrupt, heav- ing motion swung doors and rattled windows. Magnitude 7.3 MS GR, 7.2 mb ABE. (Ref. 38, 432.) 1944. Dec. 12 (Dec. 11). Rat Islands, Aleutian Islands, Alaska. Magnitude 7.0 Ms GR, 7.1 mb ABE. (Ref. 258.) 1946. Jan. 12. Gulf of Alaska. Magnitude 7.2 Ms GR, 7 .2 mb ABE. (Ref. 432.) 1946. Apr. 1, 12 28 UTC. Unimak Island region, Alaska, southeast of Scotch Cap Light- house. This major earthquake caused only minor damage to buildings on Unimak Island, but it gener- ated a tsunami that devastated the lighthouse and swept away its five occupants. The height of the wave at the lighthouse was estimated at about 35 m. Tsunami damage also occurred at Dutch Harbor and Ikatan Island in the Aleutian Islands, on the west coasts of North and South America, and in Hawaii. At Hilo, Hawaii, the tsunami took 159 lives and caused $26 million loss to property. The tsunami caused one death in California. Magnitude 7.4 Ms GR, 7.2 mb ABE. (Ref. 19, 38, 432, 533, 610.) 1946. Nov. 1 (Oct. 31). Andreanof Islands, Aleutian Islands, Alaska. Magnitude 7.0 Ms ABE, 6.9 mb ABE. (Ref. 258.) 1947. Oct. 16 (Oct. 15). Fairbanks area, Alaska. This major earthquake centered southeast of Nenana on the Salcha River fault. Small fissures formed in the ground near the Nenana Airport, southwest of Fairbanks. Streets “upheaved” at Nenana in several places, and several long cracks formed in the ground. Cracks in river mud and ice occurred from Shaw Creek on Richardson Highway to the headwaters of the Kantishna and Tolavana Rivers. Cracks 56 cm wide, as much as 30 cm deep, and several meters long were reported about 24 km below Chena Bluffs on the Tanana River. A few pres- sure ridges were observed where large, frozen blocks came together. Alaska Railroad officials reported that rails were bent between Julius, Nenana, and Browne, and that some changes were observed in the elevation of the roadbed. Landslides occurred on the Richardson Highway, and rockslides were observed between Fair- banks and Nenana on the Tanana River. In Fairbanks, merchandise in stores was damaged heavily, many windows were broken, and a powerline short-circuit occurred near the University of Alaska. Changes in the flow of water in several wells were reported both at Fairbanks and Nenana. Trees and 54 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) poles were shaken Violently. At the town of Clear, south of Nenana, some prefabricated buildings were damaged. The felt area is rather well defined to the south and west but is uncertain to the north and east because of the sparse population. The earthquake was felt over most of central and southern Alaska and at two places in the Yukon Territory of Canada, an area within a radius of about 500 km of the epi— center. This earthquake series consisted of more than 200 foreshocks and aftershocks. The strongest after- shock occurred on Oct. 20. Magnitude 7.0 MS GR, 6.9 mb ABE. (Ref. 20, 38, 260.) 1948. May 14. Alaska Peninsula area, Alaska. Magnitude 7.5 Ms GR, 7.3 mb ABE. (Ref. 432.) 1949. Sept. 27. Gulf of Alaska. Magnitude 7.0 mb ABE. (Ref. 258.) 1951. Feb. 13. Alaska Peninsula area, Alaska. Magnitude 7.1 Ms GR, 7.1 mb ABE. (Ref. 432.) 1952. Dec. 7 (Dec. 6). Shemya Island, Alaska. This earthquake disconnected a water main and elec- trical cables and cracked a cement floor at Shemya Air Force Base. (Ref. 25, 38, 265.) 1953. Jan. 5 (Jan. 4). Near Islands area, Aleutian Islands, Alaska. Felt on Attu Island, Alaska. Magnitude 7 .0 mb ABE. (Ref. 26, 432.) 1954. Oct. 3. Kenai Peninsula, Alaska. At Anchorage, the violent shaking broke water connec- tions in two 14-story buildings. North of Potter, more than 42 m of railroad track was “knocked out of commission.” Minor landslides spilled down on the Seward—Anchorage Highway. Cracks in concrete walls, fallen plaster, and shattered plate-glass win- dows were reported at Anchorage, Homer, Kenai, Seward, Sterling, and Valdez. Magnitude 6.5 Ukn BRK. (Ref. 27, 38, 447.) 1957. Mar. 9, 14 22 UTC. Andreanof Islands, Aleutian Islands, Alaska. This great earthquake destroyed two bridges on Adak Island, damaged houses, and left a 4.5-m crack in a road. On Umnak Island, part of a dock was destroyed, and Mount Vsevidof erupted after being dormant for 200 years. Further, this shock generated a 15-m tsunami that smashed into the coastline at Scotch Cap and an 8-m tsunami that washed away many buildings and dam- aged oil lines extensively at Sand Bay. This tsunami continued to Hawaii, where it destroyed two villages and inflicted about $5 million in property damage on Oahu and Kauai Islands. The tsunami also caused minor damage in San Diego Bay, Calif, before travel- ing to such distant countries as Chile, El Salvador, Japan, and other areas in the Pacific region. More than 300 aftershocks were reported along the south- ern edge of the Aleutians, from Unimak Island to Amchitka Pass. Magnitude 7.7 mb ABE, 8.3 Ukn PAS. (Ref. 30, 38, 479, 610.) 1957. Mar. 9, 20 39 UTC. Fox Islands, Andreanof Islands, Alaska. Felt on Adak Island. Magnitude 7.1 Ukn PAS, 7.0 mb ABE. (Ref. 30, 432,479.) 1957. Mar. 11, 09 58 UTC (Mar. 10). Fox Islands, Aleutian Islands, Alaska. Magnitude 6.9 Ukn PAS, 7.1 Ukn BRK, 6.9 mb ABE. (Ref. 432.) 1957. Mar. 11, 14 55 UTC. Andreanof Islands, Aleutian Islands, Alaska. Felt on Adak and Umnak Islands. Magnitude 7.0 mb ABE, 6.7 Ukn PAS, 7.1 Ukn BRK. (Ref. 30, 479.) 1957. Mar. 12, 11 44 UTC. Andreanof Islands, Aleutian Islands, Alaska. Felt on Adak and Umnak Islands. Magnitude 7.1 mb ABE, 7.3 Ukn PAS. (Ref. 30, 479.) 1957. Mar. 14, 14 47 UTC. Andreanof Islands, Aleutian Islands, Alaska. Felt on Adak Island. Magnitude 7.0 mb ABE, 7.2 Ukn PAS, 7.4 Ukn BRK. (Ref. 30, 479.) 1957. Mar. 16, 02 34 UTC (Mar. 15). Andreanof Islands, Aleutian Islands, Alaska. Felt on Adak Island. Magnitude 7.0 mb ABE, 6.7 Ukn PAS. (Ref. 30, 479.) 1957. Mar. 22, 14 21 UTC. Fox Islands, Aleu- tian Islands, Alaska. Magnitude 6.9 mb ABE, 7.0 Ukn PAS, 7.0 Ukn BRK. (Ref. 432.) 1957. Apr. 10, 11 29 UTC. Kodiak Island region, Alaska. Magnitude 7.0 mb ABE, 7.1 Ukn PAS, 7.2 Ukn BRK. (Ref. 432.) 1957. Apr. 19, 22 19 UTC. Fox Islands, Aleu- tian Islands, Alaska. Magnitude 6.5 Ms ABE, 7.1 mb ABE. (Ref. 265.) 1957. June 13. Andreanof Islands, Aleutian Islands, Alaska. Magnitude 6.7 mb ABE. (Ref. 265.) 1958. Apr. 7. Central Alaska. A major earth- quake on this date caused mud flows, widespread breakage of lake and river ice, and formation of many ground cracks within a 65- to 80-km radius of Huslia (west of Fairbanks). Observers also reported pressure ridges, thawing of ice on lakes, and craters 6 m across and about 2 m deep in the ground. Ground cracks occurred at Tanana. Minor damage to roofs and foundations of buildings was reported at Huslia. Slight damage also was observed at several central Alaska towns. Magnitude 7.3 Ukn PAS, 7.1 mb ABE. (Ref. 31, 447.) 1958. July 10, 06 15 UTC (July 9). Southeast Alaska. This was the largest earthquake in south- east Alaska since the Yakutat shocks of 1899. The only permanent settlement in the epicentral region was Yakutat; therefore, effects on man-made works were moderate for such a large earthquake. On Khantaak Island (in Yakutat Bay), three persons EARTHQUAKES IN ALASKA 55 were killed when the north end of the island slumped into the sea, and two people were missing and pre- sumed dead in Lituya Bay from a wave generated by the collapse of 300 million m3 of rock into Gilbert Bay. At Yakutat, bridges, docks, and oil lines were damaged, a water tower fell, and a few cabins were destroyed. Many sand blows and ground fissures were observed on the low coastal plain southeast of Yakutat, and large landslides were reported in the mountains. A cabin collapsed and the ground was fis- sured at Dry Bay (East River); many sand blows and ground cracks occurred at Dry Bay (Akwe River); and submarine cables were severed in the Haines-Skag- way area and at Lena Point (north of Juneau). Slight damage also occurred at Auke Bay, Baranof, Juneau, Pelican, and Sitka. A massive rockslide at the head of Lituya Bay caused water to surge about 530 m, generating a “gravity wave” that swept out of the bay. A fishing boat anchored in Anchorage Cove was carried in front of the largest wave crest, and those onboard estimated they cleared La Chaussee Spit (at the mouth of Lituya Bay) by 30 m or more. Two people on another fishing boat disappeared after being caught in the huge wave. This major earthquake was felt over a large area of southeast Alaska, as far south as Seattle, Wash., and east to Whitehorse, Y.T., Canada (see fig. 9). Magnitude 7.1 mb ABE, 7.9 Ukn PAS, 8.0 Ukn BRK. (Ref. 31, 38, 448, 533, 610.) , 1960. Nov. 13 (Nov. 12). Fox Islands, Aleutian Islands, Alaska. Magnitude 7.1 mb ABE, 7.0 Ukn PAS, 7.2 Ukn BRK. (Ref. 432.) 1961. Sept. 5. Kenai Peninsula, Alaska. Slight damage in the form of cracked plaster and broken dishes and mirrors occurred at Seward. The shock also was felt at several other towns in the region. Magnitude 5.75 Ukn BRK. (Ref. 34, 447.) 1962. Oct. 21 (Oct. 20). Anchorage area, Alaska. Slight damage to telephone lines, merchan- dise in stores and houses, and plaster was observed in the Anchorage-Girdwood-Wasilla area. Also felt at Kenai, Soldotna, and Susitna Station. (Ref. 35, 447.) 1963. June 24 (June 23). Cook Inlet, Alaska. At Seldovia, a brick chimney toppled; at Homer, a ceiling beam burst and posts were torn from the ground; and at Barbara Point (8 km north of Sel- dovia), a heavy fireplace slab was displaced about 15 cm, and a concrete foundation was cracked. Rock- slides were observed in the area. The shock also was felt at Anchorage, Cordova, and Homer area. Magni- tude 6.5—6.75 Ukn BRK. (Ref. 36, 447.) 1964. Feb. 6, 13 07 UTC. Near Chirikof Island, Alaska. Magnitude 7.1 mb ABE, 6.9 Ukn PAS, 6.9 Ukn PAL, 6.6 Ukn BRK. (Ref. 37, 432.) 1964. Mar. 28 (Mar. 27). Prince William Sound, Alaska. This great earthquake and ensuing tsunami took 125 lives (tsunami 110, earthquake 15), and caused about $311 million in property loss. Earthquake effects were heavy in many towns, including Anchorage, Chitina, Glennallen, Homer, Hope, Kasilof, Kenai, Kodiak, Moose Pass, Portage, Seldovia, Seward, Sterling, Valdez, Wasilla, and Whittier. Anchorage, about 120 km northwest of the epicen- ter, sustained the most severe damage to property. About 30 blocks of dwellings and commercial build- ings were damaged or destroyed in the downtown area. The J.C. Penney Company building was dam- aged beyond repair; the Four Seasons apartment building, a new six-story structure, collapsed; and many other multistory buildings were damaged heavily. The schools in Anchorage were almost devas- tated. The Government Hill Grade School, sitting astride a huge landslide, was almost a total loss. Anchorage High School and Denali Grade School were damaged severely. Duration of the shock was estimated at 3 minutes. Landslides in Anchorage caused heavy damage. Huge slides occurred in the downtown business sec- tion, at Government Hill, and at Turnagain Heights. The largest and most devastating landslide occurred at Turnagain Heights. An area of about 130 acres was devastated by displacements that broke the ground into many deranged blocks that were col— lapsed and tilted at all angles. This slide destroyed about 75 private houses. Water mains and gas, sewer, telephone, and electrical systems were dis- rupted throughout the area. The earthquake was accompanied by vertical dis- placement over an area of about 520,000 km2. The major area of uplift trended northeast from southern Kodiak Island to Prince William Sound and trended east-west to the east of the sound. Vertical displace~ ments ranged from about 11.5 In of uplift to 2.3 m of subsidence relative to sea level. Off the southwest end of Montague Island, there was absolute vertical displacement of about 13—15 m. Uplift also occurred along the extreme southeast coast of Kodiak Island, Sitkalidak Island, and over part or all of Sitkinak Island. This zone of subsidence covered about 285,000 kmz, including the north and west parts of Prince William Sound, the west part of the Chugach Mountains and a part of the lowlands north of the mountains, most of Kenai Peninsula, and almost all the Kodiak Island group. This shock generated a tsunami that devastated many towns along the Gulf of Alaska and left serious damage at Alberni and Port Alberni, Canada, along 56 156° 148° SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 140° 132° 124° . Fairbanks SBIVLS (131an 62° 58° PACIFIC OCEAN 54° 0 200 KILOMETERS L—.__J ...‘ VGVNVO O I Whitehorse ) l = vn ~ / «a '. \\ )3 3§\\ . 5' EXPLANATION * Epicenter XI Intensity 11 FIGURE 9.—Isoseismal map for the southeast Alaska earthquake of July 10, 1958. This map is a simplified version of figure 6 in reference 424 of table 1. the West Coast of the United States (15 killed), and in Hawaii. The maximum wave height recorded was 67 m at Valdez Inlet. Seiche action in rivers, lakes, bayous, and protected harbors and waterways along the Gulf Coast of Louisiana and Texas caused minor damage. It was also recorded on tide gages in Cuba and Puerto Rico. This great earthquake was felt over a large area of Alaska and in parts of western Yukon Territory and British Columbia, Canada (see fig. 10). Magnitude 7.9 mb ABE, 8.4 Ukn PAS, 8.6 Ukn BRK, 8.6 Ukn PAL. (Ref. 37, 38, 451, 523, 533, 611.) 1964. Apr. 14. Kodiak Island region, Alaska. At Kodiak, light fixtures broke and several cracks formed in one building. The City Hall, fire station, and library building were “further weakened.” (Ref. 37, 299.) 1964. Dec. 13 (Dec. 12). Nome area, Alaska. At Nome, a water pipe broke; concrete floor, walls, and plaster cracked; and crusted snow broke into chunks. Also felt strongly at Teller. Several after- shocks were felt in the Nome area. (Ref. 37, 299.) 1965. Feb. 4, 05 01 and 08 40 UTC (Feb. 3). Rat Islands, Aleutian Islands, Alaska. On Adak Island, cracks occurred in prefabricated wood build- ings; on Shemya Island, cracks were observed in an asphalt runway. Hairline cracks also formed in the runways at the US. Coast Guard Loran Station on EARTHQUAKES IN ALASKA 57 (191s SaMatlaushndzys' §§§§ ; Five-story J .C. Penney Building, 5th Avenue and Downing Street, Anchorage, Alaska, partly collapsed by the March 28, 1964 (Mar. 27 AST), earthquake. Note undamaged buildings nearby. Attu Island. This earthquake generated a tsunami reported to be about 10.7 m high on Shemya Island. Loss caused by flooding on Amchitka Island was esti- mated at about $10,000. An aftershock at 07 40 UTC was assigned MMI VI. Magnitude 7.7 mb ABE, 7.7 Ukn PAS, 7.7 Ukn BRK (first shock); 7.0 mb ABE, 16.9 Ukn PAS (second shock). (Ref. 75, 299, 610.) 1965. Mar. 30, 02 27 UTC (Mar. 29). Rat (Islands, Aleutian Islands, Alaska. Felt on Adak and Amchitka Islands. Magnitude 7.4 mb ABE, 7.2 Ukn PAS, 6.9 Ukn BRK, 7.7 Ukn PAL. (Ref. 75, 299.) 1965. Apr. 16. Central Alaska. Slight damage to walls and dishes occurred at Elim. River ice was ‘icracked at Kaltag and Unalakleet. Thunderous earth noises were reported. Felt over a small area of cen- tral Alaska. (Ref. 75, 299.) 1965. July 2. Fox Islands, Aleutian Islands, ‘Alaska. In one house on Umnak Island, dishes were broken and books were thrown over all the room. A minor tsunami having a 9-cm amplitude was regis- tered on Unalaska Island. Also observed at Cold Bay. Magnitude 7.0 mb ABE, 6.9 Ukn PAS, 6.8 Ukn BRK, i6.7 Ukn PAL. (Ref. 75, 299.) 1966. Aug. 7 (Aug. 6). Andreanof Islands, Aleutian Islands, Alaska. Felt on Adak Island. Magnitude 6.4 Ms ABE, 6.7 Ukn PAS, 7.0 Ukn BRK. (Ref. 81, 299.) 1967. June 21, 18 04, 18 13, and 18 24 UTC. Fairbanks area, Alaska. Three moderate earth- quakes caused minor damage to property in the Fair- banks area. The most extensive loss occurred at the State Court and Office Building in Fairbanks. Both interior and exterior walls cracked, parts of hanging ceilings and light fixtures fell, plumbing broke, and cabinets and shelves overturned. Several chimneys fell in the area, a tall chimney stack buckled, win- dows broke, and considerable loss of merchandise was reported in stores. Three ground cracks about 2 m apart were observed at Badger Pass and Peede Road, and blue mud seeped through the cracks. On Richardson Highway, water spouted from ground cracks, a sewer line broke, and chimneys were offset. Small land- slides occurred. About 6,000 aftershocks were recorded through June 28. About 60 aftershocks were observed by residents, and some caused additional SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Landslide and slumping effects in the ’I‘urnagain Heights area, Anchorage, Alaska, caused by the March 28, 1964 (Mar. 27 AST), earthquake. damage. Magnitude 5.5 Ukn PAS (first shock). (Ref. 40, 74, 452.) 1967. June 23. Fairbanks area, Alaska. The State Court and Office Building in Fairbanks sustained additional damage. Merchandise fell in stores. (Ref. 40, 74.) 1968. Oct. 29. Central Alaska. The epicentral area, southeast of Rampart on the Yukon River, was shaken badly but sustained no serious damage because most of the buildings were constructed of logs. Stock tumbled from shelves, residents ran from buildings, and equipment not bolted down was dis- placed. In the Hunter Creek area, about 16 km from Rampart, many landslides were observed on the south-facing slopes. Lake ice was cracked extensively in places. At Nenana, about 80 km southeast of Rampart, cracks formed in the ground and plaster was broken. More than 2,000 aftershocks were recorded through Nov. 12. Magnitude 6.4 Ms BRK, 6.9 Ukn PAS, 7.0 Ukn GOL. (Ref. 41, 299.) 1968. Dec. 17. Southern Alaska. Slight damage occurred at Kenai. Felt from Cantwell southeast to Kodiak. Magnitude 6.4 Ms BRK. (Ref. 38, 41, 299.) 1972. July 30. Southeast Alaska. At Sitka, a few chimneys fell and some minor landslides were reported. Slight damage also was sustained at Hoonah, Juneau, Pelican, and Yakutat. The Fair- weather fault ruptured over a length of 75 km. Seiches were observed in swimming pools as far south as Seattle, Wash. At least 19 aftershocks were felt at Sitka through Aug. 29. A tsunami of 10 cm was recorded at Juneau and 8 cm at Sitka. The main shock was felt over a large area of southeast Alaska and British Columbia, Canada. Magnitude 7.4 mb AB3, 7.2 Ukn PAS, 7.1 Ukn BRK. (Ref. 45, 74, 610.) EARTHQUAKES IN ALASKA 59 148° 140° 124° 180° 1 72° 164° 1 56° Barrow 68° 64° 60° 56° I. ‘ a a / Q. M 0 PACIFIC ‘ ZDD KILOMETERS ARCTIC ‘(fivcfimn \ V; . s1, EXPLANATION * Epicenter X Intensity 10 Figure 10.—Isoseismal map for Prince William Sound, Alaska, earthquake of March 28, 1964. This map is a simplified version of the map in reference 528 of table 1. 1972. Aug. 3 (Aug. 2), 04 40 UTC. Andreanof Islands, Aleutian Islands, Alaska. Minor damage occurred on Adak Island. Magnitude 6.4 Ms BRK. (Ref. 45, 479.) 1975. Feb. 2, 08 43 UTC (Feb. 1). Near Islands, Aleutian Islands, Alaska. A major earth- quake injured several residents and caused severe damage on Shemya Island. The Shemya Air Force Base runway sustained cracks. Crevasses having as mhch as 16.5 In of vertical displacement were observed on Shemya. Landslides occurred, water tanks twisted, and underground water pipes broke. Many aftershocks were felt during the weeks follow- ing the main shock. Also felt on Attu Island. Magnitude 7.0 mb AB3, 7.5 Ukn PAS, 7.4 Ukn BRK. (Ref. 48, 74.) 1977. Nov. 4 (Nov. 3). Andreanof Islands, Aleutian Islands, Alaska. This earthquake downed plaster and moved heavy furniture on Adak Island and cracked chimneys on Atka Island. Magnitude 7 .0 Ms BRK. (Ref. 39, 479.) 1978. Aug. 18. Southern Alaska. At Clam Gulch, southwest of Anchorage on the Kenai Penin- sula, hairline cracks formed in cinder-block walls, and plasterboard was cracked. Felt over a small area of south-central Alaska. (Ref. 74, 240.) 1979. Feb. 28. Southeast Alaska. This major earthquake was located about 50 km northwest of Mt. St. Elias, near the east end of the Chugach Mountains. It affected the area only slightly because it centered in an unpopulated area of ice fields. Seven major earthquakes have been located in the 60 region between Controller Bay and northern Chich— agof Island in southeast Alaska from 1899 to 1979, three of which were of magnitude 8 or larger. This earthquake was strongest at the Icy Bay Lumber Camp, about 76 km south of the epicenter, where a parked logging truck was bounced sideways across the road, trees and bushes were shaken strongly, and people had difficulty in standing. Minor damage occurred in Alaska at Border City, Cape Yakataga, Juneau area, Valdez, and Yakutat; minor damage occurred in Yukon Territory, Canada, at Beaver Creek, Burwash Landing, Destruction Bay, and Klu- ane Lake Fishing Camp. A 15-cm tsunami was recorded at Yakutat. Magnitude 7.3 MS BRK, 7.1 mb AB3. (Ref. 424, 455, 610.) 1979. May 20 (May 19). Alaska Peninsula area. Minor damage at Larsen Bay included cracks in plaster and drywall and hairline cracks in exterior walls. Also felt at a few other towns in the area. Magnitude 6.5 mb PAS, 6.2 mb BRK. (Ref. 74, 262.) 1983. July 12, 15 10 UTC. Prince William Sound, Alaska. The epicenter of this earthquake is near that of the great 1964 earthquake (which had a magnitude of 8.3). At Valdez, an estimated $1 million in damage occurred at the airport terminal building. Its exterior concrete-block walls cracked from roof to ground, and its inside walls also sustained cracks. Ceiling tiles fell in the high school and elementary school buildings; cracks formed in streets and side- walks. Minor damage also was observed at Girdwood. This shock was felt from Yakutat on the south to Fairbanks on the north and east to Whitehorse, Y.T., Canada. Magnitude 6.3 MS BRK, 6.3 mb BRK, 6.4 mb PAS. (Ref. 360.) 1983. Sept. 7. Prince William Sound, Alaska. This moderate earthquake, whose epicenter is near that of the great 1964 earthquake, caused property damage at Gakona and Valdez. Damage was most severe at Valdez, where chimneys and foundations cracked and hairline cracks formed in interior walls. The flow of water in wells was disturbed at Gakona, and small landslides and slumping of roadfill occurred. Magnitude 6.3 mb BRK, 6.4 mb PAS. (Ref. 360.) 1984. Aug. 14 (Aug. 13). Southern Alaska. Slight damage in the form of shattered Windows and broken dishes occurred at Palmer, Sutton, and Wil- low. Buildings were shaken strongly, and people had SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) difficulty standing. Small landslides were observed at Palmer and on Glenn Highway, near Sutton. The earthquake shook objects from walls and knocked merchandise from store shelves throughout the area. Residents observed several slight aftershocks during the week. (Ref. 74, 370.) 1985. Oct. 9 (Oct. 8). Shumagin Islands area, Alaska. Magnitude 6.6 Ms PAL, 6.0 Ms PAS. (Ref. 74, 371.) 1986. May 7, 22 47 UTC. Andreanof Islands, Aleutian Islands, Alaska. This earthquake caused moderate damage to structures on Adak Island and slight damage on Atka Island. Damage to buildings on Adak Island consisted of cracked masonry and concrete walls, failure of partitions and suspended ceilings, spalling on concrete beams and piers, and differential settlement of house foundations. Soil liq- uefaction was observed in localized areas of back- filled soil, and sand boils were observed. Laterally spreading cracks and differential ground settlement occurred along a small wharf. This earthquake caused a small tsunami that was recorded through- out the Pacific Ocean. Magnitude 7.9 MS BRK. (Ref. 562, 610.) 1986. May 15 (May 14). Andreanof Islands, Aleutian Islands, Alaska. On Atka Island, under- ground pipes were broken, bridges were slightly dam— aged, and hairline cracks formed in interior walls. Magnitude 6.4 Ms BRK. (Ref. 562.) 1986. May 17. Andreanof Islands, Aleutian Islands, Alaska. An airstrip on Atka Island was damaged and officially closed. Underground pipes were broken, furniture was overturned, and land- slides were reported. Magnitude 6.5 MS BRK. (Ref. 562.) 1987. Nov. 30, 19 23 UTC. Gulf of Alaska. Damage at Yakutat, northwest of Juneau, consisted mainly of broken glassware and cracks in plaster, drywall, windows, and a foundation. Light damage occurred at several other towns. Also, cracks in wet ground were reported at Yakutat. Strong building vibrations made it difficult to stand or walk. Two ships in the epicentral area were damaged, and three others in the area felt the shaking strongly. A small tsunami was recorded at Seward, Sitka, and Yakutat. This earthquake had the largest magnitude of any event in the region since that on Oct. 9, 1900. Magni- tude 7.7 Ms BRK. (Ref. 74, 577, 610.) 36° 34° 32° ARIZONA 1 14° 1 12° 1 10° UTAH CO NEVADA Fredonia'é 7‘51} 8 O GSagstaff z 5 C9 m z 2 g ARIZONA g ~—-E m __ A a < O O O 0 Phoenix 0 Yuma O O \ o Tucson EXPLANATION Magnitude/Intensity _ O 3.5-4.4/V| O 4.5-4.9 O 5.0-5.4/V| O 0 l 100 KILOMETERS Earthquakes in Arizona with magnitudes 2 4.5 or intensity 2 VI. 61 62 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) ARIZONA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) m. Ms M (1.000 kmz) 1878 12 17 23 30 32.7 N 114.6 W — 343 — — —- — VI 343 —- 1887 05 03 09 30.8 N 109.25 W — 343 — —— — 7.36NS 201 471 1590 1888 O8 19 1100 32.7 N 114.6 W — 343 — — — —-- VI 343 ~— 1890 06 11 0154 32.7 N 114.6 W — 343 — — — — VI 343 — 1892 02 02 08 30 35.2 N 111.6 W — 343 —— — — —— VI 343 -— 1906 01 25 213230 35.2 N 111.7 W —— 38 — — — — VII 38 233 1910 09 24 0405 35.8 N 111.5 W -— 343 — —-— —— — VII 343 116 1912 08 18 2112 36.0 N 111.5 W — 56 — — —- — VII 38 142 1916 03 30 05 47 31.4 N 110.9 W —— 272 — — —- — VI 343 — 1935 01 02 0730 32.8 N 114.2 W — 38 — — — — VI 38 — 1935 01 10 0810 36.0 N 112.1 W — 8 — — — — VI 8 — 1950 01 17 0051 35.7 N 109.5 W — 23 — — —— — VI 38 — 1951 04 12 062010 32.0 N 113.0 W — 294 —- — 4.50ML PAS -— — — — 1959 07 21 17 39 29 36.80 N 112.37 W 000 265 — — 5.60ML PAS —, VI 32 21 1959 10 13 081500 35.5 N 111.5 W —-— 266 5.0 — 5.00ML PAS — V 32 — 1961 06 18 081207.1 32.4 N 112.5 W — 266 -—- — 4.70ML PAS — — -— — 1962 02 15 07 12 42.9 36.9 N 112.4 W 026 266 — —— 4.50M; PAS —- V 35 2 1969 12 25 12 49 10.1 33.4 N 110.6 W 015 74 4.4 — — —— VI 343 — 1976 02 04 000458.1 34.655N 112.500W 012 74 4. — 5.10ML GS 4.62EBE VI 49 25 1976 02 23 140954.4 34.679N 112.432W 010 74 — — 3.50ML GS — VI 49 2 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1878. Dec. 17. Yuma, Ariz. This shock cracked walls in several houses in Yuma. Almost all the buildings in town were shaken. Also felt in Calif. The epicenter of this event probably was in Baja Califor- nia, Mexico. (Ref. 343.) 1887. May 3. Northern Sonora, Mexico. This earthquake occurred in a sparsely settled region of Northern Sonora, Mexico. It caused widespread dam- age to property, 51 deaths (ref. 494 reports 150 deaths at Bavispe, Sonora), and many injuries. From Guaymas, Sonora, Mexico to Nogales, Ariz.; Benson and Tucson, Ariz.; El Paso, Tex.; and at towns as far away as Albuquerque, N. Mex., water in tanks slopped over, railroad cars were set in motion on tracks, chimneys were thrown down, and buildings were cracked. Other US cities that sustained mod- erate to heavy damage include: Bisbee, Fairbank, Fort Huachuca, Saint David, San Simon, Solomon- ville, Tombstone, Tres Alamos, and Willcox, Ariz.; and Deming, Sabinal, and Silver City, N. Mex. Near the epicenter, liquefaction effects induced significant ground failure that led to the collapse of buildings and other structures. At Tepic, Sonora, a town about 190 km south of Tombstone, Ariz., the walls and roofs of every house were shatteredfl—many of the walls had fallen out, and the roofs had collapsed. The plaza and streets at Tepic were “ripped up” by fissures, some as wide as 15 cm, and irrigation ditches around the town were broken. At Moctezuma, about 32 km south of Tepic, the houses were wrecked, and all inhabitants were living outside. At Oputo, about 56 km north- east of Tepic, a church collapsed and killed 40 peo- ple Who had run there for shelter from the earthquake. American prospectors in that area reported that a ground fissure about 0.8 m wide was created by the earthquake. The 7 6-km—long fault scarp produced by this earth- quake is clearly exposed on the east side of the San Bernardino Valley of Northern Sonora, southeast of Douglas, Ariz. The maximum displacement on the Pitaycachi fault is 4.5 to 5.1 m, and evidence exists for previous ruptures on the fault. A significant region of liquefaction was reported as far as 100 km from the fault, and landslides were observed at far- ther distances. In late 1972, the 1887 scarp was observed from the air along its total length. This study revealed many additional scarps, previously unmapped, paralleling the main fault trace. These EARTHQUAKES IN ARIZONA 63 scarps appear to represent active faulting over the previous several thousand years. Seismic motion was felt from Toluca, Mexico (near Mexico City) on the south to Albuquerque and Santa Fe, N. Mex, on the north; and from Baja California, Mexico, and Yuma, Ariz., on the west to a point 100 km east of El Paso, Tex., on the east (see fig. 11). There also was a report that the earthquake was felt in California. Many aftershocks were observed. (Ref. 38, 343, 471, 494, 497.) 1888. Aug. 19. Yuma, Ariz. This earthquake shook down a few old sheds at Yuma. Everyone awoke and ran outside. (Ref. 343.) 1890. June 11 (June 10). Yuma, Ariz. A sharp earthquake that broke several windows at Yuma probably centered in Baja California, Mexico. (Ref. 343.) 1892. Feb. 2. Flagstaff, Ariz. At Flagstaff, the earthquake awakened many people who ran into the street. At 'va0 Guns, a land bridge collapsed; a huge rock toppled onto the entrance of a cave; and stones shook loose from the walls inside the caverns. (Ref. 343.) 1906. Jan. 25. Flagstaff, Ariz. Chimneys were thrown down and walls were cracked at Flagstaff. At the courthouse and the Coconino County Hospi- tal, plaster fell from the ceilings. At the school, plaster cracked in every room. Stones and dead trees were shaken down the San Francisco Peaks. Also felt in southern Utah and northwestern N. Mex. (Ref. 38, 343.) 1910. Sept. 24 (Sept. 23). Coconino National Forest, near Flagstaff, Ariz. At Cedar Wash, a house was moved off its foundation, its chimney was shaken down, and one corner of the house was cracked severely. Huge lava stones weighing many tons were torn from the old lava beds and thrown down the mountainside. About 80 km north of Flag- staff, in the Coconino Forest, boulders rolled down a mountain into the camp of a construction crew. Fifty- two shocks were felt by the construction crew between Sept. 10 and 23, 1910 (local time). The strongest shock was so violent that the construction crew temporarily abandoned the work site. Plaster cracked and fell at Flagstaff. (Ref. 343.) 1912. Aug. 18. Northern Arizona. Rockslides roared down the mountain in Lockett Tanks country, southeast of the Grand Canyon. Boulders were shaken from cliffs, and rocks were reportedly lifted free from the ground. An unconfirmed report stated that an earth fracture extended from Lockett Tanks to Coconino Mountain, a distance of more than 48 km. Also felt in N. Mex. and Utah. (Ref. 38, 56, 343.) 1916. Mar. 30 (Mar. 29). Nogales, Santa Cruz County, Ariz. The earthquake cracked walls at N ogales and knocked down plaster at the courthouse. People ran from the Nogales theater. (Ref. 272, 343.) 1935. Jan. 2 (Jan. 1). Wellton, Yuma County, Ariz. Walls and plaster cracked at Wellton, east of Yuma. Everyone felt the ground quiver and their houses shake. (Ref. 38, 343.) 1935. Jan. 10. Grand Canyon, Ariz. Walls or plaster cracked and windows broke at Grand Can- yon. Minor rockslides were reported. (Ref. 8, 343.) 1950. Jan. 17 (Jan. 16). Apache County, Ariz. South of the Ganado Trading Post, several cracks formed in the ground. A 6.5-m-high offset fissure occurred in the creek bed beneath a timber bridge (near lat 35.55°N., long 109.10°W.). (Ref. 23, 38, 343.) 1959. July 21. Arizona-Utah border. Minor damage to chimneys and walls was reported at Fre- donia, Ariz., and Kanab, Utah, about 15 km north of Fredonia. In addition, Windows broke in houses and stores and dishes fell from shelves at Fredonia. Almost all merchandise was shaken from shelves in stores. A rockslide at Mather Point in the Grand Canyon was attributed to the shock. (Ref. 32, 265.) 1969. Dec. 25. Southern Arizona. The tremor broke dishes and windows in the Globe-Miami area, east of Phoenix in Gila County. Hundreds of resi- dents were awakened by the strong shaking. Walls were cracked on the San Carlos Reservation. (Ref. 74, 343.) 1976. Feb. 4 (Feb. 3). Western Arizona. Slight damage occurred in Chino Valley, Cottonwood, and Miller Valley (a suburb of Prescott). At Chino Valley, one ceiling beam loosened slightly at the Buckaroo Shopping Center, and plaster separated from the ceil- ing. Waves on the ground were reported by one observer in the area. Water became muddy in a well. At Miller Valley, small cracks formed in the west wall at a supermarket. Magnitude 5.2 ML PAS. (Ref. 49, 74.) 1976. Feb. 23. Western Arizona. Plaster was cracked at Chino Valley, about 25 km north of Pres- cott. (Ref. 49, 74.) 64 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 116° 112° 108° 104° 100° 96° 1 I I \_ I I \_ I \. I ....... _ _ I 36° \ Las Vegas I ‘ ‘ ‘ I— __________________ - .1 I I '- . I Amarillo ~ — 7 z = 3;? Pheonix VI I 32° I I ‘ ' . \ 1‘8 I A I I Houston 0 . VIII I 28° VII \ \ ‘\v o \. 7 (/ ‘2 24° L l\ 17 \ O O 6:7 ¢ 20° EXPLANATION * Epicenter XII Intensity 12 o 300 KILOMETERS |___._a—.—J FIGURE 11.—Isoseismal map for the Sonora, Mexico, earthquake of May 3, 1887, which caused damage in the United States. This map is a simplified version of the map in reference 343 of table 1. 36° 34° ARKANSAS 94° 92° 90° MISSOURI Hardy 2 0 O ' a BIythevnIleoo m 0 Z Z < g g 0 < Q :1: . o m < Fort Smith S o O ' Memphis 0 0 Little Rock ARKANSAS 0 MISSISSIPPI Mm EXPLANATION 0 Magnitude/Intensity Magnolia 3.5-4.4/VI TEXAS O 4.5-4.9 LOUISIANA 0 60-64 0 100 KILOMETERS O 7.0-7.4 Earthquakes in Arkansas with magnitudes 2 4.5 or intensity 2 VI. 65 66 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) ARKANSAS [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (we) Latitude Longitude Depth Ref uses Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) ml, Ms M (1.000 km?) 1811 12 16 08 15 35.6 N 90.4 W — 114 — — 7.20Mf. NU 7.68NLI XI 114 5000 1811 12 16 14 15 35.6 N 90.4 W — 345 — 7.00Mfa SEE — X 529 — 1843 01 05 02 45 35.5 N 90.5 W — 113 — — 6.00Mf3 NTI — VII 113 1500 1843 02 17 05 35.5 N 90.5 W — 113 — 4.80M“ NTI — V 113 250 1878 11 19 05 52 35.5 N 90.7 W —— 529 —— —-— 4.90Mfa NTI -— VI 529 350 1883 12 05 15 20 36.3 N 91.2 W — 105 —— — 4.80Mfa BAR — V 105 250 1911 03 31 16 57 34.0 N 91.8 W — 529 4.70Mfa SC — VII 529 99 1923 10 28 17 10 35.5 N 90.4 W — 105 — — 4.80Mfa SC — VII 105 120 1927 05 07 08 28 35.8 N 90.4 W -—— 218 4.80Mf, BAR — VI 529 100 1938 09 17 03 34 28.3 35.413N 90.254W 001 349 — — 4.80Mf, DG V 105 250 1956 01 29 0444155 35.756N 89.803W 016 349 —— — 4.00Mf, DG — VI 29 13 1969 01 01 23 35 38.7 34.991N 92.688W 007 349 4.2 4.40M“ DG 4.33S'IT VI 42 62 1970 11 17 02 13 54.1 35.856N 89.947W 014 349 3.6 — 4.30M“ DG 4.0081'1‘ VI 43 92 1976 03 25 0041208 35.585N 90.478W 017 349 4.9 —— 4.90Mn DG 4.61HRN VI 49 280 1977 06 02 23 29 10.6 34.560N 94.172W 010 349 4.3 —— 3.60Mn DG —- VI 39 4 1982 01 21 0033 54.8 35.18 N 92.21 W (”3 350 4.5 -- 4.70Mn TUL 3.86SKI' VI 350 31 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] The first and second earthquakes occurred in Arkansas (Dec. 16, 1811—two shocks——Mfa 7.2, M811 1811. Dec. 16, 08 15 UTC. Northeast Arkan- sas. On the basis of the large area of damage (600,000 km2), the widespread area of perceptibility (5,000,000 km2), and the complex physiographic changes that occurred, the Mississippi River valley earthquakes of 1811—12 rank as some of the largest in the United States since its settlement by Europe- ans. The area of strong shaking associated with these shocks is two to three times larger than that of the 1964 Alaska earthquake and 10 times larger than that of the 1906 San Francisco earthquake. The magnitudes of these series of earthquakes, usually named the New Madrid, M0,, earthquakes, vary considerably between the rub and Ms values estimated by Nuttli (ref. 114, 569). The mb (or Mfa as listed above) was estimated from isoseismal maps, and the Ms (or MSn as listed below) was estimated from a spectral scaling relation by Nuttli (ref. 569) for mid-plate earthquakes. The value of Ms (or MSn) magnitude has a functional relationship to the rub (or Mfa). The authors have chosen to include the Mfa magnitude in the above list because it was estimated from isoseismal maps, as were most of the historical earthquakes. 8.5 and Mfa 7.0, MSn 8.0) and the third and fourth in Missouri (Jan. 23, 1812, Mfa 7.1, Msn 8.4; and Feb. 7, 1812, Mfa 7.4, MSn 8.8). Otto Nuttli (ref. 330), how- ever, has postulated another strong earthquake in Arkansas on Dec. 16 at 18 00 UTC (Msn 8.0). This would make a total of five earthquakes of magnitude MSn 8.0 or higher occurring in the period Dec. 16, 1811 through Feb. 7, 1812. Ref. 330 was published shortly after the death of Otto Nuttli, but his sources of data were never published; therefore, source data on the fifth earthquake are not included in the Arkansas table. The first earthquake caused only slight damage to man-made structures, mainly because of the sparse population in the epicentral area. The extent of the area that experienced damaging earth motion (MMI 2VII) is estimated to be 600,000 km2. However, shaking strong enough to alarm the general popula- tion (MM intensity 2V) occurred over an area of 2.5 million km2 (see generalized isoseismal map, fig. 12). This map covers an area from Canada to New Orleans, La., and from the headwaters of the Missis- sippi River to the Atlantic Ocean. At the onset of the earthquake the ground rose and fell—bending the trees until their branches inter- twined and opening deep cracks in the ground. 50° 45° 40° 35° 30° 25° EARTHQUAKES IN ARKANSAS 67 95° 90° 85° 80° 75° 70° 65° v VK ‘ . ,\ / f” \' ‘rl 1 ' \- —~J .. l L: ) E L. ; .4 \ r"\‘ . Ouawa "'3 \ - o HW§< 2’1 .. u-m LL31 . EXPLANATION \4 * Epicenter X| Intensity 250 KILOMETERS FIGURE 12.—Isoseismal map for the Arkansas earthquake of December 16, 1811, 08:15 UTC (first of the 1811—1812 New Madrid series). This map is a simplified version of figure 1 in reference 114 and figure 2 in reference 557 of table 1. 68 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Landslides swept down the steeper bluffs and hill- sides; large areas of land were uplifted; and still larger areas sank and were covered with water that emerged through fissures or craterlets. Huge waves on the Mississippi River overwhelmed many boats and washed others high on the shore. High banks caved and collapsed into the river; sand bars and points of islands gave way; whole islands disap- peared. Surface rupturing did not occur, however. The region most seriously affected was characterized by raised or sunken lands, fissures, sinks, sand blows, and large landslides that covered an area of 78,000—129,000 km2, extending from Cairo, 111., to Memphis, Tenn, and from Crowleys Ridge to Chick— asaw Bluffs, Tenn. Although the motion during the first shock was violent at New Madrid, Mo., it was not as heavy and destructive as that caused by two aftershocks about 6 hours later. Only one life was lost in falling buildings at New Madrid, but chimneys were toppled and log cabins were thrown down or were heavily damaged. Chimneys also were downed as far distant as Cincin- nati, Ohio; St. Louis, Mo.; and in many places in Kentucky, Missouri, and Tennessee. The Lake County uplift, about 50 km long and 23 km wide, upwarps the Mississippi River valley as much as 10 m in parts of southwest Kentucky, south- east Missouri, and northwest Tennessee. The uplift apparently resulted from vertical movement along several, ancient, subsurface structures; most of this uplift has occurred during earthquakes. The Lake County uplift can be subdivided into several topo— graphic bulges, including Tiptonville dome, Ridgely Ridge, and the south end of Sikeston Ridge. A strong correlation exists between modern seismicity and the uplift, indicating that stresses that produced the uplift still exist today. Tiptonville dome, which is 14 km in width and about 11 km in length, shows the largest upwarping and the highest topographic relief on the uplift. It is bounded on the east by Reelfoot scarp, which has a zone of normal faults (displacement about 3 In) at its base. Although most of Tiptonville dome formed between 200 and 2,000 years ago, additional uplifting deformed the northwest and southeast parts of the dome during the earthquakes of 1811—12. A notable area of subsidence is Reelfoot Lake in Tennessee, just east of Tiptonville dome. Subsidence there ranged from 1.5 to 6 m, although larger amounts were reported. It may be that the lake was enlarged by compaction, upwarping, and subsidence occurring simultaneously during the New Madrid earthquakes. Other areas subsided by as much as 5 m, although 1.5 to 2.5 In was more common. Lake St. Francis, in eastern Arkansas, which was formed by subsidence, is 64 km long by 1 km wide. Coal and sand were ejected from fissures in the swamp land adjacent to the St. Francis River, and the water level is reported to have risen there by 8 to 9 In. Large waves were generated on the Mississippi River by fissures opening and closing below the sur- face. Local uplifts of the ground and water waves moving upstream gave the illusion that the river was flowing upstream. Ponds of water also were agitated noticeably. Otto Nuttli (ref. 330) reported that more than 200 moderate to large earthquakes occurred on the New Madrid fault between Dec. 16, 1811, and Mar. 15, 1812 (5 of Ms about 7.7; 10 of Ms about 6.7; 35 of MS about 5.9; 65 of Ms about 5.3; and 89 of MS about 4.3). Nuttli also noted that about 1,800 earthquakes of mb about 3.0 to 4.5 occurred in that same period. Magnitude of main shock 8.5 MSn NLI. (Ref. 38, 114, 301, 330, 529, 558.) 1811. Dec. 16, l4 15 UTC. Northeast Arkan- sas. On the basis of the effects reported at the same locations, the MM intensity of this earthquake has been inferred to be similar to that of the earlier shock at 08 15 UTC (see description above). Thus, the inference is that, if the documented intensities are the same or are similar at identical locations, then the maximum intensities at the epicenter must be about the same; therefore, the intensity at the epi- center of this earthquake must be at the MM inten- sity X—XI level. The maximum documented intensity for both earthquakes on Dec. 16, 1811, is MM inten- sity VIII at Richmond, Ky. Magnitude 8.0 MSn STT. (Ref. 345, 529.) 1843. Jan. 5 (Jan. 4). Northeast Arkansas. This earthquake is the strongest to occur in this region since the 1811-12 sequence. Damage was severe at Memphis, Tenn., where walls cracked, win- dows broke, and one building collapsed. The earth sank in places near New Madrid, Mo., and uncon- firmed reports state that a lake was formed and sev- eral hunters were drowned. Chimneys were thrown down at Helena, Ark, and Hickman, Ky. The earth- quake was felt on the seacoast of Georgia and the Carolinas and northeastward to Providence, R.I., a distance of 1,400 km. The southern limit of the felt area appears to have included Natchez, Miss; the western limit passed beyond the frontier military posts; and the northern limit reached Iowa and Indi- ana. Magnitude 6.3 Ms NTL, 6.0 Mfa NTI. (Ref. 38, 109, 113, 529.) EARTHQUAKES IN ARKANSAS 69 m Lower end of Reelfoot Lake, Tennessee, showing trunks of trees killed when the land was submerged by the December 16, 1811, northeast Arkansas earthquake. (Photograph by M.L. Fuller taken about 100 years after the earthquake.) 1878. Nov. 19 (Nov. 18). Arkansas. The earth- quake was severe east of Kansas City along the Mis- souri River from Lexington to Glasgow, Mo., but the maximum disturbance occurred along the Mississippi River valley between Cairo, I11., and Memphis, Tenn. Northwest of Memphis, several stone buildings were damaged in Stone County at Batesville, Ark., and the tops of chimneys were toppled in Poinsett County at Harrisburg, Ark; loose bricks fell from chimneys at Cairo, Ill. Felt in Alabama, Arkansas, Illinois, Kan- sas, Kentucky, Missouri, and Tennessee. Magnitude 4.9 Mfa NTI. (Ref. 38, 105, 109, 529.) 1911. Mar. 31. Near Rison and Warren, Ark. The earthquake cracked walls, broke windows and dishes, and sent people rushing into the streets at Pine Bluff, Ark., south of Little Rock in Jefferson County. Walls cracked at the 14th Avenue school at Pine Bluff, and plaster fell on the pupils. Minor damage also occurred at Argenta, Dumas, Monticello, Rison, and Warren, Ark. The shock was felt throughout southeast Arkansas, northeast Louisiana, and along the Mississippi River from Memphis, Tenn., to Vicksburg, Miss. The felt area generally was confined to the soft sediments of the Mississippi River valley. Magnitude 4.3 Mfa BAR, 4.2 Mfa SG. (Ref. 38, 105, 109, 529.) 1923. Oct. 28. Marked Tree, Ark. This shock downed several old chimneys, shattered windows, and cracked walls at Marked Tree (Poinsett County), about 70 km northwest of Memphis, Tenn. It report- edly disturbed the surface of the St. Francis River. Also felt in Illinois, Kentucky, Mississippi, Missouri, and Tennessee. Magnitude 4.5 Mfa BAR. (Ref. 38, 105, 529.) 1927. May 7. Between Jonesboro and Marked Tree, Ark. At least one chimney was damaged at Jonesboro, and windowpanes and dishes were broken in the Memphis, Tenn., area. In the area of Reelfoot Lake, Tenn., the earthquake left “gravel pilings.” Felt from Decatur, Ala., to Carbondale, Ill., and from Poca- hontas, Ark., to Jackson, Tenn. Also reported in 70 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Mississippi and Missouri. Magnitude 4.8 Mfa BAR. (Ref. 38, 105, 109, 218, 529.) 1956. Jan. 29 (Jan. 28). Arkansas-Tennessee border. A few chimneys and walls were cracked at Covington, Tenn., northeast of Memphis. Also felt in Arkansas. Magnitude 4.1 Mfa BAR, 4.0 Mfa DG. (Ref. 29, 349.) 1969. Jan. 1. Central Arkansas. Walls and floors cracked and dishes broke at Little Rock, Ark. Felt in northern and central Arkansas, southern Mis- souri, and at Memphis, Tenn. Magnitude 4.5 Mn BAR, 3.3 MS BAR. (Ref. 42, 349.) 1970. Nov. 17 (Nov. 16). Northeast Arkansas. Plaster cracked and fell at Manila (Mississippi County), about 28 km west of the epicenter. At Keiser, about 27 km south of Manila, the shock shifted furniture, cracked plaster, and caused three electrical wall outlets to burn their wires. Also felt in Illinois, Kentucky, Mississippi, Missouri, and Tennes- see. Magnitude 4.4 M11 BAR, 2.9 Ms BAR, 4.4 mb NUT, 2.9 MS NUT. (Ref. 43, 263, 349.) 1976. March 25 (Mar. 24). Northeast Arkan- sas. Slight damage characterized by cracks in plaster and drywall, downed ceiling tiles, and broken win- dows occurred in several towns in Arkansas, Missis- sippi, Missouri, and Tennessee. Also felt in Alabama, Illinois, Indiana, and Kentucky. Magnitude 5.0 Mn BAR. (Ref. 49, 349.) 1977. June 2. Western Arkansas. Chimneys and exterior walls were cracked at Board Camp; foundations and sidewalks were cracked at Hatfield. Both towns are in Polk County, near the Oklahoma border. Magnitude 4.0 Mn SLM, 4.63 M JOH. (Ref. 39, 349.) 1982. Jan. 21 (Jan. 20). Area of Enola-Naylor, Faulkner County, Ark. This earthquake is the strongest of a swarm of more than 30,000 shocks that began in the area on Jan. 12, 1982. Several of the shocks were felt in the region. Leveling lines run by the Arkansas State Surveyor show an uplift of about 0.2 m in the area of the epicenters. On High- way 36, west of Naylor, hairline cracks formed in a concrete cellar, and tiles fell off a tile-lined well. In addition, a fireplace and sheetrock walls sustained cracks. Also felt in Mississippi and Missouri. Magni- tude 4.5 M11 TEC. (Ref. 350, 511.) CALIFORNIA 126° 124° 122° 120° 118° 116° 114° 42° L‘ OREGON IDAHO 0° 0 0° \J 00 O 0 0 ° 0 $69 .0 0 ° 0 o o oo o o 0?, 0 ° 0 o 0 80‘. o o (9 Bo . 0 40° 0 o o o O o _ C”— " E] NEVADA m 33° 0 36° > g W 0 1—4 a N ’5‘ g > 34° EXPLANATION Magnitude o s 5.9 O 6.0-6.4 O 6.5-6.9 O 7.0-7.4 O 7.5-7.9 32° 200 KILOMETERS Earthquakes in California with magnitudes 2 4.5 or intensity 2 VI. 71 72 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIFORNIA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (-~) indicates information is not availabIEJ Origin Hypoeenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m s (°) (°) (km) mb Ms M (1 .000 km?) 1769 07 28 33.9 N 117.8 W - 368 — — 6.00M“ ELL —— VIII 493 —- 1770 34.5 N 118.0 W — 493 — — — — Felt 493 — 1790 37.5 N 118.8 W — 368 — — -—— — Felt 493 — 18m 10 11 36.9 N 121.6 W — 368 -— — — — VII 368 — 1800 11 22 21 30 33.0 N 117.3 w -— 368 — — 6.50ML.DMG — v11 38 — 1803 04 34.5 N 118.0 W — 493 — — — — Felt 493 —- 1803 05 25 32.8 N 117.1 W 368 — — — VI 56 —— 1806 03 25 08 00 34.4 N 119.7 W -— 368 — —- —— — VI 368 — 1808 06 21 37.8 N 122.5 W 368 — —— 6.00M“ ELL —— VIII 368 — 1812 37.5 N 122.5 W — 493 — -— — Felt 493 -—- 1812 05 33.7 N 117.9 W —- 493 — — — — Felt 493 —- 1812 12 08 15 00 34.37 N 117.65 W — 521 — —— 6.90M“ DMG -—- VIII 368 1812 12 21 19 00 34.2 N 119.9 W —— 368 — 7.10M“ DMG — VIII 368 — 1821 01 01 32.8 N 117.1 W —— 493 — -- —— — Felt 493 — 1827 09 24 04 00 34.0 N 119.0 W — 368 —— — 5.50M“ DMG — VI 368 —— 1829 09 37.5 N 122.5 W — 56 -—- -— — — VII 56 1830 35.5 N 120.6 W — 368 —— -—- — — VII 368 —- 1836 04 25 13 36.5 N 122.0 W — 56 —— — — — Felt 493 — 1836 06 10 15 30 37.8 N 122.2 W —— 368 —- — 6.80M“ DMG — VIII 368 — 1838 06 37.6 N 122.4 W —- 368 — — 7.mML.DMG — VIII 368 — 1840 01 16 36.5 N 122.1 W —— 56 —— -— — — VI 56 — 1841 07 03 22 07 36.6 N 122.0 W — 368 —— ~—- — —— VI 368 — 1849 09 17 33.0 N 116.5 W — 56 ——- — — — Felt 493 -- 1849 09 22 23 33.0 N 116.5 W 56 -— — —- — Felt 493 — 1851 05 15 16 10 37.8 N 122.4 W — 368 — -—- — — VI 38 — 1852 11 23 07 37.5 N 122.4 W — 56 — -— —— — Felt 493 —— 1852 11 29 20 00 32.5 N 115.0 W — 521 -— — 6.50M” DMG — IX 368 260 1852 12 17 35.5 N 121.0 W — 56 -— —— — —- VI 56 — 1853 02 01 2100 35.6 N 121.1 W — 368 -—— —— —- -— VI 368 1853 10 23 11 00 40.8 N 124.2 W — 368 — — — — VI 368 ~— 1855 01 25 06 00 39.5 N 120.3 W -— 368 —— —— 5.50M“, DMG -— VI 56 —- 1855 03 20 00 30 40.75 N 124.20 W — 56 — —— —— — V 56 — 1855 07 ll 04 15 34.1 N 118.1 W — 368 —— — 6.00ML. ELL — VIII 38 —- 1855 08 27 11 00 38.1 N 122.5 W —- 368 — —— 4.90M“ DMG VI 368 — 1856 01 02 18 15 37.5 N 122.5 W — 368 — — 5.30M“ DMG — VI 368 — 1856 02 15 13 25 37.5 N 122.3 W — 368 -— —— 5.50M” DMG — VII 368 —- 1856 09 21 07 30 33.0 N 117.0 W — 368 -— —— — —- VI 368 — 1857 01 09 16 24 35.7 N 120.3 W —— 521 — — 7.60M” DMG 7.92HK IX 379 290’? 1858 ll 26 08 35 37.5 N 121.9 W — 368 —— 6.10M]... DMG — VII 38 —- 1858 12 16 02 30 34.0 N 117.5 W — 368 — —— — VI 368 — 1858 12 16 10 00 34.0 N 117.5 W — 521 — — 6.00MLaELL — VIII 368 -— 1859 10 05 20 16 37.8 N 122.4 W —- 368 — — —— —- VI 368 — 1860 ll 13 00 00 40.8 N 124.2 W — 368 — — —— — VII 368 — 1861 07 04 00 11 37.8 N 122.0 W —— 368 — -— 5.60MuDMG — VIII 38 — 1862 05 27 2000 32.7 N 117.2 W —— 368 — — 5.90MLaDMG — VII 368 458: 1863 12 19 22 38 37.5 N 122.2 W —— 368 —- —— 4.80M“ DMG — V 368 23 1864 02 26 13 47 37.1 N 121.7 W — 368 — — 5.90M” DMG — VI 368 — 1864 03 05 16 49 37.7 N 122.0 W -— 368 — — 5.70MLaDMG — VI 38 — EARTHQUAKES IN CALIFORNIA CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] ’73 Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 3 (°) (°) (km) mb Ms M (1,000 kmz) 1864 05 21 0201 37.6 N 122.1 W — 368 — — 5.30MLaDMG — VI 368 36 1864 07 22 0640 37.6 N 122.0 W — 368 — — 4.70MLaDMG — V 368 20 1864 08 18 1318 39.3 N 121.0 W — 368 — -— 4.50ML3DMG — V 56 14 1865 03 08 14 30 38.4 N 122.6 W — 368 — — 4.70ML3DMG — VII 38 — 1865 05 24 1121 37.1 N 121.8 W -—- 368 -— —— 5.50ML3DMG — VI 368 —— 1865 10 01 1715 40.8 N 124.1 W -— 368 —— —— 5.40ML3DMG — VII 368 30& 1865 10 08 2046 37.2 N 121.9 W — 368 — — 6.30ML3DMG — VIII 56 1008: 1866 03 26 2012 37.1 N 121.6 W —— 368 —— — 5.40ML3DMG — VII 368 — 1866 07 15 0630 37.5 N 121.3 W - 368 -— —— 5.80ML3DMG -— V 368 120 1868 09 04 1600 36.6 N 118.4 W — 368 —— — —— —— VI 368 — 1868 09 17 16 55 38.6 N 119.7 W — 368 — — 5.20ML.DMG — V 368 42 1868 10 21 15 53 37.7 N 122.1 W — 368 —— — 6.80ML3DMG — IX 368 1258; 1869 10 08 0930 39.1 N 123.1 W -— 368 —- -— 5.WML,DMG — VII 368 — 1869 12 21 0400 39.5 N 120.6 W —— 368 — — 4.80ML.DMG —— V 368 28 1870 02 17 2012 37.2 N 122.1 W — 368 — 5.80MuDMG — VII 368 —— 1870 04 02 19 48 37.9 N 122.3 W -- 368 — 5.30ML.DMG — VI 368 35& 1871 03 02 2105 40.4 N 124.2 W — 368 — — 5.90ML,DMG — VII 38 29& 1871 07 05 2106 36.4 N 118.0 W —- 368 — — 5.20ML3DMG —-— VI 38 — 1872 03 26 10 30 36.7 N 118.1 W — 368 — — 7.30ML3ELL 7.75HHT X 38 480& 1872 03 26 1406 36.9 N 118.2 W — 368 — — 6.50MuDMG — V 368 300 1872 03 28 1300 39.5 N 120.4 W — 368 — — 4.90MuDMG —— VI 368 32 1872 04 03 1215 37.0 N 118.2 W —- 368 — — 6.10ML.DMG — V 368 160 1872 04 11 1900 37.5 N 118.5 W 368 — — 6.60ML3DM6 —— IX 368 350 1872 04 18 1200 36.5 N 117.8 W 368 — — — —- VI 56 —- 1872 05 03 0100 33.0 N 115.0 W — 368 — — 5.50ML3DMG — VI 368 — 1872 05 17 2100 36.6 N 118.1 W -— 368 — — —- —- VI 368 -— 1873 11 23 0500 42.0 N 124.0 W — 38 —- — 6.70MLIDMG — VIII 368 1818i 1875 01 24 1200 40.2 N 120.5 W —— 368 —— — 5.80MLaDMG — VI 368 — 1875 09 30 12 30 40.7 N 124.0 W — 368 — —- 5.50ML.DMG — VII 368 — 1876 05 29 18 55 38.4 N 122.9 W — 368 -—- — 4.20ML3DMG — VI 368 8 1878 05 09 0425 40.1 N 124.0 W — 368 — — 5.80MLaDMG — VI[ 368 — 1878 06 12 0720 34.0 N 118.0 W —— 463 — —- — — VI 463 — 1879 02 04 0808 36.3 N 119.3 W — 463 — — — — VI 463 — 1880 01 09 13 45 36.7 N 121.3 W —- 463 — — —— Felt 463 — 1880 12 19 23 35 34.0 N 117.5 W — 463 — — — — VI 463 ~— 1881 01 07 02 25 40.0 N 122.0 W — 368 — — 5.00MuDMG -— V 368 — 1881 02 02 0011 36.0 N 120.5 W 368 — 5.60MLaDMG — VII 368 -—- 1881 04 10 1000 37.4 N 121.4 W — 368 —- — 5.%ML.DMG — VI 368 140 1882 03 06 2145 36.9 N 121.2 W — 368 — -— 5.70ML.DMG — VI 368 100 1882 06 27 13 32 37.2 N 122.0 W — 463 — — —— — VII 463 — 1883 03 30 15 45 36.9 N 121.6 W — 368 — — 5.60MLaDMG — VII 368 70 1883 09 05 12 30 34.2 N 119.9 W — 368 -— — 6.00ML3DMG — VI 368 — 1884 01 28 0730 41.1 N 123.6 W — 368 —— —— 5.70ML‘DMG — V 368 — 1884 03 26 0040 37.1 N 122.2 W — 368 — — 5.90MuDMG — VI 368 — 1884 06 14 16 43 40.6 N 125.8 W — 463 —- — — — Felt 463 —— 1885 01 31 05 45 40.4 N 120.6 W — 368 -— —— 5.70MLaDMG — VII 38 110 1885 03 31 0756 36.7 N 121.3 W — 368 -— — 5.50MLaDMG — VII 38 — 1885 04 02 15 25 36.8 N 121.4 W — 368 — — 5.40MLaDMG — V 368 81 1885 04 12 0405 36.4 N 121.0 W — 368 — — 6.20MuDMG —- VII 368 240 74 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIF ORNIA—Contin ued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km“) 1885 08 01 0010 38.8 N 123.0 W 368 —- — — — VI 368 — 1886 04 14 0320 37.2 N 117.7 W —- 54 — ~-— —— —- VI 54 — 1887 12 03 18 55 39.3 N 123.6 W 368 — — 4.%ML,DMG — VII 368 — 1888 02 18 10 50 39.2 N 123.6 W — 368 — — 4.90MLaDMG — V 368 —- 1888 02 29 22 50 38.3 N 122.7 W —- 368 — — 4.20MLaDMG —- VI 368 9 1888 04 14 0330 41.5 N 120.5 W — 368 —— — 4.wMLaDMG — VI 368 — 1888 04 29 0448 39.7 N 120.7 W — 368 — — 5.90MLaDMG —— VII 38 — 1888 09 17 1151 37.1 N 121.8 W — 368 — -— 4.50ML3DMG — V 368 15 1888 11 18 22 28 37.9 N 122.3 W — 368 — -— 4.30MLaDMG —- VII 38 11 1889 02 07 05 20 34.1 N 116.7 W -— 368 --— — 5.30ML.DMG — V 56 69 1889 04 15 0328 37.1 N 121.9 W — 368 -— — 4.80MLIDMG — VI 368 38 1889 05 19 1110 38.0 N 121.9 W —— 368 —— —-- 6.00MuDMG — VII 38 — 1889 06 20 0600 40.5 N 120.7 W — 368 —-- — 5.90ML.DMG — VII 38 120 1889 07 31 12 47 37.8 N 122.2 W -- 368 — -— 5.20ML.DMG — VI[ 38 53 1889 08 28 0215 34.1 N 117.9 W — 368 — — 5.20MLlDMG — VI 38 52 1889 09 30 05 20 37.2 N 118.7 W — 368 — — 5.wML,DMG -— V 56 92 1890 02 09 1206 33.4 N 116.3 W — 368 — —- 6.30ML.DMG 6.73HK VI 38 — 1890 04 24 1136 36.9 N 121.6 W — 368 — — 6.00MuDMG — VIII 368 —— 1890 07 26 0940 40.5 N 124.2 W -- 368 ~- — 6.00MLaDMG — VII 38 1(X)& 1891 01 02 2000 37.3 N 121.8 W —- 368 — — 5.50MLaDMG — VI 38 508: 1891 10 12 0628 38.3 N 122.4 W — 368 —- —— 5.50MLIDMG — VIII 368 54 1892 02 24 O7 20 32.55 N 115.63 W — 521 —- — 6.70ML.DMG 7.75HHT VIII 368 — 1892 04 19 1050 38.4 N 122.0 W --— 368 — -— 6.40ML,DMG —— IX 38 — 1892 04 21 1743 38.5 N 121.9 W -— 368 -— —— 6.20ML3DMG — IX 38 1708: 1892 04 30 0009 38.4 N 121.8 W — 368 -— — 5.50ML3DMG — VI 368 — 1892 05 28 1115 33.2 N 116.2 W — 368 — — 6.30MLaDMG — V 56 — 1892 06 14 13 25 34.2 N 117.5 W — 368 —- — 4.90MLaDMG — V 368 — 1892 ll 13 12 45 36.8 N 121.5 W — 368 — — 5.60MuDMG — VI 38 -— 1893 04 04 1940 34.3 N 118.6 W —— 368 —-— — 5.40ML.DMG — VIII 368 71 1893 05 19 0035 34.1 N 119.4 W — 368 -— -— 5.50MuDMG — V 368 39& 1893 06 30 13 30 38.0 N 122.4 W — 368 — — 4.60MLaDMG — V 56 19 1893 08 09 0915 38.4 N 122.6 W — 368 —- —— 5.10MLaDMG — VII 38 —— 1894 07 30 0512 34.3 N 117.6 W — 368 —- — 5.90ML.DMG — VI 368 —— 1894 09 30 1736 40.3 N 123.7 W — 368 ——- — 5.80MuDMG — VII 368 80& 1894 10 23 2303 32.8 N 116.8 W —— 368 -— — 5.70ML3DMG — VI 368 — 1896 08 17 1130 36.7 N 118.3 W —- 368 — -— 5.90MuDMG — VI 56 — 1897 06 20 2014 37.0 N 121.5 W —- 38 -- — 6.20ML.DMG —— VIII 38 1308: 1898 03 31 0743 38.2 N 122.4 W — 368 — -— 6.20MLaDMG — VIII 368 12082 1898 04 15 0707 39.2 N 123.8 W — 368 —— — 6.90M, A32 — VIII 38 ~— 1899 04 16 13 40 41.0 N 126.0 W — 521 —— — 7.00M: ELL — VI 368 — 1899 04 30 2241 36.9 N 121.7 W — 368 —— — 5.60ML,DMG — VII 38 52& 1899 06 02 0719 37.7 N 122.5 W — 368 — — 5.40MLaDMG — VII 368 — 1899 07 06 2010 37.2 N 121.5 W -— 368 —— — 5.80ML3DMG — VII 56 98 1899 07 22 0046 34.2 N 117.4 W — 368 — — 5.50MuDMG — VI 368 70 1899 07 22 20 32 34.3 N 117.5 W — 368 — -- 6.50MLaDMG 6.35HHT VH1 38 — 1899 10 13 0500 38.4 N 122.7 W -— 368 — — —- — VII 38 2 1899 12 25 12 25 33.8 N 117.0 W — 368 — —- 6.40Ms ELL 6.73HK IX 38 — 1900 04 30 224114 36.9 N 121.6 W — 3 — — 4.50MuDMG -— V 56 30 EARTHQUAKES IN CALIFORNIA CALIF ORNIA—Con tinued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1.000 kmz. Leader (--) indicates information is not available] 75 Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 me) 1901 03 03 0745 36.0 N 120.5 W — 38 — — 6.40ML3ELL — VIII 38 1048: I902 05 19 18 31 38.3 N 121.9 W — 381 — -— 5.40ML3DMG — VII 381 52 1902 06 11 0245 33.7 N 117.1 W — 380 —- — 4.50ML.DMG — V 380 33 1902 07 28 0657 34.8 N 120.4 W -— 381 —— — 5.40ML‘DMG —- VII 381 —— 1902 07 31 0920 34.7 N 120.3 W -- 381 — — 5.40MLaDMG — VIII 381 — 1902 08 01 0330 34.6 N 120.4 W — 380 — — — VIII 380 -- 1902 12 12 34.8 N 120.4 W 380 — — — — VII 38 — 1903 06 II 1312 37.4 N 121.9 W — 381 -- — 5.80ML3DMG — VII 38 100& 1903 07 24 20 26 39.5 N 122.0 W 38 — —- 4.50MLaDMG VII 38 25 I903 08 03 0649 37.3 N 121.8 W — 381 — — 5.80MLaDMG -- VII 38 1308: 1903 12 25 1745 34.0 N 118.0 W ~—- 38 — — —- -- VI 38 —- 1904 04 16 0920 40.5 N 122.4 W — 380 — — 4.50MLnDMG — V 56 14 1904 07 30 10 26 38.5 N 122.0 W — 380 —— — 4.50MLIDMG — V 56 15 1905 01 06 14 30 35.5 N 118.7 W — 380 —— — 5.00MLaDMG — V 380 50 1905 07 15 2041 34.1 N 117.3 W — 380 —- — — — VI 56 — 1905 09 03 05 40 34.0 N 118.3 W — 380 —— —- — — VI 56 — 1905 12 23 22 23 35.3 N 118.8 W — 380 —— — — — VI 56 —- 1906 03 03 20 25 33.0 N 117.0 W — 380 -— — 4.50ML3DMG — V 380 25 1906 04 18 131221 37.67 N 122.48 W 020 378 — -— 7.80Ms AB2 7.68TW XI 38 425& 1906 04 19 0030 32.9 N 115.5 W — 381 —— —- 6.20Ms ELL 6.27HI-1T VIII 38 100# 1906 04 23 0910 41.0 N 124.0 W — 38 —— —— 6.40Ms ELL — VII 38 — 1906 05 02 05 30 38.5 N 123.0 W — 38 — — — — VI 38 — 1906 05 07 0410 39.2 N 122.9 W -—- 380 — —— — — VI 56 — 1906 05 07 0500 39.2 N 122.9 W — 380 — -— — -— VI 56 ~— 1906 12 07 0640 35.3 N 120.7 W —— 380 — -— — -— VI 56 —— 1907 09 20 0154 34.2 N 117.1 W — 381 — 5.30ML3DMG 5.28HHT VII 38 130 1908 01 27 0200 40.3 N 120.3 W 380 — —- -— VII 38 — 1908 04 25 1133 36.6 N 121.8 W — 380 — — 4.50MLaDMG — V 56 25 1908 08 18 1059 40.8 N 124.0 W 380 -— 5.mML.DMG — VII 38 l6& 1908 11 04 0837 36.0 N 117.0 W —- 38 — —- 6.50Ms CFR — VI 382 150 1909 02 14 15 55 38.1 N 121.7 W — 380 — — 4.50ML.DMG — V 380 15 1909 03 03 1200 39.4 N 120.9 W —— 380 —- — 5.00MLaDMG —— V 56 50 1909 05 18 0119 41.0 N 124.0 W — 38 —— —— — — VII 38 — 1909 06 23 0724 39.4 N 120.8 W —- 380 — —— 5.70ML3DMG — VII 38 130 1909 10 29 0645 40.5 N 124.2 W — 381 — -— 6.40MLaDMG — VIII 38 260 1909 ll 22 15 21 36.7 N 121.4 W — 380 —— — 4.50MLaDMG -— V 56 15 1910 03 11 0652 36.9 N 121.8 W — 381 — — 5.80Ms ELL -— VI 38 155 1910 03 I9 0011 40.0 N 125.0 W — 38 — —— 6.00M; CFR — V 56 — 1910 04 11 0757 33.7 N 117.4 W -— 380 — — 5.00MLaDMG — V 56 30 1910 05 06 16 40 37.33 N 118.42 W — 324 — — 5.60ML3DMG — VI 56 130 1910 05 13 0620 33.7 N 117.4 W — 380 — — 5.00MLaDMG — V 56 40 1910 05 15 15 47 33.7 N 117.4 W — 381 — — 6.00Ms CFR 5.28HHT VII 38 75 1910 12 31 1211 36.83 N 121.42 W — 324 —— — 5.00MLaDMG —— VI 56 20 1911 03 11 2129' 36.83 N 121.42 W —— 324 —- -— 4.50ML3DMG — VI 56 — I911 07 01 220003 37.25 N 121.75 W — 258 — — 6.60M; GR — VIII 56 155 1911 08 11 2340 33.8 N 116.7 W — 380 — — 4.50ML3DMG — VI 56 — 1912 01 05 0352 37.33 N 118.42 W — 324 — 5.50MLaDMG — VI 56 130 1912 08 31 0453 38.92 N 120.33 W — 324 — — 4.50MLaDMG — V 56 25 1912 09 12 17 27 37.33 N 122.17 W — 324 —— 4.50MLaDMG —— V 56 2682 1912 12 14 34.0 N 119.0 W -— 38 —— — — — VI 56 — 76 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. 8:, land area only: #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (-—) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 3 (°) (°) (km) mb Ms M (1,000 km2) 1914 11 09 02 31 37.17 N 122.“) W — 324 —- — 4.70MuDMG — VII 38 78 1914 12 28 10 42 37.17 N 122.17 W — 324 — — 4.50MuDMG — V 56 26 1915 01 12 0431 34.6 N 120.2 W — 381 -— — 5.20ML3DMG — VIII 38 130 1915 02 22 40.58 N 121.83 W — 324 — — ——- — VII 56 — 1915 04 05 23 11 38.58 N 119.50 W — 324 -—- — 5.00MuDMG — V 56 65 1915 05 06 1209 39.5 N 126.5 W — 324 — — 6.75Ms GR — V 56 — 1915 05 29 0646 36.08 N 118.83 W — 324 — 5.00ML.DMG — V 56 40 1915 06 23 0359 32.8 N 115.5 W — 381 — — 6.25Ms CFR 5.48HI-IT VIII 383 2(X) 1915 06 23 0456 32.8 N 115.5 W — 381 —— — 6.25M; CFR 5.48HHT VIII 383 200 1915 10 08 052542 37.83 N 122.25 W — 324 — -—-— 4.50ML3DMG —— VI 38 9 1915 11 21 0013 42 32.0 N 115.0 W — 258 —- — 7-10Ms GR 6.93I-IHT IX 492 310 1915 12 31 12 20 41.0 N 126.0 W — 258 -- — 6.50Ms CFR — III 56 — 1916 07 05 0440 40.58 N 124.25 W — 324 — — — — VI 38 — 1916 07 16 1150 34.7 N 117.0 W — 380 — -— 4.50MLaDMG — V 56 25 1916 08 06 19 38 36.67 N 121.25 W — 324 — — 5.30MuDMG — VII 38 78 1916 08 08 165241 37.0 N 122.0 W —— 324 — — 5.00UImJON — V 56 — 1916 09 30 0211 33.5 N 116.5 W — 380 — —— 5.00MuDMG — V 56 52 1916 10 23 0244 34.9 N 118.9 W — 258 -—- — 6.00Ms CFR 5.95HHT VII 38 130 1916 10 23 0254 34.7 N 119.0 W — 380 — -— 5.50ML,DMG — V 56 70 1916 11 10 0911 35.5 N 116.0 W 521 —— —- 6.10M; GR — V 56 -— 1916 12 01 22 53 35.17 N 120.75 W 324 — —- — —- VII 38 — 1917 03 03 1600 40.83 N 124.17 W -— 324 — — 4.60UknJON V 56 — 1917 04 13 0359 34.3 N 119.5 W —- 380 — —— 4.50ML3DMG — V 56 21 1917 05 28 0606 32.8 N 115.3 W — 380 — — 5.50MLaDMG — VI 56 104 1917 07 06 1101 36.58 N 118.08 W —— 324 — — — —- VI 38 — 1917 07 09 22 22 35.25 N 120.50 W — 324 — — —- —- VI 38 — 1917 07 26 0833 35.0 N 120.5 W — 315 -— —— 4.80UknJON —- V 56 — 1917 10 26 0918 51 37.4 N 121.8 W —- 315 — — 4.80UknJON — Felt 491 —- 1918 03 12 10 30 39.58 N 120.83 W — 324 — — -— — VII 38 — 1918 04 21 22 32 25 33.75 N 117.00 W —— 258 —— — 6.80Ms GR 6.73HK IX 384 390 1918 04 22 2115 33.8 N 117.6 W — 380 — — — — VI 38 — 1918 05 01 0432 32.7 N 115.5 W — 56 —— — 5.00ML3DMG — VI 56 80 1918 06 06 22 32 33.8 N 117.0 W — 380 —— — 5.00ML.DMG — VI 56 78 1918 07 15 002300 41.0 N 125.0 W —- 258 — — 6.50Ms GR — VI 38 — 1918 11 19 2018 34.0 N 118.5 W —— 38 — -— — -- VI 38 — 1919 01 04 2300 40.58 N 121.82 W — 324 ——- —— -—- — VI 56 — 1919 02 16 15 57 35.0 N 119.0 W —— 38 — —— 5.00MLaDMG —— VII 38 78 1919 02 25 22 38 38.33 N 122.5 W — 324 —— -- 4.60UknJON — V 56 — 1919 09 15 14 07 40.83 N 124.17 W — 324 — — — VII 38 —- 1919 11 25 1103 37.08 N 121.83 W 324 — —— 4.50ML,DMG -— V 56 11& 1919 12 19 135813 38.3 N 119.5 W — 54 — -— 5.20Mx SJG — — — —— 1920 01 01 02 35 33.2 N 116.7 W — 380 — —- 5.00M;.DMG — VI 56 -— 1920 06 22 02 47 34.0 N 118.5 W -— 38 — — 4.90ML PAS - VIII 385 28 1920 07 16 18 08 34.1 N 118.3 W — 380 —- — —- — VI 386 1 1920 07 16 2127 34.1 N 118.3 W — 380 — — — — VI 386 2 1920 07 16 2130 34.1 N 118.3 W —— 380 — — — -— VI 386 6 1920 07 23 0355 40.50 N 121.83 W — 324 -—- — — — VII 38 -- 1920 10 05 1903 58 36.58 N 121.67 W — 324 — —- 5.20UknJON —- V 324 — 1920 12 05 1158 34.5 N 119.5 W — 380 — — 4.50ML3DMG —— V 56 20 1922 01 26 093120 41.0 N 126.0 W 258 —— —— 6.00M, GR — —— — —— EARTHQUAKES IN CALIFORNIA CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #. land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (-—) indicates information is not available] 77 Origin Hypocenter Magnitude Intensity Date timetum) Letttude Longitude Depth Ref uses Other Moment MMI net Fen area Yr MoDa h m 8 (°) (°) (km) mb Ms M (1,000 kmz) 1922 0131 131722 41.0 N 125.5 w — 258 — —— 7.30Ms ABE — V 56 1808: 1922 03 10 112120 35.75 N 120.25 W — 258 —— — 6.50Ms GR 6.0ELL 1X 38 230 1922 03 16 2311 35.75 N 120.33 w — 324 — — 5.00UknJON — V 324 .— 1922 08 18 0512 35.75 N 120.33 w — 324 — — 5.00ML,DMG — V 56 65 1923 01 22 090418 40.5 N 124.5 w — 258 — — 7.20Ms GR —— VIII 56 2006‘: 1923 02 09 1114 40.83 N 124.17 W — 324 — — 5.00UknJON — II 324 .— 1923 04 29 02 3129 41.0 N 125.0 W — 258 — — 5.60Ms GR — — — — 1923 07 23 07 30 26 34.00 N 117.25 w — 258 — — 6.25Ms GR 5.9 HK V11 388 180# 1923 11 05 2207 32.5 N 115.5 W —— 38 — — 5.00ML.DMG — VII 38 — I923 11 07 23 57 32.5 N 115.5 W —. 38 — — 5.70UknJON -— VII 38 — 1924 01 09 10 22 40.83 N 124.17 W — 324 — — 4.80UknJON — IV 56 — 1924 03 09 1133 29 36.58 N 121.67 W -— 324 — — 4.600knJON — Iv 272 1924 04 03 2354 37.33 N 121.67 W — 324 —— .— 4.50ML,DMG — V 56 19 1924 12 28 0421 36.67 N 121.67 w — 324 — — 4.00ML,DMG VI 56 17 1925 01 26 05 45 45 40.83 N 124.17 w — 324 —. — 4.80UknJON — II 56 — 1925 04 16 0330 32.5 N 115.5 w — 38 .— —— — — VI 56 — 1925 06 04 120252 41.5 N 125.0 W — 258 —— 6.00Ms GR — — — — 1925 06 29 144216 34.3 N 119.8 w —— 258 — — 6.25Ms GR 682HK 1x 389 130& 1925 07 03 16 37 34.3 N 119.8 W — 380 —— — -— VI 380 — 1925 07 03 1819 34.3 N 119.8 w — 380 — — — — VI 380 — 1925 08 08 1013 33.5 N 117.0 W — 380 _ — 4.50ML,DMG — V 380 25 1926 0218 18 2045 34.0 N 119.5 W — 38 — — 5.50UknJON — VI 56 — 1926 04 03 2009 34.0 N 116.0 w — 38 — — 5.50ML.DMG — V 380 15511 1926 06 29 23 21 34.5 N 119.5 W 38 — — 5.50ML,DMG — VII 38 78 1926 06 30 13 31 35.6 N 118.8 w — 380 — -— 5.00ML.DMG — V 380 78 1926 07 25 17 57 54 36.5 N 120.8 W 015 390 — — 5.mML,DMG — VI 218 70 1926 10 22 12 35 36.617N 122.350w —— 521 — —— 6.10Ms GR — VII 218 90& 1926 10 22 13 35 22 36.550N 122.183w — 521 —— — 6.10Ms GR —— VII 218 906‘: 1926 10 24 22 5149.5 37.017N 122.208w — 391 — — 5.50M._.DMG — IV 218 104 1926 12 10 0838 53 40.75 N 126.00 W —— 258 — — 6.00M; GR — — — —— 1926 12 27 0919 36.17 N 120.32 w —- 324 —— —— 5.00ML.DMG —— IV 218 65 1927 01 01 081645 32.5 N 115.5 w — 258 — — 5.75Ms GR — VIII 38 130 1927 01 01 091330 32.5 N 115.5 W — 258 — — 5.50Ms GR — VIII 38 130 1927 02 15 23 54 03.5 36.950N 122.267w —— 391 —— —— 5.00ML.DMG — V 56 78& 1927 05 28 17 3617 37.33 N 122.92 w —— 324 — — 4.90UknJON — V 56 l7& 1927 08 04 1224 34.0 N 118.5 w —— 38 — _ 5.30U'knJON — VI 218 21& 1927 08 20 200544 41.0 N 124.6 w —— 324 — 5.30UknJON — VIII 38 408: 1927 09 18 02 0707 37.5 N 118.75 w — 258 — —— 6.00Ms GR 5.48HHT VI 56 194 I927 11 04 1350 34.7 N 120.8 w — 521 7.00Ms ABE 7.28HK VIII 392 80 1927 11 19 03 3230 35.0 N 120.5 w —. 38 —— — 5.00UknJON —— VI 218 —— 1928 01 09 0245 37.00 N 121.58 w — 324 — — 4.60UknJON — V 315 — 1928 04 15 215712 39.93 N 122.78 w 015 393 — -— 4.50La DMG — VI 393 30 1928 04 18 2140 34.1 N 119.3 W — 315 — —— 5.20UknJON — III 315 — 1928 06 04 05 30 40.75 N 122.92 W — 324 — — 4.50UknJON — VI 1 — 1928 08 09 0635 37.33 N 121.92 W — 324 — — 4.80UknJON — Felt 1 — 1928 09 05 14 42 34.0 N 116.0 w — 38 — — 5.00ML,DMG — V 38 — 1928 10 02 1901 32.9 N 115.7 W —— 380 — — 5.00MLaDMG —— Felt 1 658 1929 03 13 02 28 35.0 N 119.0 w —— 380 — — 4.50ML.DMG —— IV 2 15 1929 07 08 164607 33.91 N 118.04 W 013 394 — — 4.70ML RIC — VII 394 7 I929 09 26 2000227 34.83 N 116.52 w — 395 — — 5.10ML RIC — Felt 2 — 78 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIF ORNlA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ret Felt area Yr Me Be h m 8 (°) (°) (km) mg, Ms M (1,000 kmz) 1929 10 15 220310 36.17 N 120.67 W — 324 - — 4.60UanON —- III 2 — 1929 11 28 19 49 36.9 N 118.2 W — 2 — — 5.50MLaDMG — VII 38 90 1929 12 04 12 29 40.5 N 124.0 W — 324 — — 4.50M“ DMG — V 324 15& 1930 01 09 080613 36.8 N 121.5 W — 380 — — 4.50MLaDMG -— V 380 58: 1930 01 09 08 16 36.8 N 121.5 W — 380 — —— 4.50ML3DMG — V 380 5& 1930 01 16 002434 34.2 N 116.9 W — 258 —— — 5.25Ms GR — VII 38 130& 1930 01 16 0034 34.2 N 116.9 W — 38 — -—— 5.10UknPAS —— VII 38 1308!. 1930 02 26 02 30 33.0 N 115.5 W — 38 —- —- 5.00ML RIC — VII 3 528?. 1930 03 01 2344 33.0 N 115.5 W —— 38 —- — 4.50ML RIC —— VII 3 28 1930 03 02 0150 33.0 N 115.5 W -— 380 — — 4.50ML3DMG — IV 3 26 1930 07 07 120855 35.5 N 118.0 W — 315 — — 4.70U1mJON — IV 315 — 1930 08 05 1125 34.5 N 119.5 W -— 38 — — 5.00MLaDMG — VI 3 248: 1930 08 31 004038 34.030N 118.643W 015 474 — — 5.25Ms GR — VII 38 318: 1930 09 23 02 56 55 40.83 N 124.17 W — 324 — — 5.00MLaDMG — VII 38 12& 1930 10 29 12 37 40.67 N 121.92 W —— 324 — — 4.50ML3DMG — VI 3 7 1930 12 11 08 58 55 40.08 N 124.50 W -— 324 — — 5.00ML3DMG — V 3 4082 1930 12 11 12 27 40.92 N 124.08 W — 324 — -— 5.00UknJON — IV 315 — 1930 12 12 0932 39.83 N 123.58 W — 324 — — 4.50MLaDMG — V 3 98: 1930 12 12 2016 40.67 N 124.32 W -— 324 —— — 4.50ML,DMG — V 3 10 1930 12 14 0138 40.50 N 124.08 W -— 324 -— — 4.80UknJON —- IV 315 — 1930 12 15 08 38 40.83 N 124.17 W —— 324 — — 4.60UknJON — III 315 — 1931 01 06 232840 36.50 N 124.40 W — 324 —— — 5.00UknJON —- V 4 12& 1931 02 23 1001 35.83 N 120.50 W — 324 — — 4.70UknJON — V 4 13 1931 03 10 0328 53 40.0 N 125.0 W —— 324 — —- 5.60M3 GR — V 4 —- 1931 07 21 1208 35.25 N 120.67 W —— 324 —- —-— 4.80UknJON — IV 4 10& 1931 08 23 180146 40.0 N 125.0 W — 258 -—- —- 5.30M, GR -— VI 4 128: 1931 09 02 15 34 28 41.8 N 123.0 W — 324 — — 4.50ML BRK —- — — — 1931 09 09 134030 40.80 N 125.00 W -— 324 — —- 5.80M3 GR — VI 4 39& 1931 12 04 005300 36.50 N 121.67 W —- 324 — — 5.10UknJON — IV 315 —— 1932 01 05 135904 40.42 N 124.42 W — 324 — — 4.50ML BRK — IV 5 — 1932 02 26 16 58 36.0 N 121.0 W -— 324 — —— 5.00ML BRK — IV 5 —— 1932 03 02 171436 40.2 N 127.0 W — 324 —— — 5.60ML BRK -— —— — — 1932 04 16 18 48 10 36.67 N 121.22 W —— 324 —-— -— 4.50ML BRK — III 324 —- 1932 06 06 084422 40.75 N 124.50 W — 258 -— — 6.40Ms GR — VIII 5 13082 1932 06 14 0944 17 37.25 N 122.08 W -— 324 — — 4.50ML BRK -—— V 5 158: 1932 07 26 0651583 35.800N 118.533W 016 292 —— — 4.50ML PAS ——- VI 5 30 1932 07 30 07 13 59.7 34.850N 116.583W 016 292 -— -— 4.50ML PAS —- — —- ~— 1932 10 09 22 51 32.666N 115.500W 016 292 — — 4.50ML PAS ——- IV 5 —- 1932 10 25 010723 37.75 N 122.50 W — 324 —— — 5.10UknJON —— IV 5 — 1932 10 25 0328 37.333N 118.666W 016 292 -- — 4.50ML PAS — — — — 1932 11 03 18 5440 37.16 N 122.16 W — 324 — -— 4.90UknJON — V 5 — 1933 02 03 0326 37.333N 118.833W 016 292 — —— 5.00ML PAS — IV 6 —— 1933 02 24 19 33 32.833N 115.750W 016 292 —— -— 4.50ML PAS — — -- —— 1933 03 11 01 54 07.8 33.616N 117.966W 016 292 — —— 6.30ML PAS 6.15 VIII 397 213* 1933 03 11 0204 33.750N 118.083W 016 292 — — 4.90ML PAS — — — — 1933 03 11 0209 33.750N 118.083W 016 292 — — 5.00ML PAS —- — — — 1933 03 11 0210 33.750N 118.083W 016 292 — — 4.60ML PAS — — — —— 1933 03 11 0216 33.750N 118.083W 016 292 — -—- 4.80ML PAS — — — ~— 1933 03 11 0217 33.600N 118.000W 016 292 — — 4.50ML PAS — — — -— 1933 03 11 02 27 33.750N 118.083W 016 292 -— —- 4.60ML PAS — ~—- -— — 1933 03 11 02 30 33.750N 118.083W 016 292 — — 5.10ML PAS — — — — 1933 03 ll 02 59 33.750N 118.083W 016 292 -— 4.60ML PAS -— — — — 1933 03 11 0323 33.750N 118.083W 016 292 — — 5.00ML PAS — — — -—- EARTHQUAKES IN CALIFORNIA CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. 8:, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1.000 kmz. Leader (--) indicates information is not available] 79 Origin Hypocenter Magnitude Intensity Date time (UTc) Latitude Longitude Depth Ref USGS Other Moment MMl Ref F9" area Yr Mo 0: h m 3 (°) (°) (km) m, M; M (1,000 km?) 1933 03 11 0436 33.750N 118.083w 016 292 —— — 4.60ML PAS — -- — — 1933 03 11 0439 33.750N 118.083w 016 292 — — 4.90ML PAS — — — —— 1933 03 11 0440 33.750N 118.083w 016 292 — — 4.70ML PAS — — —— — 1933 03 11 05 10 22.0 33.700N 118.066w 016 292 —— —— 5.10ML PAS — — — — 1933 03 11 0513 33.750N 118.083w 016 292 —— — 4.70ML PAS — -— — — 1933 03 11 05 18 04.0 33.566N 117.983W 016 292 _ — 5.20ML PAS — —— — — 1933 03 11 0658 03.0 33.683N 118.050w 016 292 —. — 5.50ML PAS — — — — 19,33 03 11 0808 33.750N 118.083W 016 292 — -— 4.50ML PAS —- — — — 1933 03 11 08 54 57.0 33.7(X)N 118.066W 016 292 — — 5.10ML PAS — --— — — 1933 03 11 0910 33.750N 118.083W 016 292 — — 5.10ML PAS — —- — — 1933 03 11 1104 33.750N 118.133W 016 292 — —— 4.60ML PAS —— — -— — 1933 03 11 14 25 33.850N 118.266W 016 292 — — 5.00M; PAS -— -- — — 1933 03 11 1457 33.883N 118.316w 016 292 — — 4.90ML PAS — — — — 1933 03 11 1653 33.750N 118.083w 016 292 — —— 4.80ML PAS — — -— —— 1933 03 12 0616 33.750N 118.083w 016 292 — — 4.60ML PAS — —— — — 1933 03 12 17 38 33.750N 118.083w 016 292 — — 4.50M. PAS — — — — 1933 03 12 23 54 33.750N 118.083W 016 292 — — 4.50ML PAS — —_ — — 1933 03 13 0432 33.750N 118.083W 016 292 — — 4.70ML PAS — III 259 — 1933 03 13 1318280 33.750N 118.083W 016 292 — —— 5.30ML PAS —- IV 6 — 1933 03 14 1219 33.750N 118.083W 016 292 — — 4.50ML PAS — — -— — 1933 03 14 1901500 33.616N 118.016W 016 292 —— - 5.10ML PAS — — —— — 1933 03 15 11 13 32.0 33.616N 118.016W 016 292 -— —- 4.90ML PAS — IV 6 — 1933 05 16 11 45 26.0 37.60 N 122.“) W — 324 — -— 4.50ML BRK — VII 38 40& 1933 06 22 12 36 28.0 37.583N 118.800W 016 292 — — 4.90ML PAS — IV 6 20 1933 06 22 124102.0 37.583N 118.800W 016 292 — — 4.90ML PAS — 1V 6 20 1933 08 06 0332 33.333N 116.300W 016 292 — —- 4.70ML PAS —- IV 6 —- 1933 09 28 1153 40.08 N 123.92 W — 324 — — 4.60UknJON -— IV 6 -— 1933 10 02 091017.6 33.783N 118.133W 016 292 ~— — 5.40ML PAS — VI 6 16& 1933 10 25 0700461) 33.950N 118.133W 016 292 — —— 4.30ML PAS — VI 6 6& 1933 12 13 15 34 37 37.20 N 122.“) W — 324 — — 5.00UknJON — IV 6 13& 1934 01 04 2153 32.7(X)N 115.116W 016 292 — —— 4.50ML PAS — — — —- 1934 01 09 1410 34.100N 117.683W 016 292 -— — 4.50ML PAS —— V 7 20& 1934 01 20 2117 33.616N 118.116W 016 292 — — 4.50ML PAS — IV 7 — 1934 03 02 2130 33.083N 115.983W 016 292 —— —— 4.50ML PAS — HI 7 — 1934 04 23 2120 36.750N 121.400w —— 324 — — 3.50ML BRK —- VI 259 2 1934 06 05 2148 35.80 N 120.33 W 016 292 — — 5.00ML PAS —— V 7 28& 1934 06 05 22 52 35.80 N 120.33 W 016 292 — — 4.00ML PAS —- VI 7 — 1934 06 06 22 14 40.0 N 121.0 W — 7 —— — 4.50ML BRK — IV 7 12 1934 06 08 04 30 35.80 N 120.33 W 016 292 -- —- 5.00ML PAS — VII 7 75& 1934 06 08 04 47 35.80 N 120.33 W 016 292 --— — 6.00ML PAS 6.10ELL VIII 7 88& 1934 06 08 05 42 35.80 N 120.33 W 016 292 —- —- 4.50ML PAS — m 7 -— 1934 06 14 19 26 35.80 N 120.33 W 016 292 — —— 4.50ML PAS — IV 7 — 1934 07 06 22 48 55.1 41.22 N 125.27 W 005 260 — — 6.50Ms GR —- V 7 2082 1934 11 17 17 42 40.50 N 124.08 W — 324 — — 5.00UknJON — V 7 — 1934 12 03 01 54 35.95 N 121.50 W — 324 —- —— 4.50ML BRK — IV 259 — 1934 12 15 17 0001.0 40.60 N 124.20 W —- 324 — — 4.80UknJON —- V 7 — 1934 12 17 11 10 34.583N 120.333W 016 292 —- — 4.50ML PAS --— VI 259 — 1934 12 24 16 26 35.9(X)N 120.500W 016 292 —— — 5.00ML PAS —— IV 7 — 1934 12 30 13 5214 32.25 N 115.50 W — 258 — 6.50M; CPR 6.35HHT 1X 7 155# 1934 12 31 1845 15 32.0 N 114.75 W — 258 — — 7.10Ms ABE 7.02HHT X 7 2(X)# 1935 01 02 22 40 58 40.25 N 125.25 W — 258 — — 5.70Ms GR —— V 8 — 1935 05 16 0325 37.380N 118.920W 016 292 — — 4.50ML PAS -— IV 8 — 80 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &. land area only; 1?, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m s (°) (°) (km) mb Ms M (1,000 kmz) 1935 06 03 1708 41.00 N 121.00 W — 324 — -—- 5.00ML BRK —-— — — — 1935 06 19 0955 37.250N 118.500W 016 292 — — 4.50ML PAS — V 8 33 1935 07 13 10 54 16.5 34.200N 117.900W 016 292 — — 4.70ML PAS — V 8 25& 1935 09 03 0647 34.033N 117.316W 016 292 —— — 4.50ML PAS — V 8 —- 1935 09 08 14 40 32.900N 115.216W 016 292 -— — 4.50ML PAS —- IV 8 — 1935 09 08 17 03 32.900N 115.216W 016 292 -— — 5.00ML PAS —— IV 8 ~— 1935 10 11 1406 32.900N 115.216W 016 292 -— -—— 5.00ML PAS —- III 259 — 1935 10 24 14 48 07.6 34.100N 116.800W 016 292 —- —- 5.10ML PAS — V 8 45& 1935 10 24 1451 34.100N 116.883W 016 292 -—— —— 4.50ML PAS — IV 8 — 1935 10 24 14 52 34.100N 116.883W 016 292 —— — 4.50ML PAS — IV 259 — 1935 11 04 0355 33.500N 116.916W 016 292 — — 4.50ML PAS — IV 259 22& 1935 12 20 0745 33.166N 115.500W 016 292 — — 5.00ML PAS — IV 8 -- 1935 12 25 1715 33.600N 118.016W 016 292 —- — 4.50ML PAS — V 8 — 1936 02 23 22 2042.7 34.127N 117.338W 010 292 —- — 4.50ML PAS —— V 9 28 1936 04 07 22 53 32.900N 115.216W 016 292 — —— 4.50ML PAS —- V 9 — 1936 05 07 1147 33.133N 116.083W 016 292 — —- 4.50ML PAS — V 9 — 1936 05 09 202040 40.50 N 121.65 W — 324 — — 4.50UknJON —— V 9 — 1936 05 10 174013.2 37.610N 118.368W 010 292 — — 5.00ML PAS — V 9 45 1936 05 27 19 55 36.50 N 121.17 W -— 324 — —— 4.50ML BRK —— — — — 1936 06 03 0915 40.16 N 126.45 W — 324 —— —- 5.80ML BRK —— V 9 188: 1936 09 18 1440 32.1 32.856N 115.710W 010 292 —— —— 4.50ML PAS — — — — 1936 10 10 01 25 32.0 40.3 N 126.0 W — 265 — — 5.00ML BRK — — -— — 1936 11 18 1802185 34.460N 120.522W 010 292 —— — 4.50ML PAS -— IV 9 — 1937 02 07 044134 40.50 N 125.25 W — 258 — —— 5.75Ms GR -— V 10 26& 1937 02 17 03 33 36.70 N 121.20 W —— 324 -— — 4.50ML BRK — IV 259 — 1937 O3 05 12 47 36.70 N 121.70 W — 324 -— — 4.50ML BRK — V 10 5& 1937 03 08 103112 37.80 N 122.20 W — 324 —— — 4.50ML BRK — VII 10 208: 1937 03 25 16 49 01.8 33.408N 116.261W 010 292 — —- 6.00ML PAS 5.60HHT VI 10 80# 1937 03 26 210906 40.25 N 126.75 W — 258 —— — 5.50M3 GR -— — — -— 1937 03 27 0742 33.466N 116.583W 016 292 — — 4.50ML PAS — IV 259 — 1937 08 06 0324 38.8 N 120.1 W — 10 —— — 4.50M]~ BRK — V 259 8 1937 09 01 13 48 08.2 34.210N 117.530W 010 292 — — 4.50ML PAS — V 10 17 1937 09 01 16 35 33.5 34.183N 117.548W 010 292 — — 4.50ML PAS — V 10 — 1937 10 27 15 53 36.60 N 121.50 W — 324 -— - 4.50ML BRK —- IV 10 — 1937 11 22 0412 53.8 34.370N 120.623W 010 292 - —— 4.50ML PAS — V 10 5& 1938 01 04 0029 33.466N 116.583W 016 292 — —- 4.50ML PAS —— IV 259 — 1938 02 12 200014.0 37.000N 122.000W — 324 --— — 4.50ML BRK — VI 11 881. 1938 02 15 0745 39.8 34.173N 116.257W 010 292 — -— 4.50ML PAS — V 259 -— 1938 04 13 1929 32.883N 115.583W 016 292 —- —— 4.50M; PAS — V 259 — 1938 04 28 0607 28.0 32.717N 118.172W 010 292 — -— 4.50ML PAS — IV 259 — 1938 05 10 10 32 36.200N 121.300W — 324 -— — 4.50ML BRK — IV 259 — 1938 05 31 08 34 55.4 33.699N 117.510W 010 292 — -— 5.50ML PAS —-- V 11 50# 1938 06 06 02 42 32.900N 115.216W 016 292 — — 5.00ML PAS — IV 259 — 1938 07 01 1813 41.00 N 124.00 W — 324 — — 5.00ML BRK — —— — — 1938 07 05 1806558 33.682N 117.553W 010 292 — — 4.50ML PAS -— V 259 ~— 1938 08 18 0739 45.4 34.847N 116.143W 010 292 — — 4.50ML PAS — Iv 259 .— 1938 08 31 0318143 33.759N 118.253W 010 292 — — 4.50ML PAS — VI 11 5& 1938 09 12 0610 40.00 N 124.00 W — 324 — — 5.50MI GR — VI 11 3581. 1938 09 17 1423 04.1 35.630N 117.513W — 292 —— —— 5.00ML PAS — IV 259 — 1938 09 27 12 2348 36.45 N 121.25 W — 324 — —— 5.00ML PAS — V 11 23& 1938 10 18 0505 40.00 N 124.00 W - 324 ~—- — 4.50ML BRK —- D1 259 — 1938 11 15 13 48 39.25 N 123.00 W — 324 — — — — VI 11 7 1938 11 22 15 30 35.93 N 120.48 W —— 324 — —- 4.50ML PAS — IV 259 —- 1938 12 01 1617 37.50 N 121.80 W —— 324 — — 4.50ML BRK — VI 11 — 1938 12 03 17 42 52.6 37.453N 118.603W 010 292 — — 5.70ML PAS — VI 11 62 EARTHQUAKES IN CALIFORNIA CALIF ORNIA—Con ti nued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (-—) indicates information is not available] 81 Origin Hypocenter Magnitude Intensity Date time (um Latitude Longitude Depth Ref uses Other Moment MMI Ref Felt area Yr Mo be h m 3 (°) (°) (km) mb Ms M (1,000 km?) 1938 12 03 18 4116.4 37.808N 118.323w 010 292 — — 4.50ML PAS — — -— — 1939 01 07 20 2150.2 36.007N 117.720w 010 292 — — 4.50ML PAS — IV 259 — 1939 02 23 08 4551.7 34.912N 118.973w 010 292 —— — 4.50M._ PAS — IV 259 — 1939 02 23 09 18 46.7 34.885N 119.002W 010 292 —— — 4.50ML PAS — Iv 259 — 1939 03 12 2204 41.0 N 125.9 W — 324 — — 4.90UknJON — II 11 — 1939 03 17 1309 40.75 N 126.00 w — 324 —— _ 5.00UknJON — 111 11 —- 1939 04 19 07 41 32.583N 117.8oow 016 292 — — 4.50ML PAS — IV 259 — 1939 05 01 2153180 40.20 N 124.70 w — 12 — — 4.50M._ BRK — V 259 — 1939 05 08 0248053 34.903N 119.038w 010 292 — —— 4.50ML PAS — IV 259 — 1939 05 12 1925023 33.466N 116.433w 016 292 -— — 4.50ML PAS — Iv 259 — 1939 06 24 13 0206 36.80 N 121.45 w — 324 —— — 5.50ML BRK — VII 259 268; 1939 06 25 0149 32.700N 118.200w — 292 — —— 4.50ML PAS —— 111 259 — 1939 07 17 092454 36.85 N 121.68 w — 324 — —— 4.50ML BRK —— V 12 —— 1939 11 07 18 5208.4 34.000N 117.283w 016 292 —— —— 4.70ML PAS — Iv 259 — 1939 12 27 1928490 33.783N 118.200w 016 292 —— —— 4.70M._ PAS — v1 12 15& 1939 12 28 1215 38.0 35.80 N 120.33 w — 324 — — 5.00M; BRK — VI 12 428: 1940 02 08 08 05 59.0 40.00 N 121.60 W — 324 —— — 5.70ML BRK — VII 13 72 1940 02 13 23 53 40.0 N 124.0 w —— 324 — —— — —— VI 259 2581. 1940 02 19 120655.7 34.017N 117.050w 016 292 — — 4.60ML PAS — v 259 — 1940 02 24 0938 37.500N 118.533w 016 292 — — 4.50ML PAs — Iv 259 - 1940 02 28 17 28 07.0 33.133N 116.083w 016 292 — —- 4.50ML PAS —— IV 259 — 1940 05 18 0503 58.5 34.083N 116.3oow 016 292 —— — 5.40ML PAS —— V 259 65 1940 05 18 05 5120.3 34.067N 116.333w 016 292 — — 5.20ML PAS — N 259 — 1940 05 18 0604306 34.067N 116.317w 016 292 — — 4.60ML PAS — — — — 1940 05 18 07 2132.7 34.067N 116.333W 016 292 — — 5.00ML PAS — — — — 1940 05 18 13 4719.0 34.050N 116.283w 016 292 — — 4.50ML PAS — — — .— 1940 05 19 02 26 02.0 34.050N 116.283w 016 292 — — 4.50ML PAS -— — —— — 1940 05 19 02 27 30.0 34.050N 116.283w 016 292 —— — 4.50ML PAS — — — .— 1940 05 19 0436409 32.733N 115.500w 016 292 — — 7.10Ms ABE 6.93HHT x 13 1701: 1940 05 19 0448470 32.767N 115.483W 016 292 —— — 4.50ML PAS — Felt 13 — 1940 05 19 0455 00.0 32.767N 115.483W 016 292 — — 5.50ML PAS — Felt 13 — 1940 05 19 0504 32.767N 115.483W 016 292 — — 4.50M._ PAS — Felt 13 — 1940 05 19 0544370 32.766N 115.483W 016 292 —— — 4.50ML PAS — Felt 13 — 1940 05 19 05 5134.0 32.767N 115.483W 016 292 — — 5.50ML PAS -— 1x 13 — 1940 05 19 05 5717.0 32.767N 115.483W 016 292 —- — 4.50ML PAS — Felt 13 —— 1940 05 19 0617 42.0 32.767N 115.483W 016 292 — —— 4.50ML PAS — Felt 13 — 1940 05 19 0633 20.0 32.767N 115.483W 016 292 — — 5.00ML PAS —- Felt 13 — 1940 05 19 0635400 32.767N 115.483W 016 292 — — 5.50ML PAS — Felt 13 — 1940 05 19 0701 32.767N 115.483W 016 292 — — 4.50ML PAS — — —— — 1940 05 19 15 3033.0 32.767N 115.483W 016 292 — — 4.50ML PAS — — — — 1940 05 22 1058 31.0 32.767N 115.483W 016 292 —— — 4.50M._ PAS — — — — 1940 05 23 1100 32.767N 115.483W —— 259 —— — — -— v1 259 — 1940 05 23 17 30 32.769N 115.483W — 259 .— — — — v1 259 — 1940 05 23 18 45 32.767N 115.483W — 259 —— — —— —— v1 259 — 1940 06 01 0527 01.2 34.083N 116.333w 016 292 — -— 4.70ML PAS -— Iv 259 — 1940 06 01 23 59 36.0 32.767N 115.483W 016 292 — — 4.50M._ PAS — — —— —— 1940 06 02 0613102 34.083N 116.333w 016 292 — — 4.50ML PAS — — — — 1940 06 04 1035083 33.000N 116.433w 016 292 — — 5.10ML PAS — v 259 —— 1940 07 08 1057 36.5 37.616N 118.800W 016 292 — — 4.80ML PAS — IV 259 — 1940 07 22 2300329 37.633N 118.767w 016 292 —— —— 4.60ML PAS — IV 259 — 1940 09 07 1302060 36.500N 121.500W — 324 — —— 4.50M._ BRK — III 259 — 1940 09 27 1703 36 40.5 N 125.0 w — 324 — — 4.50ML BRK — Iv 259 — 1940 1011 05 5712.3 33.767N 118.450w 016 292 — —— 4.75ML PAS — VI 13 188: 1940 10 21 0649330 33.117N 116.417w 016 292 — — 4.50ML PAS — IV 259 — 1940 10 22 1101 40.5 N 124.1 w — 324 —— —— 4.50Mx JON — VI 13 5& 82 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (»—) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 3 (°) (°) (km) mb Ms M (1.000 kmz) 1940 11 19 18 35 40.75 N 124.90 W -— 324 --— —- 4.70ML BRK — VI 13 21& 1940 12 20 23 40 42.0 40.00 N 124.00 W —— 324 — — 5.50Ms GR — VI 13 238: 1941 01 23 12 03 40.5 N 125.0 W — 324 — — 4.70ML BRK — V 14 5& 1941 02 09 0944 04.0 40.50 N 125.25 W — 258 —— — 6.60Ms GR — VI 14 508: 1941 02 11 04 51 40.00 N 125.00 W — 324 —— -— 4.50Ms GR —— —— —— -— 1941 02 23 18 36 14.0 33.500N 116.483W 016 292 — — 4.50ML PAS —- III 259 — 1941 05 01 13 29 40.00 N 121.00 W -— 324 — -— 4.50ML BRK — IV 14 — 1941 05 13 16 01 54.0 40.30 N 126.40 W —- 324 — —— 6.00Ms GR — V 14 — 1941 05 16 02 36 42.0 40.30 N 125.00 W -— 324 — — 4.50M; BRK -— — — — 1941 05 28 06 23 18.0 37.08 N 121.75 W -— 324 — — 4.50ML BRK — V 14 12& 1941 07 01 07 50 54.8 34.367N 119.583W 016 292 — — 5.90ML PAS 5.92HHT VIII 14 52# 1941 07 01 23 54 34.333N 119.583W 016 292 — —— 4.50ML PAS — IV 259 — 1941 07 12 16 18 34.333N 119.583W 016 292 — — 4.50ML PAS —— IV 259 — 1941 07 22 18 52 05.0 32.733N 115.450W 016 292 — —- 4.50ML PAS — V 259 — 1941 09 08 03 12 45.0 34.333N 119.583W 016 292 — — 4.50M], PAS — V 14 — 1941 09 14 16 43 31.8 37.567N 118.733W 016 292 — —- 5.80ML PAS — VI 259 90 1941 09 14 16 54 58.0 37.567N 118.733W 016 292 —- — 4.50ML PAS -- — — — 1941 09 14 18 21 18.7 37.567N 118.733W 016 292 — — 5.50ML PAS — VI 259 — 1941 09 14 18 39 11.9 37.567N 118.733W 016 292 -— -— 6.00ML PAS 5.48HHT VI 259 90 1941 09 14 21 16 01.0 37.570N 118.730W 016 292 — —— 5.00ML BRK — III 259 — 1941 09 21 19 53 07.2 34.867N 118.933W 016 292 — — 5.20ML PAS —— V 14 60& 1941 10 03 16 13 08.0 40.40 N 124.80 W — 324 — — 6.40Ms GR —— VI 259 308: 1941 10 06 06 59 40.40 N 125.00 W — 324 —— — 5.00ML BRK — — — —— 1941 10 22 06 57 18.5 33.817N 118.217W 016 292 — — 4.90ML PAS —- VII 14 5& 1941 10 22 10 32 21.8 33.867N 118.217W 016 292 — - 3.80ML PAS — VI 14 — 1941 10 23 2044 31.0 37.567N 118.733W 016 292 — — 4.50ML PAS — IV 259 — 1941 10 25 07 09 39.50 N 122.17 W -— 324 — — 4.60Mx JON — V 14 — 1941 11 14 08 41 36.3 33.783N 118.250W 016 292 —— — 5.40Ms GR —- VIII 259 9& 1941 12 24 07 3012.0 32.60 N 116.10 W 016 292 — — 4.50ML PAS — IV 259 — 1941 12 31 06 48 44.0 37.567N 118.733W 016 292 — —— 5.40ML PAS — VI 14 728: 1941 12 31 18 05 44.0 37.567N 118.733W 016 292 — -— 4.50ML PAS -— — — — 1942 01 01 03 41 01.0 37.567N 118.733W 016 292 — — 4.50ML PAS — IV 259 — 1942 02 01 15 18 28.0 34.400N 116.917W 016 292 — — 4.50ML PAS —- IV 259 — 1942 02 01 16 03 34.0 34.400N 116.917W 016 292 — — 4.50ML PAS —— -- -- — 1942 02 04 03 32 03.0 37.567N 118.733W 016 292 — —— 4.50ML PAS —- IV 259 — 1942 03 03 01 03 24.0 34.0(X)N 115.750W 016 292 — — 5.00ML PAS — IV 259 — 1942 05 23 15 47 29.0 32.983N 115.983W 016 292 —— — 5.00ML PAS -— V 15 16+ 1942 07 06 21 11 40.0 37.567N 118.733W 016 292 — — 4.50ML PAS — IV 259 — 1942 08 07 01 15 33.0 34.300N 116.417W 016 292 —— — 4.50ML PAS — — — — 1942 09 03 14 06 01.0 34.483N 118.983W 016 292 — — 4.50ML PAS — V 15 — 1942 09 04 06 34 33.0 34.483N 118.983W 016 292 —— — 4.50ML PAS — V 15 — 1942 10 21 16 22 13.0 32.966N 116.000W 016 292 — — 6.50Ms GR 6.59HHT VI 15 901' 1942 10 21 16 25 19.0 32.967N 116.000W 016 292 — — 5.00ML PAS -— — —— — 1942 10 21 16 26 54.0 32.967N 116.000W 016 292 —— — 5.00ML PAS — — — — 1942 10 21 16 34 39.0 32.967N 116.000W 016 292 —— — 4.50ML PAS — —-— —- — 1942 10 21 16 38 06.0 32.967N 116.000W 016 292 -— — 4.50ML PAS — — —— —— 1942 10 21 19 10 28.0 32.967N 116.000W 016 292 — —— 4.50ML PAS — — — — 1942 10 21 21 49 28.0 32.967N 116.000W 016 292 — — 4.50ML PAS -— — — — 1942 10 22 01 50 38.0 33.233N 115.717W 016 292 —— — 5.50ML PAS 5.79TH V 259 — 1942 10 22 18 13 26.0 32.967N 116.000W 016 292 —— — 5.00ML PAS — —— — — 1942 10 26 03 02 15.0 33.233N 115.717W 016 292 — - 4.50ML PAS — III 259 —- 1942 10 26 06 15 04.0 33.233N 115.717W 016 292 —— — 4.50ML PAS — — — — 1942 10 29 15 56 00.0 32.967N 116.000W 016 292 —- — 4.50ML PAS — IV 259 — 1942 10 29 16 21 57.0 32.967N 116.000W 016 292 —— —— 4.50ML PAS — IV 259 — 1942 10 30 05 35 45.0 32.967N 116.000W 016 292 —- —— 4.50ML PAS —- IV 259 — EARTHQUAKES IN CALIFORNIA CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &. land area only; 5?, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader (..) indicates information is not available] 83 Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo D: h m 8 (°) (°) (km) mb Ms M (1.000 kmz) 1942 11 02 12 59 42.0 32.967N 116.000W 016 292 —— —- 4.50ML PAS — — — — 1942 ll 03 0506290 32.967N 116.000W 016 292 — —— 4.50ML PAS — — — — 1942 ll 09 2034250 34.617N 116.000W 016 292 — —- 4.50ML PAS — — — — 1942 12 05 18 52 07.0 37.567N 118.733W 016 292 — — 4.50ML PAS —- -— — — 1942 12 17 1507 43.0 38.87 N 119.90 W — 324 -- — 5.10ML BRK — V 15 — 1942 12 20 05 47 39.0 38.72 N 119.73 W — 324 —- —- 4.50M; BRK — Felt 15 — 1943 01 02 1411 18.0 33.417N 116.417W 016 292 — —— 4.50ML PAS — IV 259 — 1943 03 17 004044.0 32.733N 115.433W 016 292 -—— — 4.50ML PAS — V 16 — 1943 03 30 2107 28.0 39.430N 120.400W —- 324 — — 5.30ML BRK — V 259 39 1943 05 31 20 16 53.0 37.383N 118.600W 016 292 —— — 4.50M,~ PAS — V 16 24 1943 06 18 16 15 46.0 33.117N 116.117W 016 292 — — 4.50ML PAS — IV 16 — 1943 08 29 0345130 34.267N 116.967W 016 292 —- — 5.50ML PAS —— VI 259 37& 1943 09 16 07 52 22.0 36.017N 117.933W 016 292 — — 4.50ML PAS -— IV 259 — 1943 10 02 0656 41.0 40.50 N 124.60 W — 324 -— — 4.60ML BRK -— IV 259 —- 1943 10 14 1428 44.0 34.333N 116.883W 016 292 —— —-- 4.50M; PAS -- III 259 — 1943 10 15 165001.0 34.350N 116.867W 016 292 — — 4.50ML PAS — IV 259 — 1943 10 26 0450330 37.43 N 121.68 W — 324 —- —- 4.90ML BRK — VI 16 658: 1943 10 31 13 1210.0 33.783N 116.200W 016 292 — — 4.50M], PAS — IV 259 — 1943 11 02 16 47 59.0 32.967N 116.000W 016 292 — —— 4.50ML PAS — IV 259 —- 1943 11 02 17 5041.0 32.967N 116.000W 016 292 — — 4.50ML PAS — IV 259 — 1943 ll 16 21 38 47.0 37.78 N 122.12 W — 324 — — 3.60ML BRK — VI 16 ~— 1943 ll 17 112841.0 33.917N 116.700W 016 292 — — 4.50ML PAS — IV 16 —- 1943 12 22 15 5028.0 34.333N 115.800W 016 292 — — 5.50ML PAS — IV 16 — 1944 01 12 1502400 40.30 N 124.90 W — 324 — — 5.10ML BRK — V 17 — 1944 01 16 0225290 40.30 N 125.10 W -— 324 — — 5.10ML BRK — IV 17 — 1944 06 10 111150.5 34.013N 116.772W 010 292 — — 4.50ML PAS 3.38TH V 17 — 1944 06 12 1045 34.7 33.977N 116.720W 010 292 — — 5.10ML PAS -—— VI 17 41& 1944 06 12 11 16 36.0 33.995N 116.712W 010 292 -— — 5.30ML PAS — VI 17 418: 1944 06 13 0827 32.0 34.667N 120.500W 016 292 —- -— 4.60ML PAS — V 17 —— 1944 06 19 0003 33.0 33.867N 118.217W 016 292 — — 4.50ML PAS — VI 17 168: 1944 06 19 0306070 33.867N 118.217W 016 292 —- — 4.40ML PAS — VI 17 1382 1944 07 03 05 38 23.5 35.350N 117.827W -— 292 — — 4.70M; PAS — V 17 — 1944 07 29 113715.0 40.30 N 125.80 W — 324 — — 4.50M; BRK —- — — — 1944 11 08 11 08 44.0 41.50 N 125.00 W -— 324 — — 4.70ML BRK — —— — — 1944 12 23 0816220 36.4mN 117.917W 016 292 -- —-— 4.70ML PAS — IV 17 —- 1945 01 07 2225330 36.730N 121.200W — 324 — -- 4.70ML BRK — VI 18 348: 1945 03 20 2155070 34.250N 116.167W 016 292 -- — 5.00ML PAS — IV 259 — 1945 04 01 23 4342.0 34.000N 120.017W 016 292 — — 5.40ML PAS 5.14TH IV 18 2& 1945 05 02 19 47 54.0 41.200N 123.500W — 324 — — 5.00ML BRK — V 18 9 1945 05 17 150647.0 36.82 N 121.37 W — 324 — — 4.60ML BRK —-— VI 18 15 1945 05 19 1507 04.0 40.25 N 126.50 W — 258 — —— 6.20Ms GR — V 18 4& 1945 06 14 0330130 37.083N 117.500W 016 292 — — 5.00ML PAS — — — —- 1945 08 15 17 56 24.0 33.217N 116.133W 016 292 —- —— 5.70ML PAS — VI 18 39# 1945 08 27 091304.0 37.27 N 121.80 W — 324 — ~— 4.50ML BRK — VI 18 34& 1945 09 28 2224050 41.90 N 126.70 W - 324 -— — 6.12M, CFR —-— — -— — 1946 01 08 1854180 33.000N 115.833W 016 292 —— — 5.40ML PAS —— V 19 31# 1946 01 13 16 31 15.0 37.317N 118.650W 016 292 — — 4.70ML PAS — VI 259 — 1946 03 15 13 21 00.9 35.753N 117.987W 016 292 — — 5.20ML PAS — VI 259 — 1946 03 15 13 49 35.9 35.725N 118.055W 022 292 — — 6.30ML PAS 6.06m VII 19 222& 1946 03 15 1400334 35.715N 118.073W 016 292 —— — 5.30ML PAS — VI 259 — 1946 03 15 19 18 53.6 35.715N 117.977W 016 292 — — 5.40ML PAS — Felt 259 — 1946 03 15 2154334 35.752N 118.029W 016 292 — — 5.20ML PAS — Felt 259 — 1946 03 16 0946173 35.745N 118.038W 016 292 -- —- 5.10ML PAS 4.54TH Felt 19 — 1946 03 17 08 16 36.0 35.632N 118.268W — 292 — — 4.60ML PAS 4.10m Felt l9 — 1946 03 18 1005 55.1 35.723N 118.035W 016 292 —- — 4.90ML PAS 4.35TH IV 259 — 84 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (um) Latitude Longitude Depth Ref uses Other Moment MMI Ref Felt area Yr Mo D: h m 8 (°) (°) (km) mb Ms M (1,000 kmz) 1946 03 18 15 49 25.7 35.780N 117.922W 016 292 — — 4.80ML PAS 4.30111 V 259 — 1946 03 18 15 5042.6 35.747N 117.908W 004 292 — — 5.30ML PAS 4.99TH V 259 — 1946 03 24 2000030 35.728N 118.098W 016 292 — — 4.50ML PAS — — — — 1946 05 02 012612.0 37.68 N 121.60 W — 324 -—— -—- 4.60ML BRK — V 19 8 1946 05 29 17 5103.0 36.77 N 121.42 W — 324 — -— 4.50ML BRK -— V 259 -—- 1946 06 04 12 05 24.0 33.917N 115.700W 016 292 — — 4.80ML PAS -- IV 259 — 1946 06 15 1946530 32.600N 116.317W 016 292 — — 4.80ML PAS -— V 19 — 1946 07 07 0655 15.0 40.500N 121.500W — 324 — -- 5.00ML BRK —_ V 19 18& 1946 07 18 14 27 58.0 34.533N 115.983W 016 292 — — 5.60ML PAS 5.39m V 259 70 1946 08 30 11 16 45.0 33.233N 115.700W 016 292 — —- 4.60ML PAS — — — — 1946 09 28 07 19 09.0 33.950N 116.850W 016 292 —- — 5.00ML PAS — VI 19 23& 1946 12 18 14 2028.0 40.30 N 124.60 W — 324 —— —— 4.70ML BRK — V 259 9& 1947 02 05 061423 36.23 N 120.65 W —— 324 -— — 5.00ML BRK — VI 20 — 1947 02 06 17 20 40.1 35.677N 118.067W 016 292 — — 4.60ML PAS — V 259 — 1947 03 30 0744 40.38 N 124.68 W —- 324 — — 4.60ML BRK — V 259 5& 1947 04 10 15 58 06.0 34.983N 116.550W 016 292 — — 6.20ML PAS 6.51HK VII 20 1518: 1947 04 10 1603 34.967N 116.550W 016 292 — -—- 5.10ML PAS — Felt 259 — 1947 04 10 17 18 22.0 34.950N 116.533W 016 292 —— — 5.00ML PAS — — — — 1947 04 11 0747 34.967N 116.550W 016 292 —— — 5.00ML PAS 4.76TH Felt 20 — 1947 04 19 02 29 09.0 34.967N 116.550W 016 292 —-— — 4.70ML PAS 4.38TH — — — 1947 05 11 0506200 34.233N 116.333W 016 292 — —— 4.90ML PAS —- Felt 20 — 1947 05 27 20 59 42 40.40 N 124.70 W — 324 — —— 5.20ML BRK — VI 20 6& 1947 06 22 23 29 33 37.00 N 121.77 W —— 324 —- —— 4.70ML BRK — VI 20 35& 1947 07 24 22 10 46.0 34.017N 116.500W 016 292 —— — 5.50M; PAS — V 20 60# 1947 07 24 22 54 26.0 34.017N 116.500W 016 292 — — 4.90M; PAS --— IV 259 —— 1947 07 25 0046 31.0 34.017N 116.500W 016 292 — — 5.00ML PAS 4.64TH — — — 1947 07 25 01 56 47.0 34.017N 116.500W 016 292 — —— 4.60ML PAS 4.15TH —— — — 1947 07 25 0619 49.0 34.017N 116.500W 016 292 — — 5.20ML PAS 5.15TH IV 259 — 1947 07 25 16 14 53.0 34.017N 116.500W 016 292 — — 4.50ML PAS 4.26TH IV 259 — 1947 07 26 02 49 41.0 34.017N 116.500W 016 292 —— — 5.10ML PAS — Felt 259 —— 1947 07 26 2304250 34.017N 116.500W 016 292 — — 4.50ML PAS — — — — 1947 08 10 215824 36.88 N 121.42 W —— 324 — — 4.40ML BRK —- VI 20 10& 1947 09 08 05 52 39.30 N 120.20 W — 324 — —— 4.50ML BRK — V 20 — 1947 09 08 07 13 39.30 N 120.20 W —— 324 — -— 4.70ML BRK — VI 20 — 1947 09 23 13 52 55.0 40.40 N 125.20 W — 324 — —— 5.30ML BRK — V 259 19& 1947 11 02 0701 40.10 N 125.30 W — 324 — — 4.80M], BRK -— —— — — 1947 11 10 02 22 55.0 34.400N 116.417W 016 292 —— —— 4.50ML PAS — III 259 ~— 1947 11 18 2159030 33.267N 119.450W 016 292 — —- 5.00ML PAS 478TH V 20 — 1948 01 10 004550 42.0 N 127.0 W — 324 — — 5.30ML BRK -- — — — 1948 02 11 03 29 28.0 36.10 N 118.80 W — 324 —-— — 4.90ML BRK —- VI 21 30 1948 02 19 08 2509.0 41.00 N 124.90 W —— 324 —— —— 4.80ML BRK — III 259 — 1948 02 20 042124.0 33.917N 118.217W 016 292 —— — 3.60ML PAS — VI 21 2 1948 02 24 0815100 32.500N 118.550W 016 292 — —-- 5.30ML PAS 5.12TH IV 21 -— 1948 03 01 0812130 34.167N 117.533W 016 292 —— — 4.70ML PAS — VI 21 318: 1948 03 28 22 38 03.0 36.850N 121.570W — 324 — — 4.60ML BRK —— V 21 10& 1948 03 28 22 45 00.0 36.850N 121.570W — 324 —— — 4.50ML BRK — V 21 10& 1948 04 16 22 26 24.0 34.017N 118.967W 016 292 — — 4.70ML PAS — VI 21 4& 1948 06 18 10 35 00.0 39.07 N 123.28 W — 324 — — 3.80ML BRK ~— VI 21 l 1948 07 26 17 5001.4 35.582N 118.158W 005 292 — — 4.50ML PAS — V 259 — 1948 08 18 191157.0 40.50 N 124.70 W — 324 — —- 5.00ML BRK — V 259 — 1948 11 12 23 10 25.0 40.40 N 124.32 W — 324 — — 4.50ML BRK — Felt 324 — 1948 12 04 23 43 17.0 33.933N 116.383W 016 292 — — 6.50ML PAS 5.95HK VII 21 180# 1948 12 05 0007 21.0 33.933N 116.367W 016 292 — — 4.90ML PAS 4.44TH Felt 259 — 1948 12 05 0042 35.0 33.967N 116.433W 016 292 — — 4.60ML PAS 4.48TH — — —— 1948 12 11 16 12 20.0 33.967N 116.450W 016 292 —— —- 4.50ML PAS — IV 259 — EARTHQUAKES IN CALIFORNIA CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; at, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader in) indicates information is not available] 85 Origin Hypocenter Magnitude Intensity Date tifl‘IO (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m s (°) (°) (km) mb Ms M (1,000 km?) 1948 12 20 0442 46.0 35.80 N 121.50 W -— 324 — —— 4.50ML BRK — III 259 -— 1948 12 29 12 53 28.0 39.550N 120.080W — 324 — — 6.00ML BRK — V11 21 104 1948 12 31 14 3546.0 35.67 N 121.40 W —- 324 — — 4.60ML BRK — V 21 — 1949 01 01 01 17 54.0 36.90 N 121.62 W -— 324 — -— 4.50ML BRK -— VII 21 9& 1949 01 03 13 43 40.0 34.967N 116.550W — 292 — — 4.80ML PAS — IV 259 -— 1949 01 20 07 59 23.0 39.55 N 120.08 W - 324 — —- 4.80ML BRK —- IV 259 — 1949 02 11 21 05 24.0 37.083N 117.750W 01 292 —- -— 5.60ML PAS 5.25TH VI 22 77 1949 02 27 13 3547.0 41.20 N 125.20 W — 324 — — 4.80ML BRK — —— — —— 1949 03 09 12 28 39.0 37.02 N 121.48 W —- 324 — -— 5.20ML BRK — VII 22 52& 1949 03 24 20 56 56.0 41.30 N 126.“) W — 324 — — 5.90ML BRK -— Felt 324 — 1949 04 13 0758 26.0 37.667N 118.383W 016 292 — -- 4.50ML PAS -- IV 259 — 1949 05 02 11 24 58.0 34.017N 115.767W 016 292 — — 4.60ML PAS —- Felt 259 —- 1949 05 02 ll 25 47.0 34.017N 115.683W 016 292 — — 5.90ML PAS — V 22 8241 1949 05 10 0406 33.0 34.017N 115.683W 016 292 — — 4.70ML PAS — — — —— 1949 05 25 17 31 46.0 34.017N 115.683W 016 292 —— — 4.50ML PAS — —- —— — 1949 06 10 0306400 37.30 N 121.67 W — 324 — -— 4.60ML BRK -- VI 22 218: 1949 06 27 1035 31.0 35.80 N 121.10 W — 324 — -- 4.50ML BRK — IV 259 — 1949 08 08 1100030 37.95 N 122.32 W — 324 -—- — 3.30ML BRK — VI 22 l& 1949 08 21 204816.0 40.27 N 121.23 W — 324 -- —- 4.50ML BRK —— IV 259 -— 1949 08 27 1451460 34.5(X)N 120.500W 016 292 —- —— 4.90ML PAS 4.39TH VI 22 l& 1949 09 19 0508135 33.960N 118.187W 000 292 — -— 3.10ML PAS — VI 22 2 1949 10 22 21 45 20.0 36.58 N 121.17 W -— 324 —-— — 4.70ML BRK — V 259 — 1949 10 28 02 29 16.0 40.90 N 124.20 W — 324 — — 4.50ML BRK — V 259 —- 1949 11 04 2042 38.0 32.2(X)N 116.550W 016 292 —— — 5.70M], PAS -— VI 22 33# 1949 11 05 0435 24.0 32.2(X)N 116.550W 016 292 — — 5.10M; PAS 4.32TH VI 22 15# 1949 12 09 12 39 02.0 37.467N 118.367W 016 292 — — 4.60ML PAS -—- IV 22 — 1950 01 14 195230 40.217N 124.417W — 324 — — 4.60M], BRK -— VI 23 — 1950 01 27 1047 20 42.0 N 125.1 W — 324 —— — 4.70ML BRK — —- — — 1950 02 26 000622.0 34.617N 119.083W 016 292 — — 4.70ML PAS — VI 23 6& 1950 03 20 15 22 17.0 40.450N 121.467W —- 324 — —- 5.50M], BRK — V 23 10 1950 03 23 04 16 50.0 40.5(DN 121.500W — 266 —— — 4.60ML BRK — -—- —— — 1950 04 15 11 56 32.0 35.750N 119.617W 016 292 — — 4.60M], PAS —-— IV 259 — 1950 06 09 1307 44 41.283N 125.733W —— 324 — — 4.80ML BRK -- — —— — 1950 07 27 1129260 33.117N 115.567W 016 292 -— — 4.80ML PAS -—- VI 23 —— 1950 07 27 22 51 33.117N 115.567W 016 292 —- — 4.50M; PAS —- — -—- -—- 1950 07 28 0325 33.117N 115.567W 016 292 -— — 4.70M; PAS —— V 259 — 1950 07 28 17 27 33.117N 115.567W 016 292 — — 4.70ML PAS 4.77TH Felt 23 — 1950 07 28 17 50 48.0 33.117N 115.567W 016 292 — — 5.40ML PAS 5.22TH VI 23 321‘ 1950 07 28 1758 12.0 33.117N 115.567W 016 292 — — 4.80ML PAS —— —— ~—- — 1950 07 29 0017 33.117N 115.567W 016 292 — — 4.50ML PAS 4.63'1'1-1 Felt 23 — 1950 07 29 14 36 32.0 33.117N 115.567W 016 292 —— — 5.50ML PAS -— VIII 23 44# 1950 07 29 1509 33.117N 115.567W 016 292 — — 4.50ML PAS — IV 259 — 1950 07 29 18 43 00.0 33.117N 115.567W 016 292 -— — 4.70ML PAS — IV 259 - 1950 08 01 08 3720.0 33.117N 115.567W 016 292 — —- 4.70M], PAS — VI 259 — 1950 08 14 19 1600.0 33.117N 115.567W 016 292 — — 4.70ML PAS — — —- — 1950 09 05 l9 19 56.0 33.650N 116.750W 016 292 — -— 4.80ML PAS — VI 23 268: 1950 10 08 122419 40.283N 124.800W — 324 — — 4.60ML BRK — —- — — 1950 11 14 023550 40.483N 121.500W —— 324 — — 4.60ML BRK — V 23 — 1950 11 14 0634 32 40.483N 121.500W — 324 — — 4.50ML BRK — Felt 23 — 1950 ll 17 034651.0 33.917N 118.317W 016 292 — — 3.80ML PAS -— VI 23 — 1950 12 14 08 59 34.0 40.083N 120.067W — 324 — —— 4.50ML BRK —- Felt 23 —- 1950 12 14 132419 40.083N 120.067W — 324 -— — 5.60ML BRK —— VII 23 80 1951 01 13 20 3132 40.4 N 125.0 W — 324 — — 4.80ML BRK — IV 24 — 86 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIF ORNIA—Con tinued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; it, land area only in the United States for an earthquake near a coastline; +. land area in the United States when the felt area did not extend to the coast; @. felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Me On h m 3 (°) (°) (km) mb Ms M (1,000 km’) 1951 01 24 07 17 02.6 32.983N 115.733W 016 292 — — 5.60ML PAS —- VII 24 56* 1951 01 25 21 (X) 18 37.750N 122.183W — 324 — —— 2.90ML BRK — VI 24 — 1951 02 15 10 47 59.0 33.483N 116.500W 016 292 — — 4.80ML PAS — V 24 18& 1951 02 15 10 49 57.0 33.433N 116.500W 016 292 —— — 4.80M], PAS — V 24 18& 1951 04 01 19 21 08 40.467N 125.300W — 324 — — 5.00ML BRK — III 24 ~— 1951 06 25 19 45 41.7 35.772N 117.948W 012 292 — — 4.60ML PAS —— V 24 —- 1951 07 29 10 53 45.0 36.583N 121.183W — 324 — — 5.00ML BRK —- VI 24 30& 1951 08 06 09 05 02 36.617N 121.217W — 324 — — 4.90ML BRK -- VI 24 6& 1951 10 08 04 10 35.0 40.283N 124.800W -— 324 — — 5.80ML BRK — VII 24 28& 1951 10 31 20 58 19 36.900N 121.417W — 324 —- -— 4.80ML BRK — V 24 6& 1951 11 13 11 24 42 40.4 N 125.3 W — 324 -— —- 4.80ML BRK -— V 24 -- 1951 11 14 08 39 53 40.433N 124.050W —- 324 —- —— 4.70M; BRK — VI 24 8& 1951 12 05 15 53 14.0 33.100N 115.400W 016 292 — — 4.50ML PAS —- VII 24 15+ 1951 12 26 0046 54.0 32.817N 118.350W 016 292 — -- 5.90ML PAS -- VI 24 35& 1951 12 28 02 49 27.0 37.567N 118.583W 016 292 — — 5.20ML PAS — V 24 33 1952 02 09 08 43 30.9 36.607N 117.905W 008 292 — — 4.10ML PAS — VI 25 -- 1952 02 13 15 13 37.0 32.867N 118.250W 016 292 — — 4.70ML PAS — IV 25 —- 1952 02 17 12 36 58.3 33.997N 117.270W 016 292 ——- —— 4.50ML PAS — IV 25 — 1952 05 06 17 21 10 41.9 N 124.6 W —- 324 —— — 4.70ML BRK — IV 259 — 1952 07 21 1152 14.0 35.000N 119.017W 016 292 — — 7.20ML BLT 7 481K XI 25 353& 1952 07 21 11 54 35.0(X)N 119.033W 016 292 — —- 4.50ML PAS — — — — 1952 07 21 11 55 35.0(X)N 119.033W 016 292 -—- —— 4.50ML PAS — — -— — 1952 07 21 11 57 35.000N 119.033W 016 292 — — 4.50M], PAS — Felt 25 — 1952 07 21 11 58 35.(XX)N 119.033W 016 292 —— -—-— 4.60ML PAS — Felt 25 — 1952 07 21 11 59 35.0(X)N 119.033W 016 292 —— — 4.50ML PAS -— —- --— — 1952 07 21 12 02 35.000N 119.033W 016 292 -- — 5.60ML PAS — Felt 25 — 1952 07 21 12 05 31.0 35.1XDN 119.000W 016 292 -— — 6.40ML PAS 6.27HK V 25 — 1952 07 21 12 06 35.000N 119.000W 016 292 — — 4.80ML PAS — — -— -— 1952 07 21 12 07 35.0“)N 119.000W 016 292 — — 4.70ML PAS —- Felt 25 — 1952 07 21 12 10 35.0(X)N 119.000W 016 292 —— — 4.50ML PAS — Felt 25 — 1952 07 21 12 12 35.000N 119.000W 016 292 — —- 4.60ML PAS — Felt 25 '— 1952 07 21 12 19 36.0 34.950N 118.867W 016 292 — — 5.30ML PAS — Felt 25 — 1952 07 21 12 22 35.(XX)N 119.000W 016 292 — — 4.90ML PAS -- -— — -- 1952 07 21 12 25 35.000N 119.000W 016 292 — -— 4.70ML PAS —- Felt 25 — 1952 07 21 12 40 35.000N 119.000W 016 292 — -- 4.90ML PAS — Felt 25 — 1952 07 21 13 08 35.0(DN 119.000W 016 292 — — 4.50ML PAS —— — — — 1952 07 21 13 13 35.000N 119.000W 016 292 — — 4.50ML PAS — — — — 1952 07 21 13 25 12.0 35.0“)N 119.000W — 292 — — 4.50ML PAS — — — — 1952 07 21 13 59 35.000N 119.000W — 292 — — 4.60ML PAS — —— — — 1952 07 21 15 13 58.0 35.183N 118.650W 016 292 -—- —— 5.10ML PAS — VI 25 — 1952 07 21 15 53 35.000N 119.000W 016 292 —- — 4.50ML PAS — V 25 ~— 1952 07 21 16 38 35.000N 119.000W 016 292 —- —- 4.50M], PAS — —- — -— 1952 07 21 17 42 44.0 35.233N 118.533W 016 292 — — 5.10M]. PAS — — — — 1952 07 21 18 (X) 35.000N 119.000W 016 292 -- — 4.50ML PAS —- —- — —- 1952 07 21 18 23 38.0 35.300N 118.533W 016 292 — — 4.50ML PAS 4.31TH —— — -— 1952 07 21 19 41 22.0 35.133N 118.767W 016 292 —— -—- 5.50M}. PAS — V 25 — 1952 07 21 23 53 28.0 34.983N 119.033W 016 292 -- — 4.50ML PAS 4.20111 —- —- — 1952 07 2 01 41 02.0 35.133N 118.517W 016 292 — — 4.50ML PAS 4.70m — —- —— 1952 07 22 08 47 34.0 35.083N 118.750W 016 292 -- — 4.70ML PAS 4.561}! IV 25 - 1952 07 22 09 10 25.0 35.233N 118.600W 016 292 —— — 4.50ML PAS — — -- —- 1952 07 22 13 31 43.0 35.000N 119.000W 016 292 — — 4.80ML PAS 4.62“! V 25 —- 1952 07 22 22 31 33.0 35.033N 118.933W 016 292 -- —- 4.70ML PAS 4.69m — —— — 1952 07 23 00 38 32.0 35.366N 118.583W 016 292 —- — 6.10M]. PAS 5.70HHT VI 25 -- 1952 07 23 00 47 38.0 35.367N 118.583W 016 292 — — 4.60ML PAS — —- — — EARTHQUAKES IN CALIFORNIA CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &. land area only; 1!, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 mg. Leader (--) indicates information is not available] 87 Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area YI' Mo D! h m 8 (°) (0) (km) ml, Ms M (1,000 km“) 1952 07 23 03 19 23.0 35.367N 118.583W 016 292 — — 5.00ML PAS — V 25 — 1952 07 23 03 49 28.0 35.283N 118.550W 016 292 — — 4.70ML PAS — — — — 1952 07 23 04 01 40.0 35.367N 118.583W 016 292 -— -— 4.70ML PAS 4.79m — — -— 1952 07 23 05 46 03.0 35.383N 118.567W 016 292 —- — 4.70ML PAS —- — — — 1952 07 23 07 37 00.0 35.283N 118.550W 016 292 — — 4.80ML PAS 4.42TH — — — 1952 07 23 07 53 19.0 35.0(X)N 118.833W 016 292 — -— 5.40ML PAS 5.23m V11 25 -— 1952 07 23 13 17 05.0 35.217N 118.817W 016 292 — — 5.70ML PAS 5.76m VII 25 — 1952 07 23 16 18 38.0 35.333N 118.600W 016 292 — —- 4.50ML PAS — — — —- 1952 07 23 16 48 53.0 35.333N 118.600W 016 292 — —- 4.50ML PAS — — — — 1952 07 23 17 22 24.0 35.335N 118.475W 007 292 —— —- 4.50ML PAS — III 25 - 1952 07 23 18 13 51.0 35.0(X)N 118.833W 016 292 -- — 5.20ML PAS — VI 25 — 1952 07 24 05 m 49.6 35.340N 118.473W 002 292 —- — 4.50ML PAS — — -— — 1952 07 25 13 13 08.3 35.310N 118.498W 003 292 — —— 5.00ML PAS -— Fall 25 — 1952 07 25 19 09 44.6 35.317N 118.495W 006 292 — — 5.70M]. PAS 5.76m VI 25 — 1952 07 25 19 43 23.7 35.315N 118.515W 011 292 —- — 5.70M]. PAS 5.94m VI 25 — 1952 07 25 2006 06.1 35.298N 118.435W — 292 — — 4.80ML PAS — IV 25 — 1952 07 26 22 41 03.0 35.183N 118.600W 016 292 —- — 4.60ML PAS —- — -- — 1952 07 29 07 03 47.0 35.383N 118.850W 016 292 ~— — 6.10ML PAS 6.27HK VII 25 -— 1952 07 29 08 01 46.0 35.400N 118.817W 016 292 — —- 5.10ML PAS - V 25 — 1952 07 29 15 49 50.0 35.183N 118.600W 016 292 —- —- 4.90ML PAS — Felt 25 — 1952 07 29 19 51 32.0 35.333N 118.917W 016 292 -— — 4.50M; PAS —— —— — — 1952 07 31 12 09 09.0 35.333N 118.600W 016 292 — —— 5.80ML PAS 5.48m VI 25 —— 1952 07 31 17 19 08.0 35.283N 118.583W 016 292 — -- 4.50ML PAS — — — — 1952 07 31 19 53 14.0 35.333N 118.9171” 016 292 — -— 4.50ML PAS — IV 25 — 1952 08 01 03 16 11.6 35.283N 118.550W 016 292 — — 4.50ML PAS —- —- -- — 1952 08 01 13 04 30.0 34.9(X)N 118.950W 016 292 — — 5.10ML PAS -— V 25 — 1952 08 07 16 31 51.0 35.033N 119.050W 016 292 — —- 4.90ML PAS — V 25 —- 1952 08 10 12 23 18.0 35.288N 118.412W 004 292 -— — 4.60ML PAS -— — — — 1952 08 13 04 29 40.6 35.293N 118.400W 014 292 — —— 4.60ML PAS — Felt 25 —— 1952 08 13 17 39 25.0 35.150N 118.683W 016 292 —- — 4.70ML PAS — VI 25 — 1952 08 18 04 40 10.0 35.033N 119.050W 016 292 -—- — 4.70M; PAS — IV 25 — 1952 08 19 19 12 26.0 35.050N 119.233W 016 292 — —- 4.50M; PAS — V 25 — 1952 08 22 22 41 24.0 35.333N 118.917W 016 292 — —- 5.80ML PAS 5.78m VH1 25 120& 1952 08 23 1009 07.1 34.520N 118.198W 013 292 — —— 5.00ML PAS 4.85m VI 25 60& 1952 08 25 06 20 26.0 35.100N 118.967W 016 292 —— — 4.70ML PAS — V 25 — 1952 08 30 04 55 59.8 35.315N 118.482W 005 292 — — 4.70ML PAS —- V 25 — 1952 09 02 12 41 32.0 35.133N 118.700W 016 292 — —- 4.60ML PAS -— V 25 — 1952 09 02 20 45 56.0 34.967N 119.000W 016 292 — -— 4.70ML PAS — V 25 — 1952 09 12 10 35 25.0 35.000N 119.050W 016 292 —— — 4.50ML PAS — V 25 — 1952 09 15 04 40 13.2 35.317N 118.487W 004 292 — — 4.90ML PAS -— -— —— — 1952 09 22 11 41 25 40.2(X)N 124.417W -- 324 —— — 5.20ML BRK — VII 25 10& 1952 11 07 08 55 35.0 35.000N 119.083W 016 292 — — 4.60ML PAS —- V 25 — 1952 11 22 0746360 35.768N 121.145W 010 476 — — 6.00M], BRK -— VII 25 82& 1953 02 23 07 42 51 41.5WN 125.133W — 324 — -— 4.70M]. BRK — — — — 1953 03 22 05 19 00 38.817N 119.983W —— 324 — — 5.00ML BRK — V 26 — 1953 04 29 12 47 45.0 35.0(X)N 118.733W 016 292 —— — 4.70ML PAS -— IV 26 — 1953 05 25 03 24 01.0 35.0CX)N 119.017W 016 292 —- — 4.80ML PAS — V 26 — 1953 05 25 04 07 59 39.3 N 123.3 W — 324 —- — 3.20ML BRK -- VI 26 -— 1953 06 14 04 17 29.9 32.950N 115.717W 016 292 — — 5.50ML PAS — VII 26 30# 1953 06 14 04 29 58.0 32.950N 115.7171” 016 292 —-— — 4.80ML PAS — V 26 — 1953 10 07 14 59 21.0 35.033N 118.850W 016 292 -— — 4.90ML PAS — V 26 — 1953 11 24 05 46 06.0 35.883N 116.967W 016 292 -— — 4.90ML PAS — IV 26 — 1953 12 15 12 44 36.0 35.217N 118.817W 016 292 — — 4.60M; PAS — V 26 —— 88 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Me Be h m 8 (°) (°) (km) mb Ms M (1.000 kmz) 1954 01 12 23 33 49.0 35.000N 119.017W 016 292 — -- 5.90ML PAS 5.63'1'H VII 27 1(X)& 1954 01 27 14 19 48.0 35.150N 118.633W 016 292 — -— 5.00ML PAS 4.841}! V 27 31 1954 02 10 23 58 38.0 34.933N 119.067W 016 292 — — 4.50ML PAS — V 27 -— 1954 02 12 0944280 33.333N 116.433W 016 292 — — 4.50ML PAS -— IV 27 — 1954 02 24 22 3022.0 35.067N 119.067W 016 292 — —— 4.50ML PAS — IV 27 — 1954 03 19 0954 29.0 33.283N 116.183W 016 292 —-— —- 6.20ML PAS 6.351-IK VI 27 1041! 1954 03 19 0955 56.0 33.283N 116.183W 016 292 —- — 5.00ML PAS — — -— -— 1954 03 19 0957 07.0 33.283N 116.183W 016 292 -— — 4.60ML PAS — — — —— 1954 03 19 10 15 22.0 33.283N 116.183W 016 292 -— — 4.50ML PAS — Felt 27 —- 1954 03 19 10 19 57.0 33.283N 116.183W 016 292 -—— — 4.50M; PAS — Felt 27 — 1954 03 19 1021 17.0 33.283N 116.183W 016 292 — —— 5.50ML PAS 5.20m Felt 27 — 1954 03 20 0419190 33.283N 116.183W 016 292 — — 4.90ML PAS — — — —- 1954 03 23 0414 50.0 33.283N 116.183W 016 292 — — 5.10M._ PAS 4.80’I'H v 27 —— 1954 04 22 185013 36.900N 121.683W — 324 — — 4.30ML BRK — VI 27 682 1954 04 25 20 3328 36.933N 121.683W — 324 — -— 5.30ML BRK — VIII 27 358: 1954 05 23 23 52 43.0 34.983N 118.983W 016 292 — —- 5.10ML PAS 4.78TH IV 27 32& 1954 08 26 1348030 33.917N 119.500W 016 292 -—- — 4.80ML PAS — VI 27 15& 1954 10 30 0202430 34.033N 115.550W 016 292 — — 4.60ML PAS — IV 27 — 1954 ll 10 180721 39.067N 123.033W — 324 — — 4.40ML BRK — VI 27 6 1954 11 25 111635 40.267N 125.633W -- 324 —— —- 6.10ML BRK — V 27 23& 1954 12 07 0432 36 40.5 N 126.0 W — 324 — —- 4.60ML BRK — —- — — 1954 12 17 0708 58 37.717N 122.133W — 324 — -— 4.50ML BRK —— VI 27 128: 1954 12 21 19 56 24.4 40.783N 124.167W 000 480 — — 6.50ML BRK — VII 27 1308: 1954 12 30 091613.0 40.783N 123.867W — 324 —- -— 4.70ML BRK — VI 27 -— 1955 02 11 1944 31.5 35.320N 118.493W 015 292 — — 4.50ML PAS — IV 28 — 1955 03 02 15 5901 36.000N 120.933W — 324 — — 4.80ML BRK —— VI 28 25& 1955 04 29 15 14 38 38.950N 122.767W -— 324 — — 3.60ML BRK — VI 28 2 1955 05 07 115039 38.933N 122.867W — 324 — --— 4.60ML BRK -—— VI 28 5 1955 05 28 1944200 35.533N 118.263W 012 292 — -— 4.50ML PAS —— V 28 — 1955 08 08 0321505 35.395N 118.620W 004 292 —— — 4.70ML PAS — V 28 15 1955 08 27 070026 40.383N 124.500W — 324 -— -—- 4.50ML BRK -— III 28 —- 1955 09 05 020118 37.367N 121.783W — 324 -— — 5.50ML BRK — VII 28 458: 1955 10 24 041044 37.967N 122.050W —- 324 — — 5.40ML BRK — VII 28 318: 1955 11 02 19 4006 36.000N 120.922W —- 324 — — 5.20ML BRK — VI 28 188: 1955 12 17 0607290 33.0(X)N 115.500W 016 292 — —— 5.40ML PAS — V11 28 23+ 1955 12 17 0652 03.0 33.000N 115.500W 016 292 — — 4.60ML PAS —— Felt 259 — 1956 01 03 0025 48.9 33.725N 117.498W 014 292 — — 4.70ML PAS — VI 29 238: 1956 02 07 03 16 38.6 34.587N 118.613W 003 292 — — 4.60ML PAS 4.52TH V 29 8& 1956 02 09 14 3238.0 31.750N 115.917W 016 292 — — 6.80ML PAS 6.511-[1-1'1' VI 29 86# 1956 03 10 055614 40.300N 124.233W —- 324 — — 4.50ML BRK — V 29 6& 1956 03 16 2029 33.6 34.307N 116.758W 001 292 —— — 4.80M; PAS 4.54'I'H V 259 21& 1956 04 05 042913 38.533N 122.517W — 324 —— — 4.40M]~ BRK — VI 29 128: 1956 05 11 16 3050.5 34.230N 116.795W 013 292 —— — 4.70ML PAS -— V 29 23& 1956 07 09 022155 42.0 N 122.4 W — 324 —-— — 4.90ML BRK — — — —-— 1956 07 23 08 0348 36.3 N 121.3 W -— 324 — — 4.70ML BRK — V 29 10& 1956 10 11 16 4850 40.667N 125.767W —- 324 — — 6.00ML BRK — V 29 9& 1956 10 11 17 18 19 40.750N 125.800W — 324 — -— 4.80ML BRK — Felt 29 — 1956 10 11 17 2230 40.7 N 125.8 W — 324 — —— 4.80ML BRK — Felt 29 — . 1956 11 16 03 23 09.0 35.950N 120.467W — 324 — — 5.00ML BRK 4.69m VI 29 218?. 1957 01 24 2054499 33.110N 116.523W 004 292 —- — 4.60ML PAS — V 30 158; 1957 01 29 211953 35.867N 122.117W — 324 — —— 4.90ML BRK — V 30 138: 1957 02 01 0752154 33.985N 116.340W 011 292 — — 4.60ML PAS — V 30 88: 1957 03 18 18 56 28.0 34.118N 119.220W 014 324 — -— 4.70ML PAS --— VI 30 6& 1957 03 22 194421 37.667N 122.483W — 324 — — 5.30ML BRK — VII 30 31& 1957 03 23 081348 37.700N 122.517W —— 324 —- — 4.20ML BRK — VI 30 98c EARTHQUAKES IN CALIFORNIA CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; 13, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader («) indicates information is not available] 89 Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Me Be h m 3 (°) (°) (km) mb Ms M (1,000 km?) 1957 04 25 21 57 38.7 33.217N 115.808W 000 292 -—— —- 5.20ML PAS — VII 30 3182 1957 04 25 222412.0 33.183N 115.850W 016 292 — — 5.10ML PAS — Felt 30 — 1957 05 26 15 59 33.6 33.232N 116.005W 015 292 — —- 5.00ML PAS —— IV 259 18# 1957 06 21 004125 37.700N 119.283W — 324 —- —— 4.60ML BRK -— V 30 —- 1957 09 03 16 38 41 41.533N 125.583W — 324 — —— 4.50ML BRK — — — -— 1957 09 28 210439 36.600N 121.233W — 324 -- — 4.50ML BRK — IV 30 —— 1957 10 31 02 4746 39.183N 123.683W — 324 — — 4.70ML BRK — V 30 6& 1958 05 24 230447 40.300N 124.050W -— 324 — — 4.90ML BRK — V 259 9& 1958 07 14 0525553 34.348N 119.492W 016 292 — — 4.70ML PAS — V 31 l3& 1958 09 21 072455 36.350N 121.117W —- 324 — — 4.60ML BRK — VI 31 — 1958 10 01 214211 39.567N 120.300W —— 324 — —— 4.60ML BRK -— VI 31 13 1958 10 10 130516 35.933N 120.500W — 324 —— — 4.50ML BRK — V 31 98: 1958 12 01 032118.0 32.250N 115.750W 016 292 — —— 5.80ML PAS — VI 31 39# 1958 12 11 0952 27 37.7(X)N 122.567W — 324 — —-— 4.70ML BRK — VI 31 178: 1959 01 05 12 36 03.3 36.148N 118.025W 003 292 — -— 4.70ML PAS 452TH V 32 —- 1959 03 02 232717 36.983N 121.600W — 324 — — 5.30ML BRK — VI 32 27& 1959 04 01 1818 30 39.717N 120.200W —— 324 -— — 5.60ML BRK —- VII 32 85 1959 04 06 0608 22 39.3 N 123.2 W — 324 — — 3.60ML BRK — VI 32 3 1959 05 26 1558 01 36.717N 121.617W — 324 -— — 4.60ML BRK —— VI 32 12& 1959 06 01 16 35 36.0 32.717N 116.033W 016 292 — — 4.60ML PAS — — — — 1959 06 14 012632 39.667N 120.550W — 324 — —— 4.50ML BRK — V 32 12 1959 06 18 002940 37.550N 118.567W — 324 — — 4.70ML PAS — V 32 8 1959 07 01 23 49 23.4 35.185N 119.100W 009 292 — — 4.70M; PAS 4.25TH V 32 15 1959 07 24 012309 41.133N 125.300W — 324 — —— 5.80ML BRK -— IV 32 — 1959 08 04 07 36 59.0 37.350N 118.550W 016 292 —— — 5.20ML PAS 4.54TH V 32 31 1959 10 01 0435 35 34.455N 120.522W 014 292 — —— 4.50ML PAS -- V 259 128: 1959 10 24 15 3515.3 35.745N 118.023W 007 292 —— —— 4.20ML PAS —— VI 32 — 1959 10 31 194214 41.3 N 125.5 W — 324 — — 4.50ML BRK — — — — 1959 12 05 081342 40.300N 125.417W -— 324 —- — 5.10ML BRK — V 32 5& 1959 12 22 02 38 57 40.267N 124.517W — 324 — —- 4.70ML BRK -— V 32 88: 1959 12 29 02 32 53 36.900N 121.483W — 324 — — 4.70ML BRK -— VI 32 13& 1960 01 20 0325530 36.783N 121.433W — 324 — — 5.00ML BRK —— VI 33 2881 1960 06 05 0747 07.0 37.517N 118.733W 016 292 — — 5.20ML PAS 4.90TH V 259 12 1960 06 06 01 17 45.5 40.84 N 124.91 W 000 480 —-— — 5.70ML BRK — VI 33 218; 1960 07 01 22 13 44.6 35.147N 117.132W 008 292 — — 4.50ML PAS — — — — 1960 08 09 073918 40.317N 127.067W — 324 — —— 6.20ML BRK -— V 33 17& 1960 12 27 10 35 26 41.517N 125.050W — 324 — — 5.40ML BRK — V 33 — 1960 12 27 110844 41.500N 125.000W -—-— 324 — — 4.70ML BRK — — —— — 1961 01 28 08 12 46.2 35.778N 118.048W 006 292 — — 5.30ML PAS — VI 34 52 1961 02 02 0004160 37.450N 118.633W 016 292 — — 5.30ML PAS — V 34 35 1961 02 02 0007 42.0 37.417N 118.667W 016 292 — -—- 5.10ML PAS — V 34 35 1961 04 06 040445 40.183N 124.750W — 324 — — 5.10ML BRK — V 259 9& 1961 04 09 072316 36.683N 121.300W — 324 —-— — 5.60ML BRK — V11 34 35& 1961 04 09 07 2541.0 36.683N 121.300W — 324 —— — 5.50ML BRK — VII 38 —- 1961 04 29 09 19 30 40.417N 127.450W — 324 —— — 5.50ML BRK —— — — — 1961 07 31 000708 35.817N 120.367W — 324 — — 4.70ML BRK —— V 34 13& 1961 08 23 010047.8 33.050N 116.238W 012 292 — — 4.70ML PAS 458WYS V 34 98: 1961 09 12 1918455 32.567N 115.452W 012 292 -— — 4.80ML PAS — IV 259 10# 1961 10 19 050943.9 35.832N 117.762W — 292 — — 5.20ML PAS — VI 34 31 1961 10 20 1949 50.5 33.653N 117.993W 005 292 —- — 4.30ML PAS — VI 34 38: 1961 11 15 05 38 55.5 34.942N 118.987W 011 292 — — 5.00ML PAS — VI 34 268: 1962 02 01 0637 57.0 34.883N 120.683W 016 292 — — 4.50ML PAS — V 35 8& 1962 03 05 20 5746 40.3 N 125.5 W — 324 — — 4.60ML BRK — IV 259 2& 1962 04 13 15 38 51.9 38.222N 119.455W 006 324 — -- 5.10ML BRK — V 35 19 1962 04 14 0753 14.7 40.268N 125.310W — 324 — — 5.40ML BRK — — — —- 90 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIF 0RNIA———Con tinued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. 8:. land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader (..) indicates information is not available] Origin Hypocenter Magnitude intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI net Felt area Yr Mo Da h m 8 (°) (°) (krn) mb Ms M (1.000 kma) 1962 04 15 0841023 36.415N 120.617W 021 324 — — 4.70ML BRK —— IV 259 — 1962 04 27 09 12 32.1 33.738N 117.187W 006 292 — — 4.10ML PAS — VI 35 12 1962 06 06 175007.2 39.116N 123.097W 010 613 —- — 5.20ML BRK — VII 35 19& 1962 07 14 19 43 46.2 40.427N 125.512W 030 324 -— — 5.10ML BRK — V 35 7& 1962 08 23 19 29 14.8 41.84 N 124.39 W 059 480 — — 5.60ML BRK -- VI 35 39& 1962 09 04 17 17 26.0 41.01 N 124.21 W 045 480 —— — 4.90ML BRK — VI 35 188: 1962 09 16 05 3616.0 35.755N 118.043W 004 292 — — 4.90ML PAS —— V 35 41 1962 10 14 10 14 28.1 38.680N 124.028W 000 324 —— — 4.70ML BRK — III 35 — 1962 10 29 02 42 53.9 34.325N 116.865W 009 292 ——- — 4.80ML PAS — VI 35 25& 1963 03 01 0025 57.9 34.932N 118.975W 014 292 — — 5.00ML PAS — V 36 218?. 1963 05 22 22 41 04.8 37.272N 122.318W — 324 — — 4.60M]. BRK —— VI 36 4& 1963 05 23 090604.7 32.982N 115.565W 025 292 — -—- 4.60ML PAS 4.60WYS Felt 36 — 1963 05 23 15 53 01.8 33.027N 115.682W 000 292 — — 4.80ML PAS -— VI 36 10# 1963 06 07 1204422 37.975N 122.048W — 324 — — 3.90ML BRK — VI 36 4& 1963 07 08 04 19 08.4 40.8(X)N 125.800W 033 266 4.7 — 4.10ML BRK — — — -- 1963 07 30 0634573 34.153N 116.210W 013 292 4.7 — 4.70ML PAS — V 36 — 1963 09 14 194617.0 36.890N 121.597W 003 467 5.4 — 5.40ML BRK -—- VII 36 13& 1963 09 14 2028112 36.925N 121.618W 006 467 4.3 — 4.60ML BRK -— Felt 36 — 1963 09 23 1441 52.6 33.710N 116.925W 017 292 5.3 —- 5.00M], PAS — VI 36 26# 1963 12 06 08 3421.5 37.648N 118.397W 002 292 4.4 —- 4.70ML PAS — VI 36 26 1964 01 06 23 47 12.8 34.380N 116.475W 012 292 — —— 4.50ML PAS — V 37 12 1964 02 26 20 3251.4 40.308N 124.892W — 324 — — 4.50M], BRK — V 37 38: 1964 03 03 20 02 33 40.3 N 125.3 W -— 324 4.8 — 4.50M], BRK — —- — — 1964 06 11 221812 40.7 N 127.0 W — 324 5.4 — 5.50ML BRK — — — —— 1964 06 21 15 32 51.8 32.692N 117.162W 003 292 —— —— 3.70ML PAS — VI 37 5* 1964 11 16 024641.7 37.055N 121.692W —— 324 5.2 —- 5.00ML BRK -— VII 37 318! 1964 12 22 205433.2 31.810N 117.130W 002 292 — — 5.60ML PAS —- VI 37 23# 1965 01 01 0804180 34.140N 117.515W 006 292 5.2 — 4.40ML PAS — VI 75 108: 1965 02 12 1050180 40.3 N 124.9 W 000 324 5.3 —— 4.50ML BRK — Felt 75 — 1965 04 15 2008 33.3 34.132N 117.427W 006 292 5.1 — 4.50ML PAS — VI 75 10& 1965 06 03 16 26 29.0 38.3 N 119.2 W 033 266 4.8 — 4.50ML PAS — V 75 10 1965 06 16 02 42 06.1 33.055N 115.620W 000 292 4.4 —— 4.40ML PAS — VI 75 3 1965 07 16 0746224 34.485N 118.522W 015 292 4.5 — 4.00ML PAS — VI 75 8 1965 08 26 13 3814.0 33.233N 116.087W — 292 4.5 — 4.50ML PAS — Felt 75 — 1965 09 10 2128343 38.010N 121.823W — 324 4.9 —- 4.90ML BRK -— VI 75 88: 1965 09 16 04 10 23.4 40.39 N 125.60 W 033 299 5.6 — 5.00ML PAS — IV 75 — 1965 09 19 15 42 07.8 35.987N 120.038W —— 324 4.9 —— 4.80ML BRK — V 75 9 1965 09 22 21 49 25.9 37.417N 118.478W 008 292 — — 4.50ML PAS — IV 75 12 1965 09 25 17 43 44.1 34.713N 116.503W 011 292 5.0 — 5.20ML PAS — VII 75 77 1965 09 25 1748024 34.713N 116.475W 005 292 — — 4.90ML PAS — Felt 75 - 1965 09 26 07(X)01.8 34.713N 116.027W 008 292 — —— 5.00ML PAS —— V 259 40& 1965 10 17 0945190 33.975N 116.775W 017 292 4.8 —— 4.90ML PAS — VI 75 15 1965 11 12 23 55 09.8 33.980N 118.392W 006 292 3.7 — 3.00ML PAS — VI 75 2& 1966 04 10 22 2700.9 41.3 N 125.6 W 033 266 5.0 —— 4.50M; BRK — — — — 1966 05 13 1725559 36.917N 121.567W -— 324 4.6 — 4.50ML BRK 3.9ZBAK V 81 2& 1966 05 24 0349 55.1 39.783N 121.770W 020 324 4.5 — 4.60ML BRK — VI 81 31 1966 06 28 0408 56.2 35.960N 120.505W — 398 4.9 -— 5.10M], BRK 5.523AK Felt 81 — 1966 06 28 042613.4 35.955N 120.498W — 398 5.3 —— 5.60ML KJ 6.053AK V11 81 60& 1966 06 28 0428 36.0 35.950N 120.500W 0(1) 292 — -— 4.50ML BRK — — — — 1966 06 29 19 53 25.9 35.943N 120.525W -— 398 5.0 — 5.00ML BRK 5.48BAK IV 81 — 1966 08 07 17 36 27.3 31.7 N 114.5 W 033 266 — — 6.30ML PAS 6.27HHT VI 81 115# 1966 09 12 16 41 02.6 39.438N 120.160W 010 457 5.7 — 6.00ML BRK 5.90KA VII 81 1758: 1966 09 12 172011 39.42 N 120.15 W 003 324 4.8 — 5.30ML BRK — V 81 ~— 1966 09 14 220028 39.42 N 120.15 W 003 324 4.3 — 4.60ML BRK — IV 81 — 1966 09 14 22 4028 39.42 N 120.15 W 003 324 4.5 — 4.60ML BRK — IV 81 —— EARTHQUAKES IN CALIFORNIA 91 CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. 8:, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader (~) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MMI Rot Felt area Yr Mo De h m 9 (°) (°) (km) mb Ms M (1.000 m2) 1966 10 02 05 12 34.5 33.968N 118.327W 002 292 3.9 — 3.50ML PAS - VI 81 — 1966 11 26 0430587 40.3 N 125.4 W 033 266 4.6 —— 4.80M], BRK — —- — — 1966 11 26 0556396 40.3 N 125.3 W 033 266 4.4 — 4.70ML BRK — — -— —- 1966 12 17 15 16 26.2 40.38 N 125.70 W 000 299 4.7 —— 4.50ML BRK — — —- — 1967 03 02 14 12 48.8 36.503N 117.632W 010 292 4.7 — 4.40ML PAS — V 259 — 1967 05 21 14 42 34.4 33.507N 116.583W 019 292 4.7 -— 4.70M], PAS — VI 40 23& 1967 06 15 0458 05.5 33.997N 117.975W 010 292 4.3 — 4.10M; PAS — VI 40 6& 1967 06 26 151535 39.3 N 123.3 W 002 324 4.2 -— 3.50ML BRK —- VI 40 4 1967 07 22 0923 26.6 36.535N 121.163W —— 324 4.0 —- 3.80ML BRK —- VI 40 — 1967 09 07 12 39 17.2 37.035N 121.777W 008 324 — —- 4.70ML BRK 4.313AK VI 40 17& 1967 09 28 15 38 36.1 37.230N 121.620W 008 324 — — 4.90M; BRK —- VI 40 198: 1967 11 24 13 5700.4 40.4 N 125.1 W 017 74 4.6 — — -— — — —— 1967 12 10 1206503 40.5 N 124.6 W 005 74 5.8 — 5.60M; BRK — VI 40 158: 1967 12 10 12 33 54.2 40.5 N 125.0 W 015 74 ‘4.6 — 4.00ML BRK — Felt 40 —- 1967 12 18 1724320 37.010N 121.788W 013 324 5.0 — 5.30ML BRK 4.64BAK VI 40 27& 1967 12 30 0804394 40.51 N 124.43 W 003 299 4.6 —- 4.50ML BRK —— V 40 — 1968 04 09 0228591 33.190N 116.128W 011 292 6.1 — 6.40ML PAS 6.47HK VII 41 158# 1968 04 09 0303 53.5 33.113N 116.038W 005 292 5.1 — 5.20ML PAS —— III 41 — 1968 04 09 0348103 33.105N 116.037W 005 292 4.7 — 4.70ML PAS — VI 41 -- 1968 04 09 18 3103.8 33.315N 116.305W 013 292 4.7 —- 4.70ML PAS — III 41 — 1968 04 16 03 30 29.9 33.048N 115.987W 008 292 4.4 —- 4.80M; PAS 4.70m V 41 — 1968 04 25 19 49 45.2 38.477N 122.725W 008 324 4.6 —- 4.60ML BRK — VII 41 13& 1968 04 29 0021386 39.540N 122.023W 023 324 5.0 — 4.70ML BRK —- VI 41 27 1968 05 09 23 27 46.5 41.2 N 125.7 W 033 74 4.7 — 4.40ML BRK — —— — ~— 1968 06 03 0705 55.0 40.4 N 124.8 W 033 74 4.5 —- 3.60M; BRK — — — — 1968 06 26 014214.6 40.29 N 124.67 W 000 480 5.5 —— 5.90ML BRK — VII 41 138: 1968 06 26 1047 45.0 40.2 N 124.3 W 010 324 5.1 — 4.80ML BRK — IV 41 — 1968 06 29 19 12 20.2 34.3 N 119.7 W 002 74 5.0 — 4.20ML PAS — V 41 — 1968 06 29 19 13 57.0 34.267N 119.567W 010 292 —— —— 4.40ML PAS -— VI 41 — 1968 07 05 004517.2 34.119N 119.702W 006 292 5.7 -— 5.20ML PAS -— VI 41 218‘: 1968 07 07 14 33 30.8 34.177N 119.755W 013 292 4.6 — 4.50M; PAS —— IV 41 — 1968 12 17 22 53 51.2 33.045N 115.863W 008 292 4.6 —- 4.70ML PAS -— IV 259 6# 1969 01 23 23 01 01.0 33.887N 116.040W 018 292 4.9 — 4.80ML PAS — V 42 13 1969 02 07 2125489 40.343N 124.365W 013 324 5.2 — 4.70M], BRK — VI 42 108: 1969 02 28 0456124 34.565N 118.113W 005 292 4.6 —— 4.30ML PAS — VI 42 128: 1969 04 28 23 2042.9 33.343N 116.347W 020 292 5.7 — 5.80ML PAS 5.75THH VII 42 78# 1969 05 19 1440330 33.348N 116.188W 009 292 4.5 —- 4.50ML PAS — V 42 17# 1969 06 07 1127 12 40.8 N 125.8 W 003 324 -— — 4.00ML BRK — VI 42 -— 1969 06 23 0121165 41.8 N 125.8 W 033 74 4.7 — 4.00UknBRK —- — — — 1969 06 28 0407267 40.3 N 124.4 W 039 74 4.5 — 3.90ML BRK — V 42 6& 1969 07 01 1200456 40.300N 124.300W 026 74 4.6 — 3.90ML BRK — V 42 — 1969 10 02 0456 46.5 38.467N 122.692W 010 399 5.2 4.8 5.60ML BRK —- VIII 42 27& 1969 10 02 06 19 57.1 38.455N 122.692W 010 399 5.1 —- 5.70ML BRK — VIII 42 27& 1969 10 03 1310103 37.625N 118.925W — 292 4.6 — 4.90ML PAS — V 42 — 1969 10 14 13 18 42.8 32.923N 116.272W 010 292 4.5 — 4.50ML PAS —- V 42 — 1969 10 22 22 51 32.1 34.77 N 121.35 W 007 299 5.9 5.2 5.40ML PAS —- V 42 — 1969 10 23 0003 34.4 34.90 N 121.30 W 010 74 5.0 — 4.10ML PAS — -— — —- 1969 10 24 08 29 12.1 33.292N 119.193W 010 292 5.1 50 5.10ML PAS -— V 42 — 1969 10 24 2026425 33.338N 119.105W — 292 4.9 — 4.70M], PAS — Felt 42 —- 1969 10 27 1059 42.8 36.790N 121.393W 013 324 4.6 — 4.60ML BRK 4.16JM VI 42 10& 1969 10 27 13 16 02.3 33.545N 117.807W 007 292 4.5 — 4.50ML PAS —- V 42 12& 1969 10 31 10 39 29.0 33.430N 119.097W 007 292 4.9 —— 4.80ML PAS — IV 42 — 1969 11 04 0040448 34.76 N 121.37 W 010 299 4.9 — 4.50ML PAS — — — — 1969 11 05 1754107 34.72 N 121.28 W 011 299 5.8 5.8 5.60ML PAS -— V 42 - 1969 11 05 184845.1 34.65 N 121.31 W 010 299 5.1 —- 4.50ML PAS — Pelt 42 — 92 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &. land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypoconter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1969 11 09 01 27 42.0 34.54 N 121.40 W 010 299 4.7 — 4.10ML PAS -—— — — — 1969 11 10 19 21 27.3 34.6 N 121.5 W 033 74 4.6 -— 4.00ML PAS — —— — ~— 1970 01 03 02 51 58.4 37.298N 122.088W — 324 4.0 — 3.70ML BRK — VI 43 3 1970 03 31 07 (72 28.6 36.868N 121.418W 008 324 4.2 — 4.70ML BRK 4.501M V 43 12& 1970 06 07 04 12 10.3 40.3 N 125.9 W 033 74 5.0 -— 4.70M; BRK — IV 43 — 1970 06 12 03 30 04.0 37.802N 121.933W 009 324 4.6 — 4.30ML BRK —— VI 43 38: 1970 06 12 16 03 32.1 37.805N 122.938W 009 324 — — 4.20ML BRK —-— VI 43 — 1970 08 04 04 14 21.4 36.647N 122.185W 008 324 4.5 —— 4.70ML BRK — VI 43 14& 1970 09 12 14 30 53.0 34.270N 117.540W 008 292 5.4 —— 5.40ML PAS — V11 43 65& 1970 09 13 21 10 23.0 40.2 N 125.1 W 033 74 5.4 — 5.40ML BRK — V 43 — 1971 02 09 14 00 41.8 34.412N 118.400W 008 400 6.2 6.5 6.40ML KJ 6.62HK XI 44 212# 1971 02 09 14 01 08.0 34.412N 118.400W 008 292 —— — 5.80ML PAS — —- — — 1971 02 09 14 01 50.0 34.412N 118.400W 008 292 —- — 4.50ML PAS — —— —— — 1971 02 09 14 02 31.0 34.412N 118.400W 008 292 -- —— 4.70ML PAS — —— —— — 1971 02 09 14 02 44.0 34.412N 118.400W 008 292 -- — 5.80ML PAS — —— —— — 1971 02 09 14 07 45.0 34.412N 118.400W 008 292 -— —- 4.50ML PAS — — — — 1971 02 09 14 08 38.0 34.412N 118.400W 008 292 — — 4.50ML PAS — — —- — 1971 02 09 14 08 53.0 34.412N 118.400W 008 292 -- — 4.60ML PAS — — — — 1971 02 09 14 10 21.5 34.362N 118.307W 005 292 — —- 4.70ML PAS 4.92TH —— —— —- 1971 02 09 14 10 28.0 34.412N 118.400W 008 292 — — 5.30ML PAS 4.60111 V 44 — 1971 02 09 14 34 36.1 34.343N 118.637W — 292 —— — 4.90ML PAS 4.23m — — — 1971 02 09 14 43 46.7 34.308N 118.453W 006 292 4.7 — 5.20ML PAS —- Felt 44 — 1971 02 09 15 58 20.7 34.335N 118.330W 014 292 5.1 -- 4.80ML PAS — IV 44 — 1971 02 10 05 18 07.2 34.425N 118.413W 006 292 4.7 — 4.50ML PAS -- Pelt 44 - 1971 02 21 05 50 52.6 34.397N 118.438W 007 292 —— — 4.70ML PAS — IV 44 — 1971 02 21 07 15 11.8 34.392N 118.427W 007 292 —- —— 4.50ML PAS — IV 44 — 1971 02 27 00 31 39.9 40.4 N 124.8 W 033 74 5.3 5.1 5.20ML BRK —— V 44 11& 1971 03 07 01 33 40.5 34.353N 118.455W 003 292 4.4 —— 4.50ML PAS — IV 44 — 1971 03 09 15 35 16.2 36.800N 122.145W 008 324 4.8 — 4.60M; BRK — V 44 9& 1971 03 31 14 52 22.5 34.285N 118.515W 002 292 4.8 —- 4.60ML PAS — VII 44 16& 1971 04 16 12 58 31.7 36.800N 122.183W 008 324 4.8 —— 4.50ML BRK — V 44 -- 1971 09 12 19 32 38.0 41.298N 123.673W 023 324 4.9 —-— 4.60ML BRK — V 44 8& 1971 09 30 22 46 11.3 33.033N 115.820W 008 292 4.9 — 5.10ML PAS — VI 44 17# 1971 11 20 13 59 04.3 40.300N 124.400W 025 74 5.0 4.6 4.90M], BRK — V 44 — 1972 01 22 02 57 19.9 37.568N 118.367W 003 324 4.4 — 4.50ML BRK — V 45 — 1972 02 24 15 5651.3 36.588N 121.197W 008 324 4.9 —— 5.10ML BRK 4.94SOM VI 45 l8& 1972 02 27 22 13 08.6 36.553N 121.093W 008 324 4.5 — 4.70ML BRK 5.21JM V 45 —- 1972 03 01 09 28 56.7 40.5 N 125.2 W 033 74 5.4 5.9 5.20ML BRK —— V 45 -— 1972 09 04 18 04 40.9 36.642N 121.263W 005 324 4.9 — 4.70ML BRK 4.8ZJM VI 45 148: 1972 09 23 02 44 05.4 41.7 N 125.5 W 021 74 4 8 5.1 4.90ML BRK — —— — — 1972 10 03 06 30 02.2 36.8(X)N 121.533W 008 324 4.8 — 4.80ML BRK 4.87JM VI 45 . 98: 1972 11 14 02 10 13.8 40.30 N 124.67 W 023 324 4.9 4.8 4.70ML BRK — V 45 — 1973 02 21 14 45 57.2 34.099N 119.039W 017 458 5.7 5.2 5.90ML PAS 5.28HK VII 46 5282 1973 03 12 12 5012.9 40.343N 124.102W — 401 4 3 —- 4.50ML BRK — V 46 — 1973 06 15 19 18 51.7 41.2 N 125.5 W 033 74 5 2 — 5.00ML BRK — — — — 1973 07 14 08 00 20.0 34.436N 116.833W 008 74 — -— 4.80M; PAS — V 46 10 1973 08 06 23 29 16.6 33.970N 119.478W 013 74 4.6 — 5.00ML PAS — V 46 8& 1973 08 09 02 18 24.6 40.228N 124.415W 003 401 5.1 4.7 4.90ML BRK — VI 46 88: 1973 09 13 17 30 39.8 32.952N 116.279W 008 74 4.5 -— 4.8OML PAS -— V 46 8# 1973 10 03 10 07 27.3 37.190N 121.590W 008 401 4.6 — 4.70ML BRK 4.1680M V 46 9& 1973 10 28 22 (X) 02.7 32.680N 118.077W 008 74 4.2 — 4.50M; PAS -—- IV 46 1973 11 12 18 17 13.6 37.203N 121.982W 013 401 4.2 —- 4.50ML BRK —— V 46 9& 1973 12 21 19 12 44.0 40.578N 124.662W 013 401 5.2 4.9 4.80ML BRK --- V 46 38: 1974 01 06 13 55 23.0 41.050N 121.483W 001 401 4.5 — 4.20ML BRK -—— VI 47 3 1974 03 03 11 37 36.8 41.9 N 125.4 W 033 47 5.1 — 4.40ML BRK — —-- -— — EARTHQUAKES IN CALIFORNIA 93 CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; 43, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr MoDa h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1974 03 16 15 57 40.7 40.374N 124.714W 023 299 4.7 — 4.50M; BRK -- IV 47 ~— 1974 03 21 21 16 05.3 38.612N 122.663W 001 401 3.8 — 3.30ML BRK —— VI 47 ~— 1974 07 03 05m58.6 40.424N 125.136W 012 74 5.4 5.2 5.10M; BRK — V 47 —- 1974 09 21 10 37 41.8 33.853N 117.110W 013 402 4.2 -— 3.90ML PAS — VI 47 — 1974 11 28 2301247 36.913N 121.478W 009 401 5.0 4.5 5.20ML BRK — VI 47 18& 1974 12 06 12 13 08.3 32.708N 115.392W 024 402 4.5 — 4.50ML PAS — V 47 — 1975 01 06 111712.3 35.931N 120.534W 010 74 4.5 4.1 4.50ML PAS — V 48 18& 1975 01 12 01 37 08.2 40.328N 124.412W 033 401 4.7 — 4.50ML BRK — VI 48 7& 1975 01 12 212215.0 32.815N 117.974W 008 355 5.1 —- 4.80ML PAS -— IV 48 — 1975 01 13 1121502 133.815N 118.076W 007 355 3.8 —— 3.60ML PAS — VI 48 28: 1975 01 21 16 47 34.7 32.944N 115.492W 002 355 — — 3.30ML PAS — VI 48 — 1975 01 23 1702303 32.949N 115.504W 005 355 4.9 4.6 4.90ML PAS — VI 48 14+ 1975 01 23 2324348 32.993N 115.506W 005 355 4.3 -— 4.10ML PAS — VI 48 — 1975 01 28 1353164 40.415N 125.446W 010 74 4.9 50 4.80ML BRK — V 48 — 1975 03 03 15 35 45.0 33.925N 118.302W 012 355 — — 3.40ML PAS — VI 48 — 1975 05 13 0021357 35.0(X)N 119.090W 017 355 4.6 — 4.50ML PAS — V 48 20 1975 06 01 01 38 48.8 34.517N 116.490W 001 355 5.1 —- 5.00ML PAS -— VII 38 —— 1975 06 07 0846232 40.538N 124.287W 022 401 5.4 5.7 5.30ML BRK — V11 48 23& 1975 06 20 0548 24.0 32.780N 115.433W 004 355 4.3 —— 4.20M; PAS — VI 48 ~— 1975 08 01 16 27 17.8 39.438N 121.537W 005 401 4.8 3.2 4.70ML BRK — IV 48 — 1975 08 01 20 2004.8 39.439N 121.528W 008 401 4.4 -— 4.50ML BRK — — -— — 1975 08 01 20 20 12.9 39.439N 121.528W — 401 5.8 5.6 5.70ML BRK 6.14HBK VIH 38 120 1975 08 01 2025 39.439N 121.528W — 401 -— — 4.70ML BRK — Felt 48 — 1975 08 01 2029 39.439N 121.528W — 401 — — 4.60ML BRK -— Felt 48 — 1975 08 02 0014 07.7 33.513N 116.559W 013 401 4.6 — 4.80ML PAS 4.49HB III 48 — 1975 08 02 20 22 16.3 39.445N 121.463W 004 401 5.3 4.5 5.10ML BRK —— Felt 48 — 1975 08 02 20 59 39.432N 121.466W — 401 5.2 4.7 5.20M; BRK — VI 48 — 1975 08 03 01 03 05.8 39.488N 121.518W 008 401 5.0 — 4.60ML BRK — Felt 48 — 1975 08 03 0635165 36.457N 120.340W 005 401 5.1 4.0 4.90ML BRK -— VI 48 18 1975 08 03 0638 36.457N 120.340W 005 401 4.1 — 4.50ML BRK — — —- — 1975 08 06 03 50 29.9 39.479N 121.524W 008 401 5.1 4.0 4.70ML BRK — IV 48 — 1975 08 08 0700501 39.502N 121.512W 008 401 5.0 —- 4.90ML BRK — IV 48 ~- 1975 08 10 05 16 40.5 37.370N 119.985W 007 401 4.0 — 4.20ML BRK — VI 48 26 1975 08 11 0611363 39.446N 121.481W 004 401 4.8 3.8 4.30M; BRK — V 48 19 1975 08 15 22 27 51.8 36.497N 120.398W 006 401 4.5 — 4.50ML BRK -— V 48 -— 1975 09 09 02 43 42.5 40.916N 124.397W 027 74 4.9 — 4.60ML BRK — V 48 — 1975 09 13 21 20 59.8 36.000N 120.558W 014 401 4.9 4.3 4.80ML BRK — VI 48 168: 1975 09 27 2234381 39.511N 121.537W 008 401 5.3 3.5 4.60ML BRK — V 48 —— 1975 11 14 0929 49.4 40.570N 124.436W 022 401 4.9 4.5 4.80ML BRK —- VI 48 -— 1975 11 15 0613 27.6 34.305N 116.335W 005 355 4.6 — 4.60ML BRK — IV 48 —— 1976 01 01 17 20 12.9 33.966N 117.897W 005 355 4.6 —- 4.30ML PAS — VI 49 6& 1976 01 14 21 43 59.3 36.108N 120.162W 005 401 5.1 — 4.90ML BRK — VI 49 34 1976 01 20 13 59 37.2 40.384N 125.336W 033 74 4.8 — 4.60ML BRK — IV 49 —- 1976 04 08 15 21 37.9 34.357N 118.669W 017 355 4.7 3.9 4.50ML PAS — VI 49 18 1976 06 20 10 15 24.8 40.427N 120.568W 005 355 4.4 — 4.50M; BRK — V 49 — 1976 08 11 152455.4 33.482N 116.513W 015 355 —— —— 4.30ML PAS — VI 49 15 1976 08 20 2205 53.0 37.787N 121.980W 004 401 — — 4.00ML BRK — VI 49 — 1976 10 17 05 38 11.3 34.462N 118.426W 016 355 4.3 -— 3.90ML PAS — VI 49 8 1976 11 04 1041375 33.131N 115.623W 001 355 4.6 5.3 5.10M]. PAS 4.93HH VI 49 25+ 1976 11 22 175511.5 33.933N 118.628W 010 355 — —— 4.20ML PAS —— VI 49 48: 1976 11 26 11 19 25.2 41.289N 125.709W 015 74 6.0 6.8 6.30M; BRK —- V 49 6& 1976 12 23 0938 58.4 41.783N 125.953W 015 74 5.5 5.5 5.10ML BRK — — — — 1977 01 08 0938 07.5 37.905N 122.183W 009 401 4.8 — 4.30ML BRK —— VI 39 7& 1977 02 22 0624061 38.480N 119.283W 022 355 5.0 —— 4.80ML BRK — V 39 22 1977 06 21 02 43 06.6 37.665N 121.670W 011 401 4.7 3.5 4.40ML BRK 4.14BAK VI 39 16& 94 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date timetUTc) Latitude Longitude Depth Ref uses Other Moment MMI Ref Felt area Yr MoDa h m 3 (°) (°) (km) m., Ms M 0,000ka 1977 07 12 0143 28.5 40.277N 123.692W 020 401 5.0 3.8 4.10ML BRK — V 39 — 1977 07 18 2149 28.6 40.380N 125.361w 015 74 4.8 39 4.70M._ BRK —— — — — 1977 08 12 0219 26.1 34.380N 118.459w 010 355 4.1 —— 4.50ML PAS — VI 39 78: 1977 10 21 0612 36.0 32.896N 115.505w 005 355 3.7 — 4.10ML PAS — VI 39 —— 1977 11 14 02 05 48.3 32.830N 115.478w 004 355 5.0 — 4.10ML PAS — VI 39 — 1977 11 22 2115 53.9 39.403N 123.273w 018 401 5.2 — 4.80M._ BRK — VII 39 15& 1978 03 26 0027 04.4 39.233N 123.233w 010 613 4.9 — 4.50ML BRK — VI 240 88: 1978 05 23 2142 02.9 40.438N 124.850w 020 401 4.4 —— 4.60ML BRK — IV 240 — 1978 08 01 0902 34.5 41.453N 121.875W 002 401 4.5 — 4.60ML BRK — V 240 — 1978 08 01 0946446 41.457N 121.870w 002 401 4.3 5.1 4.50ML BRK — Felt 401 —— 1978 08 13 2254528 34.397N 119.682w 013 468 5.5 5.6 5.10M._ PAS 5.79ED V11 240 258: 1978 08 29 001446.4 37.362N 121.737W 008 401 —— — 4.10ML BRK —— VI 240 13a; 1978 09 04 0452 32.3 38.818N 119.810W 018 401 3.9 — 4.60ML BRK — V 240 16 1978 09 04 2154532 38.813N 119.815W 019 401 4.7 — 5.30ML BRK — VI 240 45 1978 09 25 0210510 41.062N 125.380w 005 401 4.6 4.3 4.60ML BRK —— — — — 1978 10 04 16 42 48.6 37.510N 118.693w 005 355 5.4 51 5.70M._ PAS 5.45ED VI 240 105 1978 10 04 17 3903.4 37.535N 118.683W 007 355 5.0 — 5.30ML PAS — — —— .— 1978 10 05 0641302 37.485N 118.664W 011 355 — —— 4.50ML PAS — Felt 355 -— 1978 10 06 212634.4 40.375N 124.273w 020 401 4.8 4.2 4.60ML BRK — V 240 .— 1978 11 20 0655 09.1 34.156N 116.978w 015 355 4.0 —— 4.30ML PAS — VI 240 12& 1979 0101 2314 38.9 33.948N 118.688w 010 474 5.1 4.7 4.80ML PAS — VI 262 218: 1979 01 24 21 14 27.2 37.520N 118.593w 010 401 — — 4.60ML BRK —— IV 262 28 1979 02 03 0958160 40.923N 124.418w 022 401 5.2 4.6 5.20ML BRK — V11 262 11& 1979 02 22 15 57 28.8 40.000N 120.088W 005 401 5.0 4.6 5.30ML BRK — VI 262 46 1979 03 15 2017493 34.305N 116.439w 000 355 5.0 4.9 5.00ML PAS — Felt 262 — 1979 03 15 2107165 34.325N 116.444W 001 355 5.5 5.6 5.30ML PAS 5.52131) V11 262 77 1979 03 15 21 34 25.5 34.347N 116.448w 000 355 — — 4.50M._ PAs — Felt 262 —— 1979 03 15 2307580 34.336N 116.440w 002 355 4.5 4.4 4.90M._ PAS — Felt 262 — 1979 04 07 0618 33.0 41.987N 126.816w 015 74 5.5 5.3 5.00M., BRK 5.62ED — — —— 1979 05 08 0511077 37.303N 121.683w 006 401 4.3 4.0 4.80ML BRK — VI 262 108: 1979 06 14 0739 28.3 35.729N 118.023w 005 355 4.2 —— 4.60ML PAS — VI 262 4 1979 06 29 05 53 20.3 34.246N 116.898w 009 472 4.1 —— 4.60ML WK — VI 262 13 1979 06 30 0034115 34.245N 116.891w 010 472 4.6 —— 4.90ML WK — V1 262 20 1979 06 30 0703 52.8 34.249N 116.896W 010 472 4.0 —— 4.50ML WK — Felt 262 —— 1979 08 06 1705 22.7 37.102N 121.503w 006 401 5.4 5.7 5.90ML BRK 5.78ED VII 262 63& 1979 10 07 2054414 38.223N 119.355w 009 355 4.1 — 5.00ML BRK — IV 262 15 1979 10 08 0334240 38.205N 119.323W 009 355 —— —— 4.60ML BRK — Felt 262 — 1979 10 15 23 16 54.1 32.634N 115.324w 010 355 5.7 69 6.40ML PAS 6.49ED 1x 262 128# 1979 10 15 2319287 32.748N 115.586w 005 355 — — 5.00ML PAS 5.03FRK — — — 1979 10 16 0100140 32.877N 115.556w 005 355 4.3 —— 4.70ML PAS — — — — 1979 10 16 0310478 32.951N 115.535w 004 355 4.5 —- 4.60M._ PAS — — — — 1979 10 16 03 39 35.0 32.949N 115.550w 005 355 4.4 — 4.60ML PAS —- — — — 1979 10 16 0549110 32.941N 115.538w 005 355 4.9 — 5.10ML PAS — — — —- 1979 10 16 0619492 32.937N 115.532w 002 355 4.8 5.4 5.10ML PAS 5.16ED — — — 1979 10 16 0655 23.5 32.988N 115.541w 004 355 4.3 —— 4.70ML PAS — — — —- 1979 10 16 0658 43.2 32.999N 115.569w 001 355 5.2 57 5.50M._ PAS 4.96ED VI 262 — 1979 10 16 114656.1 32.913N 115.560w 005 355 4.5 — 4.80ML PAS —- —— —— — 1979 10 16 2316 32.2 33.022N 115.506W 003 355 5.4 48 5.00ML PAS — —— — — 1979 10 17 22 45 33.8 33.040N 115.503w 002 355 4.8 — 4.70ML PAS — Felt 262 — 1979 10 24 15 23 50.6 40.428N 124.703w 024 401 4.8 — 4.50ML BRK — IV 262 — 1979 11 08 0430279 40.323N 125.173w 005 401 4.7 3.7 4.50ML BRK — — — — 1979 12 21 2040234 32.483N 115.194w 005 355 4.5 —— 4.80ML PAS —— VI 262 10+ 1980 0124 1900095 37.855N 121.816w 012 466 5.3 5.9 5.80ML BRK 5.77BMU VII 300 75& EARTHQUAKES IN CALIFORNIA 95 CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not. extend to the coast; @, felt area is less than 1,000 kmz. Leader (~-) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latltude Longitude Depth Ref USGS Other Moment MMI Rot Felt area Yr Mo D: h m 8 (°) (°) (km) mb Ms M (1,000 km“) 1980 0124 1901022 37.837N 121.802W 011 466 — — 5.10ML BRK — Felt 300 — 1980 0124 1903 20.0 37.837N 121.849W 018 466 — — 4.80ML BRK — :Felt 300 — 1980 01 25 0524365 37.884N 121.833W 008 466 4.2 — 4.60ML BRK 4.123AK IV 300 — 1980 01 27 02 33 36.0 37.737N 121.740W 015 466 5.0 5.0 5.40ML BRK 5.36BMU VII 300 25& 1980 02 25 1047 38.5 33.496N 116.513W 015 355 5.1 4.7 5.50ML PAS 4.88FRK VI 300 46# 1980 03 03 14 17 01.0 40.450N 125.267W 005 401 5.0 5.2 5.10ML BRK -— IV 300 — 1980 04 13 06 15 56.3 36.772N 121.520W 007 401 4.5 — 4.70M; BRK —- V 300 208: 1980 05 25 16 33 44.2 37.590N 118.847W 008 401 6.1 6.1 6.10ML BRK 6.21ED VII 300 272 1980 05 25 16 49 26.2 37.622N 118.902W 001 401 5.5 — 6.00ML BRK — Felt 300 — 1980 05 25 170624.4 37.533N 118.930W 005 401 — —- 4.60ML BRK — Felt 300 — 1980 05 25 1708283 37.593N 118.847W 016 401 4.2 —- 4.70ML BRK — Felt 300 — 1980 05 25 1748 30.0 37.593N 118.893W 004 401 3.9 —- 4.60ML BRK — Felt 3(1) — 1980 05 25 18 3414.4 37.542N 118.907W 004 401 4.1 — 4.60ML BRK -— Felt 300 -— 1980 05 25 1904 33.9 37.542N 118.900W 005 401 — —— 4.50ML BRK — Felt 300 — 1980 05 25 194451.0 37.545N 118.842W 013 401 5.5 5.8 6.10ML BRK 5.90ED VII 300 224 1980 05 25 20 23 25.5 37.617N 118.887W 005 401 —- — 4.50ML BRK — Felt 300 — 1980 05 25 20 35 48.0 37.607N 118.858W 005 401 .2 5.3 5.70ML BRK — Felt 300 —— 1980 05 25 20 38 38.5 37.632N 118.858W 005 401 — -— 4.50ML BRK — Felt 300 — 1980 05 25 20 59 22.6 37.568N 118.818W 008 401 4.2 —— 5.00ML BRK — Felt 300 — 1980 05 26 0057 02.3 37.572N 118.943W 001 401 4.2 —- 4.50ML BRK — Felt 300 ~— 1980 05 26 01 19 02.2 37.573N 118.948W 007 401 4.4 — 4.60ML BRK —- Felt 300 — 1980 05 26 05 56 26.3 37.568N 118.897W 007 401 4.0 — 4.70M; BRK -—- Felt 300 — 1980 05 26 102031.1 37.605N 118.810W 008 401 4.0 — 4.50ML BRK -— Felt 300 —- 1980 05 26 1224251 37.567N 118.883W 007 401 4.7 — 5.10ML BRK — IV 300 — 1980 05 26 14 37 30.8 37.537N 118.882W 008 401 4.1 —- 4.50M; BRK —— Felt 300 — 1980 05 26 16 2021.6 37.547N 118.912W 005 401 4.7 — 4.80ML BRK — Felt 300 — 1980 05 26 18 57 55.9 37.542N 118.890W 008 401 5.0 -— 5.70M; BRK — Felt 3(1) — 1980 05 26 192409.4 37.513N 118.878W 007 401 — — 4.70ML BRK — Felt 300 — 1980 05 27 1450566 37.492N 118.830W 016 401 5.7 6.0 6.20ML BRK 5.86ED VI 300 240 1980 05 27 19 01 07.9 37.592N 118.787W 006 401 4.3 — 4.80M; BRK 4.54ARC Felt 300 -— 1980 05 28 05 16 23.0 37.573N 118.900W 004 401 41 — 4.90ML BRK 4.61ARC Felt 300 — 1980 05 28 0548295 37.618N 118.873W 006 401 40 — 4.60ML BRK — Felt 300 — 1980 05 29 03 38 48.5 34.975N 120.714W 006 355 ——- — 4.60ML PAS -— V 300 278: 1980 05 31 005817.3 37.492N 118.860W 009 401 4.1 — 4.50ML BRK 4.36ARC Felt 300 — 1980 05 31 151611.4 37.598N 118.792W 008 401 4.1 — 4.90ML BRK 4.71ARC IV 300 — 1980 06 01 0647 36.0 37.468N 118.853W 008 401 3.7 — 4.70ML BRK — Felt 300 — 1980 06 11 044058.5 37.542N 118.892W 008 401 3.9 — 4.70ML BRK 3.99ARC V 300 ~— 1980 06 29 0746135 38.005N 118.688W 005 401 4.2 — 5.00ML BRK — VI 300 — 1980 08 01 16 38 55.9 37.548N 118.893W 008 401 4.7 5.0 5.40ML BRK — V 300 40 1980 08 01 164854.6 37.547N 118.883W 013 401 4.2 — 4.60ML BRK — — —— — 1980 09 24 0808 38.6 36.243N 120.165W 008 401 4.8 — 4.50ML BRK — V 300 — 1980 10 31 12 55 36.6 32.660N 115.579W 003 355 4.2 —- 4.60ML PAS — VI 300 5+ 1980 11 08 1027 34.0 41.117N 124.253W 019 74 6.2 7.2 6.90ML BRK 7.24ED VII 300 978: 1980 11 08 10 47 32.9 40.357N 125.205W 015 74 4.8 — 4.80ML BRK —- — — — 1980 ll 08 1051184 40.269N 125.441W 015 74 4.7 -- 4.80ML BRK — — — — 1980 11 08 11 20 38.7 40.247N 124.742W 015 74 5.0 —— 4.70M; BRK — —— — — 1980 11 08 16 52 29.0 40.425N 125.459W 015 74 4.4 4.3 4.90ML BRK — Felt 300 — 1980 11 08 17 14 40.0 40.450N 125.602W 008 401 4.3 — 4.50ML BRK —— Felt 300 — 1980 ll 08 22 47 52.8 40.648N 125.262W 021 401 4.6 4.2 5.00ML BRK — Felt 300 — 1980 ll 08 2307063 40.448N 125.682W 008 401 4.6 5.0 4.80ML BRK — Felt 300 — 1980 11 09 0409088 40.501N 125.343W 015 74 5.0 4.3 5.40ML BRK — — —— ~— 1980 11 10 23 59 27.1 40.562N 125.669W 013 74 4.8 3.1 4.80M; BRK — Felt 300 —- 96 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; 3, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m 8 (°) (°) (km) mb Ms M (1.000 km?) 1980 11 28 18 21 12.9 39.262N 120.467W 010 401 4.9 — 5.10ML BRK — VI 300 36 1980 12 24 1548 33.6 37.577N 118.867W 016 401 4.2 — 4.70ML BRK — V 300 — 1981 01 07 11 42 33.1 36.857N 121.623W 007 401 4.3 — 4.50ML BRK — V 325 1782 1981 01 15 12 47 51.6 37.378N 121.723W 009 401 4.8 4.0 4.80ML BRK —— V 325 19 1981 03 03 1045 12.9 37.557N 121.937W 010 401 4.2 4.0 4.40ML BRK — VI 325 5& 1981 03 15 0607459 40.393N 125.160W 008 401 4.5 4.5 4.70ML BRK — III 325 — 1981 04 19 0902504 35.851N 117.842W 003 355 4.4 — 4.50M; PAS — V 325 —- 1981 04 26 120928.4 33.098N 115.618W 002 355 5.5 6.0 5.60ML PAS 5.91ED VII 325 73# 1981 05 26 1141 10.2 40.380N 124353W 021 401 4.3 — 4.60ML BRK — IV 325 —- 1981 07 02 08 10 54.0 41.103N 124.218W 024 74 4.4 3.5 4.50ML BRK — V 325 — 1981 07 17 16 37 32.6 40.20 N 124.25 W 013 401 4.9 4.1 4.60ML BRK — VI 325 8& 1981 09 04 1550504 33.661N 119.091W 005 355 5.4 5.9 5.30ML BRK 5.85ED VI 325 338: 1981 09 16 12 41 14.2 40.31 N 124.61 W 025 401 4.8 3.9 4.70ML BRK — V 325 8& 1981 09 30 ll 53 26.9 37.588N 118.887W 005 355 5.6 5.8 6.00ML PAS 5.64ED VI 325 92 1981 09 30 13 05 48.4 37.648N 118.865W 005 355 4.7 —— 5.30ML PAS -- V 325 92 1981 10 23 1728168 33.626N 119.019W 014 355 4.7 — 4.60ML PAS — V 325 6& 1981 10 23 19 15 52.3 33.619N 119.015W 012 355 4.6 —— 4.60ML PAS -- IV 325 6& 1981 ll 10 2234354 35.024N 119.138W 002 355 4.7 — 4.80ML PAS -—- V 325 24& 1982 01 13 12 26 25.8 40.419N 125.101W 010 74 4.9 5.1 4.80ML BRK — Felt 350 — 1982 02 06 120203.6 41.003N 125.(X)8W 004 401 5.1 5.1 5.20ML BRK — IV 350 —- 1982 03 07 20 51 00.3 35.740N 117.763W 005 355 4.7 — 4.70ML PAS — V 350 — 1982 03 22 08 53 28.6 33.058N 116.211W 005 355 4.4 — 4.50ML PAS — IV 350 — 1982 06 15 23 4921.3 33.558N 116.660W 012 355 4.5 — 4.90ML PAS 4.64FRK V 350 26 1982 08 10 021129.8 36.592N 121.242W 007 401 3.9 —-— 4.50ML BRK ——- IV 350 — 1982 08 11 0746412 36.630N 121.305W 009 401 4.6 —— 4.60ML BRK —- V 350 — 1982 08 18 08 43 49.8 37.017N 121.733W 011 401 4.3 — 4.50ML BRK — V 350 98!. 1982 10 01 14 29 02.5 35.731N 117.751W 009 355 4.9 — 4.90ML PAS — VI 350 29 1982 10 25 22 26 04.3 36.325N 120.502W 011 401 5.3 5.2 5.40ML PAS 4.79ED VI 350 938: 1982 12 16 0653 01.3 40.498N 124.257W 018 401 4.8 4.5 4.40ML BRK — VI 350 88!. 1983 01 07 013810.9 37.640N 118.898W 007 401 5.1 5.0 5.40ML BRK — VI 360 76 1983 01 07 032419.4 37.635N 118.988W 007 401 5.1 5.0 5.30ML BRK — VI 360 59 1983 01 25 101041.2 37.505N 118.900W 002 401 4.4 —— 4.80ML BRK — Felt 360 — 1983 05 02 23 42 38.1 36.233N 120.309W 010 360 6.2 6.5 6.70ML BRK 6.1968 360 2058; 1983 05 02 2346060 36.225N 120.295W 008 401 5.5 5.60ML BRK 1983 05 03 0017 59.0 36.210N 120.326W 008 360 4.8 4.40ML BRK 4.603RK 1983 05 03 0057 44.2 36.270N 120.315W 008 360 5.1 1983 05 03 0141460 36.142N 120.219W 007 360 4.3 1983 05 03 08 55 02.0 36.144N 120.267W 010 360 4.4 1983 05 03 15 41 41.6 36.235N 120.302W 008 360 4.7 1983 05 04 0728404 36.263N 120.335W 005 360 4.7 4.80ML BRK 4.87BRK 4.54ML BRK 4.34BRK 4.50ML BRK 4.4OBRK 4.80ML BRK 4.84BRK 4.70ML BRK 4.69BRK Felt 360 gllll ezee a.§ WW 8% Hill 1983 05 05 102044.l 36.285N 120.368W 011 360 4.5 4.61ML BRK 4.46BRK 1983 05 09 02 49 11.5 36.246N 120.299W 012 360 5.1 4.7 5.20ML BRK 4.49BRK VI 360 110& 1983 05 09 03 26 37.4 36.240N 120.299W 012 360 4.7 — 4.60ML GM —-— Pelt 360 — 1983 05 12 13 41 06.8 36.167N 120.268W 011 360 4.2 — 4.50ML BRK — Felt 360 —— 1983 05 24 0902 17.7 36.254N 120.333W 009 360 4.6 — 4.60ML BRK 4.6013RK V 360 23 1983 05 29 0655 33.1 40.457N 125.444W 010 74 5.1 5.1 5.40ML BRK -— III 360 ~— 1983 06 11 0309522 36.255N 120.450W 002 360 5.3 54 5.10ML BRK 5.28BRK VI 360 ~— 1983 06 29 0808357 32.588N 117.431W 006 355 4.4 — 4.60ML PAS —— V 360 l9# 1983 07 03 18 4008.2 37.550N 118.862W 009 401 4.8 -— 5.30ML BRK 5.03BRK V 360 39 1983 07 05 14 27 26.7 38.070N 119.018W 010 401 4.6 — 4.80ML BRK — V 360 — 1983 07 09 0740513 36.251N 120.400W 009 360 5.3 4.9 5.30ML BRK 5.153RK V 360 59 1983 07 13 2116485 33.208N 115.530W 012 360 4.3 — 4.10ML PAS -— VI 360 —— EARTHQUAKES IN CALIFORNIA 97 CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. 8:. land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1.000 kmz. Leader (-<) indicates infomiatian is not available] Origin Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr MoDe h m 3 (°) (°) (km) mb Ms M (1900ka 1983 07 22 02 39 54.1 36.241N 120.409W 007 360 6.0 5.7 6.00ML BRK 5.9OBRK VI 360 108& 1983 07 22 03 43 01.4 36.222N 120.406W 008 360 5.3 — 5.00ML BRK 4.88BRK V 360 — 1983 07 25 22 31 39.6 36.229N 120.398W 008 360 5.6 5.1 5.30ML BRK 5.16BRK VI 360 60& 1983 08 24 13 36 30.5 40.377N 124.832W 018 401 5.5 5.8 5.50ML BRK 5.613RK VI 360 10& 1983 08 29 10 10 30.9 35.836N 121.345W 007 476 5.3 43 5.20ML BRK 5.3lBRK VI 360 218: 1983 09 09 0916135 36.232N 120.265W 007 360 5.3 5.4 5.40M], BRK 5.28BRK V 360 — 1983 09 11 1148 06.6 36.242N 120.383W 010 360 5.0 — 4.70ML PAS 4.48BRK IV 360 -— 1983 09 30 16 14 00.9 37.553N 118.840W 010 401 — — 4.80M; BRK 4.49BRK IV 360 — 1983 10 21 2244133 35.926N 118.334W 000 355 4.4 — 4.50ML PAS — III 360 — 1983 11 11 1207433 40.388N 124.902W 015 401 4.9 3.8 4.30ML BRK —— Felt 360 — 1983 12 20 104105.0 40.331N 125.117W 005 299 56 5.4 5.60ML BRK 5.90ED V 360 —- 1984 01 23 0540203 36.392N 121.878W 008 401 5.1 4.6 5.10ML BRK 4.9SBRK V 370 328: 1984 01 23 0659 51.3 36.388N 121.872W 008 401 — —— 4.50ML BRK 4.283RK Felt 370 — 1984 02 27 01 36 20.6 37.375N 118.598W 010 401 4.3 — 4.50ML BRK -— I11 370 — 1984 02 28 15 16 06.7 40.357N 125.897W 005 401 4.9 4.4 5.20M; BRK — IV 370 — 1984 04 24 211519.0 37.320N 121.698W 008 401 5.7 6.1 6.20ML BRK 6.16GS VIII 370 1208: 1984 04 28 224821.0 37.622N 118.897W 003 401 4.3 —— 4.80ML PAS — IV 370 — 1984 08 04 21 45 53.2 40.255N 124.578W 005 401 4.7 4.6 4.70ML BRK 5.36GS V 370 — 1984 09 10 0314101 40.503N 126.831W 010 74 6.1 6.7 6.60ML BRK 6.67GS V 370 24& 1984 09 20 18 30 42.5 40.382N 125.617W 005 401 4.7 -— 4.80ML BRK -— IV 370 — 1984 10 10 21 22 58.9 33.138N 116.501W 012 370 4.3 — 4.50ML PAS — IV 370 — 1984 10 25 10 36 02.4 34.737N 120.148W 006 370 4.5 — 4.50ML PAS —- VI 370 108: 1984 10 26 17 20 43.5 34.016N 118.988W 013 370 4.3 — 4.60ML PAS — V 370 10& 1984 11 23 1808255 37.458N 118.605W 012 401 5.6 5.7 6.10ML BRK 5.80GS V 370 114 1984 11 23 19 12 34.6 37.433N 118.612W 014 370 4.8 4.7 5.50ML BRK — IV 370 — 1984 ll 25 2310094 37.447N 118.612W 005 401 4.3 3.1 4.70M; BRK — Felt 370 — 1984 11 26 1621 47.2 37.448N 118.653W 009 401 5.1 4.7 5.60ML BRK 5.14GS V 370 88 1984 11 26 16 31 21.4 37.422N 118.635W 010 401 — — 4.50ML BRK — — — — 1984 ll 28 16 23 26.1 37.425N 118.630W 008 401 4.3 —- 4.70ML BRK -— Felt 370 — 1984 11 28 16 57 37.9 37.463N 118.582W 005 401 4.2 —- 4.60ML BRK -— —- — ~— 1985 01 24 11 27 21.6 38.157N 118.853W 008 401 -—- — 5.20ML BRK 4.82BRK IV 371 25 1985 02 08 065816.9 35.452N 118.898W 011 371 4.6 —- 4.60ML PAS — V 371 15 1985 03 25 16 05 13.6 37.448N 118.545W 006 371 4.8 — 5.00ML PAS 4.49BRK V 371 15 1985 05 04 03 22 46.2 37.469N 118.598W 006 371 3.7 —— 4.70ML PAS — IV 371 — 1985 08 04 112916.2 36.122N 120.138W 011 401 4.7 — 4.70ML BRK 4.643RK IV 371 — 1985 08 04 120157.0 36.130N 120.127W 011 401 5.4 5.9 5.60ML BRK 6.09GS VI 371 97& 1985 08 22 002144.1 35.883N 117.717W 006 371 4.3 — 4.50ML GP — IV 371 — 1985 08 27 0304068 37.412N 118.633W 006 401 —- —- 4.50ML BRK 4.14BRK III 371 — 1985 10 02 2344124 34.023N 117.245W 015 371 4.1 — 4.80ML PAS — VI 371 13 1985 11 28 15 13 57.2 36.562N 121.060W 010 401 4.4 4.4 4.60ML BRK 4.6lBRK IV 371 15& 1986 01 14 0309363 36.572N 121.205W 007 562 5.0 — 4.80ML BRK 4.59BRK IV 562 8& 1986 01 26 19 2051.2 36.810N 121.275W 007 562 5.3 5.3 5.50ML BRK 5.483RK VII 562 368: 1986 02 11 0115572 41.634N 125.353W 010 562 5.0 5.0 4.90ML BRK 5.3lBRK —— -—— — 1986 03 31 11 55 40.1 37.488N 121.693W 008 562 5.5 5.5 5.70ML BRK 5.56BRK VI 562 41& 1986 05 31 0847 56.1 36.618N 121.255W 004 562 4.6 3.7 4.70ML BRK 4.5513RK IV 562 — 1986 07 08 0920 44.5 33.999N 116.606W 012 597 5.8 6.0 5.60ML GP 6.19GS VII 562 134# 1986 07 13 13 47 08.2 32.970N 117.869W 006 597 5.6 5.8 5.30ML GP 5.83HAV VI 562 49# 1986 07 13 1401 33.0 32.989N 117.849W 012 597 4.8 —— 4.60ML GP — — — -— 1986 07 20 14 29 45.5 37.580N 118.449W 006 597 5.6 5.6 5.90ML BRK 5.3SBRK V 562 —— 1986 07 20 18 38 52.9 37.538N 118.440W 009 562 3.9 — 4.70ML BRK 4.30BRK IV 562 — 1986 07 21 14 42 26.5 37.537N 118.450W 009 562 6.0 6.2 6.40ML BRK 6.25BRK VI 562 258 1986 07 21 14 45 21.0 37.583N 118.417W 006 562 -— — 4.60ML PAS — — —— ~— 1986 07 21 1451 10.1 37.570N 118.525W 001 562 5.1 — 5.70ML BRK 5.04BRK V 562 — 98 SEISMICITY OF THE UNITED STATES, 1568-1989 (REVISED) CALIFORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States {or an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 3 (°) (°) (km) mb Ms M (1 .000 km?) 1986 07 21 14 53 58.1 37.583N 118.583W 006 562 — — 4.90ML PAS -— — — — 1986 07 21 14 54 39.2 37.583N 118.417W 006 562 -— 4.50ML PAS — -— -—- — 1986 07 21 14 57 50.9 37.527N 118.357W 007 562 4.7 —— 4.80ML BRK 4.46BRK —- -— —- 1986 07 21 15 11 30.8 37.597N 118.485W 006 597 — — 4.70ML PAS - — —- —-— 1986 07 21 15 19 34.9 37.488N 118.370W 016 562 — — 4.70ML BRK 4.38BRK — — — 1986 07 21 15 26 49.2 37.533N 118.425W 018 562 — —— 4.60ML BRK 4.188RK —— —— — 1986 07 21 15 46 23.0 37.551N 118.420W 001 562 — —- 4.50ML BRK 4.123RK -- — — 1986 07 21 16 26 44.7 37.487N 118.393W 008 562 -— — 4.60ML BRK 4.183RK — -— — 1986 07 21 17 05 33.4 37.532N 118.462W 009 562 3.6 — 4.50M], BRK 4.183RK -— — -— 1986 07 21 17 20 00.4 37.447N 118.367W 011 562 — — 4.50M], BRK 4.IOBRK —- —- —- 1986 07 21 22 07 17.0 37.483N 118.367W 006 562 5.5 5.0 5.60ML BRK 5.03BRK Felt 562 — 1986 07 21 22 09 22.1 37.613N 118.569W 006 562 — —— 4.70ML PAS —— — — — 1986 07 22 00 09 53.8 37.610N 118.430W 004 562 4.0 — 4.50M], BRK 4.27BRK - -— —- 1986 07 22 13 33 59.8 37.517N 118.477W 009 562 4.2 -—— 4.70ML BRK 4.41BRK IV 562 — 1986 07 22 13 49 00.3 37.498N 118.520W 019 562 4.5 — 5.00ML BRK 4.58BRK — — -— 1986 07 22 18 29 43.8 37.493N 118.382W 007 562 3.7 -— 4.70ML BRK 4.15BRK — — — 1986 07 23 15 39 11.7 37.538N 118.463W 006 562 4.1 — 4.70ML BRK 4.4OBRK — — —- 1986 07 29 09 57 57.2 37.595N 118.477W 007 562 3.7 — 4.60M], BRK 4.34BRK IV 562 — 1986 07 30 06 41 52.9 37.582N 118.468W 007 562 4.1 — 4.80ML BRK 4.4ZBRK IV 562 — 1986 07 31 07 22 40.2 37.463N 118.367W 007 562 5.5 5.2 5.80ML BRK 5.4ZBRK VI 562 1(1) 1986 07 31 07 28 04.7 37.445N 118.377W 011 562 — — 4.50ML BRK 4.12BRK -— — -—- 1986 08 01 14 27 16.4 37.501N 118.398W 006 562 4.2 — 4.80ML BRK — Felt 562 —- 1986 08 01 14 28 19.6 37.468N 118.448W 014 562 4.9 -—— 5.10ML BRK 4.83BRK Felt 562 — 1986 10 15 02 28 47.8 33.953N 116.572W 009 562 4.3 -— 4.70ML GP —— V 562 — 1986 10 31 03 57 28.9 38.420N 119.323W 001 562 —— —— 4.60ML BRK 4.4OBRK IV 562 — 1986 11 21 23 33 01.7 40.372N 124.443W 015 562 5.3 5.1 5.10ML BRK 5.14BRK V1] 562 14& 1986 11 21 23 34 18.0 40.367N 124.450W 015 562 5.1 — 5.10ML BRK 5.06BRK Felt 562 —— 1987 02 14 07 26 51.7 36.148N 120.335W 013 74 5.3 4.6 5.30ML BRK 4.9SBRK V 577 — 1987 07 31 23 56 58.3 40.418N 124.373W 016 74 5.6 6.0 5.60ML BRK 5.5SBRK VI 577 18& 1987 10 01 14 42 20.0 34.061N 118.078W 010 598 5.8 5.7 5.90ML PAS 5.91HAV V111 581 110& 1987 10 01 14 45 41.4 34.049N 118.100W 014 598 —— —— 4.70ML GP —— Felt 74 — 1987 10 01 14 49 05.9 34.060N 118.100W 012 598 — — 4.70ML PAS —- Felt 74 — 1987 10 01 15 12 31.7 34.052N 118.090W 011 598 4.6 — 4.70ML GP —-— Felt 74 — 1987 10 04 10 59 38.2 34.074N 118.098W 008 598 5.2 4.8 5.30ML PAS 5.22HAV VII 577 -— 1987 11 24 01 54 14.5 33.082N 115.775W 005 598 5.7 6.2 5.80ML PAS 6.05HAV VI 577 77# 1987 11 24 02 14 35.4 33.036N 115.820W 005 598 —— — 4.50M; PAS — — — — 1987 11 24 02 15 23.2 33.048N 115.798W 005 598 -— —— 4.80ML GP — — — — 1987 ll 24 02 53 00.7 33.040N 115.812W 003 598 4.4 —— 4.7OML PAS — — — — 1987 11 24 13 15 56.5 33.013N 115.838W 002 598 6.0 6.6 6.00ML GP 6.52HAV VII 577 1(X)# 1987 11 24 13 34 39.9 32.942N 115.763W 014 598 4.8 — 4.80ML PAS —- — —— —- 1987 11 26 17 39 01.9 33.030N 115.890W 002 598 4.5 — 4.30ML PAS — — -— ~— 1987 11 27 01 1010.5 32.996N 115.816W 006 598 4.1 —— 4.70ML PAS — — — —— 1988 01 06 22 49 48.3 36.777N 120.867W 006 74 4.1 — 4.50ML BRK 4.34BRK III 578 — 1988 01 28 02 54 02.3 32.919N 115.678W 004 602 4.6 — 4.7OML GP — V 578 4+ 1988 02 11 15 25 55.6 34.077N 118.047W 012 602 4.8 — 4.70ML GP — VI 578 28& 1988 02 20 08 39 57.5 36.803N 121.302W 009 74 4.5 4.0 5.10ML BRK 4.983RK V 578 208: 1988 06 10 23 06 43.0 34.943N 118.743W 007 602 5.2 4.9 5.40ML GP — V 578 378: 1988 06 13 01 45 36.8 37.385N 121.772W 007 74 4.9 5.0 5.3OML BRK 4.9lBRK VI 578 378: 1988 06 26 15 04 58.5 34.136N 117.710W 008 602 4.5 -— 4.70ML GP 5.033RK V 578 12& 1988 06 27 18 43 22.3 37.130N 121.878W 013 74 4.8 4.1 5.30ML BRK — VI 578 11& 1988 07 05 18 18 47.5 36.392N 117.973W 005 74 4.4 — 4.80ML BRK — IV 578 — 1988 07 26 03 26 56.0 36.563N 121.182W 003 74 4.9 4.0 4.70ML BRK 4.77BRK III 578 — 1988 07 28 11 20 24.2 36.407N 117.998W 005 74 — — 4.50ML BRK —- III 578 — 1988 08 10 18 24 51.3 36.413N 117.988W 005 74 —— — 4.6OML BRK -— II 578 — 1988 10 11 13 3009.3 40.427N 125.515W 019 74 4.4 — 4.60ML BRK 4.19BRK — — — EARTHQUAKES IN CALIFORNIA 99 CALIF ORNIA—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; #, land area only in the United States for an earthquake near a coastline; +, land area in the United States when the felt area did not extend to the coast; @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yt’ M0 03 h m 3 (o) (0) (km) mb Ms M (1.000 km?) 1988 11 10 05 08 03.0 37.373N 121.757W 007 74 4.5 4.0 4.80ML BRK 4.6IBRK V 578 14& 1988 11 20 05 39 28.7 33.507N 118.071W 006 74 5.0 —- 4.50ML GP -— V 578 22& 1988 12 03 11 38 26.4 34.149N 118.135W 013 602 4.4 4.2 4.90ML GP — VI 578 428: 1988 12 16 05 53 05.0 33.979N 116.681W 008 602 4.8 -— 4.80ML GP — V 468 25& 1989 01 15 15 39 55.1 32.948N 117.736W 006 603 4.5 — 4.20ML GP — IV 579 - 1989 01 19 06 53 28.8 33.919N 118.627W 012 603 5.2 4.8 5.00ML GP —- VI 579 40& 1989 04 03 17 46 34.4 37.422N 121.795W 009 74 4.5 4.3 4.70ML BRK -— V1 579 158: 1989 04 07 20 07 30.3 33.619N 117.902W 013 603 5.0 — 4.50ML GP — VI 579 148: 1989 06 04 21 33 59.7 34.597N 116.838W 002 603 4.2 —- 4.50ML GP — V 579 7 1989 06 12 16 57 18.5 34.022N 118.178W 016 603 4.3 —- 4.40ML GP -— VI 579 14& 1989 08 08 08 13 27.5 37.130N 121.952W 015 74 4.9 4.5 5.40ML BRK -— VII 579 26& 1989 08 08 15 53 28.4 37.150N 121.973W 015 74 4.2 — 4.50ML BRK —- V 579 -— 1989 09 21 17 41 18.0 40.327N 124.705W 016 74 4.8 4.7 4.80ML BRK 5.14BRK V 579 88!. 1989 10 18 00 04 15.2 37.036N 121.883W 019 74 6.5 7.1 7.00ML BRK 7.183RK 1X 579 1708: 1989 10 18 00 25 04.9 37.043N 121.807W 005 74 5.0 -— 4.80M]~ BRK — — ——- — 1989 10 18 00 41 24.7 37.198N 122.105W 019 74 4.8 —- 5.10ML BRK -—- — — — 1989 10 18 02 15 49.9 36.995N 121.763W 004 74 4.4 — 4.50ML BRK — — -- — 1989 10 18 04 50 27.7 37.193N 122.017W 014 74 4.6 — 4.30ML BRK — -— — - 1989 10 18 05 18 34.1 36.980N 121.847W 011 74 4.5 — 4.20M], BRK — — -- — 1989 10 18 06 39 10.1 36.932N 121.712W 012 74 4.6 —— 4.30M; BRK — —- -— — 1989 10 19 09 53 50.4 36.932N 121.690W 012 74 4.3 3 6 4.50ML BRK — Felt 74 — 1989 10 19 10 14 35.1 36.963N 121.843W 013 74 4.6 4.2 4.60ML BRK — Felt 74 — 1989 10 21 00 49 43.7 37.047N 121.877W 014 74 4.4 — 4.60ML BRK --— Felt 74 —- 1989 10 21 22 14 57.0 37.057N 121.905W 013 74 4.5 — 4.90ML BRK — Felt 74 —- 1989 10 25 01 27 26.6 37.078N 121.832W 014 74 4.6 3.6 5.00ML BRK -—— IV 579 -— 1989 11 02 05 50 11.0 37.057N 121.797W 012 74 4.5 —— 4.90ML BRK — V 579 — 1989 11 03 19 09 1.6 38.567N 119.652W 011 74 — — 4.50M}, BRK — IV 579 — 1989 11 05 13 37 34.3 37.058N 121.915W 015 74 -—— — 4.50ML BRK — Felt 74 — 1989 12 28 09 41 08.2 34.192N 117.386W 015 603 —— — 4.50ML GP -— V 579 11 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude val- ues are described in the Introduction, and codes are defined in table 2.] 1769. July 28. Los Angeles, Calif., region. The Portola expedition felt four violent earthquakes while camped on the Santa Ana River, near the present site of Olive. Many strong aftershocks were observed through Aug. 3 as the expedition moved northwest- ward to near San Gabriel and then westward across Los Angeles to the Pacific. This probably was a major earthquake. (Ref. 38, 368, 493, 521.) 1800. Oct. 11. Near San Juan Bautista, San Benito County, Calif. Although the houses at San Juan Bautista were built with double walls, all were damaged from roof to foundation and were uninhab- itable. Some small cracks were observed in the ground at the rancheria; another deep fissure formed in the area of the Pajaro River. A strong shock on Oct. 18 was accompanied by “such a loud noise as to deafen them.” (Ref. 38, 368, 493.) 1800. Nov. 22. San Diego, Calif., region. Walls of adobe buildings were damaged in San Diego, and walls of a new church were cracked at San Juan Capistrano. (Ref. 38, 368.) 1803. May 25. San Diego, Calif. The mission church at San Diego sustained slight damage. (Ref. 56, 368.) 1806. Mar. 25. Santa Barbara, Calif. An earth— quake cracked the walls of a chapel at Santa Bar— bara. (Ref. 56, 368.) 1808. June 21. San Francisco, Calif. Adobe walls were damaged severely at the Presidio of San Francisco. One of the rooms collapsed at the 100 commandant’s house, and the soldiers’ quarters were ruined and nearly fell. Through July 17 and 18 shocks were felt. (Ref. 38, 56, 368.) 1812. Dec. 8. Southwest San Bernardino County, Calif. The most severe loss occurred at the Missions of San Juan Capistrano and San Gabriel. The masonry church at San Juan Capistrano Mission was destroyed, killing 40 people attending services. Other buildings at the mission were left “in bad con- dition.” The church at San Gabriel also sustained much damage, and many cracks formed in the bell tower. The upper part of the tower later fell, as did the weathervane. The living quarters of the ministers and offices of the mission also were damaged exten- sively. Three tremors described as “horrible” probably caused damage at San Buenaventura Mission (Ven- tura). Walls of buildings were impaired at Mission San Fernando Rey, but no damage was reported at San Diego or San Luis Rey Missions. This earthquake may have ruptured the San Andreas fault at Wrightwood. The rupture may have extended at least 25 km to the northwest, where it is preserved in the peat bog at Pallet Creek. The fault rupture at Pallet Creek is comparable to that formed by the 1857 earthquake in the southern Coast Ranges. The main earthquake was felt from San Buenaventura Mission west to San Bernardino Val- ley and south to San Diego. (Ref. 38, 56, 368, 521.) 1812. Dec. 21. West of Ventura, Calif., in Santa Barbara Channel. This major earthquake caused damage in Santa Barbara, Ventura, and northern Los Angeles Counties. One fatality was reported, but many lives probably were saved by a strong foreshock about 15 minutes earlier that sent alarmed residents fleeing from buildings. The earth- quakes also may have generated a tsunami because there were several reports of sea waves following the earthquakes. The sea waves reportedly did not cause loss of life or substantial loss of property. At Santa Barbara Mission, all buildings sustained many cracks, and one chapel was flattened. The ground “opened up” in this area to such an extent “that it caused horror.” At the Santa Barbara Pre- sidio, all the buildings were left uninhabitable. The church at La Purisima Concepcion Mission (Lompoc) was ruined; some of the other buildings were “flat- tened to the ground;” and others required extensive repair. Part of the adobe garden wall collapsed, and that part remaining nearly fell. Damage at the Santa Ynez Mission was considerable but not so severe as at Santa Barbara and Purisima Missions. A corner of the church fell; many new houses were demolished; and many support walls were cracked. Property loss was less severe at the San Buenaventura Mission SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) (Ventura) and the San Fernando Rey Mission. After- shocks were reported at Santa Barbara through April 1813. (Ref. 38, 56, 368, 521.) 1827. Sept. 24 (Sept. 23). Los Angeles, Calif. People in Los Angeles ran outdoors in panic. The 1827 report of the San Buenaventura Mission (Ven- tura) notes that all the buildings were in “bad condi- tion” because of the earthquakes. The same earthquake, therefore, may have affected both Los Angeles and Ventura. (Ref. 56, 368.) 1829. September. San Francisco, Calif. Sev- eral severe shocks at San Francisco were strong enough to force open locked doors and windows. No damage has been documented for this earthquake. The intensity was taken from ref. 56. (Ref. 56, 493.) 1830. Date unknown. San Luis Obispo, Calif. All the buildings at San Luis Obispo were damaged, including the hospital and part of the rancheria, which lay in ruins. The farm and building of S. Miguelito were destroyed, and the house of Santa Margarita sustained cracked and broken walls. (Ref. 38, 368.) 1836. June 10. San Francisco Bay area, Calif. This strong earthquake affected an area along the foothills from San Pablo to Mission San Jose. Large fissures formed in the ground in the area of maximum disturbance. The earthquake caused havoc in Monterey and Santa Clara and frightened all res- idents. The first shock was the most violent, and smaller aftershocks continued for a month. This earthquake may have ruptured the Hayward fault. Its intensity is similar to that of an earthquake in the same area on October 21, 1868. (Ref. 38, 56, 368, 493.) 1838. June. San Francisco area, Calif. This earthquake was associated with a probable rupture on the San Andreas fault, from near Santa Clara to San Francisco (about 60 km). It is suggested that the fault rupture may have extended throughout all or most of the line that was active in the 1906 earth— quake. Walls were cracked at Mission Dolores (San Francisco), and some adobe walls were cracked and glassware and crockery were broken at Monterey. (Ref. 56, 368, 521.) 1840. Jan. 16. Santa Cruz, Calif. An earth- quake threw down a church tower at Santa Cruz. A “tidal wave” (tsunami) was reported. Shocks contin- ued to Jan. 18. (Ref. 56, 493.) 1841. July 3. Monterey, Calif. This earthquake left the bay and shore covered with dead and beached fish. The shaking was so severe at Monterey than an observer had to support himself against a tree to keep from falling. The main earthquake was reported felt onboard ships in the harbor and on EARTHQUAKES IN CALIFORNIA inland farms. About 120 shocks were felt in Monterey in the summer of 1841, but they were sel- dom severe. (Ref. 38, 56, 368.) 1851. May 15. San Francisco, Calif. A severe earthquake lasting half a minute was felt onboard ships in the harbor. It threw merchandise to the floor in San Francisco stores and sent residents rushing outdoors. No damage has been documented for this earthquake. The intensity was taken from ref. 38 and 56. (Ref. 38, 56, 368.) 1852. Nov. 29. Baja California, Mexico. A vio- lent earthquake threw down large fragments of Chimney Rock (now called Picacho Peak) and parts of the surrounding mountains near Fort Yuma, Calif. (located across the Colorado River from what is now Yuma, Ariz.). Sand and water issued from fissures that formed all along the riverbanks and in the low alluvial plain surrounding Fort Yuma. People at the fort had difficulty standing or walking because of the shaking. Felt as far away as San Diego. Observers on the steamer Uncle Sam, Which was about 48 km south of Fort Yuma near Ogdens Land- ing (on the Colorado River), described the effects of the earthquake as follows: “The waters of the river were thrown into a sort of boiling motion with a strong rippled surface. The riverbanks on one side caved in and, on the other side, separated into a thousand cracks from which dust, sand, mud, and water were ejected. The river formed new bends, leaving portions of its old bed so suddenly that thou- sands of fish were left lying on the muddy bottom.” The earthquake caused significant changes in the course of the Colorado River near Pilot Knob, about 10 km downstream from Yuma. The schooner Capac- ity, which was anchored in about 3.5 In of water at the mouth of the Colorado River (about 32 km south of Fort Yuma), was left in about 0.5 m of water after the earthquake. Residents at Fort Yuma observed large steam gey- sers at Laguna de los Volcanoes (in Baja California, about 73 km southwest of Fort Yuma). The steam col- umn was estimated to be more than 300 m in height. Aftershocks, some of which also generated geysers, continued until September 1853. (Ref. 368, 461, 521.) 1852. Dec. 17. San Luis Obispo, Calif. Two sharp earthquakes cracked walls of two adobe houses at San Luis Obispo and threw down part of the wall of another dwelling. (Ref. 38, 56.) 1853. Feb. 1. San Luis Obispo, Calif., area. An adobe house was cracked at San Simeon, and its occupants ran outside. One report described this earthquake as a violent shock that damaged houses. (Ref. 38, 56, 368.) 101 1853. Oct. 23. Off the coast of Humboldt County, Calif., in Humboldt Bay. At Eureka, houses rolled and undulated like ships at sea, and many residents were thrown from their beds. Three heavy shocks were reported. (Ref. 38, 56, 368.) 1855. Jan. 25 (Jan. 24). Sierra County, Calif., area. Buildings in the area were shaken severely by this heavy shock. A large pinnacle of rocks on the Downieville (Sierra) Buttes was thrown down. At the Blue Banks Mine (probably in Sierra or Nevada County), miners at the 122-m level ran outside the mine. Felt from Gibsonville (Sierra County) on the north to Nashville (El Dorado County) on the south and to Keystone Ranch (Yuba County) on the west. The epicenter probably was near the Nevada border. (Ref. 56, 368.) 1855. July 11 (July 10). Near San Gabriel, Los Angeles County, Calif. Bells at the San Gab- riel Mission church were thrown down. 'vaenty-six buildings were damaged in Los Angeles, including the Star Hotel, whose walls were cracked. An adobe building sitting directly on the Raymond fault also was wrecked. Two unusually “heavy” sea waves rolled in at Point San Juan soon after the last of four shocks. (Ref. 38, 56, 368.) 1855. Aug. 27. North of San Francisco, Calif. This earthquake moved furniture at St. Ann's Valley (San Francisco) and cracked an adobe house on a ranch. It was described as violent at Petaluma and at San Francisco de Solano Mission. (Ref. 56, 368.) 1856. Jan. 2. South of San Francisco in San Mateo County, Calif. At San Francisco, masonry walls were cracked and iron shutters were warped. The shock was felt south to Monterey, where some frightened residents ran outside. (Ref. 56, 368, 610.) 1856. Feb. 15. South of San Francisco in San Mateo County, Calif. This strong earthquake threw down cornices, cracked brick walls, and knocked peo- ple from their feet in San Francisco. The water in San Francisco Bay was disturbed. Felt from Peta- luma (Sonoma County) east to Stockton (San Joaquin County) and south to Monterey. (Ref. 38, 56, 368, 610.) 1856. Sept. 21 (Sept. 20). Near Santa Ysabel, San Diego County, Calif. At Santa Ysabel, plaster was shaken down and ceilings fell. The shock also stampeded cattle and terrified residents. Plaster was cracked at San Diego. (Ref. 56, 368.) 1857. Jan. 9. Near Fort Tejon, San Luis Obispo County, Calif. This earthquake occurred on the San Andreas fault, which ruptured from near Parkfield (in the Cholame Valley) almost to Wright- wood (a distance of about 300 km); horizontal dis- placement of as much as 9 m was observed on the 102 Carrizo Plain. It caused one fatality. A comparison of this shock to the San Francisco earthquake, which occurred on the San Andreas fault on Apr. 18, 1906, shows that the fault break in 1906 was longer but that the maximum and average displacements in 1857 were larger. Property loss was heavy at Fort Tejon, an Army post about 7 km from the San Andreas fault. 'IVvo buildings were declared unsafe, three others were damaged extensively but were habitable, and still others sustained moderate damage. About 20 km west of Fort Tejon, trees were uprooted, and build- ings were destroyed between Fort Tejon and Eliza- beth Lake. One person was killed in the collapse of an adobe house at Gorman. Strong shaking lasted from 1 to 3 minutes. Instances of seiching, fissuring, sandblows, and hydrologic changes were reported from Sacramento to the Colorado River delta. Ground fissures were observed in the beds of the Los Angeles, Santa Ana, and Santa Clara Rivers and at Santa Barbara. Sand- blows occurred at Santa Barbara and in the flood plain of the Santa Clara River. One report describes sunken trees, possibly associated with liquefaction, in the area between Stockton and Sacramento. Changes in the flow of streams or springs were observed in the areas of San Diego, Santa Barbara, Isabella, and at the south end of San Joaquin Valley. The waters of the Kern, Lake, Los Angeles, and Mokulumne Rivers overflowed their banks. Changes in the flow of water in wells were reported from the Santa Clara Valley in northern California. Felt from Marysville south to San Diego and east to Las Vegas, Nev. (see fig. 13). Several slight to mod- erate foreshocks preceded the main shock by 1 to 9 hours. Many aftershocks occurred, and two (Jan. 9 and 16) were large enough to have been widely felt. (Ref. 38, 121, 368, 379, 517, 521, 599.) 1858. Nov. 26. North of San Jose in Alameda County, Calif. The earthquake was severe at San Jose, where an adobe house and the corner of a new building were knocked down. A cornice was thrown off a building in San Francisco, and part of a chim- ney collapsed at Mountain View. Felt to Downieville (Sierra County) on the north, Mariposa on the east, and Monterey on the south. (Ref. 38, 56, 368.) 1858. Dec. 16, 02 30 UTC (Dec. 15). Near San Bernardino, Calif. This minor earthquake broke dishes and cracked walls at San Bernardino. It also was felt in Los Angeles. (Ref. 368.) 1858. Dec. 16, 10 00 UTC. Near San Bernar- dino, Calif. At Agua Manza, near San Bernardino, one house collapsed. The gable end of a house was knocked down by the shock at San Bernardino. (Ref. 368, 521.) SEISMICI’I'Y OF THE UNITED STATES, 1568—1989 (REVISED) 1859. Oct. 5. San Francisco, Calif. A severe local earthquake cracked walls in several brick build- ings in San Francisco, downed plaster, and rang bells. (Ref. 56, 368.) 1860. Nov. 13 (Nov. 12). Near Eureka, Hmn- boldt County, Calif. Plaster walls cracked and chim- neys settled at Eureka; a house under construction shifted about 5 cm on its foundation. (Ref. 56, 368.) 1861. July 4 (July 3). Near Dublin, Contra Costa County, Calif. Near the present town of Dub- lin, at Dougherty's Ranch, the roof of the ranch kitchen was thrown off, chimneys were downed, and several men in the fields were thrown to the ground. A fissure about 20 km long, probably the result of surface rupture along the Calaveras fault, opened along the west side of San Ramon Valley. A new spring of water appeared. Although strong at San Francisco, the shock caused no loss to property. Felt north to Sacramento and south to Santa Cruz. (Ref. 38, 56, 368, 493.) 1862. May 27. Near San Diego, Calif. This strong earthquake caused Widespread minor damage in the Old Town and La Playa areas of San Diego. Many adobe and brick buildings sustained cracks, some of which extended completely through the walls. In some frame buildings, windows and doors were loosened in their frames and some door hinges were broken off. Landslides occurred along the steep bluffs from La Playa to Point Loma. At La Playa, north of Point Loma, cracks formed on the beach, and water was emitted from the sand on the tidal flats. Water from the bay surged inland over the beach between 3 and 4 ft. Cracks also formed in the wet, sandy ground near the San Diego River, which “washed over its banks.” This earthquake was felt north to Anaheim and Los Angeles. About 100 aftershocks occurred 'at San Diego to June 14, 1862. (Ref. 38, 56, 368, 532, 610.) 1864. Feb. 26. North of Watsonville in Santa Clara County, Calif. This earthquake cracked adobe walls at Monterey and tipped over or displaced light objects at Watsonville. Described as severe at San Francisco and Santa Cruz, the shock was felt north to Napa and south to San Luis Obispo. (Ref. 56, 368.) 1864. Mar. 5. East of San Francisco in Alameda County, Calif. Walls cracked considerably, plaster cracked, and a few plate-glass windows shat- tered at San Francisco, where the earthquake appar- ently was strongest. A few buildings in San Jose also sustained cracks in plaster. Felt north to Santa Rosa (Sonoma County) and Sacramento and south to San Juan Mission (San Benito County) and Visalia (Tulare County). (Ref. 38, 368.) EARTHQUAKES IN CALIFORNIA 103 124° 122° 120° 118° 116° 114° i 40° I l l l' .Reno '\.\ NEVADA Sacra°mento -\~\. \ 38° . \ \- \. \. \ \ \- \ \. fin ‘ K \' \ ‘ YALIFORNIA \\ \ ‘ Las Vegas \ o ,- 36° .\ \- '\ * ‘\ \. Bake’rsfield VII-IX Il-VI 34° k - 4 ~ ‘ v ' ‘osngeles 4 .7 O / A/ % O R San Diego ES uNlTEQSJAT. . ._ .- Oo ..——-“’"WTJ{EX‘CO 6‘ ‘7’» 32° EXPLANATION ‘ 0 100 KILOMETERS / * Epicenter L——-————v G U L F o F IX Intensity 9 c A L I F o R N I A FIGURE 13.—Isoseismal map for the Fort Tejon, California, earthquake of January 9, 1857. This map is a simplified version of figure 2 in reference 379 of table 1. 1864. May 21 (May 20). Southeast of San Francisco in Alameda County, Calif. At San Francisco a few windows were broken. Felt from Monterey on the south to Sacramento and Santa Rosa (Sonoma County) on the north. (Ref. 56, 368.) 1865. Mar. 8. Bennett Valley, Sonoma County, Calif. Chimneys fell, plaster cracked, and clocks stopped running in Bennett Valley, east of Santa Rosa. The earthquake was described as severe at Santa Rosa. A foreshock was felt in the Santa Rosa-San Francisco 104 area 8 hours earlier. The main shock was felt south to San Francisco and San Leandro. (Ref. 38, 56, 368.) 1865. May 24. South of San Jose, Santa Clara County, Calif. Crockery was broken at San Juan Bautista. The earthquake was “remarkably heavy” in the south San Francisco Bay counties. Felt from San Francisco on the north to Monterey on the south. (Ref. 56, 368.) 1865. Oct. 1. Near Eureka, Humboldt County, Calif. Chimneys and brickwork were dam- aged at Eureka. At Fort Humboldt, south of Eureka on Humboldt Bay, all fort buildings were impaired, redwood trees were uprooted, and a fissure formed along the edge of the parade ground. This shock was reported only in Humboldt and Trinity Counties. (Ref. 38, 56, 368.) 1865. Oct. 8. Santa Cruz Mountains, Santa Clara County, Calif. This strong earthquake caused severe damage in several towns, including New Almaden, Petaluma, San Francisco, San Jose, Santa Clara, and Santa Cruz. Property loss was estimated at $500,000. The shock knocked several houses off foundations at New Almaden and almost destroyed a large brick storehouse. At San Francisco, several poorly con- structed buildings on made land were destroyed, the City Hall was ruined, and water pipes and gas pipes were broken; a crack about 2.5 cm wide formed in Howard Street. On the marshy lands in the Howard Street area, the ground heaved in some places and sank in others. Almost all buildings in Santa Clara and Petaluma were affected to some extent, and every brick build- ing was wrecked at Santa Cruz. The walls of the jail and church fell at San Jose, and several chimneys were knocked down. At Watsonville, the earth cracked in several places, and water flowed through the cracks. Ground cracks also were reported near the San Andreas fault at Mountain Charlie's on the Santa Cruz Road. The tide at Santa Cruz was affected. This earthquake caused damage from San Juan Bautista on the south to Napa on the north. After- shocks were reported in several towns. (Ref. 38, 56, 368, 517, 530, 533, 610.) 1866. Mar. 26. Near Gilroy, Santa Clara County, Calif. Several chimneys were downed in Gilroy. Felt from Santa Rosa (Sonoma County) south to Monterey. (Ref. 56, 368.) 1868. Sept. 4. West of Lone Pine in Tulare County, Calif. A series of earthquakes occurred at the headwaters of the Kern River and at Lone Pine from Sept. 4 to Sept. 17. The earth shook terribly, tall trees swayed, and huge masses of boulders and SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) earth detached from the surrounding cliffs and tum- bled down along the river. At Lone Pine, 40 shocks were reported in 1 hour on Sept. 4. Foreshocks occurred on Sept. 3. (Ref. 38, 56, 368.) 1868. Oct. 21. Near Hayward, Alameda County, Calif. Because of its location in a highly populated area, this earthquake was one of the most destructive in the history of California. Property loss was extensive at towns in the San Francisco Bay area, and 30 people were killed. The total property loss was about $350,000. This earthquake was known as the “great San Francisco earthquake” until the shock on Apr. 18, 1906. Compared to the 1906 shock, the fault trace of the 1868 earthquake—about 32 km—was much shorter, and the amount of movement (0.9 m—whether it was horizontal or vertical is not clear) was much less. Damage was most severe in Hayward and nearby towns along the Hayward fault. Slip was observed on the Hayward fault from San Leandro to Warm Springs, a distance of about 32 km; in places, the fault trace opened 25-30 cm. At Hayward, almost every building was damaged extensively or wrecked. San Jose, which lay in the hills several meters west of the fault trace, had many wrecked buildings and demolished chimneys. At San Leandro, the second floor of the courthouse collapsed, and other buildings were wrecked. At San Francisco, the Custom house sustained severe damage, and many cornices, awnings, and walls fell,‘but, as occurred later in the shock of 1906, well-constructed buildings on firm ground sustained little damage. Damage occurred from Gilroy and Santa Cruz on the south to Santa Rosa on the north. The area shaken at MM intensity ~VIII or higher includes about 2,300 kmz. Strong aftershocks continued into November 1868. (Ref. 38, 56, 368, 517, 521, 530, 533.) 1869. Oct. 8. Near Ukiah, Mendocino County, Calif. This earthquake downed chimneys at Ukiah and in “the Clear Lake country.” Felt from Healds- burg (Sonoma County) north to Potter Valley. (Ref. 56, 368.) 1870. Feb. 17. Near Santa Cruz, Calif. At Los Gatos, several chimneys were knocked down, and at Santa Cruz, chimneys were dislocated. Felt‘south to Monterey and north to Sacramento. (Ref. 56, 368.) 1870. Apr. 2. Near Oakland, Contra Costa County, Calif. Minor damage occurred in Oakland and San Francisco. The shock also was felt in Santa Cruz, Santa Rosa, and Stockton. (Ref. 56, 368.) 1871. Mar. 2. Near Mattole, Humboldt County, Calif. Almost every chimney was knocked to the ground at Mattole, and ground fissures were EARTHQUAKES IN CALIFORNIA 105 3.: 1’?! m a R“? We ._ s... h s4,» , s. they], ,, - .q 1.!" 'w e . Courthouse at San Leandro, California, wrecked by the October 21, 1868, earthquake. (Photograph by University of California, Berkeley.) observed near Mattole. Many chimneys also were ruined at Bucksport, Hydesville, Petrolia, and Rohnerville. The earthquake shook cornices from some buildings at Eureka and damaged the light- keeper's house at Mendocino. A dozen aftershocks were reported at Mattole. ,(Ref. 38, 56, 368.) 1871. July 5. Near Lone Pine, Inyo County, Calif. Near Lone Pine, some wells went dry and oth- ers became muddy. People ran out of buildings at Swansea. This possible foreshock to the 1872 Owens Valley earthquake was felt northwest to Bear Valley in Mariposa County. (Ref. 38, 56, 368.) 1872. Mar. 26, 10 30 UTC. Owens Valley, near Lone Pine, Inyo County, Calif. The most devastat- ing effects of this earthquake occurred at Lone Pine, where 52 of 59 houses (mostly constructed of adobe or stone) were destroyed and 27 people were killed. A few fatalities also were reported in other parts of Owens Valley. One report states that the main build- ings were thrown down in almost every town in Inyo County. About 100 km south of Lone Pine, at Indian Wells, adobe houses sustained cracks. Property loss has been estimated at $250,000. Faulting occurred on the Owens Valley fault along a line a few km east of the Sierra Nevada escarp— ment. The faulting near Lone Pine involved both dip- slip and right-lateral components of movement. The largest amount of surface deformation was observed between the towns of Lone Pine and Independence, but fault scarps formed along a length of at least 160 km—from Haiwee Reservoir, south of Olancha, to Big Pine; cracks formed in the ground as far north as Bishop. The largest horizontal displacement of 7 In was measured on the fault scarps west of Lone Pine. The vertical offsets clearly were smaller, averaging about 1 m with the downthrown block on the-east. A comparison of this earthquake to the earth- quakes of 1857 and 1906 on the San Andreas fault shows the felt area and maximum fault displace— ments to be comparable. However, the shocks on the San Andreas fault ruptured the fault for signifi- Y cantly larger distances—300 km in 1857 and 430 km in 1906. This earthquake stopped clocks and awakened peo- ple at San Diego to the south, Red Bluff to the north, and Elko, Nev., to the east. MM intensity VIII or larger was observed over an area of about 25,000 km2, and MM intensity IX or larger was observed over an area of about 5,500 km2 (see fig. 14). The shock was felt over most of California and much of Nevada. Thousands of aftershocks occurred, some severe. (Ref. 38, 368, 521, 531, 533.) 106 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) A 23-ft-high fault scarp caused by the March 26, 1872, Owens Valley, California, earthquake. (Photograph by W.D. Johnson.) 42° 40° 38° 36° EARTHQUAKES IN CALIFORNIA \\ : Sacramento . I \. -— - \\ NP )\/ I San Fran’.‘ CALIFORNIA ‘ \~. V" I csco .\\ \\ I I ‘\ VIII\-\ \ I \ ‘~ \\ I \ IX \ | \'\| I Fresno * \ I I \ I 34° 0 6‘ .7 0 190 KILOMETERS EXPLANATION ‘k Epicenter IX Intensity 9 San Diego \ \ ....—- Las Vegas TES .J UNITED STA...— - 7 MEXICO i r ..................... .I. ........... _ _.__ __._I_.__._._ _._._.-._._._.| I I I I I I I I I I I /// I Red Bluff ' I I / \L/ NEVADA EurekaV \II I \ I L'\. ,r/ \ I I I I I II ‘I II I | FIGURE 14 —Isoselsmal map for the Owens VaIIey, California, earthquake of March 26, 1872. This map is a sunphfied versmn of the map in reference 368 of table 1. 107 108 1872. Mar. 28. Near Sierraville, Sierra County, Calif. In Sierraville, bottles and chinaware in stores were broken. In Reno, Nev., the earthquake reportedly was stronger than the large Owens Valley earthquake, 2 days earlier. Also felt at Grass Valley. (Ref. 368.) 1872. Apr. 11. Near Round Valley, Inyo County, Calif. At Round Valley, stone buildings were knocked down and a frame structure was twisted on its foundation. Although this shock was felt at Susanville in Lassen County, the main shock of the Owens Valley earthquake on Mar. 26, 1872, was not reported felt there. (Ref. 368.) 1872. Apr. 18. Near Cerro Gordo, Inyo County, Calif. This rather small aftershock of the Owens Valley earthquake was reported only from Cerro Gordo. It was described as being of “unusual severity.” (Ref. 56, 368.) 1872. May 3 (May 2). Imperial Valley area, Calif. A building was cracked and people ran into the streets in Arizona City (Yuma). It also was reported at San Bernardino, 300 km northwest of Arizona City. (Ref. 368.) 1872. May 17. Owens Valley, near Lone Pine, Calif. Furniture in a house was violently dis- turbed at Lone Pine, and one person was thrown from his chair. (Ref. 56, 368.) 1873. Nov. 23 (Nov. 22). Near Crescent City, Del Norte County, Calif. All chimneys were knocked down in the Smith River valley. Chimneys also fell at Crescent City, and hardly a brick building in the town escaped damage. Chimneys were dam- aged in many places as far north as Port Orford, Oreg., and east to Jacksonville, Oreg. Cracks in the ground were observed on the trail from Crescent City to Gasquet in Del Norte County. Felt south to San Francisco and north to Portland, Oreg. (Ref. 38, 56, 368, 521.) 1875. Jan. 24. South of Janesville in Plumas County, Calif. One chimney was downed at Janes- ville, and stone walls sustained cracks at Susanville (Lassen County). This shock awakened residents as far south as Sacramento. (Ref. 56, 368.) 1875. Sept. 30. Near Eureka, Humboldt County, Calif. At Eureka, most chimneys were cracked and some were knocked down. Residents of Weaverville in Trinity County were awakened. (Ref. 368.) 1876. May 29. Freestone, Sonoma County, Calif. At Freestone, some plaster was cracked and bottles and crockery were overturned. (Ref. 368.) 1878. May 9 (May 8). Near Petrolia, Hum- boldt County, Calif. At Petrolia, all chimneys in the city were knocked down. The earthquake also SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) triggered large landslides along the coast in southern Humboldt County. (Ref. 368.) 1878. June 12 (June 11). Los Angeles, Calif. This earthquake shook down plaster and broke glass- ware at Los Angeles. Four distinct shocks occurred on June 12. (Ref. 463.) 1879. Feb. 4. Visalia, Tulare County, Calif. 'IVvo shocks occurred at Visalia, the second of which was the strongest. The second shock, which was felt over all the surrounding country, cracked walls and overturned furniture. (Ref. 56, 463.) 1880. Dec. 19. San Bernardino, Calif. Walls of the courthouse building were cracked from top to bottom. Three shocks were reported at Los Angeles. The main shock was felt south to San Diego. (Ref. 56, 463.) 1881. Feb. 2 (Feb. 1). North of Imusdale, San Luis Obispo County, Calif. In Imusdale, at the north end of Cholame Valley, several chimneys were knocked down and an adobe storeroom and part of an adobe barn collapsed. Large cracks extending across the road were reported. (Ref. 56, 368.) 1881. Apr. 10. Southwest of Modesto, Stanis- laus County, Calif. Minor damage to property was reported from Hollister to Stockton. Chimneys were damaged in the Modesto region. Felt from Greenville (Plumas County) on the north to Visalia (Tulare County) on the south. (Ref. 38, 56, 368.) 1882. Mar. 6. East of Hollister, San Benito County, Calif. Windowpanes were broken at Sali- nas, and crockery was broken at Hollister. The shock, which was rather strong at Charleston and Merced, was reported from San Francisco on the north to San Luis Obispo on the south. Many aftershocks occurred. (Ref. 38, 56, 368.) 1882. June 27. Santa Cruz area, Calif. Chim- neys were overturned and windows were broken in the Santa Cruz Mountains. The walls of several buildings were cracked severely at San Jose, and crockery and glassware were broken at San Fran— cisco. Reports from towns along the coast between Hollister and Petaluma (and as far east as Stockton) state that this shock was the most severe since the October 1868 earthquake. (Ref. 56, 463.) 1883. Mar. 30. Near Gilroy, Santa Clara County, Calif. This earthquake knocked down chim- neys at Old Gilroy and Sargents. Plaster fell in all brick buildings at Hollister, and several large win- dows were broken; slight damage was sustained at Santa Cruz and Watsonville. At Gilroy, 8 to 12 after- shocks were reported, two of which were felt widely. The main shock was felt from Sacramento south to San Luis Obispo. (Ref. 38, 56, 368.) EARTHQUAKES IN CALIFORNIA 1883. Sept. 5. Off the coast near Santa Bar- bara, Calif. Plaster fell at Santa Barbara, and bot- tles were overturned at Los Alamos. Felt along the coast from Cayucos (near San Luis Obispo) south to Wilmington (Los Angeles County). (Ref. 38, 56, 368.) 1884. Mar. 26 (Mar. 25). Near Santa Cruz, Calif. Plaster fell, walls cracked, and vvindowpanes broke at Santa Cruz. Similar effects were reported at San Francisco. Felt along the coast from Monterey north to Santa Rosa (Sonoma County). (Ref. 56, 368.) 1885. Jan. 31 (Jan. 30). Near Susanville, Las- sen County, Calif. Chimneys were damaged in the Honey Lake Valley towns of Buntingville and Susan- ville. Shocks were most severe near Janesville. Felt north to Alturas (Modoc County), south to Sacra- mento, and at a few towns in Nevada. More than 100 aftershocks were felt in the area to Feb. 8, 1885. (Ref. 38, 56, 368.) 1885. Mar. 31 (Mar. 30). South of Hollister, San Benito County, Calif. Chimneys were thrown down at Mulberry, and plaster fell at Hollister. Extensive fissures formed in the soft riverbanks at the junction of the Pajaro and San Benito Rivers. The shock was reported felt as far north as San Rafael. One foreshock and three aftershocks were felt at Hollister on Mar. 31. (Ref. 38, 56, 368.) 1885. Apr. 12 (Apr. 11). Southern San Benito County, Calif. This earthquake threw down two chimneys at Las Tablas, 48 km northwest of San Luis Obispo. Slight damage was reported at Monterey (where cracks in adobe walls were wid- ened), Salinas, and San Luis Obispo. Felt north to Marysville (Yuba County), south to Ventura, and east to Keeler (Inyo County). Toppozada and Wong (ref. 612) have determined that this event was located about 50 km northwest of the May 2, 1983, Coalinga earthquake. Toppozada (1991, oral commun.) has also determined that the April 2, 1885 earthquake was located about 50 km southeast of its listed location and was near the location of this April 12 event. (Ref. 38, 56, 368.) 1885. Aug. 1 (July 31). Near Cloverdale, Sonoma County, Calif. A strong local earthquake cracked walls in several buildings at Cloverdale. It was not reported in nearby towns. (Ref. 38, 368.) 1886. Apr. 14 (Apr. 13). Inyo County, Calif. This local earthquake broke considerable crockery and dishes in Lida Valley on the California-Nevada border. A dull, thunderlike noise preceded the shock. (Ref. 54.) 1887. Dec. 3. Near Halfway House, Mendo- cino County, Calif. At Halfway House, on the road from Mendocino to Ukiah, chimneys were 109 downed and a stove overturned. A chimney was cracked at Christine, and clocks stopped at Ukiah. (Ref. 56, 368.) 1888. Feb. 29. North of Petaluma, Sonoma County, Calif. A sharp earthquake cracked the walls of several buildings at Petaluma. Felt north to Geyserville (Sonoma County) and south to San Fran- cisco. (Ref. 38, 56, 368.) 1888. Apr. 14 (Apr. 13). Alturas, Modoc County, Calif. The earthquake rang a school bell and knocked down plaster at Alturas. It was reported felt only at a few towns in the area. (Ref. 368.) 1888. Apr. 29 (Apr. 28). Near Cromberg, Plu- mas County, Calif. Chimneys were downed at Cromberg, at the north end of Mohawk Valley. Rock- slides were reported north of Downieville on the North Fork of the North Yuba River and in Rattle- snake Canyon. South of Cromberg, walls of the court- house were cracked at Nevada City, and tops of chimneys were knocked off at Grass Valley. Felt from San Francisco northeastward into Nevada. Many aftershocks were felt during the night in the Down- ieville area. (Ref. 38, 56, 368.) 1888. Nov. 18. San Francisco Bay area, Calif. Several chimneys were overthrown at East Oakland and Oakland, which lie at the southern limit of the felt area. Felt from Napa south to San Lorenzo. Two slight aftershocks were felt at Oak- land. (Ref. 38, 56, 368.) 1889. Apr. 15 (Apr. 14). Near Santa Cruz, Calif. This shock cracked plaster in several houses in Santa Cruz. Felt from Corral de Tierra (Monterey County) north to Martinez (Contra Costa County). (Ref. 56, 368.) 1889. May 19. West of Antioch, Contra Costa County, Calif. Many chimneys were demolished at Antioch, and two small fissures formed on Main Street. At Collinsville, one house was toppled and chimneys were knocked down. Slight loss to property also was reported at Lodi, Napa, Rio Vista, and San Francisco. Felt north to Nevada City, south to Santa Cruz, and east to Sonora (Tuolumne County). (Ref. 38, 368.) 1889. June 20 (June 19). North of Susanville, Lassen County, Calif. The earthquake was most severe in the Susanville—Willow Creek area, where chimneys were thrown down, and the water in Eagle Lake was muddied. As many as 75 aftershocks occurred, 28 of which were felt within 2 hours of the main event. Felt north to Alturas (Modoc County), south to Sacramento, and east to Virginia City, Nev. (Ref. 38, 56, 368.) 1889. July 31. San Francisco Bay area, Calif. Chimneys were knocked down at Oakland and San 110 Leandro, and a brick pier was cracked at the Chabot Observatory in south Oakland. Felt from Salinas (Monterey County) north to Healdsburg (Sonoma County) and east to Modesto (Stanislaus County). Aftershocks were reported felt at San Francisco. (Ref. 38, 56, 368.) 1889. Aug. 28 (Aug. 27). Near Pomona, Los Angeles County, Calif. Windows and crockery were cracked and broken at Pomona, where two distinct shocks threw several people to the floor. Several towns between Los Angeles and Ontario reported minor damage, including fallen plaster and bottles knocked from store shelves. Felt mainly over an east- west area from San Jacinto in the east to Santa Monica in the west. (Ref. 38, 56, 368.) 1890. Feb. 9. Northeast San Diego County, Calif. It is inferred from the lack of reports of dam- age that the epicenter was in the sparsely populated region between Los Angeles and Yuma, Ariz. Win- dows were broken at Pomona, and residents were awakened, but little loss was reported in the region. Telegraph dispatches from all towns along the South- ern Pacific Line (from Pomona to Yuma) reported the shock was of equal intensity at each town. A possible foreshock on Feb. 6 was reported felt from San Ber- nardino to San Diego. (Ref. 38, 56, 368.) 1890. Apr. 24. Near Corralitos, Santa Cruz County, Calif. This severe earthquake caused exten- sive loss of chimneys and some damage to brick and frame buildings from San Juan Bautista to Green Val- ley. Chimneys were knocked over at Watsonville and Corralitos, and buildings were twisted on their foun- dations at Corralitos. The San Andreas fault probably ruptured in the area where it crosses the Pajaro River. Fissures were reported on or near the fault, and a railroad bridge across the Pajaro River (near the fault) shifted about 5 m out of alignment. Aftershocks occurred for many days. (Ref. 38, 56, 368.) 1890. July 26. Near Ferndale, Humboldt County, Calif. A severe earthquake knocked down chimneys at Grizzly Bluff (near Ferndale) and at the Walker residence (near Petrolia). Although strong at Eureka and Mendocino City, the shock caused little or no damage. A spring at the Walker “place” that had stopped flowing 3 days before the shock became murky and flowed at a faster rate than before. An aftershock at 16 00 UTC was reported at Ferndale, Hydesville, and Rohnerville. The main shock was reported from Crescent City and Sisson (Mt. Shasta City) in the north to Petaluma (Sonoma County) in the south. (Ref. 38, 56, 368.) 1891. Jan. 2. Near San Jose, Santa Clara County, Calif. At Mount Hamilton, several large SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) pieces of plaster were dislodged and ceilings cracked. Plaster was knocked to the floor at Santa Cruz, and Windows were broken at San Jose. Although this earthquake was strong at Gilroy, little or no damage was reported. Felt to Vallejo in the north, Monterey in the south, and Merced in the east. (Ref. 38, 56, 368.) 1891. Oct. 12 (Oct. 11). Near Napa, Calif. In Napa and Sonoma, many chimneys were overthrown and several brick buildings were cracked and thrown out of plumb. Not one house in Sonoma Valley escaped damage of some kind. A foreshock was felt at Napa and Sonoma at 05 15 UTC, and many after- shocks were observed. The main shock was felt north to Lakeport and Colusa and south to Salinas. (Ref. 38, 56, 368.) 1892. Feb. 24 (Feb. 23). California-Mexico border area. At the old Carrizo station in San Diego County, all adobe buildings were destroyed. In Para- dise Valley, a church and schoolhouse built on stilts were knocked down and demolished; chimneys and plaster were broken in San Diego. Ground fissures were reported at McCain Valley and Jewel Valley; rockslides were observed between Campo and Carrizo and at Dulzura and Jewel Valley. About 155 tremors were felt at Campo during the 12 hours following the main shock, and aftershocks continued there every few days into April 1892. Observers reported that 135 aftershocks were felt as far away as National City, on San Diego Bay. Felt north along the coast to Santa Barbara, east to Yuma, Ariz., and south to San Quintin, Baja Califor- nia. One report stated that the tremor was felt at Visalia, Tulare County, about 700 km north of San Quintin. (Ref. 38, 56, 368, 521.) 1892. Apr. 19. Near Vacaville, Solano County, Calif. This earthquake caused severe damage at Allendale, Dixon, Vacaville, and Winters. Property loss was estimated at $225,000, and one fatality was reported. At Allendale, between Vacaville and Winters, sev- eral buildings in the area collapsed, shifted off their foundations, or were wrenched apart. Ground fis- sures formed near Allendale, which suggests possible faulting. At Vacaville, almost all brick structures were destroyed, many frame buildings were impaired, and chimneys were twisted or knocked to the ground. Similar damage was reported from Win- ters (Yolo County). Although damage in general was less serious in Dixon, many school buildings were almost ruined. MM intensity VIII or higher was observed over an area of 1,100 km2. Felt north to Redding, east to Virginia City, Nev, and south to Salinas and Fresno. (Ref. 38, 56, 368, 533, 599.) EARTHQUAKES IN CALIFORNIA 111 Brick walls of a hotel in Winters, California, collapsed by the April 19, 1892, earthquake. (Photograph from California Geology.) 1892. Apr. 21. Near Winters, in Solano County, Calif. Weakened structures in the commu- nities hit by the Apr. 19 earthquake were further damaged. At Winters, where the damage was most severe, many buildings that withstood the Apr. 19 shock were leveled. Not one building on Main Street was left habitable. At Esparto, every brick chimney fell and wood-frame buildings were wrenched out of shape. Many chimneys were wrecked at Sacramento and Woodland, but additional loss was slight at Dixon and Vacaville. The area shaken at MM inten- sity VIII or larger was about 890 km2, but the gen- eral felt area was about the same as that of the Apr. 19 shock. (Ref. 38, 56, 368.) 1892. Apr. 30 (Apr. 29). Near Davis, Solano County, Calif. This aftershock 0f the Apr. 19 earth- quake knocked a few loose bricks from buildings at Davisville (Davis) and sent people at Sacramento run- ning from their houses. Felt from San Jose north to Yuba City and east to Carson City, Nev. (Ref. 56, 368.) 1892. Nov. 13. West of Hollister, San Benito County, Calif. At Hollister, a chimney was displaced and plaster fell; at Monterey, chimneys were cracked; and at Salinas, windows and dishes were broken. Three less severe aftershocks were felt at Hollister. Felt from Monterey north to Napa. (Ref. 38, 56, 368.) 1893. Apr. 4. Near Newhall, Los Angeles County, Calif. Northwest of Newhall, an old but sturdy adobe house was shaken down at the} Newhall Ranch. In the area of Newhall and Pico Canyon, chimneys were wrecked, the ground was fissured, and boulders were shaken down the hillsides. After- shocks were reported almost daily at Tapo Ranch in the Simi Hills. Felt from Santa Barbara east to San Bernardino. (Ref. 38, 56, 368.) 1893. Aug. 9. East of Santa Rosa, Sonoma County, Calif. Most of the loss to property occurred at Santa Rosa: chimneys were downed, plaster in the courthouse was cracked and broken, and windows were broken. At Petaluma, plaster was cracked and crockery was thrown from shelves. Felt north to Mid- dletown (Lake County), south to Alameda, and east to Sacramento. (Ref. 38, 368.) 1894. July 30 (July 29). Northwest of San Bernardino, Calif. An earthquake caused minor damage from the Los Angeles basin to Mojave in 112 Kern County. At Los Angeles, three distinct tremors broke a few vvindowpanes and knocked bottles of ink off shelves. Earlier in the evening, several foreshocks were reported at Riverside. Felt north to Mojave and south to San Diego. (Ref. 56, 368.) 1894. Sept. 30. Southern Hmnboldt County, Calif. This earthquake knocked down chimneys in southern Humboldt County. It was felt strongly on two schooners at sea, about 56 km southwest of Shel- ter Cove. An aftershock was felt at Eureka and Men— docino at 17 58 UTC. The main shock was reported north to Crescent City, south to Ukiah, and east to Bedding and Sisson (Mt. Shasta City). (Ref. 38, 368). 1894. Oct. 23. Near San Diego, Calif. Plaster was broken and brick walls were cracked in San Diego; mission bells rang in San Juan Capistrano (Orange County). A dust cloud was seen along the summit of the mountains above Buckman's Springs, and boulders were heard rolling down the canyons. Several aftershocks were felt in the area through Oct. 28. Felt north to Los Angeles and San Bernar— dino. (Ref. 38, 56, 368.) 1896. Aug. 17. Near Independence, Inyo County, Calif. This earthquake probably occurred along or near the eastern front of the Sierra Nevada. “Crumbled adobes slid to the ground” at Indepen- dence. Loose plaster was knocked down at Hanford, and clocks stopped as far distant as Bakersfield and Merced. The shock was felt from Big Pine (Inyo County), west to Merced, and south to Bakersfield. (Ref. 56, 368.) 1897. June 20. Near Gilroy, Santa Clara County, Calif. The earthquake caused much loss to brick buildings in the Gilroy—San Felipe area. Few brick structures escaped damage at Hollister; chim- neys were thrown down and fire walls fell into the street at Salinas. Damage in Gilroy was similar to that in Hollister and Salinas. A fissure was observed near Soap Lake House on the Pacheco Pass Road, and a fissure 295 In long formed on a ranch near San Felipe. Because the Calaveras fault crosses the Pacheco Pass Road 5 km northwest of San Felipe, the fissures could have resulted from rupture on the Calaveras. Felt from Woodland on the north to San Luis Obispo on the south and Visalia (Tulare County) on the east. (Ref. 38, 56, 368.) 1898. Mar. 31 (Mar. 30). Southern Sonoma County, Calif. At Mare Island Naval Yard and Tubbs Island, several buildings either partly or totally collapsed. Property loss was estimated at $350,000. The earthquake also caused severe damage at Schellville, Greenwood Estate, and along Petaluma Creek in Sonoma County, where houses were moved off their foundations. Extensive cracks developed in SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) the ground at Greenwood Estate, Mare Island Naval Yard, and Schellville. Moderate damage occurred in San Francisco. Felt north to Chico, east to Carson City, Nev, and south to Monterey. Magnitude 6.5 Ms ELL. (Ref. 56, 368, 521, 615.) 1898. Apr. 15 (Apr. 14). Near Greenwood, Mendocino County, Calif. Two wood-frame houses were wrecked at Greenwood, and one was toppled at Noyo. Chimneys were knocked down in several towns in Mendocino County, including Fort Bragg, Little River, Mendocino, Pine Grove, and Ukiah. Property loss at Point Arena included cracking of the lighthouse tower. Cemetery monuments fell or were twisted on their bases at Mendocino. Landslides and fallen trees made the mountain roads east of Mendo- cino impassable. A foreshock was felt at Mendocino at 06 45 UTC, and many aftershocks were felt there. The main shock was felt north to Eureka, east to Red Bluff and Willows, and south to San Francisco. Mag— nitude 6.7 Ms ELL. (Ref. 38, 56, 368, 521, 615.) 1899. Apr. 16. Off the coast of Humboldt County, west of Eureka, Calif. This long-duration earthquake caused some minor impairment to a flue at a lumber mill in Eureka. It was described as one of the most severe shocks ever experienced. Felt along the coast from Crescent City on the north to Albion (Mendocino County) on the south. (Ref. 38, 56, 368, 521.) 1899. Apr. 30. Near Watsonville, Santa Cruz County, Calif. Damage from this earthquake included downed chimneys and displaced cemetery monuments in Green Valley and Watsonville, fallen plaster in Hollister, and broken crockery and win- dowpanes in Salinas. Felt from southern Sonoma and Napa Counties on the north to northern Monterey County on the south. (Ref. 38, 56, 368.) 1899. June 2 (June 1). Near San Francisco in northern San Mateo County, Calif. In San Fran- cisco, chimneys were knocked down, parts of several cornices fell, and windows and glassware were bro- ken. Chimneys also were toppled in Oakland. This moderate earthquake was felt south to Santa Cruz, north to Calistoga and Sacramento, and east to Modesto (San Joaquin County). (Ref. 38, 368.) 1899. July 6. Northeast of Watsonville in Santa Clara County, Calif. Several chimneys were toppled at Watsonville; a few lamp chimneys and win— dows were broken in Salinas. At Pleasanton (Alameda County), about 85 km north of Watsonville, brick buildings were cracked, and some wooden structures were “more or less twisted.” Because the intensities at sites between these two towns were not high (MM intensity V—VI), there may have been. two earth- quakes at about the same time—one near Watsonville EARTHQUAKES IN CALIFORNIA and the other near Pleasanton. Felt north to Napa, south to San Luis Obispo, and east to Merced and beyond. (Ref. 56, 368.) 1899. July 22, 00 46 UTC (July 21). West of Squirrel Inn, San Bernardino County, Calif. This foreshock to the earthquake at 20 32 UTC (see below) knocked off tops of chimneys at Squirrel Inn. Landslides were reported in the Cajon Pass area. Felt north to Barstow, west to Santa Monica (Los Angeles County), and south to San Diego. (Ref. 368.) 1899. July 22, 20 32 UTC. Lytle Creek Can- yon, San Bernardino County, Calif. North of San Bernardino, in Lytle Creek Canyon, one old adobe house was knocked down. Streams greatly increased their flow of water in the mountains north of Cucamonga and San Bernardino, and extensive landslides were observed. This severe earthquake caused loss to property from Anaheim to Barstow. Felt north to Barstow, west to Ventura, and south to San Diego. Nine aftershocks were felt in the San Bernardino area. Magnitude 5.6 Ms ELL (Ref. 38, 56, 368, 521.) 1899. Oct. 13 (Oct. 12). Near Santa Rosa, Sonoma County, Calif. This earthquake toppled some chimneys and knocked plaster from walls in Santa Rosa. It was felt only to Petaluma, about 23 km south of Santa Rosa. Aftershocks were reported in the area. (Ref. 38, 368.) 1899. Dec. 25. Hemet—San Jacinto, Riverside County, Calif. Property damage from this earth- quake was most severe at Hemet and San Jacinto, west of Palm Springs. Six people were killed by fall- ing adobe walls at Saboba, a few kilometers east of San Jacinto. The estimated property loss of about $50,000 appears to be low. Only two chimneys remained standing in Hemet, where brick buildings partly collapsed and wood- frame buildings shifted off their foundations. A ground fissure about 46 m long extended under a house near Hemet; the house was wrenched and twisted severely. The fissure may have been surface rupture in the San Jacinto fault zone. Many brick buildings were partly wrecked at San Jacinto. At Riverside, chimneys were overthrown, and brick buildings were cracked. This severe shock was felt north to Bakersfield (Kern County), south to Jacumba (San Diego County), and northeast to Nee- dles (San Bernardino County). It also was reported felt at Seligman, Ariz. Many aftershocks occurred on Dec. 25 and 26. Magnitude 6.6 MLa DMG. (Ref. 38, 56, 368, 384.) 1901. Mar. 3 (Mar. 2). Near Parkfield, Monterey County, Calif. Chimneys were toppled at Bradley, Echo Valley, Parkfield, Slacks Canyon, 113 Stone Canyon, and Warthan Canyon. At Parkfield, three houses were twisted out of shape and one was almost wrecked. Slight loss to property also was incurred at Adelaida, El Monte, Estrella, Monterey, Paso Robles, and San Miguel. Ground cracks as much as several meters in length and 15—30 cm in width and vertical displacement of about 30 cm were observed in Stone Canyon. Felt from San Francisco on the north to San Luis Obispo on the south and Porterville (Tulare County) on the east. Magnitude 5.8 MLa DMG. (Ref. 38, 56, 381.) 1902. May 19. South of Elmira, Solano County, Calif. Almost all chimneys fell at Elmira, and every flue was out of line; a few chimneys top- pled at Vacaville, where many brick buildings were cracked badly. Only slight damage occurred at Fair— field, Nevada City, and Suisun City. Felt north to Colusa, south to San Francisco, and east to Ione (Amador County) and beyond. (Ref. 38, 56, 381.) 1902. July 28 (July 27). Near Los Alamos, Santa Barbara County, Calif. At Los Alamos, store buildings were damaged, chimneys were bro- ken, and walls were cracked. Two tanks, each con- taining about 3,000 barrels of oil, were destroyed on the property of the Western Union Oil Company. An adobe house at the Orena Ranch, a few kilometers south of Lompoc, was affected severely and later destroyed by the July 31 aftershock. At Lompoc, chimneys toppled, one brick building was ruined, and pipelines were broken; at Santa Maria, several chimneys fell from buildings. Felt along the coast from San Luis Obispo to Ventura. Many aftershocks occurred. (Ref. 38, 56, 381.) 1902. July 31; Aug. 1 (July 31). Near Los Ala- mos, Santa Barbara County, Calif. Two strong earthquakes affected Los Alamos and environs, and many slight shocks were felt during the day. The two events are described together because the effects for each cannot be separated. These earthquakes “com- pleted the ruin” begun on July 28. All houses were damaged at Los Alamos, and not one chimney was left upright. The main effects were confined to an area about 24 km long and 6 km wide. Fissures formed in the ground, landslides occurred, and water began flowing in a formerly dry streambed. The shocks were felt along the coast from Cayucos (San Luis Obispo County) to Oxnard (Ventura County). (Ref. 38, 56, 380, 381.) 1902. Dec. 12. Near Los Alamos, Santa Bar- bara County, Calif. At Santa Maria, plaster fell in many houses and walls of a brick school were cracked. Dishes and glassware were thrown from shelves at Los Alamos. (Ref. 38, 56, 380.) 114 1903. June 11. Near San Jose, Santa Clara County, Calif. One chimney fell, other chimneys lost their tops, and a brick wall was downed at San Jose. A few chimneys also toppled at Hayward, Liv— ermore, Santa Cruz, and Watsonville. Felt north to Fort Ross (Sonoma County) and south to King City (Monterey County). Because an earthquake also was reported at San Luis Obispo, it is possible that there were two different events. Magnitude 5.4 Ms ELL. (Ref. 38, 56, 381, 521.) 1903. July 24. Near Willows, Glenn County, Calif. At Willows, plaster fell from many buildings and several brick walls were cracked. Felt from Sac- ramento north to Greenville (Plumas County) and from Willows east to Nevada City (Yuba County). (Ref. 38, 56.) 1903. Aug. 3 (Aug. 2). Near San Jose, Santa Clara County, Calif. Few large buildings in San Jose were left undamaged, and many were damaged severely. Scores of chimneys were shaken down; brickwork on many of the larger buildings was ruined; and stone trimmings fell to the streets. At Evergreen, a few kilometers southwest of San Jose, one house was shifted on its foundation, and another house lost its chimney. Chimneys were broken to the roofline in Santa Clara. Only slight loss to property was reported at Edenvale, Mount Hamilton, Oak- land, San Francisco, Santa Cruz, and Stockton. Felt from Guerneville on the north to Jamesburg on the south to Stockton on the east. Magnitude 5.3 Ms ELL. (Ref. 38, 381, 521.) 1903. Dec. 25. Los Angeles, Calif., region. Plas- ter and bricks were knocked down in Los Angeles, and bottles were thrown to the floor in a drug store. The shock also was reported at Pasadena, Riverside, San Bernardino, and Sierra Madre. (Ref. 38, 56.) 1905. July 15. Near San Bernardino, Calif. No damage could be documented for this earthquake. The intensity listed was taken from ref. 56. (Ref. 56, 380.) 1905. Sept. 3 (Sept. 2). Los Angeles, Calif., region. Plaster fell in the "Baker block" of Los Angeles, and a heavy bookcase was overturned in the City Hall. (Ref. 56, 380.) 1905. Dec. 23. Bakersfield, Kern County, Calif. Wide cracks formed in buildings in Bakers- field, and large quantities of plaster fell as a result of this strong local earthquake. Objects were thrown from shelves. Two small foreshocks occurred. (Ref. 38, 56, 380.) 1906. Apr. 18. Near San Francisco, Calif. This earthquake is one of the most devastating in the history of California. The earthquake and resulting fires caused an estimated 3,000 deaths and $524 million in property loss. Damage in San Francisco SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) resulting only from the earthquake was estimated at $20 million; outside the city, it was estimated at $4 million. The sensible duration of the shaking in San Francisco was about 1 minute. The earthquake damaged buildings and structures in all parts of the city and county of San Francisco, although over much of the area, the damage was moderate in amount and character. Most chimneys toppled or were badly broken. In the business dis- trict, which was built on ground made by filling in the cove of Yerba Buena, pavements were buckled, arched, and fissured; brick and frame houses of ordi- nary construction were damaged extensively or destroyed; sewers and water mains were broken; and streetcar tracks were bent into wavelike forms. On or near the San Andreas fault, buildings were destroyed (one was torn apart), and trees were knocked to the ground. The surface of the ground was torn and heaved into furrow-like ridges. Roads crossing the faultline were impassable, and pipelines were broken. One pipeline that carried water from San Andreas Lake to San Francisco was broken, shutting off the water supply to the city. The fires that ignited soon after the onset of the earthquake quickly raged through the city because of the lack of water to control them. They destroyed a large part of San Francisco and intensified the loss at Fort Bragg and Santa Rosa. This earthquake caused the most lengthy rupture of a fault that has been observed in the contiguous United States. The displacement of the San Andreas Fault was observed over a distance of 300 km from San Juan Bautista to Point Arena, where it passes out to sea. Additional displacement was observed far- ther north at Shelter Cove in Humbolt County, and, assuming the rupture was continuous, the total length of rupture would extend to 430 km. The larg- est horizontal displacement—6.4 m—occurred near Point Reyes Station in Marin County. In areas where dislocation of fences and roads indi- cated the amount of ground movement, motions of 3 to 4.5 m were common. Near Point Arena, in Mendo— cino County, a fence and a row of trees were dis- placed almost 5 m. At Wright's Station, in Santa Clara County, a lateral displacement of 1.4 m was observed. Vertical displacement of as much as 0.9 m was observed near Fort Ross in Sonoma County. Ver- tical displacement was not detected toward the south end of the fault. . Although Santa Rosa lies about 30 km from the San Andreas fault, damage to property was severe, and 50 people were killed. The earthquake also was severe in the Los Banos area of the western San Joaquin Valley, where the MM intensity more than EARTHQUAKES IN CALIFORNIA 115 The new stone-faced brick library at Stanford University, Palo Alto, California, was destroyed by the San Francisco, California, earth- quake on April 18, 1906. (Photograph by W.C. Mendenhall.) 48 km from the fault zone was DC. Santa Rosa lies directly inland from the region of greatest motion on the San Andreas fault. Trees swayed Violently, and some were broken off above the ground or thrown down. The water in springs and artesian wells either increased or decreased its flow. A few sand craterlets formed in areas where water was ejected through cracks or fissures. The region of destructive intensity extended over a distance of 600 km. The total felt area included most of California and parts of western Nevada and southern Oregon (see fig. 15). The maximum inten- sity of XI was based on geologic effects, but the high- est intensity based on damage was 1X. Several foreshocks probably occurred, and many aftershocks were reported, some of which were severe. Magni- tude 8.3 Ms CFR, 8.25 Mg GR, 7.4 mb ABE, 7.8 MLa DMG (Ref. 38, 56, 378, 381, 517, 533, 567, 571, 572, 573.) 1906. Apr. 19 (Apr. 18). Near Brawley, Impe- rial County, Calif. A strong earthquake almost destroyed the Van Ness and Marlour buildings in Brawley. Walls fell into the streets, and chimneys fell to the ground. Not one brick or adobe building in the Brawley area escaped damage. Observers reported that banks along the New River collapsed. Water tanks were destroyed at Cocopar, Baja Califor- nia. Slight damage was reported at Calexico, El Centro, Holtville, and Imperial. Felt north to Los Angeles, south to Baja California, and east to Yuma, Ariz. Magnitude 6+ Ms CFR, 5.8 MLa DMG. (Ref. 38, 56, 381.) 1906. Apr. 23. Near Ferndale, Humboldt County, Calif. Chimneys were toppled and loose objects were knocked down at Ferndale. The earthquake stopped clocks at Cape Mendocino, Eureka, and Trinidad Head. It was reported felt into Oregon. (Ref. 38, 56.) 116 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Ground slumping tilted a row of two-story buildings in San Francisco, California, during April 18, 1906, earthquake. This block of structures was destroyed by the ensuing fire. 1906. May 2 (May 1). Near Guerneville, Sonoma County, Calif. At Guerneville, much plaster cracked and articles were thrown about. (Ref. 38, 56.) 1906. May 7, 04 10 and 05 00 UTC (May 6). Near Upper Lake, Lake County, Calif. These earthquakes were reported to be violent at Upper Lake, about 80 km north of Santa Rosa. Many clocks stopped during the second shock. No damage could be documented for this earthquake. The intensity listed was taken from ref. 56. (Ref. 56, 380.) 1906. Dec. 7 (Dec. 6). Near Piedras Blancas, San Luis Obispo County, Calif. This earthquake cracked the tower at the Piedras Blancas Lighthouse. It also was reported at Cambria, San Luis Obispo, and Santa Maria. (Ref. 56, 380.) 1907. Sept. 20 (Sept. 19). Near San Bernar- dino, Calif. A few walls of buildings were cracked and dishes were broken at San Bernardino, and the Shaver Building was damaged at San J acinto. Many landslides occurred in the mountain district north of San Bernardino, and a pipeline in the Santa Anita Mountains was broken. At the Declez quarry, large rocks were thrown down the mountainside. Felt from Los Angeles south to San Diego and east to Sal- ton. Magnitude 6 MS CFR. (Ref. 38, 56, 381.) 1908. Jan. 27 (Jan. 26). Honey Lake region, Lassen County, Calif. Chimneys were toppled at Amedee and Milford in the Honey Lake region. After- shocks were reported. (Ref. 38, 56, 380.) 1908. Aug. 18. Near Eureka, Humboldt County, Calif. A few chimneys toppled at Eureka; buildings walls and plate-glass windows cracked; and statues on the courthouse fell or were broken. At the Seazy Ranch, about 10 km north of Eureka near Freshwater, a fissure extending about 0.8 km in length formed in the ground. Several chimneys were thrown down in the area. (Ref. 38, 56, 380.) EARTHQUAKES IN CALIFORNIA 117 Streetcar rails on Howard Street, San Francisco, California, compressed by April 18, 1906, earthquake. (Photograph by GK. Gilbert.) 118 5? SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Fence offset 2.6 m on the main fault, 0.4 km northwest of Woodville, by the April 18, 1906, California, earthquake. (Photograph by GK. Gilbert.) 1908. Nov. 4. Inyo County, Calif. This earth- quake was the strongest of a series of shocks that occurred in late October and early November. The epi- central area was uninhabited except for a few pros- pectors, and several of them left the area because of the continuing earthquakes. This shock was felt in Tehachapi and probably to San Bernardino. No dam- age could be documented for this earthquake. The intensity listed was taken from ref. 382. (Ref. 38, 56, 380, 382.) 1909. May 18 (May 17). Upper Mattole, Hum- boldt County, Calif. This earthquake ruined all chimneys at Upper Mattole and displaced monuments in the cemetery. The shock was reported only in Humboldt County at Blocksburg, and Rohnerville. (Ref. 38, 56.) 1909. June 23 (June 22). South of Downieville in Sierra County, Calif. Minor damage to chimneys, plaster, lumber flumes, and dishes occurred in parts of Sierra and Plumas Counties. The region most strongly affected by the earthquake included the area south and southeast of Downieville, where chimneys were broken and plaster was knocked down. Plaster was shaken from ceilings at Sacramento, and walls were cracked slightly. The shock also was felt at Sparks, Nev. Many aftershocks were reported in the epicentral region. (Ref. 38, 56, 380.) Eureka, 124° EARTHQUAKES IN CALIFORNIA 122° 120° 118° 1160 440 Eugene . I 3" I Boise . I I / I . I D A H O O R E G O N | I I Mediord \/\ I . . 420 I . _ _______ 1.- _ _ _ ________ I l | / I IV I II-III Winnersucca / Eureka I / I I | | VII W V > I 40° / I I I Eureka I, I .Reno '4 V" I N E V A D A '4 " Ukiah. \ p VIII Q .\ \(I/ b Sacramento ‘\. . \ Santak Rosa ‘\I | IX \' \- 380 VI \‘ VII _\ \ Safanciscok \- VIIIV \ '\ san Jose Bishop ‘\ \ \ \\ C A L I F O R N | A , \ \ VIII HolIisIer > \,\\ MonIerey 0\"' V % N \'\ \i \ \I ‘ v \ 36° \ //-D V 4 70 BakersIIeId ’4‘ . 7o o I|~|II o <6 71 \ A I 340 Q N IV . Los ngees Q EXPLANATION k ?___._1100 * Epicenter san 0.990 ms ' KILOMETERS Ix Imensity 9 “’HENIT::%O .1 FIGURE 15.—-Isoseismal map for the San Francisco, California, earthquake of April 18, 1906. Isoseismals are based on M intensity estimates from data listed in references 381, 517, 571, 572, and 573 of table 1. 119 120 1909. Oct. 29 (Oct. 28). Near Scotia, Hum- boldt County, Calif. The most serious loss of prop- erty, estimated at $100,000, occurred in the Fortuna— Rohnerville area. All chimneys were toppled at Rohnerville, and concrete construction was wrecked. At Upper Mattole, about 40 km south of Rohnerville, most chimneys were wrecked. At Rio Dell, every chimney was downed, houses moved on foundations, and water pipes were broken. At Eureka, Fortuna, Ferndale, and Scotia, a few buildings were damaged, and many chimneys were leveled. Felt north to Gold Beach and Grants Pass, Oreg., south to Point Arena, and east to Chico and Nevada City. It also was observed onboard a ship at sea, 40 km southwest of Cape Mendocino. Aftershocks continued for weeks. Magnitude 6+ Ms CFR, 5.8 Ms ELL. (Ref. 38, 56, 381, 521, 523.) 1910. Mar. 11 (Mar. 10). Near Watsonville, Santa Cruz County, Calif. Plaster fell at Santa Cruz; a marble slab was knocked out of the wall; and windows were broken. Windows and crockery broke at Watsonville. The intensity was about the same down the Pajaro Valley to Monterey Bay; aftershocks were felt over that area also. Felt north to Santa Rosa (Sonoma County), south to Priest Valley (Monterey County), and east to Modesto (Stanislaus County). Magnitude 5.5 MLa DMG. (Ref. 38, 56, 381.) 1910. May 6. Near Bishop, Inyo County, Calif. This earthquake generated rockslides in Owens River Valley and Rock Creek Canyon, northwest of Bishop, and overturned shelves at Bishop. New cracks opened in a building at Visalia, about 130 km southwest of the epicenter in Tulare County. The event was felt east into Nevada, northwest to Sacramento, and south to Bakersfield (Kern County). The felt area was simi- lar to that of the shock on Sept. 30, 1889, southwest of Bishop. (Ref. 56, 324, 381.) 1910. May 15. Lake Elsinore region, River- side County, Calif. Chimneys were shaken down at Corona, Riverside, and Temescal. At Wildomar, bricks fell from chimneys and rocks rolled down the hillside. At Beaumont, a concrete-block building was cracked and plate-glass windows were broken. Felt from Barstow on the north to San Diego on the south and from Redondo Beach on the west to Palm Springs on the east. Moderate foreshocks occurred on Apr. 11 (07 57 UTC) and May 13 (06 20 UTC); slight aftershocks occurred on May 15 (20 57 UTC) and May 22 (04 15 UTC). Magnitude 6.0 MLa DMG, 5.5 MS ELL. (Ref. 38, 56, 381, 521.) 1910. Dec. 31. East of Salinas in San Benito County, Calif. The earthquake was reported to be the “heaviest since 1906” at Salinas, where a water main and dishes were broken. The shock was “hard” SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) at Hollister but caused little damage. It also was reported in Sonoma County, about 220 km to the north. (Ref. 38, 56, 324.) 1911. Mar. 11. Near Hollister, San Benito County, Calif. At Hollister, chimneys and windows were damaged, plaster cracked, and objects were thrown from walls. Effects of the earthquake were light at Salinas (Monterey County) and Campbell, Los Gatos, and San Jose (Santa Clara County). (Ref. 38, 56, 324.) 1911. July 1. Near Coyote, Santa Clara County, Calif. This earthquake destroyed chimneys and cracked brick walls at Gilroy, Los Gatos, Morgan Hill, San Jose, Santa Clara, and other nearby towns. One three-story brick building at Mount Hamilton (Lick Observatory) was damaged so severely it had to be rebuilt, and chimneys on several houses were damaged. Near Coyote, three 7 .5-m—high water tanks were knocked down. Slight damage to some buildings was reported at San Francisco. The shock was observed north to Woodland (Yolo County) and south to San Ardo (Monterey County). Isolated reports of this shock were received from as far east as Reno and Carson City, Nev. Several light after- shocks were felt through December 1911. Magnitude 6.2 MLa DMG, 6.6 MS CFR, 6.5 MS ELL. (Ref. 38, 56, 258, 381, 521.) 1911. Aug. 11. Near San Jacinto, Riverside County, Calif. A few walls sustained cracks and crockery was broken at San Jacinto. The shock was sharp at Redlands and San Bernardino but was slight at Los Angeles. A light foreshock occurred on Aug. 11 at 18 20 UTC. (Ref. 56, 383.) 1912. Jan. 5 (Jan. 4). Near Bishop, Inyo County, Calif. Breakable goods and merchandise were damaged in some stores at Bishop, and loose articles were knocked to the floor. The shock also was reported at Bakersfield, Fresno, and Visalia, and one doubtful report was received from Blair, Nev. (Ref. 56, 324.) 1912. Dec. 14. Southeast of Oxnard, Ventura County, Calif. 'lyvo sharp earthquakes overturned desks at the Ocean View School and wrecked two nearby barns. The tremors were “very marked in the country districts.” (Ref. 38, 56.) 1914. Nov. 9 (Nov. 8). Santa Clara County, Calif. Near Laurel (Santa Cruz County), two chim- neys were knocked down and articles were thrown from shelves. North of Laurel, two water pipes were broken at the Montezuma School. Six chimneys and several windowpanes were cracked at Los Gatos, and small amounts of plaster fell to the floor. Felt from Santa Rosa on the north to San Joaquin Valley on EARTHQUAKES IN CALIFORNIA the east and to Soledad (Monterey County) on the south. (Ref. 38, 324, 381, 414.) 1915. Jan. 12 (Jan. 11). Near Los Alamos, Santa Barbara County, Calif. Some chimneys were shaken down at Los Alamos; almost every chimney was damaged to some extent; and water pipes were pulled apart at their unions. Chimneys also were downed at Careaga, Santa Ynez, and at several ranches in Santa Barbara County. Brick buildings were damaged at Lompoc, about 20 km southwest of Los Alamos. In the epicentral area, cracks formed in the alluvial soil and many small landslides occurred. Felt north to San Jose, east to Bakersfield, and southeast along the coast to Los Angeles. Many after- shocks occurred for about a month. (Ref. 38, 56, 381.) 1915. Feb. 22. Near Whitmore, Shasta County, Calif. A highly localized shock in the moun- tains near Whitmore, northwest of Lassen Peak, caused severe dislocation of the ground at a ranch about 30 km from the foot of Lassen Peak. The earth cracked near the ranch, and fissures formed at points along the road leading to the ranch. Water spurted from the ground in many places; bubbling springs formed; and a barn sagged where the earth sank beneath its foundation. Other unusual phenomena also were reported. This event may have been a land- slide because it was not recorded on seismographs at Berkeley. (Ref. 38, 56, 324, 381.) 1915. June 23, 03 59 and 04 56 UTC (June 22). North of Calexico, Imperial Valley, Calif. 'IXvo destructive earthquakes wrecked buildings, overturned chimneys, and knocked down walls in the Calexico—El Centro area. The second shock, which was as strong as the first, completed the destruction of the buildings that already were weakened. This shock killed six people in Mexicali, Mexico. A fore- shock occurred at O3 40 UTC. The area of heaviest property damage extended from Mexicali north to Calexico, El Centro, and Heber, Where almost every brick and adobe building was damaged. Property loss, estimated at $900,000 for both Mexico and the United States, was due as much to the poor quality of construction as to the intensity of the earthquake. Damage at El Centro, the largest city in the Imperial Valley at this time, was estimated at $600,000. Property damage in Cal- exico, Heber, and Mexicali was almost as severe, but the rebuilding cost was less because the towns were much smaller than El Centro. A few cracks formed in the alluvium parallel to the levees in the Imperial Valley, but the irrigation ditches were damaged only slightly, if at all. Many unstable banks of the Alamo and New Rivers slid into the water; cracks formed in the marshy bed of 121 the New River northwest of El Centro. Residents about 25 km north of the mud volcanoes, which are west of Laguna de los Volcanes, Mexico (about 40 km south of Calexico), reported that columns of steam were seen rising from the vents for several days fol- lowing the earthquakes and that occasional explo- sions were heard from that direction. A foreshock occurred about 20 minutes before the first shock, and several aftershocks occurred through August 1915. The main earthquakes were felt north to Los Angeles and San Bernardino, east to Parker and Yuma, Ariz., and south at least to Ensenada, Mexico, and probably farther. Magnitude 5.6 MLa DMG (both earthquakes), 6.0 Ms ELL (03 59), 5.9 MS ELL (04 56). (Ref. 38, 381, 383, 521.) 1915. Oct. 8 (Oct. 7). Near Piedmont, Alameda County, Calif. This sharp earthquake knocked down a few chimneys at Piedmont, and Win- dows were broken. A small amount of plaster fell on the campus at Berkeley. Felt from Sebastopol, Sonoma County, to Santa Clara. Three aftershocks were reported. (Ref. 38, 56, 324, 442.) 1915. Nov. 21 (Nov. 20). Baja California, Mexico. A major earthquake left large cracks in a levee at Laguna de los Volcanes, Mexico, an uninhab- ited area about 40 km south of Calexico, Calif. 'leo hunters near Laguna de los Volcanes, Mexico, reported that a column of steam shot up about 180—200 In high and was followed by a column of black mud that reached about the same height. This column alternated between steam and mud for about 1 hour. The observers, although on level ground, had trouble standing during the earthquake. Cracks were observed on both sides of the New River for a distance of about 3 km. Felt only slightly at Los Angeles, but felt strongly at Calexico and San Diego and at Yuma, Ariz. Magnitude 7.1 MS ABE, 6.8 mb ABE. (Ref. 38, 258, 492.) 1915. Dec. 31. Off coast of Humboldt County, Calif. Felt inland only slightly at Eureka and Shively. Magnitude 6.5 Ms ELL, 6.5 Ms GR (Ref. 56, 258, 521.) 1916. July 5 (July 4). Near Ferndale, Hum- boldt County, Calif. About 3 km west of Ferndale, two chimneys were cracked, and a woodpile was overturned. One plate-glass window at Ferndale was broken, and vases were thrown from shelves. (Ref. 38, 56, 324.) 1916. Aug. 6. Near Paicines, San Benito County, Calif. Chimneys on a hotel at Paicines were destroyed; damage was slight at Hollister. Huge boul- ders rolled onto the highway at Chittenden Pass in Santa Cruz County. Felt to San Francisco on the 122 north, Monterey on the west, and Paso Robles on the south. (Ref. 38, 56, 324, 381.) 1916. Oct. 23, 02 44 UTC (Oct. 22). Near Lebec, Kern County, Calif. The epicentral area of this earthquake was sparsely populated, and so intensity information was meager. In San Emigdio Canyon (Kern County), the top one-third of a large rock chimney was knocked off, and many rocks rolled off nearby mountains. Near Frazier Mountain (Ven- tura County), about 10 km southwest of Tejon Pass, a crack opened in the ground; on the Snedden Ranch in Lockwood Valley, an adobe house was cracked so severely that it could not be repaired. On the north side of Lockwood Valley, at the Frazier Borax mine, the shock detached the porch from a frame house. On Alamo Mountain, about 18 km southwest of Tejon Pass, limbs fell from pine trees and rocks fell from the canyon walls at several places. Near Gorman, a crack several meters in length and a few centimeters in width formed in the cement surface of the high- way. Cracks also were reported in the highway at Bailey's Patrol Station, northwest of Quail Lake. A strong aftershock was observed in the area 10 minutes later, and several lighter aftershocks were reported. The main earthquake was felt from Shatter (Kern County) on the north to Los Angeles on the south and from Roosevelt (Los Angeles County) on the east to Los Olivos (Santa Barbara County) on the west. Isolated felt reports, however, were received from such distant points as Fresno and San Diego. Magnitude 5.5 Ms GR, 5.2 MLa DMG. (Ref. 38, 56, 258, 534.) 1916. Dec. 1. Near Avila, San Luis Obispo County, Calif. Some smokestacks toppled at the Union Oil Company refinery buildings in Avila. Plas- ter fell in several houses; much glass was broken; and merchandise fell from shelves. In Dairy Canyon, about 3 km north of Avila, a landslide covered the railroad tracks. One brick fell from a building in San Luis Obispo. Water in the San Luis Obispo Bay was disturbed. The shock was “severe” at Port San Luis but was slight to the southeast, at Santa Maria (Santa Barbara County). (Ref. 38, 56, 324.) 1917. May 28 (May 27). Imperial Valley, near Holtville, Calif. Walls were cracked at Brawley, and residents were panic stricken. Felt in Imperial, Riv- erside, and San Diego Counties and probably into northern Mexico. (Ref. 56, 380.) 1917. July 6. Owens Valley, Inyo County, Calif. This earthquake caused a break about 30.5 m long in the flume of the Los Angeles aqueduct south of Owens Lake. Chimneys cracked in the area, and rocks rolled down the mountain. Nine shocks occurred from July 7 to 9. The shock was reported SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) from Little Lake in the south to a point 18 km north- west of Independence in the north. (Ref. 38, 56, 324.) 1917. July 9. Lopez Canyon, San Luis Obispo County, Calif. Chimneys cracked and rocks rolled down the hillsides in Lopez Canyon, near San Luis Obispo. Four foreshocks and three aftershocks were felt in the area from July 7 at 20 57 UTC to July 10 at 00 45 UTC. (Ref. 38, 56, 324.) 1918. Mar. 12. Downieville, Sierra County, Calif. Chimneys were knocked over at Downieville. This sharp shock was reported only in Sierra County. An aftershock was reported 2 hours later. (Ref. 38, 56, 272, 324.) 1918. Apr. 21. Near San Jacinto, Riverside County, Calif. Major damage occurred in San Jacinto, about 120 km southeast of Los Angeles and at Hemet, about 3 km south of San Jacinto. Several residents were injured, and one was killed. An earth- quake of similar intensity occurred in the same area on December 25, 1899. In the business section of San Jacinto, a town of about 1,000 population, only one new concrete build- ing and one frame building remained standing after the earthquake. Most of the ruined buildings were of poor construction, however. Property damage at Hemet was not as severe as in San J acinto. No build- ings were wrecked, and no buildings of good con- struction were damaged seriously. Total property loss in the two towns was estimated at $200,000. Light damage to structures occurred in several towns within a 160-km radius of San Jacinto. Con- crete irrigation canals were broken in several places in the Hemet—San Jacinto area. Many lengthwise cracks were observed in the high- way between San Jacinto and Hemet, but cracks were not observed at the sides of this highway. About 1.5 km from the center of San Jacinto, the concrete highway was buckled, and a section about 1 m wide was torn up. Cracks in the ground were noted in four areas, but all were believed to be due to the shaking, not to the surface rupture along the San Jacinto fault. Many small sand craters were observed on a farm about 1.5 km northwest of San Jacinto. Felt from Taft (Kern County) in the north along the coast to San Diego (and probably into Mex- ico) and from Needles (San Bernardino County) in the east, south to Yuma, Ariz. Many aftershocks occurred, including a strong tremor on June 6, 1918. Two moderate shocks on Apr. 22 (16 07 and 16 14 UTC) shook down loose bricks and tottering walls in Hemet and San J acinto. Magnitude 6.9 Ms ELL, 6.6 MLa DMG (Ref. 38, 56, 258, 381, 384, 521, 533, 599.) EARTHQUAKES IN CALIFORNIA Collapsed building at San J acinto, California, caused by the April 21, 1918, earthquake. (Photograph by University of California, Berkeley.) 1918. Apr. 22. Near Corona, Riverside County, Calif. Chimneys were cracked, and plaster was thrown down at Corona. (Ref. 38, 56, 380.) 1918. May 1 (Apr. 30). Calexico, Imperial County, Calif. Plate-glass windows were broken at Calexico, and stock was thrown from shelves at El Centro. Felt over an area that included San Diego County on the west, San Jacinto on the north, west- ern Arizona on the east, and an unknown distance into Mexico on the south. (Ref. 56, 272.) 1918. June 6. Near Hemet, Riverside County, Calif. A strong aftershock of the event on Apr. 21, 1918, cracked plaster 7 km southeast of Hemet, loos- ened rocks on the mountainside, and cracked the ground around large trees. It was felt in Imperial, Los Angeles, Riverside, San Bernardino, and San Diego Counties. (Ref. 56, 380.) 1918. July 15 (July 14). Off the coast of northern Humboldt County, Calif. Buildings swayed alarmingly at Eureka, and most residents ran outside. The shock also was felt in Mendocino and Trinity Counties. Magnitude 6.5 MS ELL, 5.9 MLa ELL. (Ref. 38, 56, 258, 521.) 1918. Nov. 19. Near Venice, Los Angeles County, Calif. At Venice, plaster was downed and dishes were thrown to the floor; at Santa Monica, chimneys were cracked. The earthquake was reported only in Los Angeles and Orange Counties. (Ref. 38, 56.) 1919. Jan. 4. East of Redding, Shasta County, Calif. In the Clover Creek area, between Fern and Whitmore, the earthquake damaged chimneys and broke dishes. A surface fracture cut across a road near Fern and caused vertical displacement of sev- eral feet. This local event was not felt at Millville, about 30 km distant, and was not recorded on seismographs. This event may have been a landslide similar to one that occurred at the same location on Feb. 22, 1915. (Ref. 56, 324.) 1919. Feb. 16. Near Maricopa, Kern County, Calif. The earthquake cracked buildings at Maricopa and the Grapevine pump station. At Belridge, an oil tank was split, and at Lebec, rocks rolled down the hillsides. This shock also was felt in Fresno, Los Angeles, San Luis Obispo, and Tulare Counties. Mag- nitude 5.7 Ukn JON. (Ref. 38, 56.) 1919. Sept. 15. Near Eureka, Humboldt County, Calif. Some chimneys were demolished at Eureka, and Windows were broken. Three after- shocks occurred within about 5 hours. (Ref. 38, 56, 324.) 124 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Collapsed exterior wall of Hotel Inglewood, Inglewood, California, caused by the June 22, 1920 (June 21 PST), earthquake. (Photograph by University of California, Berkeley.) 1920. Jan. 1 (Dec. 31, 1919). Near Warner Springs, San Diego County, Calif. Adobe walls were cracked at Warner Springs. The shock also was observed in Imperial, Los Angeles, and Riverside Counties. (Ref. 56, 380.) 1920. June 22 (June 21). Near Inglewood, Los Angeles County, Calif. This earthquake mainly dam- aged poorly built structures in the area of Inglewood, about 16 km south of downtown Los Angeles. Property loss was estimated at more than $100,000. The destructive effects of the shock were most prominent along Commercial Street, where damage commonly was more severe to two-story buildings than to one- story buildings. The Inglewood grammar school was wrecked, and walls of the Inglewood Hotel and a nearby electric substation fell into the street. Many chimneys on pri- vate houses in Inglewood were broken at the roofline. The water mains and plant of the Inglewood Water Company were damaged. At Hyde Park, 3 km north- east of Inglewood, about 30 percent of the chimneys were overthrown, and brick facings on the fronts of five school buildings were knocked down. In a ceme- tery east of Inglewood, tombstones were twisted and overturned. Many aftershocks occurred, but most were felt only in the Inglewood area. (Ref. 38, 56, 385, 537.) 1920. July 16, 18 08, 21 27, and 21 30 UTC. Los Angeles, Calif. A series of more than 100 earthquakes occurred in the Los Angeles area from Feb. 1 to Sept. 30, 1920. The strongest shocks were observed on July 16. Damage from the July 16 events included cracked walls, fallen plaster from ceilings and walls, and fallen bricks from cornices and chimneys. Most of the earthquakes were felt only in the Los Angeles area. The second shock on July 16 was felt at Mount Wilson and Pasadena, and the third was felt at Pomona and Santa Ana. (Ref. 56, 380, 386.) 1920. July 23 (July 22). Hot Springs, Shasta County, Calif. Chimneys and dishes were broken and dishes were shaken from shelves at Hot Springs. It was felt from Redding northeast to Fall River Mills and McArthur and along the McCloud River. Three sharp aftershocks were observed on July 23 at 14 00, 16 00, and 20 00 UTC. (Ref. 38, 56, 324, 537.) 1922. Jan. 31. Off the coast of Humboldt County, Calif. This potentially damaging earth- quake was felt from Eugene, Oreg, to San Francisco. Magnitude 7.6 Ms CFR, 7.3 Ms GR, 7.3 mb ABE. (Ref. 56, 258, 272.) 1922. Mar. 10. Cholame Valley area, San Luis Obispo County, Calif. Houses were damaged severely along the San Andreas fault zone in Monterey and San Luis Obispo Counties. Chimneys fell at Parkfield and in southern Cholame Valley. One house was jolted from its foundation onto the EARTHQUAKES IN CALIFORNIA ground, and its porch was displaced 30 cm away from the house. Another severely damaged house was twisted into two parts. A large water tank on a ranch at Cholame was knocked down and broken into pieces, and oil pipelines broke between Shandon and Antelope. A ground crack, 15—30 cm wide and about 800 m long, was reported in Cholame Valley. Small ground cracks also formed in the San Andreas fault zone. Felt from San Jose on the north to Los Angeles on the south and east to Springville (’I‘ulare County). A moderate aftershock occurred on Mar. 16 at 23 11 UTC. Magnitude 6.3 MLa DMG, 6.3 Ms ELL. (Ref. 38, 56, 258, 324, 381, 521.) 1923. Jan. 22. Off the coast of Humboldt County, Calif. Houses were damaged severely at Ferndale, Petrolia, and Upper Mattole; many chim- neys were downed; and water lines were broken. At Pepperwood, one house was shaken from its founda- tion and split apart, and another was twisted from its base. Chimneys also were knocked over at Alton, Dyerville, Fortuna, Loleta, Ocean House, and Scotia. Several landslides occurred in the canyon. Felt from Walker (Siskiyou County) south to San Francisco and beyond and east to Grass Valley (Nevada County). It also was observed on several ships at sea. Many aftershocks occurred in the Petrolia—Upper Mattole region. Magnitude 7.2 MS ABE, 7.3 Ms CFR, 6.5 MLa DMG. A small tsunami was recorded. (Ref. 38, 56, 258, 381, 610.) 1923. July 23 (July 22). Near Redlands, Riv- erside County, Calif. Many chimneys were broken in Redlands, San Bernardino, and along Base Line Road, west of Harlem Springs. The fronts of three buildings were cracked badly in Redlands, and a few fire walls were thrown down. At San Bernardino, two cornices were thrown down; parts of brick walls collapsed; and pavement buckled. Damage to walls and chimneys also occurred at Colton, Loma Linda, and Patton. Felt north to Mojave (Kern County) southeast to Calexico (Imperial County) and east to Big Bear Valley (San Bernardino County). Magni- tude 6.25 Mg CFR, 6.0 MLa DMG, 6.3 Ms ELL. (Ref. 258, 381, 388.) 1923. Nov. 5. Baja California, Mexico. At Ca1— exico, Calif., a hotel shifted several centimeters on its foundation, and other structures sustained minor damage. The intensity of the earthquake was similar at El Centro, where five pronounced shocks were reported. The earthquake also was felt at Brawley and San Diego. (Ref. 38, 56.) 1923. Nov. 7. Baja California, Mexico. This earthquake was stronger than that on Nov. 5, 1923. Additional property damage occurred at Calexico, 125 Calif., and one fire resulted. Felt only in Imperial and San Diego Counties. (Ref. 38, 56.) 1924. Dec. 28 (Dec. 27). Salinas, Monterey County, Calif. Considerable minor damage to plas- ter occurred at Salinas, where residents rushed into the streets in panic. The dining room of one house was “practically a wreck” from fallen plaster. Felt from King City (Monterey County) north to Palo Alto (Santa Clara County) and west of the Mount Hamil- ton Range. (Ref. 56, 324, 539.) 1925. Apr. 16 (Apr. 15). Baja California, Mex- ico. At Calexico, Calif., plaster was shaken from walls at the public library and residents ran outside. (Ref. 38, 56, 218.) 1925. June 29. Near Santa Barbara, Calif., in the Santa Barbara Channel. This destructive earthquake caused property damage estimated at $8 million and killed 13 people. Most of the damage occurred at Santa Barbara and nearby towns along the coast, but the earthquake caused moderate dam- age at many points north of the Santa Ynez Moun- tains, in the Santa Ynez and Santa Maria River valleys. North of Santa Barbara, the earth dam of the Sheffield Reservoir was destroyed, but the water released caused little damage. In Santa Barbara, few buildings on State Street escaped damage. Because parts of the main business district and the area near the seashore were built on land fill, many of the structures there were demol- ished, and others were so shattered that they had to be razed. In general, however, buildings of reinforced concrete were damaged little, except where work- manship was poor; frame buildings covered with stucco, sheathing, or lath also withstood the shock well. Loss to the sewage system was heavy only in areas of land fill, but the disposal plant was destroyed above the surface of the ground. Among the most conspicuous building failures in Santa Barbara were the Arlington Hotel (a composite building of irregular shape), the Californian Hotel (a new four-story brick building), the San Marcos office building (a four-story reinforced concrete structure), the El Camino Real Hotel (a two-story brick and wood structure), and the Potter Theater building (a three-and-one-third-story brick and wood structure). Other public buildings seriously damaged included the courthouse, jail, library, schools, and churches. Structures built on solid ground or pavement of all types withstood the earthquake well. The only severely damaged pavement was that on the boule- vard paralleling the beach, where the shoulders of the pavement were displaced 20—36 cm horizontally. The pavement sustained cracks as wide as 40 cm at 126 z, ., a — , 3,. V “me \ ‘ a .15.. ~..- SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Wall of the Hotel Californian at Santa Barbara, California, downed by the June 29, 1925, earthquake. (Photograph by University of California, Berkeley.) several points along the beachfront. Concrete curbs buckled in almost every block in Santa Barbara. The earthquake caused damage on the Southern Pacific Company Railroad from Gaviota (mile 331 as measured from San Francisco) on the north to Ven- tura (mile 598) on the south. Heavy subsidence of the larger fills and slope failure of the sides of deep cuts were noted on the railroad track from Naples to Santa Barbara. Many of the bluffs in the Naples area, adjacent to the ocean, fissured and caused extensive landslides. A section of ground (about 2 acres), adjacent to the track between Naples and Santa Barbara, subsided about 30 cm. Felt from Paso Robles (San Luis Obispo County) on the north to Santa Ana (Orange County) on the south and to Mojave (Kern County) on the east. Sev- eral strong aftershocks occurred on July 3, and lighter shocks occurred throughout July 1925. Magnitude 6.3 MS CFR, 6.1 MLa DMG. (Ref. 38, 258, 381, 389, 533, 540, 541, 542.) 1925. July 3, 16 37 and 18 19 UTC. Near Santa Barbara, Calif. The first aftershock of the June 29 earthquake toppled a few damaged chimneys at Santa Barbara and left cracks in walls. The second tremor was larger than the first because as surface waves were reported only for the second tremor (from Honolulu, Hawaii, and Cambridge, Mass). The lack of information on damage from the second shock probably is due to its occurrence so soon after the first shock. (Ref. 56, 218, 380.) 1926. Feb. 18. Near Santa Barbara, Calif. Windows were broken in a Santa Barbara school, and a water main was broken in the roundhouse. Tele- phone equipment was damaged at Simi (Ventura County). Felt along the coast from San Luis Obispo on the northwest to south of Santa Ana, a distance of about 320 km. Magnitude 5.0 MLa DMG. (Ref. 38, 56, 218.) 1926. June 29. Near Santa Barbara, Calif. Some chimneys fell at Santa Barbara, and one child was killed by falling bricks. A streetcar was derailed; telephone wires became tangled; plate-glass windows were broken; and old cracks in walls enlarged. The shock was felt strongly at Buellton and Ventura and was reported as far southeast as the Los Angeles beaches. (Ref. 38, 56, 218, 533.) EARTHQUAKES IN CALIFORNIA 127 El Camino Real Hotel and garage in Santa Barbara, California, severely damaged by the June 29, 1925, earthquake. 1926. July 25. Near Idria, San Benito County, Calif. Rocks rolled down the hillside in the area of Idria and Panoche. The earthquake cracked plaster in the San Joaquin Valley. It was felt southeastward across the San Joaquin Valley to Kemville and north and northwestward to Sacramento and San Jose. (Ref. 56, 218, 390.) 1926. Oct. 22, 12 35 and 13 35 UTC. Off the coast of Monterey County, Calif. ’IVvo large- magnitude earthquakes caused considerable damage in the Monterey Bay region. The first shock was severe at Santa Cruz, where many chimneys were knocked down, and old brick buildings sustained dam- age. A few chimneys also were knocked down at Car- mel and Monterey. A lamp was thrown from its base, and a lens was broken at the lighthouse on Ano Nuevo Island, northwest of Santa Cruz. Lighter effects were reported as far away as San Francisco (120 km from the epicenter), Where the tile surfaces of a few buildings were damaged, windows were broken, and plaster was cracked extensively. The second shock, an hour later, was almost as Widely felt as the first, and appears to have been stronger than the first earthquake at towns north of Monterey Bay. The shaking again was heavy on Ano Nuevo Island. The shocks were felt over about the same area—north to Middletown (Lake County), south along the coast to Lompoc (Santa Barbara County), and east to Turlock (Stanislaus County). Many small aftershocks occurred. Magnitude 6.1 Ms CFR (both earthquakes), 6.1 MLa DMG (12 35 UTC). (Ref. 56, 218, 381, 391, 521.) 1927. Jan. 1, 08 16 and 09 13 UTC. Imperial Valley, Calif. Two strong earthquakes began a long series of shocks, although none of the aftershocks exceeded MM intensity VI. Refer to June 23, 1915, above, for a description of a similar double earth- quake occurrence at about the same location. Many buildings were damaged severely at Calexico (Impe- rial County), and several people were injured by col- lapsing roofs and walls. At Mexicali, Mexico, some buildings were destroyed and many were damaged. Water mains were broken in both towns. Slight damage to buildings also was reported at El Centro, Heber, and Imperial. Felt northwest to Orange County and east into Arizona. Hundreds of after- shocks occurred. (Ref. 38, 56, 258, 381.) 128 1927. Aug. 4. Santa Monica Bay, Calif. Only minor damage occurred in the area. A water main was broken in downtown Los Angeles. The shock was reported north to Ventura, east to San Bernar- dino, and south to Anaheim (Orange County). Mag— nitude 5.0 MLa DMG. (Ref. 38, 56, 218.) 1927. Aug. 20. Off the coast of Humboldt County, Calif. At Eureka and Arcata, chimneys were destroyed, vsn'ndows and water pipes broke, and walls cracked. Plaster fell in buildings, and some doors jammed. People driving automobiles had steer- ing problems. Cracks formed in mud and gravel in Redwood Park (Eureka), and moderate landslides occurred. Chimneys also were damaged at Fortuna, Ferndale, Freshwater, and Scotia. Felt north to the Smith River area near the Oregon-California border and south to Westport, in Mendocino County. Magni- tude 5.0 MLa DMG. (Ref. 38, 218, 324, 543.) 1927. Sept. 18 (Sept. 17). Northwest of Bishop, Inyo County, Calif. The intensity of this earthquake probably was highest near Bishop, where several chimneys were downed, many windows were cracked or broken, and parked cars moved back and forth. The shock also appears to have been strong in the sierra regions of Fresno and Madera Counties. A landslide caused damage at the powerhouse in Owens River Canyon, north of Bishop. Felt from Mono County in the north to Los Angeles County in the south and from Kings County in the west to western Nevada in the east. A slight aftershock was felt on Sept. 19 at O5 23 UTC. Magnitude 5.5 MLa ELL. (Ref. 56, 218, 258, 521, 535.) 1927. Nov. 4. Off the coast of Santa Barbara County, west of Lompoc, Calif. The most severe damage to property occurred in the areas west and north of Lompoc. Chimneys were wrecked at several towns, including Arroyo Grande, Berros, Guadalupe, Halcyon, Lompoc, Los Alamos, and Nipomo. On the Roberd's ranch, an earthquake fountain created between 10 and 20 sand craters; lurches and cracks were observed in the water-soaked soil. The Roberd ranch house was shifted on its foundation about 5 cm, and small outbuildings were pushed from their foundations. The walls of a poorly built block build- ing collapsed at White Hills. At Santa Maria and other towns in the area, chimneys were damaged, old brick walls and interior walls formed cracks, and cor- nices fell. Near Surf, west of Lompoc, the Southern Pacific Railroad bridge was thrown out of alignment near its center; a concrete highway was cracked; and small rockslides and earthslides occurred. Cracks formed in the ground about 6.5 km north of Arlight. Felt from Morgan Hill south to Redondo Beach and from SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) the coast east to Kernville. A tsunami was recorded on tide gages at San Francisco, La J olla, San Diego, and Fort Point, and waves were observed at Pismo, Port San Luis (1.5 m), and Surf (1.8 m). Many after- shocks occurred. Magnitude 7.3 Ms GR, 7.3 mb ABE, 7.5 MS CFR, 6.2 MLa DMG. (Ref. 38, 56, 381, 392, 521, 610.) 1927. Nov. 19 (Nov. 18). Near Santa Maria, Santa Barbara County, Calif. Chimneys, weak- ened by the shock on Nov. 4, 1927, fell at Santa Maria, and windows cracked. Plaster was cracked at Betteravia. Felt from San Miguel (San Luis Obispo County) and Parkfield (Monterey County) on the north to towns in the area of Santa Barbara Channel on the south. (Ref. 38, 56, 218.) 1928. Apr. 15. West of Paskenta, Tehama County, Calif. At Paskenta, one chimney was cracked and standing automobiles were moved back and forth. At a ranch near Newville, south of Paskenta, a chimney was knocked off one house. In Lyonsville, at the northeast edge of the macroseismic region, a laborer reported three tombstones fell and six graves collapsed. Felt from Rockport (Mendocino County) in the west to Stirling City (Butte County) in the east and from Jelly (Tehama County) in the north to Lakeport (Lake County) in the south. Mag- nitude 5.7 Ukn JON. (Ref. 393.) 1928. June 4 (June 3). Near Weaverville, Trinity County, Calif. This earthquake, which was as strong at Carrville and Trinity Center, threw chimneys down at Weaverville. It was felt west to Eureka and Scotia. Magnitude 4.5 MLa DMG. (Ref. 1, 324.) 1929. July 8. Near Whittier, Los Angeles County, Calif. This earthquake was strongest in an area southeast of Whittier. Within that area, a schoolhouse and two private dwellings were damaged seriously, and several others were damaged by falling chimneys. At nearby Santa Fe Springs, the shock broke flanges on oil towers and left a few short, par- allel cracks in loose ground; two oil wells were plugged by incaving. Felt generally from Mount Wilson on the north to beyond Santa Ana on the south and from Hermosa Beach in the west to Riverside in the east. Many aftershocks occurred within a few hours of the main earthquake and continued to occur at increasingly long and irregular intervals through March 1931. Several small foreshocks were felt in the Whittier area from May 4—18, 1929. (Ref. 2, 394.) 1929. Nov. 28. Southeast of Aberdeen, Inyo County, Calif. About 8 km southeast of Aberdeen, concrete reservoirs were cracked and dishes were broken. A large landslide was reported about 25 km EARTHQUAKES IN CALIFORNIA northwest of Independence at the headwaters of Goodale Creek. Five heavy shocks were reported at Fresno. The earthquake generally was felt northwest to Stockton (San Joaquin County), south to Kernville, and east to Mina, Nev. Magnitude 4.9 Ukn JON. (Ref. 2, 38.) 1930. Jan. 16, 00 24 and 00 34 UTC (Jan. 15). Near Summit, San Bernardino County, Calif. Two strong earthquakes knocked down chimneys and broke dishes in Fawnskin and Summit. The first shock was heavier. The tremors were felt strongly as far as Los Angeles. Magnitude 5.9 Ukn JON (00 24 UTC), 5.5 Ukn JON (00 34 UTC). (Ref. 3, 38, 258.) 1930. Feb. 26 (Feb. 25). Near Westmorland, Imperial County, Calif. At Westmorland, chimneys were knocked down, and walls were cracked. Modern buildings were undamaged. East of Westmorland, craterlets formed where mud and water were forced from the ground. Felt in Imperial, Riverside, and San Diego Counties and at a few towns in western Arizona. Several foreshocks and many aftershocks occurred. Magnitude 5.7 Ukn JON. (Ref. 3, 38.) 1930. Mar. 1. Near Brawley, Imperial County, Calif. At Brawley chimneys and overhanging cor- nices toppled, roofs displaced, and walls were cracked severely. Aftershocks were felt through Mar. 6, 1930. (Ref. 3, 38.) 1930. Aug. 5, 11 25 UTC. Near Santa Bar- bara, Calif. Two local earthquakes broke windows at Santa Barbara and cracked walls at Ventura. One aftershock was observed. Magnitude 4.7 Ukn JON. (Ref. 3, 38.) 1930. Aug. 31 (Aug. 30). Santa Monica Bay, Calif., west of the Los Angeles Basin. A cornice fell from a building at Venice, and ground cracks formed long the edge of Palisades Park bluff at Santa Monica, north of Venice. Small earthslides and rock- slides were reported. At Los Angeles, minor cracks formed in buildings, plaster fell, and dishes broke. Light damage also occurred at Chatsworth, Holly- wood, Owensmouth, and Pasadena. Felt throughout the Los Angeles Basin—from Kern County in the north to San Diego County in the south and east to the Palm Springs area. A tsunami of 0.6 m was observed at Santa Monica. A comparison of the Jan. 1, 1979, Malibu earth- quake and the 1930 Santa Monica earthquake sug- gests that they occurred on the Anacapa—Dume and Santa Monica faults, respectively. The epicenters of these earthquakes can be interpreted to define an 8- to 10-km north-south distance between the two faults, which suggests that the faults are unlikely to rupture simultaneously in one large event. (Ref. 3, 38, 396, 474, 610.) 129 1930. Sept. 23 (Sept. 22). Near Eureka, Hum- boldt County, Calif. Chimneys were toppled at Arcata, Eureka, and Fields Landing. Slight damage occurred at Capetown, Crannell, and Korbel. Felt south to Briceland, north to the Oregon border, and about 90 km inland from the coast. Two light after- shocks occurred on Sept. 23. Magnitude 5.1 Ukn JON. (Ref. 3, 38, 324.) 1930. Oct. 29. Near Whitmore, Shasta County, Calif. This earthquake caused damage at La Moine (50 km north of Bedding) and Whitmore (40 km east of Redding). A series of 13 shocks was felt from Mineral and Viola in the east to Redding and La Maine in the west. (Ref. 3, 324.) 1931. Aug. 23. Off the coast, southwest of Cape Mendocino, Calif. This earthquake was strongest south of Eureka, along the lower course of the Eel River. At the Punta Gorda Lighthouse, the mantle on the revolving lamp was broken. Damage, if any, was superficial at other towns. Felt north to southern Oregon and south into Mendocino County. Magnitude 5.9 Mx JON. (Ref. 4, 258.) 1931. Sept. 9. Off the coast of Humboldt County, northwest of Cape Mendocino, Calif. This earthquake was strongest at towns along the lower course of the Eel River. Chimneys were dam- aged south of Eureka, at Weott, and bricks were dis- lodged a few kilometers east of Weott, at Blocksburg. Branches fell from trees in wooded areas of Hum- boldt County. Several aftershocks were reported. Magnitude 6.3 Mx JON. (Ref. 4, 324.) 1932. Feb. 26. Near Big Sur, Calif. The location given in the California list for this earthquake has been redetermined by Toppozada (1991, oral com- mun.) to have occurred about 70 km to the north- northwest, in the coastal area south of Big Sur. 1932. June 6. Off the coast of Humboldt County, west of Eureka, Calif. This earthquake, the strongest in the region since Jan. 22, 1923, killed one person at Eureka and injured several others. Property damage was severe at Eureka, where hun- dreds of chimneys were damaged and many fell, plate-glass windows were shattered, and water mains were broken. Several small houses were shaken down in Arcata, and most chimneys were damaged. Hardly a chimney remained standing at Fields Land- ing, and a 15—cm crack formed in the highway. Many chimneys also toppled at Loleta, where a brick wall was shaken into the street. A 70-cm ground crack developed on Cock Robin Island, at the mouth of the Eel River, and many blowholes, some as much as 2.5 m in diameter, were observed. Felt north to Coos Bay, Oreg, south to 130 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Wood-frame building in Long Beach, California, damaged by the March 11, 1933 (Mar. 10 PST), earthquake. San Jose, and east to Nevada City (Nevada County). Several aftershocks occurred. Magnitude 5.9 MLa DMG. (Ref. 5, 38, 258, 381, 533, 544.) 1932. July 26 (July 25). Near Springville, Tulare County, Calif. An earthquake loosened sev- eral tons of rock from a peak on the south edge of Sequoia National Park, near Mineral King, and cracked brick chimneys at Springville (about 45 km southeast of Tulare). Magnitude 4.9 Ukn JON. (Ref. 5, 292.) 1933. Mar. 11, 01 54 UTC (Mar. 10). South- east of Long Beach, near Newport Beach, Calif. Although only moderate in terms of magnitude, this earthquake caused serious damage to weak masonry structures on land fill from Los Angeles south to Laguna Beach. Property damage was estimated at $40 million, and 115 people were killed. Severe property damage occurred at Compton, Long Beach, and other towns in the area. Most of the spectacular structural damage was due to land fill, or deep water-soaked alluvium or sand, and to badly designed buildings. Minor disturbances of ground water, secondary cracks in the ground, and slight earth slumps occurred, but surface faulting was not observed. Along the shore between Long Beach and Newport Beach, the settling or lateral movement of road fills across marshy land caused much damage to the concrete highway surfaces and to approaches to highway bridges. At Compton, almost every building in a three-block radius on unconsolidated material and land fill was destroyed. At Long Beach, buildings collapsed, houses were pushed from foundations, walls were knocked down, and tanks and chimneys fell through roofs. Damage to school buildings, which were among the structures most commonly and severely damaged by this earthquake, led to the State Legis- lature passing the Field Act, which now regulates building-construction practices in California. This destructive earthquake was associated with the Newport—Inglewood fault. Shocks similar in mag- nitude and intensity to this event have occurred in this area in the past—notably July 28, 1769; Dec. 8, 1812; and July 11, 1855. The earthquake was felt almost everywhere in the 10 southern counties of California and at some points farther to the northwest and north in the Coast EARTHQUAKES IN CALIFORNIA 131 Front wall of the John Muir School, Pacific Avenue, Long Beach, California, downed by the March 11, 1933 (Mar. 10 PST), earthquake. (Photograph by W.L. Huber.) Range, the San Joaquin Valley, the Sierra Nevada, and the Owens Valley (see fig. 16). It also was reported in northern Baja California. A sharp fore- shock occurred near Huntington Beach on Mar. 9, and many aftershocks occurred through Mar. 16. For several years, minor aftershocks continued to occur, most often centering near the two ends of the dis- turbed segment of the Newport-Inglewood fault. Magnitude 6.25 Mg GR, 6.3 MS CFR, 6.2 MLa DMG, 6.43 ML KJ. (Ref. 6, 292, 381, 397, 460, 533.) 1933. May 16. Near Niles, Alameda County, Calif. All chimneys were thrown down and some houses were damaged in the area of Overacker Sta- tion, between Niles and Irvington. North of Niles, cornices fell from buildings at Walnut Creek; chim- neys fell, and the City Hall was damaged at Mar- tinez. Rockfalls blocked the road in Niles Canyon. Felt north to Marysville (Yuba County), from the coast east to Merced, and south to Spreckels (Monterey County). Magnitude 5.8 Ukn JON. (Ref. 38, 324, 536.) 1933. Oct. 2. Near Los Angeles, Calif. Wide- spread minor damage occurred in the business sec- tion of Los Angeles, including broken windows and dishes, cracked plaster, and damaged street lamps. Minor damage also occurred at Bell, Compton, Long Beach, and other towns in the area. Felt north along the coast to Santa Barbara, south to San Diego, and east to Victorville and San Bernardino. Magnitude 5.4 Ms GR. (Ref. 6, 38, 292.) 1933. Oct. 25 (Oct. 24). Near Los Angeles, Calif. At Huntington Park, some chimneys were downed, windows were broken, and brick was dam- aged slightly. The shock generally was felt in the suburbs of Los Angeles. (Ref. 6, 259, 292.) 1934. Apr. 23. Near Aromas, Monterey County, Calif. A local earthquake downed chimneys at Aromas and knocked merchandise from shelves. 132 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Jefferson Junior High School in Long Beach, California, destroyed by the March 11, 1933 (Mar. 10 PST), earthquake. Felt at Hollister, Salinas, Spreckels, and Watsonville. An earlier shock was reported at 16 08 UTC. (Ref. 259, 324, 559.) 1934. June 5, 22 52 UTC. Adelaida, San Luis Obispo County, Calif. A foreshock of the June 8 earthquakes, this local event knocked down two walls and several trees at Adelaida. It was reported only at a feW towns in the area. (Ref. 7, 292.) 1934. June 8, 04 30 and 04 47 UTC (June 7). Near Parkfield, Monterey County, Calif. A series of earthquakes occurred in the Parkfield area from June 5 to 14. The strongest foreshock—0n June 8 at O4 30 UTC—caused damage in and around Parkfield and Stone Canyon. The principal earthquake, which occurred 17 minutes later, caused severe damage at Parkfield—a concrete-block house was wrecked, walls fell, and chimneys were downed. Highway bridges near Parkfield shifted slightly on their footings. Chimneys were knocked down in the area along the San Andreas fault—from Stone Canyon to the south- ern boundary of Monterey County. On Middle Mountain, northwest of Parkfield, two zones of cracks about 7.5 m wide formed in the soil parallel to the surface traces of two faults in the San Andreas system. The largest single crack was about 17 m long and 46 cm deep. Neither vertical nor hori- zontal displacement, however, was observed along the cracks. Felt to Alviso in the north, Santa Ana in the south, and Kernville in the east. Magnitude 6.0 Ms GR, 6.0 Ms CFR, 5.6 ML,I DMG. (Ref. 7, 38, 292, 381, 536.) 1934. Dec. 17. Near Los Alamos, Santa Barbara County, Calif. A few chimneys and plas- ter fell at Los Alamos, and plaster and chimneys EARTHQUAKES IN CALIFORNIA 133 122° 120° 118° 116°, 114° \‘\. \‘\ 38° '\. NEVADA .\ \. San Francisco \‘ f ‘_ K \ \- \ \~ / / \ \\‘\ / \ \- \ \‘\ / \ ‘x. \. / \'\ / Fre.sno II-III \ \\\ 36° \_ \. . \\ \\ CALIFORNIA \\~ ’-—~ I .V I v. 32° ARIZONA }-~I ‘Los Ange|e O 34 Q _ kt. __ ‘1 ll \ \ _. (, f h ‘. BI I e l V .1 _ r II III J. l 1 I I?! ‘I IV /(,5 UNITEQ_§I‘.‘IES.. .--‘ -/7-"" San Diego .___'__ __..—-~—~-""""‘uMEX‘CO 1 i/ \ I——.—l 0 100 KILOMETERS EXPLANATION * Epicenter VIII Intensity 8 FIGURE 16.—Isoseismal map for the Long Beach, California, earthquake of March 11, 1933. Isoseismals are based on intensity estimates from data listed in references 6, 259, 381, and 397 of table 1. sustained cracks. Felt along the coast of Santa Bar- bara and San Luis Obispo Counties. Several after- shocks were reported at Los Alamos. Magnitude 4.8 MX JON. (Ref. 259, 292.) 1934. Dec. 30. Baja California, Mexico. Bridges were damaged, railroad tracks were twisted, and adobe houses were wrecked in the epicentral region in the Laguna Salada district south of Calex- ico. The strong shock cracked chimneys, walls, and windows in several California towns in the Imperial Valley. Many aftershocks occurred. Magnitude 6.7 Mx JON. (Ref. 7, 38, 258.) 1934. Dec. 31. Baja California, Mexico. This earthquake was stronger than that of Dec. 30, 1934, 134 and its epicenter was in the same general area. In the epicentral region, irrigation ditches were dam- aged, roads were buckled, and crevices opened in the ground. The shock was felt strongly throughout the Imperial Valley in southern California. At Calipa- tria, chimneys and walls were thrown down and win- dows were broken, and at Gadsden, Ariz., considerable damage to brick and masonry was reported. Slight damage occurred at several towns in California and western Arizona. The earthquake also was felt slightly at Las Vegas, Nev. Magnitude 7.1 MS CFR, 7.0 Ms GR. (Ref. 7, 38, 258.) 1937. Mar. 8. San Francisco Bay region, Calif. An earthquake caused minor damage at Albany, Berkeley, El Cerrito, Elmhurst, and Oakland. Damage was heaviest in north Berkeley, where one poorly built house was condemned; several chimneys fell and many were twisted and cracked; walls were cracked; and plaster fell from walls. Felt north to Santa Rosa (Sonoma County) and south to Aptos (Santa Cruz County). (Ref. 10, 259, 324.) 1937. Mar. 25. Terwilliger Valley, San Diego County, Calif. This earthquake caused less damage than might have been expected because its origin was in a mountainous district having few residents within about 50 km. Slight to moderate damage to chimneys, windows, plaster, or walls was reported from Anza, Garnet, Hemet, Keen Camp, Palm Springs, Ramona, and Warner Springs. Felt over most of southern California. Magnitude 6.0 Ms CFR, 6.0 Ms GR, 5.9 MLa ELL. (Ref. 11, 259, 292, 545.) 1938. Feb. 12. Near Santa Cruz, Calif. One chimney toppled, and chimneys and windows cracked at Santa Cruz; plaster fell at Coyote and Morgan Hill. Felt north to San Rafael (Marin County) and south to Big Sur (Monterey County). (Ref. 11, 259, 324.) 1938. Aug. 31 (Aug. 30). Near Long Beach, Los Angeles County, Calif. A heavy china cabinet was overturned at Keystone (6 km north of Wilming- ton); beds were displaced about 20 cm; and cracks formed in plaster. Cracks also formed in walls from top to bottom. Merchandise was knocked from shelves in stores and dishes were knocked to the floor at Long Beach and Huntington Beach. Felt along the coast between Santa Monica and Laguna Beach and inland to Mount Wilson. Several after- shocks occurred. (Ref. 11, 259, 292.) 1938. Sept. 12 (Sept. 11). South of Pepper- Wood, Humboldt County, Calif. One chimney fell at Pepperwood, and chimneys were cracked or twisted at Eel Rock and Ferndale. In the Redwoods, the ground was covered with branches fallen from SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) trees. Felt along the coast north to Brookings, Oreg., east to Forbestown, Calif. (Butte County), and south to Elk, Calif. (Mendocino County). (Ref. 11, 259, 324.) 1938. Nov. 15. Near Talmage, Mendocino County, Calif. The heaviest reported damage occurred at Talmage, where one chimney fell and oth- ers were cracked. Some walls of buildings were cracked at Potter Valley. Felt generally in Lake, Men- docino, and Sonoma Counties. (Ref. 11, 259, 324.) 1938. Dec. 1. Alameda County, north of San Jose, Calif. Some chimneys were cracked at San Jose, and plaster cracked at Saratoga. Felt slightly at a few other towns in the area. (Ref. 11, 324.) 1938. Dec. 3, 17 42 UTC. Inyo County, north- west of Bishop, Calif. West of Bishop, a large boul— der crashed into a house and caused much damage. Other slides in the mountains reportedly occurred nearby. In the Owens River Gorge, buildings and pipelines were damaged by loosened rocks that cas- caded down the mountains. Felt from Stockton (San Joaquin County), south to Bakersfield, and east into western Nevada. (Ref. 11, 292.) 1939. June 24. Southwest of Hollister, San Benito County, Calif. About 14 km southwest of Hollister, structural damage was sustained at the Mano ranch and the Orhwall ranch. Several chim- neys fell or were twisted at the rooflines; many adobe walls were severely cracked; and several cracks in the ground were observed. The highway also was cracked in several places. At the San Benito Winery, chimneys were toppled and damage was consider- able. Felt along the coast as far north as Half Moon Bay (San Mateo County), south to Nipomo (San Luis Obispo County), and inland to Tranquillity (Fresno County). (Ref. 12, 259, 324, 381.) 1939. Dec. 27. Near Long Beach, Los Angeles County, Calif. Moderate damage to property occurred at Huntington Beach and Long Beach. At Long Beach, several street lights were broken, a fire- place was shaken down, and chandeliers in stores were knocked from ceilings to the floor. At Hunting- ton Beach, floors buckled in one house, and plaster fell from walls. Felt along the coast from Newport Beach north to Venice, inland to Altadena and San Bernardino, and southeast to Palm Springs. (Ref. 12, 292, 324.) 1939. Dec. 28. Near Cholame, San Luis Obispo County, Calif. Slight damage occurred at San Lucas, where dishes were broken and plaster was cracked. The general limits of the felt area extended from Santa Cruz south along the coast to Point Arguello and inland to Hollister, Lost Hills, and Fresno. (Ref. 12, 324.) EARTHQUAKES IN CALIFORNIA 135 Furniture store in Brawley, California, destroyed by the Imperial Valley earthquake of May 19, 1940 (May 18 PST). (Photograph by F. Ulrich.) 1940. Feb. 8. North of Paradise, Butte County, Calif. Damage was confined to a few twisted and cracked chimneys and several broken windows and dishes in the Chico-Paradise area. The press reported that several chimneys were downed at Chico. Several landslides and dislodged rocks were reported along roads. Felt north to Dunsmuir (Siskiyou County), south to Stockton (San Joaquin County), west to the Platina area (Tehama County), and east to Reno, Nev. Magnitude 6.0 Ms CFR, 6.0 MS GR. (Ref. 13, 259, 324.) 1940. Feb. 13. Near Branscomb, Mendocino County, Calif. Chimneys were cracked at Branscomb, and furnishings were displaced. The shock also was fairly strong in Humboldt County, at Ferndale and Scotia, and in Mendocino County, at Elk, Ukiah, and Westport. (Ref. 259, 324.) 1940. May 19, 04 36 and 05 51 UTC (May 18). Imperial Valley, near El Centro, Calif. The main earthquake took nine lives and caused property dam- age estimated at $6 million. Damage from a strong aftershock near Brawley at 05 51 UTC is included in this estimate. The first shock damaged about 80 percent of the buildings in Imperial. Many buildings in the business district were condemned, and older residences sus- tained severe damage. Four people were killed in the collapse of a grocery store. Damage to a lesser extent occurred at El Centro and Holtville. Elevated water tanks at Holtville and Imperial collapsed, and a water tank at Brawley was damaged. The downtown business area at Brawley was dam- aged severely by the second shock, and about 25 per- cent of the houses in the residential area were damaged. About half of the business structures had to be condemned. Many breaks in water mains occurred and water pipes were broken. Damage to the structures and canals of the Impe- rial Irrigation District in the United States and Mex- ico was widespread. Breaks occurred over almost the entire length of the Ash Canal, from Holtville to the Mexico border. The Alamo Canal, the main feeder for the entire system, had eight major breaks; a section of the Solfatara Canal in Baja California was destroyed south of Cocopar. The earthquake demol- ished the New River flume, a 427-m-1ong timber structure on the West Side Main Canal south of Mexicali. Right-lateral offset occurred along the Imperial fault. The pattern of offset indicates that the main part of the offsets occurred along a surface fracture about 20 to 25 km long, extending from the epicenter of the main shock southeast, about 5 km past Coco- par. Rupture of the northwest section of the fault may have occurred during a damaging aftershock at 05 51 UTC. Where the surface fracture crosses the All American Canal east of Calexico, the largest 136 displacement of 4.5 m occurred. At one point on the Solfatara Canal, the slip was as much as 3.7 m. In Baja California, the Inter-California Railroad track was displaced at Grape, and about 300 m of railroad track settled north of Grape. At Cocopar, the track shifted 2 m, and at Meloland, it shifted about 46 cm. Many sand boils were observed near Gadsden on the Yuma Project in Baja California. Geysers spout- ing water several meters high also were reported. Canals, drainage channels, flumes, and bridges were damaged near Gadsden. The main earthquake was felt over much of southern California, southwest Ari- zona, and northern Baja California. About 48 after- shocks occurred through the end of 1940. Those on May 23 caused more damage at Brawley. Magnitude of first shock 6.9 mb ABE, 6.7 Ms GR, 7.1 Ms CFR, 6.4 MLa DMG, 7.2 Ms ELL, 7.2 ML KS. (Ref. 13, 292, 381, 521, 533, 546, 547.) 1940. May 23, 11 00, 17 30, and 18 45 UTC. Near Brawley, Imperial County, Calif. Three strong aftershocks of the Imperial Valley earth- quakes (see May 19, 1940, above) cracked chimneys, walls, and plaster and broke windows and dishes at Brawley. (Ref. 259.) 1940. Oct. 11 (Oct. 10). Santa Monica Bay, Calif. This earthquake was strongest at Keystone (6 km north of Wilmington), where chimneys and walls were cracked, and dishes were broken. Slight dam- age also was reported at Long Beach, Los Angeles, Manhattan Beach, Maywood, and Redondo Beach. Felt along the coast north to Santa Barbara, south to San Diego, and east to the Big Bear Lake area (San Bernardino County). Magnitude 4.6 Mx JON. (Ref. 13, 259, 292.) 1940. Oct. 22. Near Scotia, Humboldt County, Calif. At Scotia, three underground pipes, windows, and plaster walls were broken. Felt over a small area of Humboldt County, extending along the coast from about Arcata to Shelter Cove and inland to the Brid- geville area. Several aftershocks were reported at Scotia. (Ref. 13, 259, 324.) 1940. Nov. 19. Off the coast of Humboldt County, west of Eureka, Calif. Loose bricks were thrown from a chimney at Upper Mattole, and fur- nishings were shifted. Slight damage also occurred at Garberville and Westport. Felt along the coast north to the Arcata area, south to Elk (Mendocino County), and east to the Forest Glen area (Trinity County). (Ref. 13, 259, 324.) 1940. Dec. 20. Southwest of Benbow, Hum- boldt County, Calif. This slight earthquake broke dishes and knocked books down at Fort Bragg and SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) cracked plaster and overturned small objects at Ben- bow. Felt along the coast from Arcata south to Ukiah and east to Weaverville (Trinity County). (Ref. 13, 259, 324.) 1941. Feb. 9. Off the coast of Humboldt County, west of Ferndale, Calif. At Punta Gorda Light Station, slight cracks in plaster were observed. At Shelter Cove, the bluff slid in several places. Felt along the coast from San Francisco on the south to Port Orford, Greg, on the north. Magnitude 6.4 ML ELL. (Ref. 14, 258, 259, 381.) 1941. July 1, 07 50 UTC (June 30). Near Santa Barbara, Calif. Moderate damage to prop- erty occurred in the Carpinteria—Santa Barbara area. Property damage was estimated at $100,000. About 25 chimneys and several walls fell at Carpinteria, and the cornice of a building was shaken to the ground. At Santa Barbara, one chimney toppled, bricks were dislodged from buildings, several build- ings were cracked, and plate-glass windows were shattered. In addition, sidewalks buckled in places, and many water mains were broken. Several after- shocks occurred. The main earthquake was felt from near Stockton (San Joaquin County) in the north to Havilah (Kern County) in the south and from Coal- inga (Fresno County) in the west to Mina, Nev., in the east. Magnitude 5.9 MS GR, 5.9 MS CFR, 5.5 MLa DMG. (Ref. 14, 292, 381, 533.) 1941. Sept. 14, 16 43, 18 21, and 18 39 UTC. Near Mammoth Lakes, Mono County, Calif. Five earthquakes occurred on this date, the three largest at the times given. Rockslides in the mountains blocked roads and trails, and one cabin was destroyed. Cracks formed in walls and chimneys at the Pineridge Shaver Ranger Station, and several chimneys were damaged at Yosemite Valley. Slight damage also was reported at Benton, Doyles, Miami Ranger Station, and Pinedale. Magnitude 5.8 Ms GR (first shock); 6.0 MS CFR, 6.0 Ms GR (third shock), 5.6 MLa DMG (first and third shocks). (Ref. 259, 292, 381.) 1941. Oct. 3. Off the coast of Humboldt County, Calif. This earthquake was strongest at Eureka, where chimneys twisted and cracked, and plaster cracked and fell. Slight damage also occurred at Ferndale, Fields Landing, Korbel, Pepperwood, Punta Gorda, Rio Dell, Rockport, and Upper Mattole, where chimneys and walls cracked and plaster fell. Felt north to southwest Oregon and south, along the coast, to the San Francisco Bay area. Magnitude 6.4 Ms CFR. (Ref. 259, 324.) 1941. Oct. 6 (Oct. 5). Off the coast of Hum- bolt County, Calif. Magnitude 5.25 Mg GR, 5.4 Mx JON. EARTHQUAKES IN CALIFORNIA 1941. Oct. 22, 06 57 UTC (Oct. 21). Near Gardena, Los Angeles County, Calif. Property damage generally was confined to an area that included Compton, Hynes, Moneta, Gardena, Los Angeles, and the West Dominguez Oil Field, east of Gardena. Widespread minor damage—mainly cracked walls, fallen plaster, and broken windows and dishes—occurred at Gardena and Compton. At Keystone (6 km north of Wilmington), chimneys were twisted, plaster and dishes were broken, and walls were cracked; at Moneta, the east and west fire walls on one brick building were knocked down. Felt along the coast from Montalvo (Ventura County) on the north to Newport Beach on the south and inland to Riverside and San Bernardino Counties. (Ref. 14, 259, 292.) 1941. Oct. 22, 10 32 UTC. Near Gardena, Los Angeles County, Calif. This slight aftershock of the earthquake described above (06 57 UTC) cracked chimneys, walls, and plaster at Hondo. At Gardena and Pacific Palisades, the shock cracked plaster and overturned small objects. It also was observed by residents in a few other towns in the area. (Ref. 14, 259, 292.) 1941. Nov. 14. Near Gardena, Los Angeles County, Calif. This strong earthquake caused prop- erty damage estimated at $1.1 million in the Gar- dena-Torrance area. No deaths or injuries were reported, perhaps because the earthquake occurred a little after midnight (local time) when most residents were at home sleeping. In nearby oil fields, two tanks were demolished, two were buckled, and a pipeline was broken. Damage was most severe in Torrance, where hardly a building escaped damage. ’I\N0 schools sus- tained heavy structural damage, and one was condemned; the fire station was abandoned because of heavy damage. The shock also moved several houses off their foundations. About 50 percent of all brick chimneys and fireplaces either were twisted, broken loose, or thrown down. Severe damage also occurred in the city of Gar— dena. The walls of a two-story structure fell on and destroyed the roof of an adjoining building. The Gar- dena Elementary School building was condemned; the Bank of America Building was damaged severely; and the roof of a newspaper building almost col- lapsed. Several fire walls and many chimneys were knocked down or otherwise damaged. Felt from Carpinteria (Santa Barbara County) on the north to San Diego on the south and inland to Cabazon and San Jacinto in Riverside County. Magnitude 5.5 Mx JON. (Ref. 14, 259, 292, 533, 599.) 137 1941. Dec. 31, 06 48 UTC (Dec. 30). Near Bishop, Inyo County, Calif. A moderate earth- quake twisted chimneys and cracked plaster at the Adams Main Powerhouse in Owens River Gorge, near Bishop. Reports of damage were not received from other towns in the area. Felt from Georgetown (Eldo- rado County) on the north to Kernville on the south and from Coalinga on the west to Mina, Nev., on the east. Magnitude 5.4 Ms GR. (Ref. 14, 259, 292.) 1942. Oct. 21, 16 22 UTC. Near Borrego Val- ley, Imperial County, Calif. At Carrizo Gorge, about 19 km north of J acumba, landslides broke tim- bers and wiring on a railroad bridge. Slight damage was observed at several towns in the area. Several aftershocks occurred, the strongest at 01 50 UTC on Oct. 22. Felt from the coast east to Mobile, Ariz., and from Crucero (San Bernardino County) on the north to Baja California on the south. Magnitude 6.5 Ms CFR, 6.0 MLa DMG. (Ref. 15, 292, 381.) 1943. Aug. 29 (Aug. 28). Near Lake Arrow- head, San Bernardino County, Calif. The earth- quake was most severe in the Big Bear Lake—Lake Arrowhead—Seven Oaks area. At Redlands, plaster fell, dishes broke, and bricks fell into a chimney. Slight damage also occurred at Lake Arrowhead. One foreshock and two aftershocks were recorded. The main shock was felt north to Mojave (Kern County), south to San Diego, and from the coast east to Lud- low. (Ref. 16, 259, 292.) 1943. Oct. 26 (Oct. 25). Near San Jose, Santa Clara County, Calif. In San Jose, a gas main was broken, plate-glass windows were shattered, and plaster was knocked off walls. A water line was broken at Sunnyvale. Slight damage to plaster occurred at several towns in the area. Felt along the coast from Santa Rosa (Sonoma County) south to San Ardo (Monterey County) and east as far as Bridgeport (Mono County), near the Nevada border. (Ref. 16, 259, 324.) 1943 Nov. 16. Near San Leandro, Alameda County, Calif. At San Leandro, chimneys were cracked, windows were broken, and plaster and knickknacks fell to the floor. One chimney pulled away from the wall of a house, leaving a 6.5-cm crack at the eaves. Felt slightly over a small area in and around San Leandro. (Ref. 16, 259, 324.) 1944. June 12, 10 45 and 11 16 UTC. East of Banning, Riverside County, Calif. Plaster cracked and fell, dishes broke, and vases overturned at Ban- ning; plaster cracked at Corona. Several light after- shocks were reported. The felt area extended from Oxnard (Ventura County), along the coast, south to San Diego and northeast to Ludlow (San Bernardino County). (Ref. 17, 259, 292.) 138 1944. June 19, 00 03 and 03 06 UTC (June 18). Near Redondo Beach, Los Angeles County, Calif. Two sharp earthquakes caused minor damage to property in the Los Angeles area at Compton, Gardena, Huntington Park, Lynwood, and Maywood. The damage commonly included cracked chimneys and plaster and broken windows. Other damage included the dislodging of a large marble slab from the front of a store in Redondo Beach. Both shocks were felt along the coast south to San Diego and east to the Palm Springs area (Riverside County). Several light aftershocks were observed in the area. (Ref. 17, 259, 292.) 1945. Jan. 7. Near Hollister, San Benito County, Calif. This minor earthquake cracked chimneys and plaster at Hollister and broke win- dows and displaced stock on store shelves. It also knocked books and pictures from shelves at Paicines and San Benito. Two chimneys were damaged at the old Santa Anita ranch. Felt from San Francisco, south along the coast, to Big Sur (Monterey County) and east as far as Yosemite National Park. (Ref. 18, 259, 324.) 1945. May 17. Near Hollister, San Benito County, Calif. Buildings were damaged slightly at Hollister, Where brick fell from chimneys; chimneys were cracked; several windows were broken; and plaster fell from walls. Considerable damage also was done to stock in stores. Felt north to San Fran- cisco, east to Merced, and south to San Ardo (Monterey County). (Ref. 18, 259, 324.) 1945. May 19. Off the coast of southern Hum- boldt County, Calif. This earthquake was felt through most of the coastal towns, from Crescent City south to Fort Bragg and Willits. Magnitude 6.2 Ms CFR, 6.0 ML BRK. (Ref. 18, 258.) 1945. Aug. 15. Near Borrego Valley, San Diego County, Calif. Some damage to cables and power- lines was reported at Fullerton, and plaster was cracked at Fall Brook and San Jacinto. Felt from Los Angeles south along the coast to San Diego and east to the ’I‘wentynine Palms area (San Bernardino County). (Ref. 18, 259, 292.) 1945. Aug. 27. Near San Jose, Santa Clara County, Calif. One chimney was shaken loose and plaster was cracked at San Jose. Felt to Saint Helena (Napa County) on the north, Big Sur on the south, and Pinecrest (Tholumne County) on the east. (Ref. 18, 259, 324.) 1946. Jan. 13. West of Bishop, Inyo County, Calif. Near Bishop, at the Owens River Gorge, this earthquake cracked chimneys, walls, and plaster and displaced heavy furniture. Many rocks rolled down SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) the sides of the canyon. Felt over a small area, which included Hawthorne, Nev. (Ref. 259, 292.) 1946. Mar. 15, 13 21, 13 49, and 14 00 UTC. North of Walker Pass, Kern County, Calif. The main shock at 13 49 UTC caused moderate damage at Onyx, about 19 km southwest of the epicenter. Damage to wood, brick, masonry, and concrete was reported to be conside rable. Chimneys, walls, plas- ter, and windows cracked; dishes broke; and plaster, books, and pictures fell. Cracks formed in the ground and concrete along the Los Angeles Aqueduct. Rock- slides occurred in the canyons. Elsewhere in the region of Walker Pass and the South Fork of the Kern River, adobe houses were damaged, brick chim- neys cracked, and plaster fell. The earthquakes were felt from Commache (Cala- veras County) on the north to San Diego (an isolated report) on the south and from Cambria (San Luis Obispo County) on the coast to Death Valley (see fig. 17). Several aftershocks occurred. Magnitude of sec- ond shock 6.25 Mg CFR, 6.25 Mg GR, 6.1 MLa DMG. (Ref. 19, 259, 292, 381.) 1946. Sept. 28 (Sept. 27). Near Banning, River- side County, Calif. Slight damage was reported at Banning, Cabazon, Cathedral City, Palm Springs, and ’I‘Wentynine Palms. Felt in parts of Los Angeles, Riverside, San Bernardino, and San Diego Counties. (Ref. 19, 259, 292.) 1947. Feb. 5 (Feb. 4). East of King City, Monterey County, Calif. Buildings swayed visibly at Lonoak (Priest Valley), Where plaster cracked and fell and small objects fell. Felt over a small area of Fresno, Monterey, and San Benito Counties. (Ref. 20, 259, 324.) 1947. Apr. 10, 15 58 UTC. Near Manix, San Bernardino County, Calif. This moderate shock was strongest in the Newberry Springs area, about 40 km east of Barstow. One schoolhouse was con- demned at Newberry Springs, and three adobe and brick houses were damaged severely. Minor damage, including one toppled chimney, fallen walls, cracks in chimneys and concrete, and cracked and slumped highways, were reported in the area. Also, cracks formed in the banks of the Mojave River. Felt over most of the southern half of California, a small part of southwest Nevada, and at several towns in west- ern Arizona (see fig. 18). Several light aftershocks occurred. Magnitude 6.4 MS CFR, 6.4 Ms GR, 6.3 MLa DMG. (Ref. 20, 259, 292, 381.) 1947. May 27. Off the coast of Humboldt County, Calif. This moderate earthquake cracked plaster at Upper Mattole and shook trees and bushes strongly. Felt over a small area in Humboldt County. (Ref. 20, 259, 324.) EARTHQUAKES IN CALIFORNIA 122° 1 139 118° 116° Sacramento 38° UTAH NEVADA '// (‘6‘ Fresno o Monterey 36° CALIFORNIA V 34° fl\ ® VIII 0 k Bakersfield ARIZONA EXPLANATION * Epicenter V||| Intensity 8 O 100 KILOMETERS ;_.__._I San Diego ‘ FIGURE 17.—-Isoseismal map for the Kern County, California, earthquake of March 15, 1946. Isoseismals are based on intensity estimates from data listed in references 19, 259, and 381 of table 1. 1947. June 22. Near Santa Cruz, Calif. Chim- neys were damaged at Corralitos and Watsonville; windows were broken at Santa Cruz; and plaster fell at Gilroy, Hollister, and Watsonville. It was reported that boulders blocked a highway near Chittenden Pass and that landslides closed Hecker Pass in Santa Clara County. Felt over most of the San Francisco Bay area. (Ref. 20, 259, 324.) 1947. Aug. 10. Near Hollister, San Benito County, Calif. The shock was strongest at Hollister, where stones were dislodged from a masonry pillar, plate—glass Windows were cracked, a water main was broken, and stock was knocked from store shelves. The felt area extended from Glenwood (Santa Cruz County) southeast to Los Banos Creek (Merced County) south to San Ardo (Monterey County) and northwest to Big Sur on the coast. (Ref. 20, 259, 324.) 1947. Sept. 8, 07 13 UTC (Sept. 7).. Placer County, Calif., southwest of Reno, Nev. A series of small earthquakes was observed in the Reno, Nev., 140 120° 118° SEISMICITY OF THE UNITED STATES, 1568-1989 (REVISED) 116° 112° 38° ‘\. 0 Fresno ‘\ NEVADA \ CALIFORNIA 0 VI Bakersfield o Barstow @ Q \ Los Angeles 34° \1 . a, :7? C/ “o o m C 6 b M EXPLANATION \ S _.._. * Epicenter ‘ qw—T-Efie‘E'EEE'I’ V|| Intensity 7 t o 100 KILOMETEF L_——J 32° FIGURE 18.—Isoseisma1 map for the San Bemardino County, California, earthquake of April 10, 1947. Isoseismals are based on intensity estimates from data listed in references 20 and 259 of table 1. area. The main shock knocked plaster from the ceil- ing in one house southeast of Reno and loosened mortar in the stone walls. Unusual activity in the hot springs was observed after the tremors. The earthquakes were felt over a small area of western Nevada and probably in a few towns in California. (Ref. 20, 259, 324.) 1948. Feb. 11 (Feb. 10). East of Tipton, Tulare County, Calif. A moderate earthquake cracked plas- ter at Ducor, Kingsburg, Lindsay, Springville, and Tipton. School buildings near Fresno, Dinuba, and Clovis were closed because of cracked walls. Felt extensively in the southern Sierra Nevadas and along the east side of the southern Joaquin Valley. (Ref. 21, 259, 324.) 1948. Feb. 20 (Feb. 19). Near Los Angeles, Calif. This shock sent many people running into the streets in the Los Angeles area. Slight damage to plaster was reported at North Hollywood. Felt over a small area of Los Angeles County. (Ref. 21, 259, 292.) 1948. Mar. 1. Northwest of San Bernardino, Calif. Slight damage to plaster and walls was reported at Burbank and Pasadena. Near Devore, cracks formed in the concrete floor of a cabin and dishes were broken. Felt over an area that included parts of Kern, Los Angeles, Orange, Riverside, San Bernardino, and San Diego Counties. (Ref. 21, 259, 292.) 1948. Apr. 16. Southeast of Oxnard, Ventura County, Calif. This earthquake was strongest at Oxnard, where plaster cracked and fell, dishes were broken, and lamps were knocked over. Felt at towns near the coast, southeast to Long Beach, and inland about 40 km. (Ref. 21, 259, 292.) EARTHQUAKES IN CALIFORNIA 1948. June 18. Near Ukiah, Mendocino County, Calif. Chimneys were cracked and vases overturned at Ukiah, and plaster was damaged at Lakeport and Talmage. Felt over a small area of Lake, Mendocino, and Sonoma Counties. (Ref. 21, 259, 324.) 1948. Dec. 4. Near Desert Hot Springs, River- side County, Calif. The earthquake probably was caused by displacement on the Mission Creek fault, one of the major branches of the San Andreas fault system in southern California. The highest intensi- ties in the area were reported from the upper Coach- ella Valley from Thousand Palms to White Water, which also was the most densely populated area near the epicenter. Considerable structural damage and slight cracks in the ground were observed in Desert Hot Springs. Some minor structural damage also occurred at Palm Springs. At Willis Palms, cracks formed in the ground and cliffs, riverbanks slumped, and springs increased in flow. Landslides and cracks in the ground were reported in the Indio Hills. Felt throughout southern California and at a few towns in western Arizona, southwest Nevada, and northern Baja California (see fig. 19). About 72 aftershocks were accurately located in a zone 18 km long, paral- lel to (but 5 km north of) the trace of the Mission Creek fault. Magnitude 6.5 Ms CFR, 6.5 MS GR, 6.2 MLa DMG. (Ref. 21, 259, 292, 381, 548.) 1948. Dec. 29. West of Reno, Nev., in Sierra County, Calif. The town of Verdi, Nev., which lies at the sharp bend of the Truckee River, sustained the most damage to property. The west wall of the old general store at Verdi collapsed, and the building was wrecked. Chimneys on houses were toppled or twisted out of line, sections of parapet walls on a schoolhouse fell, and many windows were broken. Minor damage also occurred at Reno and at Chilcoot, Calif. Felt over a large area of central California and western Nevada. Magnitude 6.0 Ms CFR, 6.0 MS GR, 5.7 MLa DMG. (Ref. 21, 259, 324, 381.) 1949. Jan. 1 (1948. Dec. 31). Near Watson- ville, Santa Cruz County, Calif. Near Chittenden, six houses standing on stilts or blocks were dis- placed a few centimeters on their foundations, chim- neys were broken off two of the houses, and a small landslide nearby partly blocked the Old Chittenden Road. Slight damage also occurred at Hollister and Santa Cruz. Felt over a small area of the coastal region of central California from Oakland (Alameda County) south to Big Sur (Monterey County). (Ref. 21, 259, 324.) 1949. Feb. 11. Southeast of Bishop, Inyo County, Calif. Slight damage, in the form of cracks 141 in brick, walls, and plaster, was reported at Ash Mountain (Sequoia National Park), Bakersfield, Big Pine, and Olancha. Felt over a large area of south- central California and into Nevada as far as Beatty and Goldfield. (Ref. 22, 259, 292.) 1949. Mar. 9. Northwest of Hollister, San Benito County, Calif. Although felt strongly in the area, this shock was most severe at Hollister. Three chimneys were toppled, and a brick wall separating two stores split lengthwise. One market sustained severe cracks in plaster and walls. Considerable loss also was sustained from damaged merchandise in stores. Slight damage was reported from several other towns in the area. Felt over the western half of north-central California from Santa Rosa (Sonoma County) south to Paso Robles (San Luis Obispo County). A few aftershocks were reported, the larg- est on Mar. 14 at O6 10 UTC. Magnitude 5.8 ML KJ. (Ref. 22, 259, 324, 460.) 1949. Mar. 24. Off the coast of southern Humboldt County, Calif. Reported felt along the California and Oregon coasts. Magnitude 6.2 Ms CFR, 6.2 MS GR. (Ref. 324.) 1949. June 10 (June 9). Near San Jose, Santa Clara County, Calif. A series of three earth- quakes occurred, the strongest at O3 06 UTC. At San Jose, a water main was split open, windows were shattered in houses, and stock tumbled from store shelves. The main shock was felt north to Pet- aluma (Sonoma County) and south to Big Sur (Monterey County). (Ref. 22, 259, 324.) 1949. Aug. 8. Near Richmond, Contra Costa County, Calif. Slight damage was reported at Rich- mond (windows broke and dishes fell from shelves) and Vallejo (plaster cracked). Felt over a small area of the San Francisco Bay region. (Ref. 22, 259, 324.) 1949. Aug. 27. Near Point Concepcion, Santa Barbara County, Calif. Slight damage occurred at Arlight and Sudden, where a chimney fell and dishes broke, and at Lompoc, Where dishes broke and knick- knacks fell. Felt over a small area along the coast in Santa Barbara and San Luis Obispo Counties. (Ref. 22, 259, 292.) 1949. Sept. 19 (Sept. 18). Near Huntington Park, Los Angeles County, Calif. Broken win- dows and dishes and cracks in cement driveways were reported in Los Angeles. The shock also was felt strongly at Long Beach and San Gabriel. It was reported over a small area of central Los-Angeles County. (Ref. 22, 259, 292.) 1949. Nov. 4. Baja California, Mexico. A mod- erate earthquake caused minor property damage at Guadalupe, Mexico. In California, slight damage also occurred at Borrego Valley, Campo, Coronado, Del 142 122° 120° 118° 116° SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 112° 38° NEVADA Monterey 36° CALIFORNIA ( ""“ \ 34° Los Angeles yd '\, /\'V- C'\ kw 32° Blythe \ Palm Springs 3’ o E \ / phoenix '2 ), \ 2 . 0 s ..—--—- ""7” - N\TED STATE - — ~ San D_Iego 9"ije’)(’\(:()’ f / é \ / \ \ 100 KlOMETERS EXPLANATION * Epicenter VII |ntensity 7 < 2 O E n: < FIGURE 19.—Isoseismal map for the Riverside County, California, earthquake of December 4, 1948. Isoseismals are based on intensity estimates from data listed in references 21 and 259 of table 1. Mar, San Diego, Santee, San Ysidro, and Spring Val- ley. Felt from Baja California north to Palmdale (northern Los Angeles County). (Ref. 22, 259, 292.) 1949. Nov. 5 (Nov. 4). Baja California, Mexico. An aftershock of the Nov. 4 earthquake (see above) caused slight damage to plaster and walls at Gross- mont, La Jolla, and San Diego. (Ref. 22, 259, 292.) 1950. Jan. 14. Near Punta Gorda, Humboldt County, Calif. The earthquake was strongest at the Punta Gorda Light Station, where cracks formed in plaster, in the light tower, and in the concrete floor. Felt over a small area along the coast of Humboldt County in northern California. (Ref. 23, 259, 324.) 1950. Feb. 26 (Feb. 25). North of Santa Paula, Ventura County, Calif. A few bricks fell from an old chimney at Ventura, and a Window was broken. Damage to plaster and fallen merchandise was reported from Oxnard and Santa Paula. The felt area extended along the coast from Lompoc (Santa Bar- bara County) to Van Nuys and in the east from Wheeler Ridge (Kern County) to Palmdale. (Ref. 23, 259, 292.) 1950. July 27, 11 29 UTC; July 28, 17 50 UTC; and July 29, 14 36 UTC. Near Calipatria, Impe- rial County, Calif. A series of damaging earth- quakes occurred in the Imperial Valley from July 27 to July 29. The first two earthquakes caused only EARTHQUAKES IN CALIFORNIA slight damage in the Brawley-Calipatria area. Dam- age from this series of earthquakes was estimated at $300,000. Near Calipatria, several concrete stand-pipes were broken and a small railroad bridge was shifted 15 to 20 cm. Many sand boils were formed; irrigation ditch banks sloughed; and the ground settled and cracked. An old sheet piling broke when the levee settled at the North End Dam, about 3 km west of Calipatria. The main shock on July 29 was felt from the Mexican border to Banning, Calif., and Parker, Ariz., and from San Diego, Calif., to Yuma, Ariz. Aftershocks occurred through Aug. 14, 1950, and probably beyond. Magnitude 5.4 MS GR (second shock); 5.4 Ms GR (third and main shocks). (Ref. 23, 259, 292, 560.) 1950. Aug. 1. Near Calipatria, Imperial County, Calif. An aftershock of the July 29 earth- quake collapsed a small part of a wall at Calipatria and knocked a few bricks from houses. In addition, ground cracks in the area of the North End Dam opened wider, and new sand boils were observed at the dam site and along the levees of the Vail Canal. Felt over a small area of southern California and at Somerton, Ariz. (Ref. 23, 259, 292.) 1950. Sept. 5. Near Idyllwild, Riverside County, Calif. Dishes were broken at Idyllwild and San J acinto, plaster was cracked at San J acinto, and a clock was thrown from its shelf at Idyllwild. Felt from Barstow (San Bernardino County) in the north to San Diego in the south and from the coast to Twentynine Palms in the east. (Ref. 23, 259, 292, 561.) 1950. Nov. 17 (Nov. 16). Near Hawthorne, Los Angeles County, Calif. Scattered reports of cracked plaster and broken dishes were received from southwest Los Angeles. This was the strongest of three small earthquakes that were felt in the area between 01 59 and 19 46 UTC on Nov. 17. The shocks were felt only in Los Angeles County. (Ref. 23, 259, 292.) 1950. Dec. 14, 13 24 UTC. Near Herlong, Las- sen County, Calif. This main shock of a series caused considerable structural damage at Herlong. Many structures sustained cracks from about 0.3 to 0.6 cm in width to as much as 24 m in length. Many chimneys were broken, trusses and roof rafters were split, and several buildings were displaced on their foundations. Damage to water mains, steam pipes, and sewers also was reported. Felt from Alturas (Modoc County) south to Sacramento and east to Lovelock, Nev. Several foreshocks and aftershocks were felt in the area. Magnitude 5.6 Ms GR. (Ref. 23, 259, 324, 561.) 143 1951. Jan. 24 (Jan. 23). Near Westmorland, Imperial County, Calif. About 5.5 km southwest of Westmorland, in the Imperial Valley Irrigation Dis- trict, 30 m of ground running northwest-south east settled 2.5 cm; a water main in the Trifolium area was cracked; and canal banks were cracked. Slight damage also was reported in the nearby towns of Brawley, Calexico, Coachella, El Centro, Holtville, and Imperial. Felt over a large area of southern California and into southwest Arizona. (Ref. 24, 259, 292.) 1951. Jan. 25. Near San Leandro, Alameda County, Calif. Windows were broken or cracked and dishes fell from shelves at Oakland. Large chunks of plaster fell in the San Leandro Post Office, and dishes broke in houses. Felt over a small area of Alameda and Contra Costa Counties. (Ref. 24, 259, 324.) 1951. July 29. Pinnacles National Monument area, San Benito County, Calif. Chimneys twisted, plaster fell, and concrete pipes were damaged slightly at Pinnacles. Plaster fell in some houses in San Benito, and the highway from San Benito to Hernandez Valley was covered with boulders. Out- side stucco and plaster walls were damaged slightly at Bitterwater (Lonoak). Felt from Pescadero (San Mateo County) in the north to San Luis Obispo in the south and Caruthers (Fresno County) in the east. (Ref. 24, 259, 324.) 1951. Aug. 6. Pinnacles National Monument area, San Benito County, Calif. Plaster was downed and vases were overturned south of Hollister, at the Harris Ranch. This earthquake was felt over the coastal area of west-central California. Two aftershocks were felt at 09 54 and 17 21 UTC. (Ref. 24, 259, 324.) 1951. Oct. 8 (Oct. 7). Off Cape Mendocino, Humboldt County, Calif. Damage was consider- able to a partly completed bridge over the Van Duzen River near Alton: columns were out of plumb, spans were out of position, diagonals were bent, and anchor bolts and grout pads were damaged. Cracks about 36 m in length formed in the pavement of both approaches to the bridge and in fill beside the approaches. Chimneys were broken or toppled at Bridgeville, Fortuna, Grizzly Blufl‘ (a fireplace also was damaged considerably), Metropolitan, Rio Dell, Scotia, and Weott. This strong shock was felt along the coast from Orick (Humboldt County) in the north to Manchester (Mendocino County) in the south and east to Red Bluff (Tehama County) and Richvale (Butte County). Magnitude 6.0 MS CFR. (Ref. 24, 259, 324, 563.) 1951. Nov. 14. South of Eureka, Humboldt County, Calif. A large window was broken in the Humboldt Times building in Eureka; windows and 144 dishes were broken at Fields Landing; and plaster was cracked in a store at Fortuna. Felt over a small area in the Eel River Valley in northwest California. (Ref. 24, 259, 324, 563.) 1951. Dec. 5. Near Brawley, Imperial County, Calif. About 16 km north of Brawley, a crack about 30 m long and 4 cm wide formed in a gravel road; canal banks were damaged; plumbing broke in several houses; windows broke and stucco was damaged; and ceiling lights crashed to the floor. A bridge across the Highland canal also was dam— aged. One artesian well ejected water 3 In during the shock, and another well ran muddy water. Felt over a small area of the Imperial Valley in southeast California. (Ref. 24, 259, 292, 563.) 1951. Dec. 26 (Dec. 25). Near the southeast point of San Clemente Island, Calif. This Christ- mas Day earthquake caused slight damage to plaster, windows, or chimneys at Avalon, Long Beach (a large piece of tile also fell), San Diego, San Clemente Island, and San Pedro. The sharp shock was felt over a large area of southwest California and proba- bly into northern Baja California. Magnitude 5.9 MS CFR, 5.9 Ms GR. (Ref. 24, 259, 292.) 1952. Feb. 9. Northeast of Lone Pine, Inyo County, Calif. A series of three earthquakes occurred in the Lone Pine area. A building was cracked by the main shock at 08 43 UTC, and plaster fell in several houses. A cafe sustained a large crack that extended halfway around the building and com— pletely through the wall. Felt only at a few towns in Inyo County. (Ref. 25, 259, 292.) 1952. July 21, 11 52 UTC. South of Bakers- field, Kern County, Calif. This earthquake was the largest in the conterminous United States since the San Francisco shock of 1906. It claimed 12 lives and caused property damage estimated at $60 million. MM intensity XI was assigned to a small area on the Southern Pacific Railroad southeast of Bealville. There, the earthquake cracked reinforced-concrete tunnels having walls 46 cm thick; it shortened the distance between portals of two tunnels about 2.5 In and bent the rails into S-shaped curves. At Owens Lake (about 160 km from the epicenter), salt beds shifted, and brine lines were bent into S-shapes. Many surface ruptures were observed along the lower slopes of Bear Mountain, in the White Wolf fault zone. The somewhat flat, poorly consolidated alluvium in the valley was erratically cracked and recontoured. The cracking along Bear Mountain indi- cated that the mountain itself moved upward and to the north. Southwest of Arvin, on the San Joaquin Valley floor, ground cracks traversed and split the concrete foundation of one house, causing partial SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) collapse. The ground slumped; cotton rows were off- set more than 30 cm; and pavement on one highway was crumpled for more than 300 In. East of Caliente, one large crack, about 1.5 In at its widest point and more than 60 cm deep, was observed. Fill areas in the mountainous region along US. Highway 466 (now State Highway 58) settled from a few centime- ters to more than 30 cm in places, and a large part of the highway was cracked and wrinkled. Northeast of that highway, the ground was displaced vertically about 60 cm and horizontally about 45 cm. Maximum MM intensities in nearby cities did not exceed VIII. At Tehachapi, Bakersfield, and Arvin, old and poorly built masonry and adobe buildings were cracked, and some collapsed. Property damage was heavy in Tehachapi, where both brick and adobe buildings were hit hard, and 9 people were killed. Three people were killed in other towns. Although damage was severe, the total extent of damage to property did not exceed that in Long Beach in 1933. Only a few wood-frame structures were damaged seriously in this earthquake, com- pared to the 1933 shock in which many such struc- tures were thrown off foundations. The generally moderate damage in Bakersfield was confined mainly to isolated parapet failure. Cracks formed in many brick buildings, and older school buildings were damaged somewhat. In contrast, how— ever, the Kern General Hospital was damaged heavily. Multistory steel and concrete structures sus- tained minor damage, which commonly was confined to the first story. Similar kinds of damage also occurred at Arvin, which lies southeast of Bakersfield and west of Tehachapi. Reports of long-period wave effects from the earth- quake were widespread. Water splashed from swim- ming pools as far distant as the Los Angeles area, where damage to tall buildings was nonstructural but extensive. Water also splashed in pressure tanks on tops of buildings in San Francisco. At least one building was damaged in San Diego, and in Las Vegas, Nev., a building under construction required realignment of the structural steel. The main shock was felt over most of California and in parts of western Arizona and western Nevada (see fig. 20). It was observed at such distant points as Stirling City, Calif, Phoenix, Ariz., and Gerlach, Nev. The California Institute of Technology at Pasa- dena recorded 188 aftershocks of magnitude 4.0 and higher through September 26, 1952; six aftershocks on July 21 were of magnitude 5.0 and higher. Mag- nitude 7.8 MS ABE, 7.3 mb ABE, 7.7 Ms CFR, 7.7 Ms GR, 7.0 MLa ELL, 7.21 ML KJ. (Ref. 25, 38, 292, 460, 521, 533, 549.) EARTHQUAKES IN CALIFORNIA 145 Building in Bakersfield, California, damaged by the Kern County earthquake of July 21, 1952. (Source of photograph unknown.) 1952. July 21, 12 05 UTC. Kern County, Calif., aftershock. This earthquake was felt at Huasna. Magnitude 6.4 Ms CFR. (Ref. 25, 292.) 1952. July 21, 15 13 UTC. Kern County, Calif., aftershock. A strong aftershock (time reported as 07 20 PST) caused additional damage to buildings in the Arvin area. (Ref. 25, 259, 292.) 1952. July 23, 00 38 UTC (July 22). Kern County, Calif., aftershock. A large aftershock of the July 21 earthquake caused damage to an old brick building in Arvin that was damaged in the main shock. Slight damage also occurred south of Bakersfield and at Fresno. This shock was reported mainly in Kern County. Magnitude 6.1 MS CFR. (Ref. 25, 259, 292.) 1952. July 23, 07 53 (July 22), 13 17, and 18 13 UTC. Kern County, Calif., aftershocks. One house at Arvin that sustained only minor damage in the main event on July 21 was almost destroyed by the aftershock at 07 53 UTC. Walls and fronts of buildings of weakened structures collapsed; gas and water mains were broken; and transformers were torn off. The second aftershock also caused serious damage to already weakened buildings at Arvin and Tehachapi, and the third caused only minor damage at Arvin. These aftershocks were reported only at a few towns in Kern County. (Ref. 25, 259, 292.) 1952. July 25, 19 09 and 19 43 UTC. Kern County, Calif., aftershocks. Some pipeline damage and changes in ground level occurred 8 km south of Bakersfield (at Fairfax) as a result of these strong aftershocks. Light damage to buildings was reported from several towns in the area. Ground cracks were enlarged in Tejon Canyon, 16 km southeast of Arvin. 146 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Railroad tracks near Bealville, California, bent and twisted by the July 21, 1952, earthquake. (Photograph from the National Geophysical Data Center, NCAA.) Landslides occurred in the Caliente Creek Canyon, Oiler Canyon Grade, State Highway 178 (between Bakersfield and Kernville), and White Wolf Ranch. Both shocks were felt over a wide area of south-cen- tral California. (Ref. 25, 259, 292.) 1952. July 29, 07 03 UTC (July 28). Kern County, Calif., aftershock. Another strong after- shock of the July 21 earthquake caused severe dam- age to buildings that were damaged in the main earthquake. One store at Bakersfield sustained additional damage, including a collapsed parapet and a crumbled wall. Cracks formed in several large buildings, and bricks tumbled from the tops of previ- ously damaged structures. At least 10 fires were ignited in the area. Moderate damage to chimneys and walls occurred at Edison. This aftershock was felt widely in south-central Californiaf Magnitude 6.1 MS CFR. (Ref. 25, 259, 292.) 1952. July 31, 12 09 UTC. Kern County, Calif., aftershock. Another aftershock at Arvin jarred bricks loose and broke windows. Slight dam- age also occurred at Bakersfield and in the area of Taft. Felt over a small area of south-central Califor- nia. (Ref. 25, 259, 292.) 1952. Aug. 13, 17 39 UTC. Kern County, Calif., aftershock. The earthquake caused slight damage to brick at Arvin. The shock also was reported felt in Los Angeles. (Ref. 25, 259, 292.) 1952. Aug. 22. East of Bakersfield, Kern County, Calif. Heavy damage, estimated at $10 million, occurred in the downtown area of Bakers— field. Two people were killed and several were injured. Damage was confined mainly to brick buildings in a 64-block area of downtown Bakersfield. Larger, multistory, concrete and steel frame buildings sus- tained rather light damage. There were few complete collapses of buildings, but out of 396 structures that were damaged, 90 or more had to be razed. Many of these buildings had suffered considerable damage EARTHQUAKES IN CALIFORNIA 147 124° 122° 120° 118° 116° 114° ! I I ! ' ! 'V"V : i I I .0rovme l . I. II III I new 1' ‘ I D ' l ‘ I. i ‘ ‘- NEVADA i UTAH .\ . I r .\ I '\ ' I ‘~ 1 38° \\ . ‘4 ' _ San Francisco ‘ \~\ \ § CALIFORNIA 'x. @ V-Vl - lo BishOpQ Monterey ' V-Vl 'zresno % ‘ @113 36° (f \ ,0 / ARIZONA o I O N ., 1 ‘ 34° G M EXPLANATION * Epicenter VIII Intensity 8 ‘ 32° '\--\_ Figure 20.—Isoseismal map for the Kern County, California, earthquake of July 21, 1952. Isoseismals are based on intensity estimates from data listed in references 25, 259, and 549 of table 1. from the earthquake on July 21, 1952, and the after- shocks. Outside the downtown area, chimneys twisted and fell, and plaster and walls cracked. Felt over a large part of south-central California—from Hollister south to Los Angeles and from the coast east to the Nevada border. (Ref. 25, 292, 549.) 1952. Aug. 23. Near Acton, Los Angeles, County, Calif. Southwest of the epicenter, slight damage was reported in Ventura County at Camarillo, Moorpark, and Oxnard. Chimneys were cracked at Moorpark, and a water tower was dam- aged at Amboy (San Bernardino County). The higher intensities reported north into Kern County and at Amboy (northeast of San Bernardino) may be due to confusion with other shocks on Aug. 22. (Ref. 25, 259, 292.) 1952. Sept. 22. Southwest of Petrolia, Hum- boldt County, Calif. At Petrolia, some houses were 148 displaced as much as 5 cm on their foundations. Several chimneys fell and many were others were damaged. An oil well casing cracked at the Petrolia Oil Well Company, and a bunkhouse was displaced from its foundation. This shock generally was felt from the Eureka area on the north, south along the coast to Elk (Mendocino County), and east from the coast to the Ruth area (Trinity County). (Ref. 25, 259, 324.) 1952. Nov. 22 (Nov. 21). Near Bryson, Monterey County, Calif. Chimneys twisted and fell in the Bradley area and at San Luis Obispo; five or more old chimneys were knocked down at Bryson. Cracks formed in walls of buildings and in the ground in the Bryson area. Felt along the coast from San Francisco on the north to the Los Angeles area on the south and as far east as Olancha (Tulare County). Magnitude 6.0 MS CFR, 6.0 Ms GR. (Ref. 25, 259, 476.) 1953. May 25, 04 07 UTC (May 24). Near Cal- pella, Mendocino County, Calif. This earthquake reportedly cracked walls and twisted doors out of line at Calpella. Felt only at a few other towns in the area. (Ref. 26, 259, 324.) 1953. June 14, 04 17 UTC (June 13). Brawley area, Imperial County, Calif. Damage was consid~ erable near Brawley, where chimneys cracked and fell. At the Thistle Lateral Canal (5 km south of Westmorland), the shock damaged one of the canal structures and cracked several meters of bank along the canal. The ground settled extensively at the Tokay Canal. Felt north to the Palm Springs area (Riverside County), west to San Diego, and southeast to Yuma, Ariz. Several aftershocks occurred. (Ref. 26, 259, 292.) 1954. Jan. 12. West of Wheeler Ridge, Kern County, Calif. The epicenter of this earthquake was close to that of the major shock of July 21, 1952. This shock caused minor damage at the Maricopa Seed Farm, about 25 km east of Maricopa. The dam- age included broken bracing rods in three steel-frame corrugated-iron buildings and a shattered base of one elevated water tank. Near the farm, unanchored platform pole transformers were toppled. Slight damage was reported from many towns in the area. The earthquake also was observed slightly in tall buildings in Sacramento, San Diego, and San Fran- cisco. (Ref. 27, 259, 292.) 1954. Mar. 19, 09 54 UTC. Santa Rosa Moun- tains, Riverside County, Calif. Minor damage reported at several towns in the area included fallen plaster from walls, broken windows and dishes, bro- ken water pipes, cracked swimming pools, and dam- aged stock in stores. The main shock was felt over a SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) large area of southern California and parts of west- ern Arizona and southwest Nevada. Of the many aftershocks that were located, the largest occurred on Mar. 19 at 10 21 UTC. Magnitude 6.2 Ms CFR, 6.2 MLa ELL (main shock). (Ref. 27, 259, 292, 521.) 1954. Apr. 22. East of Watsonville, Santa Cruz County, Calif. Plaster fell and walls cracked at Gilroy, and dishes broke and knickknacks fell at Aptos. Felt over a small area of the coastal region of west-central California. (Ref. 27, 259, 324.) 1954. Apr. 25. East of Watsonville, Santa Cruz County, Calif. Several poorly built houses, east of Watsonville along the Chittenden Road, were damaged severely when they were shifted on their foundations; ground cracks formed along the Pajaro River. Several chimneys toppled at Aromas and in the lnterlaken District. The shock was strong enough to shatter a few windows and knock plaster from walls in the San Francisco Bay area. It was felt along the coast from Santa Rosa (Sonoma County) on the north to San Ardo (Monterey County) on the south and east as far as Fresno. (Ref. 27, 259, 324.) 1954. Aug. 26. Off the coast of Ventura County, near Anacapa Island, Calif. This slight earthquake shook plaster from the ceiling of the Ven- tura County Courthouse. Felt slightly at several towns in the area. (Ref. 27 , 259, 292.) g 1954. Nov. 10. Near Lakeport, Lake County, Calif. Slight damage in the form of cracks in win- dows, concrete, and plaster occurred at Nice, Potter Valley, Talmage, Willits, and Witter Springs. The earthquake was observed over a small area of Lake and Mendocino Counties. (Ref. 27, 259, 324.) 1954. Nov. 25. Off Cape Mendocino, Calif. The shock caused no damage but was felt over a large area of Humboldt and Mendocino Counties. Magnitude 6.5 Ms CFR. (Ref. 27 , 259, 324.) 1954. Dec. 17 (Dec. 16). East of San Leandro, Alameda County, Calif. Chimneys and a water main were broken at Oakland, and plaster fell. Cracks in plaster and walls were reported at Hay- ward and San Leandro. Felt over a moderate area of west-central California. (Ref. 27 , 259, 324.) 1954. Dec. 21. Near Eureka-Arcata, Hum- boldt County, Calif. This earthquake and a strong aftershock on Dec. 30 caused property damage esti- mated at $2.1 million. One person was killed when he fell into Humboldt Bay, and several people were injured by falling objects. The shock caused only slight structural damage to reinforced concrete and concrete block and wood- frame buildings in the Eureka-Arcata areas. The Eureka City Hall and the Humboldt County Court- house in Eureka were cracked extensively. The main EARTHQUAKES IN CALIFORNIA damage in both Arcata and Eureka was to chimneys, plaster, plate-glass windows, and merchandise in stores, but several old and poorly constructed brick walls bulged, and some parapet damage was sus- tained. Damage to structures and underground pipe- lines occurred in areas of unstable ground. Previous ground settling, as well as subsidence at the time of the shock, were observed in some of the damaged areas. Between Eureka and Arcata, US. Highway 101 was cracked and bulged in places. Felt from southern Oregon on the north to San Francisco on the south and to Lake City (Modoc County) on the east. A strong aftershock occurred on Dec. 30. Magnitude 6.6 MS CFR (main shock). (Ref. 27, 259, 480, 533, 550.) 1954. Dec. 30. Near Eureka-Arcata, Hum- boldt County, Calif. An aftershock of the Dec. 21 earthquake broke plate-glass windows, cracked chim- neys, and further damaged the Eureka water-supply pipeline. (Ref. 27, 259, 324, 550.) 1955. Mar. 2. Near San Ardo, Monterey County, Calif. About 1.5 km west of San Lucas, a brick chimney collapsed on a house. Plaster was cracked at Adelaida, Indian Valley (northeast of San Miguel), and Templeton. Felt north along the coast to Pescadero (San Mateo County), south to Lompoc (Santa Barbara County), and east to Avenal (Kings County). (Ref. 28, 259, 324.) 1955. Apr. 29. Near Lower Lake, Lake County, Calif. Chimneys, Windows, and dishes were broken, and plaster and walls were cracked at Lower Lake. Felt mainly in Lake County over a small area. (Ref. 28, 324.) 1955. May 7. Near Lower Lake, Lake County, Calif. A few weak chimneys on older houses fell at Lower Lake, and plaster cracked and fell. Minor damage also was sustained at Clearlake Highlands— walls, ceilings, and floors cracked; a chimney was damaged; and much plaster fell. Felt mainly in Lake County over a small area. Several slight aftershocks were reported. (Ref. 28, 259, 324.) 1955. Sept. 5 (Sept. 4). East of San Jose, Santa Clara County, Calif. This earthquake caused extensive minor damage, estimated at $100,000 in the San Jose area. The damage con- sisted mainly of toppled chimneys and broken plate- glass windows. Damage was most severe in the Wil- low Glen District of San Jose, about 13 km west of the epicenter, where about 100 chimneys were dam- aged and many collapsed. One house was displaced on its foundation. Walls were cracked at the County Hospital and County Jail, and a brick garden wall toppled. Felt north to Santa Rosa (Sonoma County), south to San Ardo (Monterey County), and east to 149 the La Grange area (Stanislaus County). (Ref. 28, 259, 324.) 1955. Oct. 24 (Oct. 23). Concord-Walnut Creek area, Contra Costa County, Calif. This earthquake killed one person and caused property damage estimated at $1 million. The damage gener— ally was minor, however, consisting mainly of cracked walls and plaster, broken windows, and loss from damaged merchandise. Damage was most severe at Walnut Creek where walls cracked, 80 plate-glass windows were broken, and much damage occurred to store merchandise. Minor damage to brick chimneys (some toppled) and walls occurred at several other towns in the region. Felt over a moderate area of west-central California. Several aftershocks occurred. Magnitude 5.4 Ms CFR. (Ref. 28, 259, 324, 533.) 1955. Nov. 2. Near San Ardo, Monterey County, Calif. This earthquake cracked plaster at Bryson, King City, and San Miguel and broke dishes at San Ardo. Felt over a small area along the coastal region of west-central California. (Ref. 28, 259, 324.) 1955. Dec. 17, 06 07 UTC (Dec. 16). Near Brawley, Imperial County, Calif. This main shock of a series caused minor damage at Brawley. The ceiling in a hardware store buckled; cracks formed in walls of buildings and existing cracks were enlarged; 12 water mains broke; street lights and about 20 plate-glass windows broke; and merchandise in stores was damaged. Slight damage also was reported at Calexico, El Centro, Holtville, and Impe- rial. Felt over a moderate area of southern Califor- nia and western Arizona. About 81 earthquakes were felt in Brawley through 11 51 UTC, Dec. 19. (Ref. 28, 259, 292, 564.) 1956. Jan. 3 (Jan. 2). Near Glen Ivy, River- side County, Calif. Broken windows, dishes, and plaster were reported from several nearby towns. Rockslides were reported in the area of Glen Ivy, in Temescal Canyon. Felt along the coast of southern California. (Ref. 29, 259, 292.) 1956. Feb. 9. Baja California, Mexico. Near El Alamo, Mexico, a new fault line, 29 km long, was reported, and new springs formed along the fault line. Minor damage, consisting mainly of broken windows, cracked plaster, and damaged stock in stores, was reported from Yuma, Ariz., and from sev- eral towns in southern California. Felt over a large area of southern California and western Arizona. Many aftershocks occurred through Apr. 26, 1956. (Ref. 29, 38, 259, 292.) 1956. Apr. 5 (Apr. 4). Near Saint Helena, Napa County, Calif. In the Angwin—Saint Helena Sanitarium area, residents reported many instances 150 of cracks in plaster walls and concrete foundations. Tile flooring was cracked at the sanitarium. At Saint Helena, plaster fell from a ceiling and pine walls were cracked. Felt over a small part of the coastal area of north—central California. (Ref. 29, 259, 324.) 1956. Oct. 11, 16 48 UTC. Off the coast of Humboldt County, Calif. With the exception of a few broken dishes at Eureka, no damage was reported. Felt over a small area of Humboldt County. Magnitude 6.0 Ms CFR. (Ref. 29, 259, 324.) 1956. Nov. 16 (Nov. 15). Northwest of Park- field, Monterey County, Calif. Plaster cracked at the Mee Ranch (Lonoak). The shock was reported felt in Fresno, Kings, Monterey, San Benito, San Luis Obispo, Santa Barbara, and Santa Cruz Counties. (Ref. 29, 259, 324.) 1957. Mar. 18. South of Oxnard, Ventura County, Calif. Minor damage at Oxnard, Port Huen- eme, and Ventura consisted mainly of cracked walls, fallen plaster, and loss from breakage of stock in stores. Felt over a small area of southern California, mainly in Ventura County. (Ref. 30, 259, 324.) 1957. Mar. 22 and 23. West of Daly City, San Mateo County, Calif. These earthquakes caused property damage estimated at $1 million and injured about 40 people. The first and strongest shock caused one death. Minor damage at several houses was reported along the ocean in the Westlake-Palisades tract, west of Daly City. Many chimneys were dam- aged at Daly City. In San Francisco, damage to chim- neys, plaster, windows, and merchandise was widespread. The pavement along the edge of Lake Merced sloughed off into the lake, and both ends of a pedestrian bridge collapsed. Landslides blocked State Highway 1 near Mussel Rock, and the shoulder of the highway was cracked extensively. The main shock was felt over a moderate area of west-central California, and many aftershocks were observed. The shock on Mar. 23 caused slight dam- age at Menlo Park and San Francisco. Magnitude 5.3 Ms CFR, 5.27 ML KJ (both Mar. 22). (Ref. 30, 259, 324, 460, 533, 599.) 1957. Apr. 25, 21 57 UTC. Southwest end of Salton Sea, Imperial County, Calif. The most severe effects of this earthquake occurred in the Cali- patria area, about 2.5 km north of Vail Canal, where a strip of land about 0.6 km wide and 1.5 km long was broken and cracked; water seeped from hun- dreds of blowholes that formed. Only slight damage was reported at other towns in the area. The main shock was felt over much of southern California and western Arizona. Many aftershocks occurred. (Ref. 30, 259, 292.) SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 1958. Sept. 21 (Sept. 20). Southeast of Soledad, in San Benito County, Calif. This local earthquake cracked a fireplace and broke dishes in the San Benito area. A landslide and damage to two other houses were reported in the area also. (Ref. 31, 324.) 1958. Oct. 1. Southeast of Sierraville, Sierra County, Calif. This earthquake cracked chimneys at Hallelujah Junction (about 30 km northwest of Reno, Nev.) and broke dishes at Reno. Felt over a small area of northeast California and western Nevada. (Ref. 31, 259, 324.) 1958. Dec. 1 (Nov. 30). Baja California, Mex- ico. A series of moderate earthquakes in Mexico caused minor damage in California at Calexico, Nestor, Potrero, and Seeley. The damage included fallen plaster from walls and slight cracks in chim- neys, walls, and windows. The main shock at 03 21 UTC was felt over much of southern California and in parts of western Arizona. (Ref. 31, 259, 292.) 1958. Dec. 11. Southwest of SanFrancisco, Calif. Cracked plaster and windows, broken dishes, and damaged stock in stores were reported from sev- eral Bay area towns. Near Daly City, a minor land- slide occurred on State Highway 1. Felt over a small area of west-central California. (Ref. 31, 259, 324.) 1959. Mar. 2. Near Gilroy, Santa Clara County, Calif. Residents of several towns near Gil- roy reported slight damage, including broken win- dows, cracked plaster, and loss from fallen stock. One minor earthslide occurred east of Watsonville, and boulders rolled onto a highway between Gilroy and Watsonville. In San Francisco, 70 windowpanes were broken in one store. Felt along the coastal area from Jenner on the north to Big Sur on the south and inland to Gustine. (Ref. 32, 259, 324.) 1959. Apr. 1. Northeast of Loyalton, Sierra County, Calif. Most of the serious property damage occurred at Loyalton, where several chimneys fell, windows were broken, and plaster and walls were cracked. Felt over a large area of northeast Califor- nia and western Nevada. (Ref. 32, 259, 324.) 1959. Apr. 6 (Apr. 5). North of Ukiah, Men- docino County, Calif. Chimneys cracked and win- dows broke at Redwood Valley. Felt in Lake and Mendocino Counties in northwest California. (Ref. 32, 259, 324.) 1959. May 26. Near Salinas, Monterey County, Calif. Windows and dishes were broken at Salinas, and a wall was cracked. Slight damage also occurred at Camp McCallum and Hollister. Felt most strongly in the area around Monterey Bay. (Ref. 32, 259, 324.) EARTHQUAKES IN CALIFORNIA 1959. Oct. 24. Near Owens Peak, Kern County, Calif. A series of four earthquakes occurred in the Owens Peak area, the first of which was the strongest. Two hunters in the area reported that boulders tumbled down the mountainside and that a landslide occurred. Tops of dead trees were snapped off. Several shocks also were reported by residents of nearby Onyx. (Ref. 32, 259, 292.) 1959. Dec. 29 (Dec. 28). Northwest of Hollis- ter, San Benito County, Calif. A few chimneys toppled at Hollister, and a large piece of timber fell from the roof of the City Hall building. Felt over the coastal area of west-central California from San Francisco south to San Miguel (San Luis Obispo County). (Ref. 32, 259, 324.) 1960. Jan. 20 (Jan. 19). South of Hollister, San Benito County, Calif. Minor damage occurred south of Hollister at a winery and a nearby ranch. At the Winery, small bits of a ceiling fell, a chimney cracked at its roofline, cracks formed in pavement, and an underground pipeline broke. At the ranch, walls were cracked and an existing crack in a reser- voir was enlarged. Felt along the coastal areas north of San Luis Obispo to San Francisco and inland to Merced. (Ref. 33, 259, 324.) 1960. June 6 (June 5). Off the coast of Hum- boldt County, Calif. Slight damage occurred at Eureka, where plaster fell in the Old City Hall. At Crannell, north of Eureka, a brick chimney on one house was twisted slightly. Felt mainly in Humboldt and Trinity Counties. (Ref. 33, 259, 480.) 1961. Jan. 28. Near Walker Pass, Kern County, Calif. Slight damage was reported at Johannesburg, where the floor of a carport was cracked, and at Bodfish, where dishes were broken. At Kernville, rocks rolled down the mountainside. Felt over a large area, mainly in Kern and Tulare Counties. Many aftershocks were recorded. (Ref. 34, 259, 292.) 1961. Apr. 9, 07 23 and 07 25 UTC (Apr. 8). South of Hollister, San Benito County, Calif. Two strong earthquakes damaged many buildings at Hollister, but major damage was confined to the County Courthouse, the Dabo Hotel, and the Elks building. Property damage was estimated at $250,000. South of Hollister, on Cienega Road, a 15- m-long fissure occurred near a winery, which also sustained severe damage. Some chimneys in the area were damaged or fell, and water lines were ruptured. Felt along the coast of west-central California from the San Francisco Bay area south to Creston (San Luis Obispo County). (Ref. 34, 38, 259, 324.) 1961. Oct. 19 (Oct. 18). East of Brown, Kern County, Calif. This shock shifted heavy machinery 151 and changed the water level in one well near Brown. The only damage was reported from Mojave, where slight cracks formed in a bathroom. The earthquake was reported in a few scattered areas of northern Los Angeles and San Bernardino Counties in south-cen- tral California. (Ref. 34, 259, 292.) 1961. Oct. 20. Near Huntington Beach, Orange County, Calif. This earthquake was one of a series of nine sharp tremors, that were felt mainly in Orange County. The main shock caused slight damage, including broken windows, cracked plaster and walls, and damaged stock in stores, in several towns in the County. (Ref. 34, 259, 292.) 1961. Nov. 15 (Nov. 14). Near Wheeler Ridge, Kern County, Calif. At Wilsona, in Antelope Valley, cracks formed in the walls of a building, the bottom of swimming pool, and in the ground. Damage was not reported from other towns in the area. This shock was felt mainly in Kern County, but also was observed in scattered areas of Kings, Los Angeles, Santa Barbara, Tulare, and Ventura Counties. (Ref. 34, 259, 292.) 1962. Apr. 27. Near Perris, Riverside County, Calif. Damage was slight at Romoland where win- dows and dishes were broken and at Winchester where cracks formed in walls, plaster, and Windows. Felt over a small area of southern California, mainly in Riverside and San Bernardino Counties. (Ref. 35, 259, 292.) 1962. June 6. Near Lakeport, Lake County, Calif. In the area near Lakeport, water in Scott Creek (which was almost dry before the shock) rose about 0.5 m and flowed steadily for 11 days. The water in several wells in Scott Valley rose 2—3 m and turned milky white for 3—5 days. About 16 km south- west of Lakeport, a geyserlike spout of water was observed in Clear Lake. Slight damage, which occurred mainly in the Lakeport-Ukiah area, included fallen bricks from fireplaces and cracks in chimneys and walls. One chimney fell at Finley. Felt mainly in Lake and Mendocino Counties. (Ref. 35, 259, 324.) 1962. Aug. 23. Off the coast of Del Norte County, Calif. Slight damage occurred, mainly in the Crescent City—Smith River areas of Del Norte County. Damage consisted of broken windows, cracks in chimneys and walls, and loss from fallen stock in stores. The tops of some redwood trees were snapped off. Felt over a moderate area of northern California and southwest Oregon. (Ref. 35, 259, 480.) 1962. Sept. 4. Northwest of Arcata, Hum- boldt County, Calif. Plaster fell at the Eureka County Courthouse; new cracks formed in the walls of the old high school building; and windows broke at 152 a drugstore. At Orick, plaster and walls were cracked and stock fell in stores. Felt over a small area of northern California, mainly in Humboldt County. (Ref. 35, 259, 480.) 1962. Oct. 29 (Oct. 28). Near Big Bear, San Bernardino County, Calif. A window was broken and stock fell from shelves at Big Bear City, and a water main was broken at Redlands. Rocks rolled onto the highway between Bear Valley and Lucerne Valley. Felt mainly in Riverside and San Bernardino Counties. Many aftershocks were recorded. (Ref. 35, 259, 292.) 1963. May 22. West of Sunnyvale, in Santa Cruz County, Calif. One roof reportedly caved in at Sunnyvale. Felt over a small part of the coastal area of west-central California. (Ref. 36, 259, 324.) 1963. May 23, 15 53 UTC. Imperial Valley, Calif. The main shock of a series on May 22—23 caused minor damage at Brawley (plate-glass win- dow broke; plaster cracked) and Westmorland (plas- ter fell; windows and dishes broke). Felt mainly in the Imperial Valley of southern California. (Ref. 36, 259, 292.) 1963. June 7. West of Antioch, Contra Costa County, Calif. Slight damage occurred at Antioch, where cracks formed in the walls and foundation of a school, old cracks were enlarged, and beams and doors “twisted.” Plaster was cracked at Clayton, Con- cord, and Cowell. Felt in the San Francisco Bay area, mainly in Contra Costa County. (Ref. 36, 259, 324.) 1963. Sept. 14, 19 46 UTC. Near Watsonville, Monterey County, Calif. The earthquake caused minor damage east of Watsonville in the Chitten- den—Soda Lake area. In this small area along the San Andreas fault, the second floor of a wood-frame house was displaced; a water tank shifted on its foundation; one stone chimney was shaken loose, and one was cracked; and footings of a bridge across the Pajaro River were damaged slightly. Landslides were reported in the Soda Lake and Pajaro Gap areas. Felt along the coastal area of west—central California from Bolinas to Big Sur. (Ref. 36, 259, 467.) 1963. Sept. 23. Near San Jacinto, Riverside County, Calif. Chimneys were cracked and twisted at Hemet. Plaster cracked and fell at Hemet and San Jacinto, and windows and dishes were broken. Felt over a large part of southern California—from Los Angeles east to 'IVventynine Palms (San Bernardino County) and south to San Diego. (Ref. 36, 259, 292.) 1963. Dec. 6. Near Toms Place, Mono County, Calif. Plaster was cracked at Bishop and in the Par- adise area northwest of Bishop. Also, a 230-kV—trans- former bushing was cracked at Bishop. Felt over a SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) moderate area of east-central California and western Nevada. (Ref. 36, 259, 292.) 1964. June 21. California-Mexico border region. Plaster fell from a 2-m-long crack in the ceil- ing of a building at San Diego, and new cracks formed in the beams at the post office. Slight damage also was reported at Coronado. Felt over a small area of southwest California. (Ref. 37, 259, 292.) 1964. Nov. 16 (Nov. 15). Near Corralitos, Santa Clara County, Calif. The most serious dam- age to property occurred in Corralitos. Several chim- neys were toppled there, other chimneys were twisted, and water service was disrupted. Minor damage occurred at several towns in the Corralitos area. Felt along the coast of west-central California from Napa on the north to San Simeon (San Luis Obispo County) on the south. Magnitude 4.5 mb NUT, 4.3 Ms NUT. (Ref. 37 , 259, 263, 324.) 1964. Dec. 22. West of Ensenada, Mexico. The San Diego area sustained the most severe dam- age, which included fallen stones from a chimney, exterior crack in a fire station wall, broken windows, and fallen light fixtures. Slight damage also occurred at Boulevard, Imperial Beach, La Mesa, and Potrero. Felt along the coast from Los Angeles to Tijuana (Mexico) and inland to Calipatria (Imperial County). Magnitude 5.0 mb NUT, 5.5 MS NUT. (Ref. 37, 259, 263, 292.) 1965. Jan. 1. Southwest of Fontana, San Ber- nardino County, Calif. Glassware and dishes were broken at Fontana, and the ceiling of one house was shattered. A cement sidewalk was cracked at Lytle Creek, northwest of San Bernardino. Felt over a small area, mainly in Riverside and San Bernardino Counties. (Ref. 75, 259, 292.) 1965. Apr. 15. San Bernardino Valley, Calif. The press reported broken windows and merchan- dise shaken from shelves throughout the San Ber— nardino Valley, including Chino, Colton, Fontana, Rialto, and San Bernardino. Felt in Los Angeles, Orange, Riverside, and San Bernardino Counties. (Ref. 75, 259, 292.) 1965. June 16 (June 15). Imperial Valley, Calif. This was the main shock of a series that occurred in the Imperial Valley June 15—17. Slight damage was sustained at Westmorland, where plate- glass windows and dishes were broken, and at Impe- rial, where walls were cracked. Felt over a small area of Imperial County. (Ref. 75, 259, 292.) 1965. July 16 (July 15). Near Saugus, Los Angeles County, Calif. Stucco was cracked in sev- eral places in a house at Saugus, and one existing crack in cement was enlarged. Felt mainly in Kern and Los Angeles Counties. (Ref. 75, 259, 292.) EARTHQUAKES IN CALIFORNIA 1965. Sept. 10. Near Pittsburg, Contra Costa County, Calif. Windows were broken in two houses at Concord, and in two stores at Pittsburg. At Cow- ell, chimneys were cracked and dishes were broken. Small rockslides were observed in Mount Diablo State Park. Felt over a small part of the San Fran- cisco Bay region, mainly in Contra Costa County. (Ref. 75, 259, 324.) 1965. Sept. 25, 17 43 UTC. Southeast of Newberry, San Bernardino County, Calif. The main shock of a series of three events on Sept. 25 and 26 first increased and then decreased the flow of a spring at the Camp Cady Ranch, south of Manix Station. Gas pipes were damaged at Newberry, caus- ing an explosion; an underground water tank was cracked at Hodge; and plaster cracked and fell at Kelso. The main shock was felt over a large area of southern California and at a few towns in southern Nevada and southwest Arizona. Two strong after- shocks were felt in the area at 17 48 UTC on Sept. 25 and 07 00 UTC on Sept. 26. Magnitude 4.7 mb NUT, 4.4 Ms NUT. (Ref. 75, 259, 263, 292.) 1965. Oct. 17. Near Palm Springs, Riverside County, Calif. At Palm Springs, windows cracked and dishes broke, and at Cathedral City, a garden wall cracked. Felt mainly in Riverside and San Ber- nardino Counties. (Ref. 75, 259, 292.) 1965. Nov. 12. South of Glendale, Los Ange- les County, Calif. Minor cracks formed in concrete on the 30th floor of the Occidental Center in Los Angeles, and plaster was cracked slightly in the Fed- eral Building in Glendale. Felt only in a small area of southwest Los Angeles County. (Ref. 75, 259, 292.) 1966. May 24 (May 23). Near Chico, Butte County, Calif. This light shock generated a rock- slide at Las Plumas, near Oroville, and cracked plas- ter northeast of Chico, at Forest Ranch. Felt over a moderate area in east-central California. Magnitude 3.8 mb NUT, 4.0 Ms NUT. (Ref. 81, 259, 263, 324.) 1966. June 28, 04 26 UTC (June 27). Near Parkfield, Monterey County, Calif. This earth- quake occurred in a sparsely populated region near Parkfield, so little building damage was sustained. The main damage included broken windows, cracked walls and swimming pools, and overturned tomb- stones in the Parkfield cemeteries. Minor surface faulting, about 35 km long, occurred in a narrow zone along the San Andreas fault—from a few kilometers northwest of Parkfield almost to Cholame. About 1.5 km northeast of Cholame, the white dividing line on Highway 466 was offset about 10 cm. At that same site, a small concrete bridge sustained minor cracks and the pavement buckled. Bridges on the Parkfield-Cholame Highway, which 153 parallels and crosses the fault trace several times, sustained minor damage. It was felt generally from Santa Cruz to Oxnard and northeastward into the Sierra Nevada foothills. It was preceded by a strong shock at 04 08 UTC on June 28 and followed by shocks of lower magnitude on June 28 and 29. More than 200 aftershocks occurred through December 1966. Magnitude 6.0 Ms ELL, 5.7 MLa ELL, 5.91 ML KJ. (Ref. 81, 259, 398, 521, 551.) 1966. Aug. 7. Gulf of California, Sonora, Mex- ico. This earthquake cracked the ground 48 km south of San Luis and Rio Colorado in the E1 Golfo de Santa Clara area of Mexico. Damage in the United States was most severe at Yuma, Ariz., where a sidewalk sagged about 10 cm and the facades of several buildings sustained cracks. Slight damage also occurred at Blythe, Holtville, and Winterhaven, Calif, and at Picacho and Somerton, Ariz. The earth- quake was felt widely in southern California and southwest Arizona and also was reported felt at Boulder City, Nev. (Ref. 38, 81, 259, 266.) 1966. Sept. 12, 16 41 UTC. Near Boca, Nevada County, Calif. Minor but extensive frac- tures in the ground were observed in the area north- east of Truckee, extending 16 km on a trend N. 30° E. from Prosser Reservoir to Hoke Valley. Chimneys toppled and masonry walls were cracked at Boca, Hirschdale (near Boca Dam), Hobart Mills (near Prosser Dam), Loyalton, and Sierraville. Pipelines were ruptured at Loyalton and Boca Dam. Several bridges on Highway 80 sustained minor damage, and Boca and Prosser earthfill dams were cracked. Land- slides, rockslides, and slumping occurred on area highways and on the Southern Pacific Railway road- bed. This was the main shock of a series occurring near Boca. It was felt over a large area of east-cen- tral California and northwest Nevada. Magnitude 5.2 mb NUT, 5.6 Ms NUT. (Ref. 81, 259, 263, 324, 457, 555.) 1966. Oct. 2 (Oct. 1). Palos Verdes Penin- sula, Los Angeles County, Calif. On Palos Verdes Peninsula, two windows were broken, the curb and street were split, and the ground pulled away from the courtyard wall. Felt mainly in southwest Los Angeles County and western Orange County. (Ref. 81, 259, 292.) 1967. May 21. Near Anza, Riverside County, Calif. The shock rolled rocks onto Highway 74 from Nightingale to Palm Desert. A water reservoir at Norco sustained about $40,000 damage. Near Anza, well water appeared murky later in the day. Although this earthquake was felt mainly in River- side, San Bernardino, and San Diego Counties, it 154 was reported in scattered towns in Los Angeles and Orange Counties. (Ref. 40, 72, 292.) 1967. June 15 (June 14). Near Whittier, Los Angeles County, Calif. At Whittier, a plate-glass window broke at a market, a water pipe broke in an office building, and a wall cracked in a garage. Hairline cracks formed in a house foundation at San Gabriel, and plaster fell from a house in north Los Angeles. Felt mainly in the Whittier and San Gab- riel Valley areas of Los Angeles County. (Ref. 40, 72, 292.) 1967. June 26. Near Redwood Valley, Mendo- cino County, Calif. Brick chimneys and dishes were damaged at Ukiah, and chimneys and walls were cracked in Redwood Valley, about 11 km north of Ukiah. At Coyote Dam, northeast of Ukiah, concrete spalled slightly on the curb of the intake tower access bridge. Felt over a small area of Lake and Mendocino Counties. (Ref. 40, 72, 324.) 1967. July 22. Near Paicines, San Benito County, Calif. At the Bear Valley Fire Control Sta- tion at Paicines, bricks and plaster were cracked and furniture was displaced. Felt only at a few towns in San Benito County and at Coalinga in Fresno County. (Ref. 40, 72, 324.) 1967. Sept. ‘7. Near Corralitos, Santa Cruz County, Calif. The only damage reported was at San Jose, about 40 km north of the epicenter, where cracks in a cement fence and in plaster were enlarged. Felt from Point Reyes Station (Marin County) south to King City (Monterey County). Magnitude 4.0 Mb NUT, 4.1 Ms NUT (Ref. 40, 72, 263, 324.) 1967. Sept. 28. Northeast of Morgan Hill, Santa Clara County, Calif. Rockslides were observed within 5 km of the epicenter. At San Jose, exterior walls of a house were cracked. Felt from Marin County south to Monterey County and east to Merced County. Magnitude 4.3 mb NUT, 4.1 Ms NUT. (Ref. 40, 72, 263, 324.) 1967. Dec. 10, 12 06 UTC. Off the coast of Humboldt County, Calif. Minor damage occurred at several towns, including Crannell (chimney twisted), Denny (brick chimney cracked), Ferndale (windows cracked), and Scotia (plate-glass window cracked). The first shock was felt mainly in Hum- boldt County. ’va0 aftershocks were observed, the strongest at 12 33 UTC. Magnitude 5.6 mb NUT, 5.5 Ms NUT. (Ref. 40, 72, 74, 263.) 1967. Dec. 18. Near Corralitos, Santa Cruz County, Calif. Minor damage occurred mainly in the area of Corralitos, Gilroy, and Watsonville. It included cracks in chimneys and plaster, broken win- dows, and damage to fallen stock in stores. Felt from SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Marin County south to Monterey County and east to Merced County. Magnitude 4.8 mb NUT, 4.7 Ms NUT. (Ref. 40, 72, 263, 324.) 1968. Apr. 9, 02 28 and 03 48 UTC (Apr. 8). Borrego Mountain earthquake, near Ocotillo Wells, San Diego County, Calif. Along the Coyote Creek fault, surface rupture 31 km in length was observed. Highway 78 sustained cracks adjacent to Ocotillo Wells. Rockslides occurred in Palm Canyon, Split Mountain, and Font's Head in the Anza—Bor- rego Desert State Park, and huge boulders blocked the Montezuma-Bonego Highway. The walls of one house at Ocotillo Wells were split over doorways and at corners of rooms, and the bedroom was separated from the rest of the house. The main shock at 02 28 UTC was felt over a large area, including southern California, southwest Arizona, and southern Nevada (see fig. 21). Several aftershocks were reported. The largest one at O3 48 UTC knocked plaster to the floor in a theater at Calexico. Magnitude 7.0 Ms ABE, 6.6 mb ABE, 6.8 MS ELL, 6.3 MLa ELL, 6.0 mb NUT, 6.7 Ms NUT, 6.93 ML KJ (main shock). (Ref. 41, 263, 292, 521, 552, 554.) 1968. Apr. 25. Near Santa Rosa, Sonoma County, Calif. Damage in the Santa Rosa area was limited to broken chimneys, windows, plaster, and stock in stores. One chimney toppled in the Lark- field housing tract north of Santa Rosa, about 20 per— cent of the chimneys were damaged visibly, and many windows were broken. Considerable damage to plaster was reported in light wood-frame build- ings. Several tombstones were rotated in the ceme- tery north of Santa Rosa. Felt over a small area of west-central California from Mendocino County on the north to San Mateo County on the south. Magni- tude 4.6 MS NUT. (Ref. 41, 263, 324.) 1968. Apr. 29 (Apr. 28). South of Willows, Glenn County, Calif. Most of the damage from this shock was to merchandise in stores in the Chico area. One water well near Tehama went dry after the earthquake. At Chico, a sliding glass door and a glass trophy shelf were broken at a high school. Felt mainly in Butte, Glenn, and Tehama Counties in northern California. (Ref. 41, 324.) 1968. June 26, 01 42 UTC (June 25). Near Petrolia, Humboldt County, Calif. Several chim- neys were toppled in the Honeydew-Petrolia area, and much damage to plaster and windows was reported. In Mattole Valley, a porch on a building collapsed and several fireplaces were damaged. Landslides and cracks in the ground were observed near the mouth of the Mattole River. Felt mainly in Humboldt and Mendocino Counties in northern Cali- fornia. Several aftershocks were felt in the area. EARTHQUAKES IN CALIFORNIA 155 120° 118° 116° 114° 112° .\ I '\. ! '\> I \\ i .\ I' \‘\ NEVADA ' '\. I . I ‘ I . . I o . 36 l v I Bakersfield 0 CALIFORNIA ARIZONA 34° \ Los Angeles Palan Springs ‘¥ ‘ / «W 3 San Diego 0 umED SWEEN— l 11111 ~""‘,,}E‘§5'co 32° EXPLANATION 0 mo KILOMETERS * Epicenter gh—‘—l VII Intensity 7 FIGURE 21.——Isoseismal map for the Borrego Mountain, California, earthquake of April 9, 1968. Isoseismals are based on intensity estimates from data listed in references 41 and 72 of table 1. Magnitude 5.4 Ms ELL, 4.9 mb NUT, 5.6 Ms NUT. (Ref. 41, 263, 480, 521.) 1968. June 29. Off the coast of southern Cali- fornia in Santa Barbara Channel. At Goleta, a bridge at one overcrossing had spalled concrete chips and cracked tar and mortar. Much stock was dam- aged in the stores at Goleta. The only other town reporting the shock was Santa Barbara. Several light tremors were felt in the area from June 23 to July 31, the strongest on July 5 at 00 45 UTC (see next paragraph). (Ref. 41, 292.) 1968. July 5 (July 4). Off the coast of south- ern California in Santa Barbara Channel. Only minor damage was sustained at Carpinteria (light fixtures and plaster fell; one chimney cracked), Goleta (plate-glass windows broke; tile panels and lights fell), and Santa Barbara (tile panels fell). Felt over a moderate area of southwest California from Santa Barbara and Kern Counties south to Orange County. Magnitude 5.2 mb NUT, 4.8 Ms NUT. (Ref. 41, 72, 263, 292.) 1969. Feb. 7. Off the coast of Humboldt County, Calif. Chimneys were twisted at Petrolia and landslides occurred. One tombstone toppled at Ferndale, and several small cracks formed in the walls of a school building. Slight damage to mer- chandise occurred in several stores in Rio Dell and Scotia. Felt over a small area of Humboldt, Mendo- cino, and Trinity Counties. More than 40 aftershocks were recorded. (Ref. 42, 72, 324.) 1969. Feb. 28 (Feb. 27). Near Palmdale, Los Angeles County, Calif. Slight damage occurred at Palmdale, where fluorescent lights fell and windows were broken. Felt mainly in the Palmdale area of northern Los Angeles County. (Ref. 42, 72, 292.) 156 1969. Apr. 28. Near Borrego Springs, San Diego County, Calif. At Borrego Springs, large pieces of the ceiling fell at a bank, light fixtures were damaged, and brick walls were cracked. Several plate-glass windows were shattered in the town, and loss of merchandise in stores was common. Several rockslides occurred in the Santa Rosa Mountains, northeast of Borrego Springs. Felt over much of southern California and northern Baja California and at a few towns in southwest Arizona and southern Nevada. Magnitude 5.5 mb NUT, 5.1 Ms NUT. (Ref. 42, 72, 263, 292.) 1969. June 7. Off the coast of Humboldt County, Calif. Near Capetown (between Ferndale and Petrolia), the top of a chimney fell, one chimney was cracked, and dishes were broken. The shock was felt only slightly at three other towns in Humboldt County. (Ref. 42, 72, 324.) 1969. Oct. 2, 04 56 and 06 19 UTC (Oct. 1). Near Santa Rosa, Sonoma County, Calif. These earthquakes caused one fatality and left severe prop- erty damage in Santa Rosa: several old brick and wood-frame buildings were damaged beyond repair; chimneys were destroyed; sidewalks buckled; and underground pipes ruptured. Other buildings in Santa Rosa that sustained substantial damage included Fremont Elementary School, Sonoma County Social Service Building, J.C. Penney Com- pany store, and Veterans Memorial Building. Total damage was estimated at $8.35 million. Significant cracking or offset of roads was not observed, except for some settlement of fill at one freeway overpass. On the north side of Santa Rosa, about 36 transverse fractures were observed in the asphalt of Poppy Drive; and fresh, irregular cracks formed in the dry dirt roads in the Rural Cemetery near Poppy Drive. Many tombstones in cemeteries were thrown down or twisted. Both earthquakes were felt over a moderate area of west-central Cali- fornia—from Sonoma County east to Sacramento County and south to Santa Cruz County. Several aftershocks were felt in the Santa Rosa area. Magni- tude 4.8 mb NUT, 4.5 Ms NUT (first shock.) (Ref. 42, 72, 263, 399, 599.) 1969. Oct. 27, 10 59 UTC. Near Hollister, San Benito County, Calif. Slight damage occurred at Hollister, where a wall joint opened slightly, plaster was cracked, and stock was dam- aged in stores. Felt over a small area of central California. (Ref. 42, 72, 324.) 1970. Jan. 3 (Jan. 2). Near Cupertino, Santa Clara County, Calif. At Cupertino, plaster broke and fell and bottles toppled from shelves in a store. This light shock was felt over a small area, mainly SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) in the Cupertino region west of San Jose. (Ref. 43, 72, 324.) 1970. June 12, 03 30 UTC (June 11). Near Danville, Contra Costa County, Calif. This earth- quake was the strongest of a series of shocks that occurred in the Danville area in May and June. One chimney fell in Danville, and a brick pillar partly crumbled at the Greenbrook Clubhouse. Also dam- aged in Danville were several outside brick facades, a fence, and several windows. Felt over a small area of the San Francisco Bay region, mainly in the Danville area. (Ref. 43, 72, 324.) 1970. June 12, 16 03 UTC. Near Danville, Contra Costa County, Calif. At the Danville Post Office, a wooden upright support beam was damaged slightly and existing plaster cracks were enlarged. Much stock was damaged in local stores. Felt mainly in the area of Danville. (Ref. 43, 72, 324.) 1970. Aug. 4 (Aug. 3). Off the coast of cen- tral California in Monterey Bay. Plaster cracked and fell at Monterey; a window broke; and a few tele- phone lines were knocked down. Damage was slight at Carmel Valley, where beams in one building twisted and cracked. Felt from the San Francisco Bay area south to Monterey County. Magnitude 4.4 mb NUT, 3.6 Ms NUT. (Ref. 43, 72, 263, 324.) 1970. Sept. 12. Lytle Creek area, San Ber- nardino County, Calif. This was the main shock of a series that centered northwest of San Bernardino near Lytle Creek. Chimneys and tombstones were twisted and overturned and cracks formed in the ground at Lytle Creek. Several roads in the area were blocked by rockslides. Felt over a large area of southern California. Magnitude 5.7 ML KJ. (Ref. 43, 72, 292.) 1971. Feb. 9, 14 00 UTC. North of San Fernando, Los Angeles County, Calif. This destructive earthquake occurred in a sparsely popu- lated area of the San Gabriel Mountains, near San Fernando. It lasted about 60 seconds, and, in that brief span of time, took 65 lives, injured more than 2,000, and caused property damage estimated at $505 million. The earthquake created a zone of discontinuous surface faulting, named the San Fernando fault zone, which partly follows the boundary between the San Gabriel Mountains and the San Fernando— Tujunga Valleys and partly transects the northern salient of the San Fernando Valley. This latter zone of tectonic ruptures was associated with some of the heaviest property damage sustained in the region. Within the entire length of the surface faulting, which extended roughly east-west for about 15 km, the maximum vertical offset measured on a single EARTHQUAKES IN CALIFORNIA 157 Collapsed stair tower at the west end of wing B, Olive View Hospital, Sylmar area, California, caused by the February 9, 1971, San Fernando earthquake. (Photograph from the National Geophysical Data Center, NOAA.) scarp was about 1 m, the maximum lateral offset about 1 m, and the maximum shortening (thrust component) about 0.9 m. The most spectacular damage included the destruc- tion of major structures at the Olive View and the Veterans Administration Hospitals and the collapse of freeway overpasses. The newly built, earthquake- resistant buildings at the Olive View Hospital in Syl- mar were destroyed—four five-story wings pulled away from the main building and three stair towers toppled. Older, unreinforced masonry buildings col- lapsed at the Veterans Administration Hospital at San Fernando, killing 49 people. Many older build- ings in the Alhambra, Beverly Hills, Burbank, and Glendale areas were damaged beyond repair, and thousands of chimneys were damaged in the region. Public utilities and facilities of all kinds were dam- aged, both above and below ground. Severe ground fracturing and landslides were responsible for extensive damage in areas where faulting was not observed. The most damaging land- slide occurred in the Upper Lake area of Van Nor- man Lakes, where highway overpasses, railroads, pipelines, and almost all structures in the path of the slide were damaged severely. Several overpasses col- lapsed. 'I\No dams were damaged severely (Lower Van Norman Dam and Pacoima Dam), and three others sustained minor damage. Widespread landslides and rockfalls blocked many highways in the area. Felt throughout southern California and into west- ern Arizona and southern Nevada (see fig. 22). No foreshocks were recorded, but aftershocks were reported in the area for several months. Magnitude 6.5 ML BRK, 6.5 MLa ELL, 6.2 mb NUT, 6.6 Ms NUT, 6.35 ML KJ. (Ref. 44, 72, 263, 400, 521, 553, 599.) 1971. Mar. 31. Near San Fernando, Los Ange- les County, Calif. This was the most damaging after- shock of the Feb. 9 earthquake. The main damage was reported in the Granada Hills—Northridge—Porter Ranch area of San Fernando Valley. More than 300 158 gm newer. { sum-us 1"} o SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Partial collapse of first floor of Olive View Hospital Medical treatment and care unit, Sylmar area, California, caused by February 9, 1971, San Fernando earthquake. (Photograph from the National Geophysical Data Center, NOAA.) buildings sustained some kind of damage, including cracked foundations, shifted walls, damaged or destroyed chimneys, and broken Windows. Many out- door concrete garden walls fell, and some water lines were damaged. Felt over a large area of southern California, including Kern, Los Angeles, Orange, Riv- erside, San Bernardino, Santa Barbara, and Ventura Counties. Magnitude 4.2 mb NUT, 4.3 Ms NUT. (Ref. 44, 72, 263, 292.) 1971. Sept. 30. West of Brawley, Imperial County, Calif. Near Westmorland, dishes and food were knocked to the floor. An observer northwest of Brawley reported she was knocked to the floor and that dishes fell from shelves. Felt over a small area of southern California and at Ehrenberg, Ariz. A few small aftershocks were felt in the epicentral area. (Ref. 44, 72, 292.) 1972. Feb. 24. Southeast of Hollister, San Benito County, Calif. This was the main shock of a series that occurred on this date. Many rockfalls along the San Benito River and the renewed movement of an old landslide east of Paicines were the main ground disturbances. Much cracking of the ground was observed on or near the old landslide. Mouldings separated slightly from walls at the Bear Valley Fire Control Station. At the nearby Melendy Ranch, a brick chimney on the ranch house was damaged severely. The main shock was felt over a moderate area of west-central California. Fourteen aftershocks of magnitude 2.5 to 3.6 were recorded on Feb. 24, and many were recorded for several days thereafter. (Ref. 45, 72, 324.) 1972. Sept. 4. Southeast of Hollister, San Benito County, Calif. Slight damage was reported at the Bear Valley Fire Control Station, including small cracks in brick and mortar and plaster, and displacement of a vertical pipe in the ceiling, which damaged the sheetrock. Many rockfalls occurred EARTHQUAKES IN CALIFORNIA 159 Collapsed overpass at the Route 14—Route 5 interchange, northwest of San Fernando, California, caused by the February 9, 1971, earthquake. (Photograph by the Newhall Signal.) along the banks of the San Benito River; landslides and cracks in the ground were observed at Paicines. Felt over a small area of west-central California. Several light aftershocks were reported. Magnitude 4.6 mb NUT, 4.3 Ms NUT. (Ref. 45, 72, 263, 324.) 1972. Oct. 3 (Oct. 2). South of San Juan Bau- tista in Monterey County, Calif. In the San Juan Bautista area, old asphalt road cracks were widened, and fresh cracks formed in areas previously repaired. At the San Juan Bautista Mission, the top section of an old adobe wall was thrown down. Plaster cracked and fell at ranch houses southeast of San Juan Bau- tista. Much merchandise was thrown from shelves in San Juan Bautista and the surrounding area. Felt over a small area of west-central California. Several fore- shocks and afiershocks were recorded. Magnitude 4.1 mb NUT, 4.1 Ms NUT. (Ref. 45, 72, 263, 324.) 1973. Feb. 21. Off the coast of Ventura County, near Point Mugu, Calif. Property damage in the Oxnard, Point Mugu, and Port Hueneme areas was estimated at about $1 million. The heaviest damage occurred in downtown Oxnard, where walls failed in a few unreinforced brick buildings. Many chimneys were damaged, mainly in the older part of Oxnard; false ceilings and acoustical tiles fell to the floor and many plate-glass windows were broken. Chimneys were twisted and overturned northeast of Point Mugu at the Camarillo State Hospital. Some large boulders fell onto the Pacific Coast Highway in the Point Mugu area, and a long narrow crack was observed in the highway in the Solromar area. Sev- eral hundred sand craters (as much as 2 In in diame- ter) formed in Mugu Lagoon, and water spouted from a few of them. Lurch cracks associated with clusters 160 122° 120° SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 118° 116° 114° \ : ‘\, l x. l \. 'l 330 \. Tonfpah l C Stockton NEVADA l UTAH ! l. '\, l \. l \, i \. i \. ______________ i. . ! Fresno l Monterey l } 1 Las Vegas I W n /\ '1“ I CALIFORNIA V \.\ 5‘ l 0 Barstow l Santa Maria 0 K. \ AR|ZONA 34° EXPLANATION * Epicenter XI Intensity 11 100 KILOMETERS 32° \ u—uv ( \ \ San Diego 1' \ . _,.. FIGURE 22.——Isoseisma1 map for the San Fernando, California, earthquake of February 9, 1971. Isoseismals are based on intensity estimates from data listed in references 44 and 72 of table 1. of craters occurred as far as 8 km inland from the lagoon. The main shock of this series of earthquakes was felt over a large area of southern California—from Lompoc (Santa Barbara County) northeast through the Bakers- field area to northeast Kern County, southeast to the Palm Springs area, and then southwest to the San Diego area. Many aftershocks were recorded. Magni- tude 5.6 ML BRK. (Ref. 46, 72, 458.) 1973. Aug. 9 (Aug. 8). Off the coast of Hum- boldt County, Calif. Damage sustained in the Ferndale-Scotia area consisted mainly of broken win- dows, cracked and broken plaster, and loss from damaged merchandise in stores. Felt over a small area of Humboldt and Mendocino Counties. (Ref. 46, 72, 401.) 1974. Jan. 6. Southwest of Nubieber in Shasta County, Calif. The earthquake knocked plaster to the floor at Bieber and ruptured a gas pipe at Nubieber. It was felt over a small area, including parts of Lassen, Modoc, Shasta, and Siskiyou Coun- ties. (Ref. 47, 401.) 1974. Mar. 21. Near Healdsburg, Sonoma County, Calif. The floor at the Union Oil workshop at Cloverdale was cracked; boulders rolled down hill- sides; and several cracks formed in the earth. Felt EARTHQUAKES IN CALIFORNIA over a small area of Napa and Sonoma Counties. (Ref. 47, 107, 401.) 1974. Sept. 21. Near Sunnymead, Riverside County, Calif. Three walls were cracked at a ranch in Sunnymead, and damage was reported at San Bernardino. Felt over a small area of Riverside and San Bernardino Counties. (Ref. 47 , 402.) 1974. Nov. 28. Near Hollister, San Benito County, Calif. Widespread minor damage occurred at Hollister, including fallen bricks from one chimney, broken windows, cracked water pipe, and cracks in wall and ceiling. Felt over a moderate area of west- central California. (Ref. 47, 401.) 1975. Jan. 12, 01 37 UTC (Jan. 11). Near Petrolia, Humboldt County, Calif. A small amount of chimney damage was reported at Petrolia, and one television antenna fell. Felt along the coast of Humboldt County from Trinidad on the north to Piercy (northern Mendocino County) on the south. (Ref. 48, 87, 401.) 1975. Jan. 13. Near Long Beach, Los Angeles County, Calif. Plaster cracked and fell at Long Beach. The press reported minor damage at Lake- wood. The tremor was felt along the coast of Los Angeles County south to the Vista area and from the coast east to Bloomington (San Bernardino County). (Ref. 48, 87, 355.) 1975. Jan. 21. Near Calipatria, Imperial County, Calif. At Calipatria, bricks were separated and plaster fell. This earthquake was part of a series that centered in the Brawley area through early February. It was felt over a small area of Imperial County near the U.S.-Mexico border. (Ref. 48, 87 , 355.) 1975. Jan. 23, 17 02 UTC. South of Calipa- tria, Imperial County, Calif. This was the main shock of a swarm that struck Imperial Valley in late January and early February. It generated surface ruptures along a 10.4—km segment of a newly recog- nized fault southeast of Brawley, now designated the Brawley fault. Displacement, which apparently was vertical at the surface, reached a maximum of more than 0.2 m at Keystone Road. The shock knocked down several light fixtures and bits of plaster from a store ceiling in Brawley; it also broke windows in houses and cracked plaster. Plaster also fell at Cali- patria and a large crack formed in one wall. Resi- dents throughout the Imperial Valley reported feeling this shock. (Ref. 48, 355, 565.) 1975. Jan. 23, 23 24 UTC. Near Brawley, Imperial County, Calif. Ceiling tiles fell to the floor at two stores in Brawley, and a small crack formed in a store wall. This earthquake was reported only at Brawley. (Ref. 48, 355.) 161 1975. Mar. 3. Near Compton, Los Angeles County, Calif. Joints in a concrete walk were separated and plaster was cracked at Compton. Win- dows were broken at Gardena. (Ref. 48, 355.) 1975. June 1 (May 31). Galway Lake area, San Bernardino County, Calif. Property damage was not reported from the epicentral area, which is in the Mojave Desert and virtually uninhabited. Ground ruptures observed followed a preexisting, unmapped fault in the Galway Lake area. The rup- tures began about 1 km north of Galway Lake and extended south toward Emerson Lake, a distance of 6.8 km. Boulders were overturned in the area, and cracks formed in the ground. Felt mainly in San Ber- nardino County. (Ref. 38, 355.) 1975. June 7. Near Fortuna, Humboldt County, Calif. At Fortuna, 10 weak chimneys top- pled and 20 others were damaged; sidewalks cracked and some sank. Minor damage to chimneys also occurred at Carlotta, Fernbridge, Ferndale, Hydes- ville, Loleta, Petrolia, Rio Dell (water main also broke), Rohnerville, Scotia, and Waddington. Land- slides were observed in the Fortuna—Rio Dell areas. Felt along the coast from Crescent City south to Albion (Mendocino County) and from the coast east to Lewiston (Trinity County). (Ref. 48, 401.) 1975. June 20 (June 19). Near Calexico, Imperial County, Calif. Slight damage was reported, but not described, at Calexico. The shock was felt at a few other towns in Imperial County and in southwest Arizona. (Ref. 48, 355.) 1975. Aug. 1, 20 20 UTC. Near Oroville, Butte County, Calif. Structural damage, consisting mainly of cracks in chimneys and walls, broken windows and plaster, and loosened light fixtures, occurred at sev- eral schools, hospitals, and houses in the Oroville- Thermalito area. Many chimneys toppled or had to be taken down in Oroville and Palermo. Property damage was estimated at $2.5 million. This earthquake was associated with the first recorded surface faulting in the western foothills of the Sierra Nevada. New fractures in the ground were observed in a 3.8-km-long north- to north-north- west-trending zone. The block east of the fault moved upward relative to that on the west, as shown by about 55 mm of slip across the surface ruptures and 180 mm of vertical movement of benchmarks near the rupture zone. Felt over a large area of northern California and western Nevada. (Ref. 38, 401, 566, 599.) 1975. Aug. 2. Oroville area, Butte County, Calif. The University of California at Berkeley assigned MM intensity VI to this earthquake but did 162 not describe the damage. Felt throughout Butte and surrounding counties. (Ref. 48, 401.) 1975. Aug. 3, 06 35 UTC (Aug. 2). Near Firebaugh, Fresno County, Calif. A water line broke and plaster cracked at Firebaugh; a church was damaged at Three Rocks. Felt mainly in Fresno and surrounding counties. Magnitude 4.9 ML PAS. (Ref. 48, 401.) 1975. Aug. 10 (Aug. 9). South of Mariposa, Calif. Rockslides and broken windows were reported at Mariposa; slight damage was reported at San Joaquin in Fresno County. Felt over a small area of central California. (Ref. 48, 401.) 1975. Sept. 13. West of Avenal in Monterey County, Calif. Cracks formed in plaster and ground at Avenal. Felt along the coast of Monterey and San Luis Obispo Counties and east to Fresno County. Magnitude 5.0 ML PAS. (Ref. 48, 401.) 1975. Nov. 14. Near Eureka, Humboldt County, Calif. Damage was slight at Eureka, where windows were broken. Dishes and dolls were broken at a store in Ferndale. The press reported that the shock was felt north to Oregon and south to San Francisco. (Ref. 48, 401.) 1976. Jan. 1. Near Brea, Los Angeles County, Calif. This New Year's Day earthquake disturbed millions of residents in the Los Angeles region but caused no injuries and only slight dam- age. Damage occurred at Brea (windowpane broke and fireplace cracked), La Habra (water pipe broke), and Yorba Linda (walls and ceilings cracked). A strong-motion record obtained at Whittier, about 13.8 km west of the epicenter, recorded a maximum acceleration of 0.28 g (gravity). The shock also was felt in Orange, Riverside, and San Bernardino Coun- ties. (Ref. 49, 355.) 1976. Jan. 14. North of Avenal in Fresno County, Calif. At Avenal, plaster was cracked and a light fixture was knocked from the ceiling at a school. The shock also was felt in Kings, Monterey, and San Luis Obispo Counties. Magnitude 4.6 ML PAS. (Ref. 49, 401.) 1976. Apr. 8. Near Granada Hills, Los Ange- les County, Calif. Plaster was cracked at Granada Hills, and slight damage was reported, but not described, at Inglewood. Felt from Bakersfield (Kern County) to San Diego. Magnitude 4.8 ML BRK. (Ref. 49, 355.) 1976. Aug. 11. Near Borrego Springs in Riv- erside County, Calif. In Borrego Springs, mud- slides and cracks in the ground were reported in Anza-Borrego State Park. A cement curb buckled at Palm Desert. Felt in Imperial, Orange, San Bernar- dino, and San Diego Counties. (Ref. 49, 355.) SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 1976. Aug. 20. Near Danville, Contra Costa County, Calif. This earthquake was the largest of a series in the San Francisco Bay area Aug. 15—16 and 20—22. The only reported damage occurred in Danville, where plaster was cracked in some houses. Felt throughout the San Francisco Bay area. (Ref. 49, 401.) 1976. Oct. 17 (Oct. 16). Near Newhall, Los Angeles County, Calif. Slight damage was observed at Newhall, where a water main was bro- ken, and at Tarzana, where plaster and masonry sustained cracks. The shock also was felt in Kern and Ventura Counties. Magnitude 4.1 ML BRK. (Ref. 49, 355.) 1976. Nov. 4. Northwest of Brawley, Imperial County, Calif. A series of earthquakes was recorded on this date, but only slight damage occurred. Plaster and drywall were cracked at Braw- ley; fences were displaced slightly, and cracks formed in plaster and tiles at El Centro; and cracks formed in plaster and ground at Westmorland. Felt over a large area of southern California (including Imperial, Riverside, and San Diego Counties) and southwest Arizona (including the towns of San Luis and Yuma). Magnitude 5.5 ML BRK. (Ref. 49, 355.) 1976. Nov. 22. West of Los Angeles, Calif. Windows were broken and plaster was cracked at North Hollywood; slight damage was reported at Long Beach and Los Angeles (cracks in plaster). Felt over a small area along the west coast of Los Angeles County. (Ref. 49, 355.) 1977. Jan. 8. Near Oakland, Contra Costa County, Calif. This main shock of a series of 58 tremors caused minor damage at several towns, including Berkeley (broken windows, enlarged cracks in walls); El Cerrito (dislodged chimney brick, cracks in walls); Napa (cracks in plaster and drywall); Oak- land (cracks in plaster in several houses); San Fran- cisco (chandelier knocked down, cracks .in ceilings); and Walnut Creek (cracks in drywall). Felt along the coast of California from Sonoma County south to Santa Cruz County. (Ref. 39, 401.) 1977. June 21 (June 20). Southwest of French Camp in Alameda County, Calif. This earthquake cracked sidewalks slightly at French Camp and left cracks in plaster and drywall at El Granada. It was felt along the coast from Point Reyes Station (Marin County) south to Santa Cruz and from the coast east to the Sonora area (Tuol- umne County). (Ref. 39, 401.) 1977. Aug. 12 (Aug. 11). Near San Fernando, Los Angeles County, Calif. One person was injured at San Fernando when a shelf of dishes fell on her. Windows were broken in Los Angeles, Northridge, EARTHQUAKES IN CALIFORNIA and Van Nuys; exterior walls were cracked at Reseda; and plaster was cracked at Studio City. Water sloshed onto sides of pools at Glendale and Van Nuys. Felt along the coast of southern California from Santa Barbara south to San Pedro (Los Angeles County) and from the coast east to Palmdale and Riverside. (Ref. 39, 355.) 1977. Oct. 21 (Oct. 20). Imperial Valley, Calif. At Brawley, plaster was cracked and small objects were shifted. Felt in many towns in the Imperial Valley. (Ref. 39, 355.) 1977. Nov. 14 (Nov. 13). Near El Centro, Imperial County, Calif. At El Centro, plaster fell in the Post Office and some Windows were broken; at Imperial, cracks formed in plaster walls. Slight dam- age (cracks in windows) also was reported at Somer- ton, Ariz. Felt over a small area of southern California and southwest Arizona. (Ref. 39, 355.) 1977. Nov. 22. Near Willits, Mendocino County, Calif. Moderate structural damage occurred at Willits, where 65 chimneys were dam- aged, and windows and walls were cracked and bro- ken. Cracks and offsets of as much as 12 mm were formed in the walls of a store on Main Street; con- crete columns were cracked and the ceiling dropped as much as 50 mm. A few interior walls collapsed in older houses. An interior wall collapsed in one house, and its chimney fell apart both inside and outside the house. East of Willits, in Little Lake Valley, a chimney was cracked above the roofline, heavy furniture was displaced, toilet-tank lids flew off their bases, and a water pipe broke. Felt along the coast from Scotia (Humboldt County) in the north to Stewarts Point (Sonoma County) in the south and from the coast east to the Willows area (Glenn County). (Ref. 39, 401.) 1978. Mar. 26 (Mar. 25). Near Ukiah, Mendo- cino County, Calif. Near Ukiah, huge storage tanks in a new warehouse at the Parducci Winery were damaged by sloshing liquids. Loss to merchandise at stores in the Ukiah area totaled about $10,000. Win- dows were broken at Comptche. Felt northwest to Westport (Mendocino County), south along the coast to Stewarts Point (Sonoma County), and from the coast east to Clearlake Highlands (Lake County). (Ref. 240, 401.) 1978. Aug. 13. Near Goleta, Santa Barbara County, Calif. This moderate earthquake injured 65 people and caused property damaged estimated at $12 million. The most severe damage occurred at Santa Barbara and at the University of California Santa Barbara campus at Goleta. There, nine build- ings sustained extensive cracks in shear walls. Plaster, ceilings, and light fixtures were damaged 163 throughout the campus. A few old adobe or wood- frame buildings were damaged severely. In the com- mercial district of Goleta and in the Santa Barbara area, similar but less severe property damage was sustained. In Santa Barbara, multistory, reinforced- concrete structures sustained diagonal cracks in the shear walls of their lower stories. The roof on a res- taurant being remodeled collapsed. The most com- mon damage to residential and small commercial buildings consisted of differential settlement of foun- dations, failure of reinforced chimneys, cracked and fallen plaster, and breakage of glass. Three overpasses on US. Highway 101 in the Goleta area sustained severe damage. The most extensive damage occurred at the Ward Memorial bridges, Where the superstructures shifted relative to the abutments, causing the concrete to crack and spall in several places. West of Goleta, a freight train derailed when passing over a “kink” in the tracks, apparently caused by failure of the roadbed fill. Sev- eral rockslides occurred on US. Highway 101 between Goleta and Santa Barbara. Felt over a moderate area of southern California— from Morro Bay (San Luis Obispo County) on the north to Santa Ana (Orange County) on the south and from the coast east to Bakersfield (Kern County) and Lake Hughes (Los Angeles County). (Ref. 38, 240, 468, 599.) 1978. Aug. 29 (Aug. 28). Near San Jose, Santa Clara County, Calif. At San Jose, acoustical ceiling tiles fell to the floor in a market. In addition, walls and ceilings sustained cracks in a house and its walls were elevated 1.7 cm from the floor. Felt over a small area of northern California, mainly in Alameda, Contra Costa, Santa Clara, and Santa Cruz Counties. (Ref. 240, 401.) 1978. Sept. 4, 21 54 UTC. Lake Tahoe‘region, El Dorado County, Calif. This is the largest of a series of earthquakes that occurred in the area south of Lake Tahoe on Sept. 3 and 4. Cracks in drywall and hairline cracks in exterior walls were sustained at Mt. Aukum, Calif, and Genoa, Nev. Water splashed onto sides of lakes and pools at Mt. Aukum. Felt from Dobbins (Yuba County) and Stockton (San Joaquin County) on the west to Vernon, Nev., in the east and from Surcliffe, Nev., on the north to Mari- posa, Calif, on the south. (Ref. 240, 401.) 1978. Oct. 4, 16 42 UTC. Lake Crowley area, Mono County, Calif. The strongest effects from this earthquake occurred in the Bishop area. Large amounts of merchandise fell from store shelves throughout the area, and pictures were knocked from walls. Minor landslides occurred in the canyon areas near Bishop, and boulders rolled onto roads. Slight 164 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Books shaken off shelves in library of the University of California, Santa Barbara, at Goleta, California, by the August 13, 1978, earthquake. EARTHQUAKES IN CALIFORNIA damage to walls, plaster, and windows occurred at Benton, Bishop, Easton, Friant, Mammoth Lakes, and Paradise Camp. Felt over a large area of north- ern California and into western Nevada—from Sacra- mento on the north to Santa Barbara on the south and east to Mina and Beatty, Nev. Magnitude 5.8 ML BRK. (Ref. 240, 355.) 1978. Nov. 20 (Nov. 19). Near Redlands, San Bernardino County, Calif. This earthquake caused slight damage at Redlands, where interior plaster walls cracked and split and hairline cracks formed in exterior walls. Felt in parts of Los Ange- les, Orange, Riverside, San Bernardino, and San Diego Counties. (Ref. 240, 355.) 1979. Jan. 1. Near Malibu, Los Angeles County, Calif. Windows were reported broken in Culver City, Malibu, Santa Monica, Tustin, and Ven- ice. Slight damage to walls (mainly cracks) occurred at Studio City and Woodland Hills. Boulders fell onto the Pacific Coast Highway in the Malibu area, and mud and boulders tumbled onto other roads in Mal- ibu. The main earthquake was felt along the coast from Santa Barbara south to Bonita (San Diego County) and from the coast east to the area of Bar- stow (San Bernardino County) and Palm Springs (Riverside County). The California Institute of Tech- nology recorded about 50 aftershocks in the next 2 hours. (Ref. 262, 474.) 1979. Feb. 3. Off the coast of Humboldt County, Calif. Many store windows were broken and stock tumbled from shelves in stores in the downtown areas of both Arcata and Eureka. At Eureka, chimneys were cracked and broken (one fell through a roof); drywall, plaster and exterior walls were cracked; three water mains were broken; and ceiling tiles and light fixtures fell in some stores. Felt in parts of Del Norte, Humboldt, Mendocino, Siskiyou, and Trinity Counties and in southwest Ore- gon. (Ref. 262, 401.) 1979. Feb. 22. Honey Lake Valley, Lassen County, Calif. This earthquake interrupted tele- phone service in the epicentral area but caused only minor property damage. Drywall was cracked at Doyle, near the Nevada border, and desks were dis- placed. The earthquake was felt over a large area of northeast California and western Nevada. It was preceded by a small foreshock and was followed by aftershocks through Feb. 23. (Ref. 262, 401.) 1979. Mar. 15, 21 07 UTC. Near Landers, San Bernardino County, Calif. This earthquake was the strongest of a series of shocks in the area on Mar. 15. A surface rupture formed in the Homestead Val- ley area along the east bank of Pipes Wash and at three sites west of the Pipes Wash fault. The highest 165 intensity was observed at Landers, where moderate damage to buildings and their contents occurred (downed chimney, cracked walls, broken windows and dishes), and electric and telephone services were dis- rupted for several hours. Slight damage to plaster and walls was reported from several other towns in the area. The main shock was felt in Los Angeles, Orange, Riverside, San Bernardino, and San Diego Counties and at a few towns in southwest Arizona and western Nevada. (Ref. 262, 355.) 1979. May 8 (May 7). Near San Jose, Santa Clara County, Calif. This earthquake was stron- gest in East San Jose, where windows were broken, plaster was cracked, pictures fell from walls, and a refrigerator fell over. Felt mainly in the coastal area around San Francisco Bay. (Ref. 262, 401.) 1979. June 14 (June 13). Near Onyx, Kern County, Calif. Minor damage consisting of large cracks in plaster walls and cracks in brick fences and sidewalks occurred at Onyx. The earthquake was felt only at a few towns in the epicentral area. (Ref. 262, 355.) 1979. June 29 (June 28). Big Bear Lake, San Bernardino County, Calif. This earthquake was felt strongly in the Big Bear Lake recreation area, where large cracks formed in plaster, a foundation cracked, a plate-glass window shattered, and several burglar alarms were triggered. Felt in the Los Ange- les Basin and as south as San Diego. (Ref. 262, 472.) 1979. June 30, 00 34 UTC (June 29). Near Big Bear Lake, San Bernardino County, Calif. This earthquake is the largest of a series in the area that began on June 29. At Big Bear City, several windows were broken, walls were cracked, and a large section of acoustical-tile ceiling fell. At Sugarloaf, chimney bricks loosened and ceiling tile and a foundation cracked. Felt west to Long Beach, south to San Diego, and north to Yermo (San Bernardino County), but the felt area east of Big Bear City is unknown. (Ref. 262, 472.) 1979. Aug. 6. Near Gilroy, Santa Clara County, Calif. No fatalities occurred, but 16 people were injured in Hollister and Gilroy. Property dam- age in the two towns, estimated at $500,000, con- sisted mainly of damaged chimneys, broken glassware in stores, and structural damage to five buildings in Gilroy. Many chimneys were damaged in older houses near Gilroy's downtown area. A crack split a wall in the City Hall, and the ceiling in a court room of the Municipal Courthouse caved in. Beams and uprights were damaged at Fords Department Store and the store was closed. At Hollister, a parapet toppled and caved in the roof of a real estate office; a ceiling 166 partly collapsed at a new building on San Felipe Road. The J .C. Penney Store sustained a 3-m hole in its ceiling, and extensive cracks formed in the ceiling throughout the store. A service station at nearby Casa de Fruta sustained extensive damage, including fallen bricks from the chimney, bulging of exterior walls, and separation of interior walls from ceiling or floor. The fire station at Pacheco Pass, about 16 km northeast of Hollister, sustained extensive damage, and the nearby lookout station was vacated because of structural damage. Ground displacement was observed along the Cala- veras fault zone from Hollister north to the Anderson Lake area, about 39 km. The maximum horizontal displacement, 5—6 mm, occurred about 10 km east of Gilroy, where the Calaveras fault zone intersects Highway 152. Ground lurching, settlement, and slumping were observed in many places between Anderson Lake and Hollister. Felt from about 60 km north of Bakersfield, north to Sacramento, east to the area of Reno—Lake Tahoe, Nev., and west to the Pacific Ocean. During August, most of the 31 located aftershocks were clustered in the area south of the epicenter of the main shock. Magnitude 5.6 MLa ELL. (Ref. 262, 401, 521.) 1979. Oct. 15, 23 16 UTC. Imperial Valley area, on the Baja Calif., Mexico-California bor- der. This major earthquake injured 91 people and caused an estimated $30 million in property damage in the Imperial Valley area. It destroyed two houses and 11 commercial buildings and damaged 1,565 houses and 440 commercial buildings. The most severe damage (MM intensity Di) was to the Impe- rial County Services building in El Centro, which had to be razed. The support pillars failed on this six-story reinforced concrete—frame structure, causing partial collapse of the east part of the building. It was designedunder the 1967 provisions of the Cali— fornia Uniform Building Code. Other property dam- age caused by this earthquake at El Centro, Brawley, and Calexico and at Mexicali, Mexico, is typical of MM intensity VII, which is the highest intensity assigned to any location except the Imperial County Services building. Movement along the Imperial fault also caused damage to the irrigation system in the Imperial Val- ley. The All American Canal, which brings water from the Colorado River to the Imperial Valley, was damaged most severely. East of Calexico, the earth- quake shook down levees on both sides of the canal. The banks settled more than 1 m in places. Ground displacement on the Imperial fault extended from about 4 km north of the International Border to about 4 km south of Brawley. The SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) maximum lateral displacement—about 55 cm—was observed in Heber Dunes; the maximum vertical dis- placement—19 cm—occurred southeast of Brawley. Ground rupture followed the same trace as that in the shock on May 18, 1940, and showed many of the same features and characteristics. Aftershock activity shifted to the north in both earthquakes, and both sustained damaging aftershocks near Brawley. There also is evidence that the Brawley fault experienced sympathetic movement in both earthquakes. Felt over a large area, including southern Califor- nia, southern Nevada, western Arizona, and an unknown area in Mexico. Many aftershocks occurred, the most damaging of which were on Oct. 16 and Dec. 21 (see descriptions below). Magnitude 7.0 ML BRK, 6.0 MLa ELL. (Ref. 38, 262, 355, 521.) 1979. Oct. 16, 06 58 UTC (Oct. 15). Imperial Valley area aftershock. Aftershocks of the major earthquake on Oct. 15 caused additional damage at Brawley and Imperial. According to the press, near midnight on Oct. 15, an aftershock at Imperial buck- led the floor in one house, displaced walls, and crum- bled the porch steps. (Ref. 262, 355.) 1979. Dec. 21. Imperial Valley area after- shock. Another aftershock of the major earthquake on Oct. 15 left large cracks in exterior walls at Impe- rial and cracked windows and stone fences. Felt over a small area of southern California and western Ari- zona. (Ref. 262, 355.) 1980. Jan. 24, 19 00 UTC. North of Livermore Valley in Contra Costa County, Calif. This earth- quake injured 44 people and caused an estimated $11.5 million in property damage (of which $10 mil- lion damage occurred at the Lawrence Livermore Laboratory at Livermore). The shock was associated with surface rupture along the Greenville fault. The rupture propagated more than 15 km to the south- east along the Marsh Creek—Greenville faults, ceas- ing in the area of Interstate Highway 580. Most of the damage to property, including that at the Lawrence Livermore Laboratory, was nonstruc- tural. It consisted mainly of fallen ceiling tiles, fallen bricks from chimneys, broken gas lines and water lines, broken windows, and displacement of mobile houses from supporting foundations. However, at the Ordway Ranch (on Vasco Road north of Livermore), a brick-and-stone fireplace was cracked and displaced from the wall, as was a smaller fireplace in another room. At Interstate 580 and Greenville Road (about 4 km north of the Lawrence Livermore Laboratory), pavement on the overpass settled about 30 cm and concrete on one abutment cracked and spalled. Faulting was observed for a distance of about 6 km along the Greenville fault, beginning near the overpass EARTHQUAKES IN CALIFORNIA 167 Support pillar failure on the ground level of the Imperial County Services building, El Centro, California, caused by the October 15, 1979, Imperial Valley earthquake. at Interstate Highway 580 and Greenville Road. Where the fault crosses Vasco Road, right-lateral offset was as much as 2 cm; on Laughlin Road and to the northwest for about 300 m, right-lateral offset of 5 to 10 mm was observed. Felt over a large area of central California and at a few towns in western Nevada. A small foreshock occurred at 18 58 UTC on Jan. 24, and a sequence of 59 aftershocks followed in the next 6 days. A second principal earthquake occurred on Jan. 27 (see description below). (Ref. 300, 466.) ‘ 1980. Jan. 27 (Jan. 26). Near Livermore, Alameda County, Calif. A second damaging earth- quake, near the south end of the Greenville fault (about 14 km south of the Jan. 24 epicenter), occurred on Jan. 27. Six persons were injured at Livermore by flying glass and falling ceiling tiles and supports. It caused 1—2 mm of additional right- lateral movement on the Greenville fault across Laughlin Road as well as additional movement and displacements along the surface rupture of Jan. 24, north of Vasco Road. The most severe property damage reported was in the Tassajaro Valley area and at Danville, about 17 and 28 km, respectively, northwest of the epicenter. In Tassajaro Valley (east of Danville), about 50 houses sustained minor damage, including one fire— place damaged, walls and concrete cracked, walls separated from ceiling, Windows broken, and a chim- ney toppled. Damage at Danville included one brick chimney broken at the roofline; a fireplace damaged; a stone wall demolished; and walls, ceilings, side— walks, and patio cracked. Light damage was sus- tained at several other towns in the area. Felt over a moderate area of central California. (Ref. 300, 466.) 1980. Feb. 25. Southeast of Anza, Riverside County, Calif. Slight damage consisting of broken Windows, large cracks in diywall and plaster, loos- ened bricks on chimneys, and a broken gas line occurred in the Anza—Idyllwild—Palm Desert area. 168 Several small landslides forced the closing of State Highway 74 between Spring Crest and Palm Desert; cracks as wide as 3.8 cm were reported in State Highway 74. Felt over a large area of southern Cali- fornia and an unknown area in Mexico. It was reported from Eagle Mountain (Riverside County) and Palo Verde (Imperial County) on the east to Los Angeles and San Diego on the west. (Ref. 300, 355.) 1980. May 25, 16 33 and 19 44 UTC. Mam- moth Lakes area, Mono County, Calif. In the Mammoth Lakes region, property damage caused by these earthquakes (plus a third strong shock on May 27, 14 50 UTC) to schools, other public buildings, highways, and merchandise in stores has been esti- mated at $1.5 million. Nine people were injured by the two largest earthquakes, mainly from falling rocks. Landslides and rockfalls were common in this area and in Yosemite National Park. The most severe property damage occurred at Mammoth Lakes: chimneys toppled, water mains broke, windows shattered, and plaster cracked. The 20—year-old Mammoth Elementary School was dam- aged severely by faulting beneath the school build- ing. Ground cracks were abundant in fill along both paved and dirt roads. A 17-km-long zone of discon- tinuous surface fractures associated with the Hilton Creek fault was observed. It had a net vertical dis- placement of less than 50 mm and more than 200 mm of slip on single fractures. The first earthquake was felt over a large area of California and western Nevada—from Reno and Las Vegas, Nev., to the coast at Los Angeles and San Francisco. The second shock was felt over a similar area. Hundreds of aftershocks, many of which were felt in the Mammoth Lakes area, occurred through 1980. Magnitude 6.4 ML PAS (first shock), 6.6 ML PAS (second shock). (Ref. 300, 401, 599.) 1980. May 27, 14 50 UTC. Owens Valley area, Mono County, Calif. It was difficult to differ- entiate the effects of this earthquake from those caused by the two shocks on May 25. It was felt over a similar area, however, and four people were injured. Minor damage was reported in several towns in the area. Landslides and falling rocks were common in Yosemite National Park. Old US. High- way 395, east of Mammoth Lakes, was closed because of severe cracks. Felt from Eureka and Las Vegas, Nev., in the east to La Honda (San Mateo County) and Los Angeles on the coast. Many after- shocks were felt in the Mammoth Lakes area. Mag- nitude 6.4 ML PAS. (Ref. 300, 401.) 1980. June 29 (June 28). Owens Valley area, Mono County, Calif. Slight damage at Mono Hot Springs included cracks in plaster walls, foundation, SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) and exterior stone walls. Felt over a small area of California and western Nevada. Magnitude 4.7 ML PAS. (Ref. 300, 401.) 1980. Oct. 31. Near Calexico, Imperial County, Calif. Hairline cracks formed in plaster and drywall at Calexico. Furniture was overturned and windows were cracked. The shock was reported felt only at a few towns in the area. (Ref. 300, 355.) 1980. Nov. 8, 10 27 UTC. Off the coast of Humboldt County, Calif. A major earthquake, the largest in this area in 24 years, injured six people and caused property damage estimated at $2 million. Most of the damage occurred east of Fields Landing, where two sections of an overpass on US. Highway 101 collapsed onto the railroad tracks below. At Fields Landing, two houses were displaced from their foundations, one unreinforced chimney fell, and gas, water, and sewer lines were broken. This shock and most of its aftershocks occurred on a large, left-lat- eral, strike~slip fault that strikes about N. 50° E. from the Mendocino Fracture Zone. Felt over a large area, including parts of Oregon, western Nevada, and northern California—from Eugene, Oreg, south to the San Francisco Bay area and from the coast east to Fallon, Nev. Many aftershocks occurred. Magni- tude 7.2 Ms ABE. (Ref. 74, 300, 599.) . 1980. Nov. 28. East of Truckee, Nevada County, Calif. Centered in a sparsely populated mountainous area, this earthquake caused only minor damage at Georgetown and Soda Springs. At Georgetown, large cracks formed in exterior walls and drywall, bricks fell from walls, and hairline cracks occurred in plaster walls; at Soda Springs, windows were broken and merchandise was thrown from shelves. Felt from the San Francisco Bay area to Reno, Nev. (Ref. 300, 401.) 1981. Mar. 3. Near Fremont, Alameda County, Calif. A rockslide blocked the Niles Canyon Road between Fremont and Sunol. Windows were broken and burglar alarms were activated in one store. Felt from Sonoma County south along the coast to Monterey and east to Waterford (Stanislaus County). (Ref. 325, 401.) 1981. Apr. 26. Near Westmorland, Imperial County, Calif. Property damage in the Calipatria— Westmorland area was estimated at $1—3 million. At Westmorland, 12 buildings sustained severe damage, 30 minor damage, and 70 percent of the 900 dwell- ings sustained damage of some kind. City officials ordered the razing of 10 downtown buildings and condemned five dwellings. The main effects in Calipatria and Westmorland were downed chimneys, cracked and destroyed foun- dations, partial collapse of exterior adobe and wood EARTHQUAKES IN CALIFORNIA 169 Tompkins Hill Road overpass collapsed on US. Highway 101, about 2 mi south of Fields Landing, California, during November 8, 1980, earthquake. (Photograph by RT. Kilbourne, California Division of Mines and Geology.) walls, collapse of interior walls, and broken underground pipes. In the rural areas, the main damage consisted of broken concrete-lined irrigation canals, which were not reinforced. Concrete cracked on two stretches of the Vail Canal between Calipatria and Westmorland, and the earthen embankment beneath the cracked concrete washed away. Also, the concrete on several bridges was cracked and chipped; cracks in road pavement and ground were ubiqui- tous. This earthquake was the largest in a swarm of at least 40 shocks in the area from Apr. 24—28. It was felt over a large part of southern California, southwest Arizona, and an unknown area in Mexico. (Ref. 325, 355.) 1981. July 17. Near Honeydew, Humboldt County, Calif. Light furniture was overturned and much glassware and dishes were broken at Honeydew. This shock also was felt in Mendocino and Sonoma Counties. (Ref. 325, 401.) 1981. Sept. 4. Off the coast of Los Angeles County, Calif. This was the largest magnitude earthquake in the area since the San Fernando Val- ley shock of February 1971. Some windows were broken at Marina del Rey and exterior walls were cracked. Telephone service was interrupted briefly in some areas, burglar alarms were activated, and ele- vators became inoperative. Felt in southern Califor- nia from San Luis Obispo to the US. Mexico border. (Ref. 325, 355.) 1981. Sept. 30, 11 53 UTC. Near Mammoth Lakes, Mono County, Calif. This earthquake was the first, and the largest, of a swarm of shocks in the area. It knocked out electric service at the Mono County sheriffs substation in Crowley Lake and at 170 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Vail Irrigation Canal, between Calipatria and Westmorland, California, damaged by the April 26, 1981, Imperial Valley earthquake. (Photograph by the Imperial Valley Press.) the Mammoth Lakes Airport. Chimneys cracked at Mammoth Lakes, and hairline cracks formed in plas- ter and drywall. A shopping center under construc- tion sustained damaged walls and broken windows. Flowing spring water was muddied at the Hot Creek Fish Hatchery, near Mammoth Lakes, and gas lines were broken. Felt over a large area of California and at a few towns in western Nevada. Magnitude 5.9 ML BRK. (Ref. 325, 355.) 1982. Oct. 1. Near Inyokern, Kern County, Calif. Many large cracks formed in interior drywalls at Barstow and Inyokern; bricks shifted in a fire- place at Ridgecrest, and hairline cracks formed in interior stucco walls. Items were thrown from store shelves in several towns. Felt in Inyo, Kern, Los Angeles, San Bernardino, and Tulare Counties. (Ref. 350, 355.) 1982. Oct. 25. Near Coalinga, Fresno County, Calif. Tiles fell from interior walls at Coalinga, and many items were thrown from store shelves. At Ave- nal, small amounts of plaster fell from a ceiling, and some cracks formed in interior plaster walls. A hunter reported that, about 40 km northwest of Coal- inga, cracks formed in the wet ground. Felt from Kern County on the south to Santa Clara County on the north and from the coast in San Luis Obispo County to Mono County on the eastern slope of the Sierra Nevada. (Ref. 350, 401.) 1982. Dec. 16 (Dec. 15). Near Fortuna, Hum- boldt County, Calif. Chimneys were cracked and windows were broken at Ferndale and Fortuna. Windows were broken, and items were thrown from store shelves at Rio Dell. Felt mainly in Humboldt County. (Ref. 350, 401.) 1983. Jan. 7, 01 38 and 03 24 UTC (Jan. 6). Mammoth Lakes area, Mono County, Calif. The first earthquake damaged a few buildings at Mam- moth Lakes and knocked out electric service at Crowley Lake and Mammoth Lakes. The second one collapsed a metal hangar at the Mammoth Lakes Airport and toppled display cases. The first shock was felt from western Nevada to Merced County in the west and from El Dorado County in the north to Kern County in the south; the second one was reported from a similar but slightly smaller area. Magnitude 5.6 ML PAS (both shocks). (Ref. 360, 401.) EARTHQUAKES IN CALIFORNIA 171 Building on 5th Street, Coalinga, California, destroyed by the May 2, 1983, earthquake. (Photograph by the Fresno Bee.) 1983. May 2, 23 42 UTC. Near Coalinga, Fresno County, Calif. This earthquake caused an estimated $10 million in property damage (according to the American Red Cross) and injured 94 people. Damage was most severe in Coalinga, where the 8-block downtown commercial district was almost completely destroyed. Here, buildings having unrein- forced brick walls sustained the heaviest damage. Newer buildings, however, such as the Bank of America and the Guarantee Savings and Loan build- ings, sustained only superficial damage. The most significant damage outside the Coalinga area occurred at Avenal, 31 km southeast of the epicenter. A disaster assessment by the American Red Cross listed the following statistics on damage in the area: almost destroyed—309 single-family houses and 33 apartment buildings; major damage—558 single-fam- ily houses, 94 mobile homes, and 39 apartment build- ings; and minor damage—811 single-family houses, 22 mobile homes, and 70 apartment buildings. Most public buildings, including the City Hall, hospital, schools, fire house, post office, and police station, sus- tained only minor damage. Only six bridges of 60 surveyed in the area sus- tained measurable structural damage. This damage consisted of hairline cracks and spalling at the top of the support columns, fracturing and displacement of wingwalls and parapets, and settlement of fill. All public utilities were damaged to some degree. The water system continued to function despite many leaks in its transmission piping. Gas was shut off for several days because of broken piping and leaks, but only temporary interruptions of electric and tele- phone services were reported. One large section of old concrete sewer pipe west of the downtown area partly collapsed, but this system also continued to function. In the oil fields near Coalinga, surface facilities such as pumping units, storage tanks, pipelines, and support buildings were all damaged to some degree. 172 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Building at 187 South 6th Street, Coalinga, California, severely damaged by the May 2, 1983, earthquake. (Photograph by the Fresno Bee.) One oil company administration building, about 7 km north of Coalinga, sustained major structural dam- age and its two brick chimneys were toppled. Sub- surface damage, including collapsed or parted well casing, was observed only on 14 of 1,725 active wells. This earthquake triggered thousands of rockfalls and rockslides as far as 34 km northwest, 15 km south, and 26 km southwest of the epicenter. Only a few slope failures occurred east of the epicenter because of the absence of steep slopes in that direction. This damaging earthquake was caused by an 0.5-m uplift of Anticline Ridge northeast of Coalinga, but surface faulting was not observed. Ground and aerial searches immediately after the earthquake revealed ground cracks and fissures within about 10 km of the instrumental epicenter, none of which appeared to represent movement on deeply rooted fault structures. About 5 weeks later, on June 11, however, an aftershock caused surface faulting about 12 km northwest of Coalinga (see description below.) Felt from the Los Angeles area north to Susan- ville (Lassen County) and from the coast east to western Nevada (see fig. 23). Through July 31, more than 5,000 aftershocks were recorded, of which 894 had a magnitude of 2.5 or larger. Most of the larger magnitude shocks were felt in Coalinga. Magnitude 6.1 ML PAS, 6.7 ML GM. (Ref. 360, 593.) 1983. May 9, 02 49 (May 8). Coalinga, Fresno County, Calif., aftershock. This is one of the strongest aftershocks of the May 2 earthquake. It injured two residents at Coalinga, but additional structural damage was not observed. Felt over a moderate area in central California and at Schurtz in western Nevada. Magnitude 5.2 ML PAS, 5.3 ML GM. (Ref. 360.) 1983. June 11 (June 10). Coalinga, Fresno County, Calif., aftershock. This strong aftershock of the May 2, 1983, earthquake caused surface faulting about 12 km northwest of Coalinga along a 3.3-km-long stretch of the previously unnamed Numez fault. Maximum reverse and right-lateral components of slip in the north segment of the fault were 64 and 20 cm, respectively. Slip along the northern quarter of the southern segment of the fault was similar to that along the north segment. Maximum reverse and right-lateral components of slip in the southern three-fourths of the south seg- ment were 8 and 11 cm, respectively. Maximum net slip for the north and south segments of the fault were 65 and 13 cm, respectively. In the area northwest of Coalinga, along Los Gatos Creek Road, one house that was damaged heavily in EARTHQUAKES IN CALIFORNIA 173 State Theater on Elm Avenue, Coalinga, California, damaged the May 2, 1983, earthquake. (Photograph by the Fresno Bee.) 174 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 122° 120° 1 18° 1 16° I I Susanville I . . Red Bluff ! ' I 40° . l A | I Eureka Marysville - Carson Ci‘y fl ' ‘\ \ \~ \ Il-IV ~ o\- 4/ «N 38° 60' 4 L \ O 0,;‘4 San Francisco /1,/\ \ Modesto 4 '\ \. / . \. Bishop 0 Fresno Momerey VI 3 < v Coalin a& H Las Vegas 36° 9\ VIII 4 \/ Trona 7 C I D O 16 ’0 Bakersfield : II-IV 7 O o <0 .7 ’Iv Los Angeles 340 \ Q M N) I . K, v“ m EXPLANATION ‘k Epicemer E W" Intensity 8 Q 0 100 KILOMETERS \ . L—*—' .s an Diego umeos’TAfEi. . . — .v ’M‘Exxco ..,—-- FIGURE 23.-——Isoseismal map for the Coalinga, California, earthquake of May 2, 1983. This map is a simplified version of figure 13 in reference 360 of table 1. EARTHQUAKES IN CALIFORNIA the main shock on May 2 was reported destroyed. Several houses sustained minor damage, and a few mobile homes were shifted off their supports. Felt over a small area in central California. Magnitude 5.1 ML PAS, 5.2 ML GM. (Ref. 360, 593.) 1983. July 13. Imperial Valley area, Calif. Slight damage occurred at Niland, a few kilometers north of Calipatria, where windows were broken, large cracks formed in walls, and plaster fell to the floor. Felt only at a few towns in the area. (Ref. 360.) 1983. July 22, 02 39 UTC (July 21). Coalinga, Fresno County, Calif., aftershock. A large after- shock of the Coalinga earthquake of May 2, 1983, caused minor damage to property at Coalinga (fluo- rescent lights fell in store; chimneys, walls, and foun- dation cracked; minor landslides occurred) and injured two people. Slight damage also was observed at Lemoore Naval Air Station and Stratford. Felt over a large area in central California—from Sacra- mento on the north to Bakersfield and beyond on the south and from the coast east to the Nevada border. Magnitude 5.6 ML PAS, 6.0 ML GM. (Ref. 360.) 1983. July 25. Coalinga, Fresno County, Calif., aftershock. Another aftershock of the Coal- inga earthquake of May 2, 1983, caused minor dam- age and two injuries at Coalinga. Some chimneys were damaged, mobile homes were displaced from their supports, cracks formed in interior and exterior walls, and windows were broken. Damage to utilities included one ruptured gas line, two cracked water mains, and temporary interruption of telephone ser- vice. Felt over a small section of central California. Magnitude 5.4 ML PAS, 5.3 ML GM. (Ref. 360.) 1983. Aug. 24. Off the coast of Humboldt County, Calif. This earthquake broke windows and overturned small objects at Scotia. Felt mainly in Humboldt, Mendocino, and Trinity Counties of northern California. Several moderate aftershocks occurred on Aug. 26, Nov. 11, and Dec. 20. (Ref. 360, 401.) 1983. Aug. 29. Northwest of San Simeon in Monterey County, Calif. About 20 km northwest of San Simeon, near Ragged Point, a few buildings were reported damaged, and cracks formed in chim- neys. Felt mainly in Monterey, San Benito, and San Luis Obispo Counties. (Ref. 360, 476.) 1984. Apr. 24. Near Morgan Hill, Santa Clara County, Calif. The Morgan Hill earthquake injured 27 people and caused property damage esti- mated at $8 million. Most of the loss occurred in Santa Clara County, where 522 private dwellings and 43 commercial buildings were damaged severely. MM intensity VIII effects were confined to a small area east of Morgan Hill on two streets: Oak Ridge 175 Lane and Oak Ridge Court, both in the Jackson Oaks subdivision, near Anderson Lake. Five houses were condemned in the Jackson Oaks area of Morgan Hill, two of which fell off their con- crete foundations and partly collapsed. A ranch house at Jackson Ranch (east of Anderson Lake) reportedly shifted off its foundation and collapsed. Other damage included cracks in exterior walls around garage doors and windows and a house thrown out of plumb but still on its foundation. Sev- enteen mobile homes were shaken off their support systems in Morgan Hill, and many partly fell. Three schools in Morgan Hill sustained damage to walls, ceiling panels, and light fixtures. Several under- ground water lines were broken. Near Coyote, at the United Technologies Chemical Systems Plant, damage was estimated at $1.5 mil- lion. Column base connections were damaged on sev- eral steel-frame buildings, and diagonal steel braces buckled. Concrete buildings at the plant had cracked walls and broken weld connections, and one wall panel was separated from its roof. At the IBM Santa Teresa Laboratories, south of Coyote, suspended ceil— ing panels and a light fixture fell, and an under- ground sprinkler pipe ruptured. This structure was designed for seismic loading and therefore did not sustain significant structural damage. Other effects in the Morgan Hill area included slight damage to Leroy Anderson Dam, Coyote Lake Dam, Coyote Creek Bridge, and Anderson Reservoir Bridge, fallen chimneys, small landslides, and changes in flow of water in springs or wells. At Coy- ote Lake Dam, about 25 km southeast of the main shock, a large acceleration of gravity (1.29 g) was recorded on strong-motion instruments. This damag- ing earthquake was felt over a large area of Califor- nia and western Nevada. (Ref. 370, 401.) 1984. Oct. 25. Near Santa Ynez, Santa Barbara County, Calif. Minor damage occurred at Santa Ynez and north of Los Olivos at the Fire- stone Winery. Effects at the winery included dam- age to several steel storage tanks and to the foundations of several large oak vats. The ware- house sustained one stress crack, and the water line to the sprinkler system ruptured. At Santa Ynez, brick fences were cracked; large cracks formed at the joints between a concrete-block wall and a wood-frame wall; and interior plaster walls were cracked. Felt over a small area of Santa Barbara and Ventura Counties. (Ref. 370.) 1985. Aug. 4, 12 01 UTC. Near Avenal, Kings County, Calif. A few stores and houses were dam- aged at Avenal, and six residents were injured. 176 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Damaged home in the Jackson Oaks subdivision of Morgan Hill, California, caused by the April 24, 1984, earthquake. (Photograph by the Morgan Hill Times.) Damage included the partial collapse of porches at two houses, cracked and broken chimneys, cracks in sidewalks and walls, broken water mains, and bro- ken windows and glassware. About 8 km northeast of Avenal, four adobe houses sustained cracks in the walls and ceilings, parts of the ceilings fell, and concrete porches were cracked. Several water lines and one gas main were broken at Kettleman City, and a cast-iron elbow on a water tank was broken. Felt over a large area of central California. More than 130 aftershocks were recorded in the next 27 hours. Magnitude 5.8 ML PAS. (Ref. 371, 401.) 1985. Oct. 2. Near Grand Terrace, San Ber- nardino County, Calif. Plaster fell at the Grand Terrace fire station, and minor cracks formed in its ceiling. In a log house at Lake Gregory Village, one beam was split and others were cracked. Felt in parts of Los Angeles, Orange, Riverside, San Bernar- dino, and San Diego Counties. (Ref. 371.) 1986. Jan. 26. Near Paicines, San Benito County, Calif. At a winery in Paicines, a huge vat full of wine was displaced 6 In from its foundation and shattered. Damage to wine vats at the winery was estimated at $800,000. Damage to property in the form of broken gas pipes and ruptured water lines occurred at Hollister. At Tres Pinos, two chimneys fell at the 19th Hole Bar, and the kitchen stove was displaced. At a ranch in the Santa Ana Valley, masonry walls at the entrance to the drive- way were partly collapsed. Felt generally north to San Joaquin County, south to San Luis Obispo County, and from the coast east to Fresno County. (Ref. 562.) 1986. Mar. 31. Near San Jose, Santa Clara County, Calif. This earthquake injured six resi- dents and caused slight damage to property in Fre- mont, Mount Hamilton, Newark, and San Jose. The main damage was characterized by broken water lines, fallen ceiling tiles, cracks in chimneys and EARTHQUAKES IN CALIFORNIA walls, and damaged stock. Known as the Mt. Lewis earthquake, it was preceded by two minor foreshocks on Mar. 24 and Mar. 31 and was followed by 22 after- shocks. The main earthquake was felt along the coast north to Sonoma County and south to San Luis Obispo County. (Ref. 562.) 1986. July 8. Near North Palm Springs, Riv- erside County, Calif. This strong earthquake injured 40 people in the North Palm Springs area and caused property damage estimated at $6 million. Sixteen business structures and four houses were destroyed; 102 houses (mostly mobile homes) and 117 business structures were damaged to some degree. The earthquake disrupted electrical and telephone service, broke water lines and gas lines, and caused failure of two pumping stations in the Metropolitan Water District. North of Palm Springs, en echelon fractures formed along the Banning fault for a dis- tance of about 9 km on both sides of State Highway 62. Several highways were closed temporarily by minor landslides. Major damage to a highway bridge was observed on Interstate 10 in Coachella Valley northwest of Palm Springs. The bridge was displaced laterally, leaving a small gap between the deck and abut- ment. Three houses were destroyed and chimneys fell in the Whitewater Canyon area. Also sustaining damage was the Southern California Edison Devers substation, 3 km northwest of North Palm Springs. Many of the ceramic columns were broken at the substation, and one transformer was displaced about 4 cm, shearing retaining bolts. Several light after- shocks were reported felt. The main shock was felt over a large area, including parts of western Ari- zona, southern California, and southern Nevada. (Ref. 562, 597.) 1986. July 13. Off the coast of San Diego County, Calif. This earthquake caused damage in San Diego County estimated at $700,000 and injured one person. Damage in San Diego and nearby towns consisted mainly of broken plate-glass windows, cracked walls and plaster, and broken chimneys. Through Apr. 30, 1987, 99 aftershocks of magnitude greater than 3.0 occurred. Felt over most of south- ern California and reported as far away as Las Vegas, Nev., and Yuma, Ariz. (Ref. 562, 597.) 1986. July 17. North Palm Springs, Riverside County, Calif., aftershock. At Whitewater, chim- neys were broken at the roofline, tombstones were toppled, foundation and interior walls were cracked, and underground pipes were broken. Rockslides were reported on Whitewater Road. Felt mainly in south- ern California, but also was reported at Las Vegas, Nev. (Ref. 562.) 177 1986. July 21, 14 42 UTC. Near Chalfant, Mono County, Calif. Known as the Chalfant Valley earthquake, this shock injured two people and caused an estimated $2.7 million damage to property in the Bishop-Chalfant area. At Bishop, a few chimneys cracked, windows broke, ceiling tile and plaster fell, and exterior walls cracked in several buildings. The brick facade on a bank on Main Street also sustained cracks. Most of the damage at Chalfant was due to mobile homes being shaken off their supports, which damaged water and gas lines. Fractures in the ground were observed in the White Mountain frontal fault zone. Many small landslides and spectacular rockfalls occurred in the epicentral area. The shock was felt mainly in California and west- ern Nevada but was reported in multistory buildings as far distant as Salt Lake City, Utah. A foreshock occurred on July 20 at 14 29 UTC, and an aftershock occurred on July 31 at 07 22 UTC (see next para- graph). Thousands of smaller aftershocks occurred through Sept. 30, 1986. Magnitude 5.9 ML PAS, 6.6 ML REN. (Ref. 562.) 1986. July 31 (July 30), 07 22 UTC. Near Bishop, Inyo County, Calif. A strong aftershock of the Chalfant Valley earthquake (July 21, 14 42 UTC) broke plate-glass windows in Bishop and toppled stock from shelves. Light fixtures were knocked down at the National Weather Service office. Felt over a small area of California and western Nevada. Magnitude 5.9 ML PAS, 5.5 ML REN. (Ref. 562.) 1986. Nov. 21, 23 33 UTC. Near Petrolia, Humboldt County, Calif. The most severe damage occurred at Petrolia, where chimneys were cracked and twisted and small appliances were overturned. An old building at the Mattole Union Elementary School was knocked off its cinder-block foundation. Slight damage also occurred in several other towns in the area. A strong aftershock occurred at 23 34 UTC, but its effects could not be differentiated from those of the earthquake about 1 minute earlier. The first earth- quake was felt over a moderate area of northern Cal- ifornia, mainly in Humboldt, Mendocino, and Trinity Counties. (Ref. 562.) 1987. July 31. Near Petrolia, Humboldt County, Calif. Minor damage was reported at Petro- lia, where underground pipes and windows were bro- ken, cracks formed in chimneys and in wood foundations, and water in springs or wells was mud- died. One report from Ferndale indicated that chim- neys were toppled, windows were broken, and sidewalks were cracked. Felt only in Humboldt, 178 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Adobe walls of a recently remodeled house in Whitewater Canyon, northwest of Palm Springs, California, cracked by the July 8, 1986, earthquake. (Photograph by G. Borchardt, California Division of Mines and Geology.) Mendocino, Siskiyou, and Trinity Counties in north- ern California. (Ref. 74, 577.) 1987. Oct. 1. Near Whittier Narrows, Los Angeles County, Calif. The Whittier Narrows earthquake caused eight fatalities, injured several hundred, and left property damage estimated at $358 million in the east Los Angeles area, mainly at Whit- tier. MM intensity VII to VIII covered an area of about 500 ka—from Monrovia and Pasadena in the north to beyond Whittier in the southeast. MM intensity VI was assigned to an additional area of 1,500 km2. Business structures in the 01d Whittier commercial district were the most severely damaged by the main earthquake. In the 24-square-block shopping area known as Whittier Village, 12 commercial buildings EARTHQUAKES IN CALIFORNIA had to be razed, and another 20 buildings were declared unsafe. An inspection of residential houses in Los Angeles, Orange, and ‘Ventura Counties indi- cated that 123 single-family houses and 1,347 apart- ment units were destroyed, and about 513 single- family houses and 2,040 apartment units sustained major damage. Property damage on the Los Angeles campus of California State University (about 10 km west of the epicenter) was estimated at more than $20 million. The most severe damage to transportation systems was to the Interstate 605—Interstate 5, a major nine— span bridge that was built in 1964. The five support ing columns sustained severe shear fractures and the overpass was closed temporarily. Minor damage also occurred on 23 other bridges in the area. Damage and dysfunction of lifelines included the often observed failure of ceramic elements on high- voltage substation equipment, damage to large liquid-storage tanks, and saturation of the telephone system with inappropriate calls. The natural-gas transmission system was not damaged, and only one cast-iron pipe failed in the distribution system. How- ever, about 1,400 gas leaks occurred on customer property, and many fires were ignited. This earthquake sequence ruptured a small and previously unidentified, gently north-dipping, west- striking thrust fault beneath the uplifted Puente Hills and Elysian Park—Montebello Hills. However, tectonic slippage was not observed during a field study of the faults in the epicentral area. Geologic surface expression appeared to be limited to second- ary nontectonic breaks caused by acceleration at the surface. Although many ground cracks formed along the base of the Puente Hills between Turnbull Can- yon and Norwalk Boulevard, ground breakage in that area was limited to slope failures, including exten- sional cracks, minor landslides, and rockfalls. Ground-surface cracks also were observed at Wor- sham Creek oil field and Whittier Narrows golf course. The main shock was followed by about 500 locat- able aftershocks, an unusually small number for an earthquake of this magnitude. The largest after- shock, which occurred on Oct. 4 about 3 km north- west of the epicenter of the main shock (see description below), caused further damage to weak- ened buildings. (Ref. 74, 577, 580, 581, 582, 598.) 1987. Oct. 4, aftershock. Near Whittier Nar- rows, Los Angeles County, Calif. A strong after- shock of the Oct. 1 Whittier earthquake killed one person, injured several, and caused additional prop- erty damage in Alhambra, Los Angeles, Pico Rivera, and Whittier. Several chimneys twisted, fell, or broke 179 at the roofline; stone fences cracked and toppled; windows broke; and large cracks formed in sidewalks and highways. The press reported that one of the two bell towers collapsed on the San Gabriel Civic Audi- torium. Also felt in Orange, Riverside, San Bernar- dino, and San Diego Counties. (Ref. 74, 577, 598.) 1987. Nov. 24, 01 54 (Nov. 23) and l3 15 UTC. West of Westmorland, Imperial County, Calif. The Superstition Hills earthquakes caused an esti- mated $3 million property damage in Imperial County. Epicenters of the shocks were in the western Imperial Valley on a fault system comprising the northwest-striking Superstition Hills fault and a pre- viously unknown northeast-striking structure. The earthquake sequence consisted of foreshocks, .the first main shock, and aftershocks on the northeast trend, followed by the second main shock about 11 hours later and aftershocks on the northwest trend. Signifi- cant surface ruptures occurred along the Superstition Hills fault. Damage reported in the epicentral region at El Centro, Imperial, and Westmorland included fallen chimneys, broken underground pipes, broken win- dows, and large displacements in highways or streets. The Worthington Road Bridge across the New River needed to be replaced, owing to liquefac- tion damage to the approach fill on both sides of the bridge. Damage at the Desert Test Range Control Center near Westmorland, which included equipment falling through a Window and small water tanks tip— ping against the building, was sufficient to stop oper- ations for several days. Damage to canal facilities in the Southern Califor- nia Irrigation District was estimated to be between $600,000 and $750,000. The first main shock caused minor buckling of the concrete lining in canals on the west side of the valley; the second main shock col- lapsed thousands of feet of concrete canal lining, mainly in the northwest corner of the valley nearest the earthquake epicenters. The shock at 01 54 UTC was associated with left- lateral surface rupture on many faults in and near the Superstition Hills. A maximum surface slip of 12.5 cm was observed on the Elmore Desert Ranch fault. The shock at 13 15 UTC ruptured the surface of the right-lateral Superstition Hills fault for a distance of 27 km southeastward from its epicenter. This right-lateral movement continued to increase over the following 339 days. The maximum vertical slip observed on the southernmost ruptured part of the Superstition Hills fault zone (named the Wienert fault) was 25 cm, but that rupture also continued to increase. Both shocks were felt over most of southern 180 California and in parts of ,western Arizona and southern Nevada. (Ref. 74, 577, 587, 588, 598, 601.) 1988. Feb. 11. Near Whittier, Los Angeles County, Calif. A small aftershock of the Whittier earthquake of Oct. 1, 1987, cracked chimneys, dry- wall, plaster, and Windows at Los Angeles, Pasadena, Pico Rivera, and Whittier. Further, foundations of houses were cracked and exterior walls were dam- aged at Pico Rivera and Whittier. Also felt in Kern, Orange, Riverside, San Bernardino, and San Diego Counties. (Ref. 578, 602.) 1988. June 13 (June 12). Near San Jose, Santa Clara County, Calif. Slight damage occurred at San Jose, where open cracks formed in stone or brick fences and interior walls were cracked. Hairline cracks formed in drywall and plaster at nearby Santa Clara. Felt north along the coast to Humboldt County, east to Amador and Tulare Counties, and south to Monterey and Kern Counties. (Ref. 74, 578.) 1988. June 27. Near Santa Cruz, Calif. Slight damage occurred at Holy City (near Los Gatos, Santa Cruz County), where cracks formed in plaster, dry- wall, and a house foundation. Press reports described minor damage in Santa Clara County, at the Sunny- vale Town Center, where chunks of concrete fell from the parking garage, and at Los Gatos, where store- front Windows were shattered. After the earthquake, the flow of water increased in a well at Holy City. Felt north along the coast to Marin County, south to Monterey County, and east to Fresno County. (Ref. 74, 578.) 1988. Dec. 3. Near Whittier, Los Angeles County, Calif. Windows were broken at Whittier, and hairline cracks formed in plaster, drywall, and a house foundation. Several bricks were knocked to the ground at the San Gabriel Mission. Press reports noted that several people were injured in the San Fernando Valley and that electricity was knocked out briefly. Also felt in Kern, Orange, River- side, San Bernardino, San Diego, and Ventura Coun- ties. Several small aflzershocks were reported. (Ref. 578, 602.) 1989. Jan. 19 (Jan. 18). Off the coast near Malibu, Los Angeles County, Calif. An earth- quake off the coast of California, south of Malibu, caused minor damage in Los Angeles County at Hol- lywood, Lancaster, Malibu, Monterey Park, and Whittier. rIypical damage included broken windows; cracks in chimneys, foundations, fences, and walls; and damaged stock in stores. An observer at Monterey Park also reported that large amounts of plaster fell from walls and that some walls fell. Rocks rolled onto the highway in Santa Monica and on Malibu Canyon Road. According to press accounts, SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) this shock was felt from Santa Barbara south to San Diego and east to San Bernardino. Several after- shocks occurred. (Ref. 579, 603.) 1989. Apr. 3. Northeast of San Jose, Santa Clara County, Calif. At San Jose and Santa Clara, many cracks formed in drywall, plaster, and founda- tions of houses. One large window was knocked out of an airport control tower in San Jose. Felt north to Marin and Solano Counties, south to San Luis Obispo County, and east to Stanislaus County. (Ref. 74, 579.) 1989. Apr. 7. Near Newport Beach, Orange County, Calif. Slight damage was reported in Orange County at Corona Del Mar, Costa Mesa, and Newport Beach. Typical damage consisted of broken windows; fallen bricks from chimneys; cracked chim- neys, walls, and plaster; and damaged merchandise in stores. In addition, ceiling tiles fell in several stores in Newport Beach, and part of a wall of a brick building toppled. Felt north to Los Angeles County, south to San Diego County, and east to Riv- erside and San Bernardino Counties. (Ref. 579, 603.) 1989. June 12. Near Bell Gardens, Los Ange- les County, Calif. Minor damage reported west of Whittier, at Bell Gardens, included large cracks in exterior walls of a reinforced-concrete building and hairline cracks in plaster and drywall. Slight dam- age (fallen plaster and cracked ceiling) also was reported in the downtown Los Angeles area. Also felt in Orange, Riverside, San Bernardino, and Ven- tura Counties. An aftershock was felt about one-half hour after the main shock. (Ref. 579, 603.) 1989. Aug. 8. Near Redwood Estates, Santa Clara County, Calif. This earthquake caused one death and moderate damage to property in Santa Clara County near San Jose. Toppled and broken chimneys were reported at Cupertino (west of San Jose), Los Gatos (about 15 km northeast of the epi- center), and Redwood Estates (about 7.5 km north- east of the epicenter). Other damage observed included broken underground pipes, cracks in foun- dations and walls, walls separated from ceilings, and toppled water heaters and propane tanks. Light dam- age occurred at several other towns in Santa Clara and Santa Cruz Counties, including Ben Lomond, Brookdale, Holy City, Santa Cruz, and Saratoga. Felt to Sonoma County in the north, San Luis Obispo County in the south, and Stanislaus County in the east. (Ref. 74, 579.) 1989. Oct. 18, 00 04 UTC (Oct. 17). In the Santa Cruz Mountains in the forest of Nisene Marks State Park, about 16 km northeast of Santa Cruz and about 7 km south of Loma Pri- eta Mountains, Calif. This major earthquake EARTHQUAKES IN CALIFORNIA LOIM mar; EA ‘1' MAhmi 013mm" October 17, 1989 Collapsed apartment building in the Marina District, San Francisco, California, caused by the October 18, 1989 (Oct. 17 PST), Santa Cruz Mountains (Loma Prieta) earthquake. (Photograph by the Earthquake Engineering Research Institute.) caused 63 deaths, 3,757 injuries, and an estimated $6 billion in property damage. It was the largest earthquake to occur on the San Andreas fault since the great San Francisco earthquake in April 1906. The most severe property damage occurred in Oak- land and San Francisco, about 100 km north of the fault segment that slipped on the San Andreas. MM intensity IX was assigned to San Francisco's Marina District, where several houses collapsed, and to four areas in Oakland and San Francisco, where rein- forced-concrete Viaducts collapsed: Nimitz Freeway (Interstate 880) in Oakland, and Embarcadero Freeway, Highway 101, and Interstate 280 in San Francisco. Communities sustaining heavy damage in the epicentral area included Los Gatos, Santa Cruz, and Watsonville. Liquefaction, as evidenced by sand boils, lateral spreading, settling, and slumping, occurred as far as 110 km from the epicenter. It caused severe damage to buildings in San Francisco's Marina district as well as along the coastal areas of Oakland and Alameda in the east San Francisco Bay shore area. Liquefaction also contributed significantly to the property damage in the Santa Cruz and Monterey Bay areas, which lie near the epicentral zone. Struc- tures damaged by liquefaction include buildings, bridges, highways, pipelines, port facilities, airport runways, and levees. Subsurface soil conditions, which amplified accelerations in the San Francisco Bay area, strongly influenced structural damage pat- terns and probably contributed to liquefaction problems in loose, sandy fills underlain by deep, cohesive soil deposits. Engineered buildings, including those near the epi- center, performed well during the earthquake. Hos- pital buildings in the region sustained only minor system and cosmetic damage, and operational inter- ruptions did not occur. Only five schools sustained severe damage, estimated at $81 million. 182 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Span of the San Francisco—Oakland Bay bridge, collapsed by the October 18, 1989 (Oct. 17 PST), Santa Cruz Mountains (Loma Prieta), California, earthquake. (Photograph by E.V. Leyendecker.) Most of the spectacular damage to buildings was sustained by unreinforced masonry buildings con- structed of wood-frame roof and floor systems sup- ported by unreinforced brick walls. These structures failed in areas near the epicenter as well as in areas far from the epicenter, at San Francisco and Monterey. The severe shaking near Santa Cruz caused heavy damage to the unreinforced masonry buildings in that area, particularly in the Santa Cruz Pacific Garden Mall, which consisted of several blocks of unreinforced masonry store buildings. More than 80 of the 1,500 bridges in the area sustained minor damage, 10 required temporary supports, and 10 were closed owing to major struc- tural damage. One or more spans collapsed on three bridges. The most severe damage occurred to older structures on poor ground, such as the Cypress Street Viaduct (41 deaths) and the San Francisco—Oakland Bay Bridge (one death). Damage to the transpotation system was estimated at $1.8 billion. Most of the more than 1,000 landslides and rock- falls occurred in the epicentral zone in the Santa Cruz Mountains. One slide, on State Highway 17, disrupted traffic for about 1 month. The earthquake produced a pattern of northwest- trending extensional fractures in the north end of the aftershock zone northwest of the epicenter, but throughgoing right-lateral surface faulting was not found above the rupture defined by the main shock and its aftershocks. Six feet of right-lateral strike-slip EARTHQUAKES IN CALIFORNIA 183 ' iuiamwxmhiimmw Nimitz Freeway along Cypress Street (Interstate 880) in Oakland, California, collapsed by the October 18, 1989 (Oct. 17 PST), Santa Cruz Mountains (Lorna Prieta) earthquake. (Photograph by E.V. Leyendecker.) and 4 feet of reverse-slip was inferred from geodetic data. The only surface fracturing that might be attrib- uted to primary tectonic faulting occurred along a trace of the San Andreas near Mount Madonna Road in the Corralitos area, Where en echelon cracks showed 2 cm of right-lateral displacement. Extensional fractures (maximum net displacement of 92 cm) were observed about 12 km northwest of the epicenter, in the Summit Road—Skyland Ridge area, east of State Highway 17, whereas zones of compressional deformation were found along the northeast foot of the Santa Cruz Mountains between Blossom Hill and Palo Alto. In Los Altos and Los Gatos, ground deformation appeared to be associated closely with zones of heavy structural damage and broken underground utility lines. Other towns in the area that also experienced severe property damage include Boulder Creek, Cor- ralitos, Hollister, Moss Landing, and several smaller communities in the Santa Cruz Mountains. This earthquake was felt over most of central Cali- fornia and in part of western Nevada (see fig. 24). The rate of aftershock activity decreased rapidly with time, but the total number of aftershocks was less than that expected from a generic California earth- quake of similar magnitude. Fifty-one aftershocks of magnitude 3.0 and larger occurred during the first day after the main shock, and 16 occurred during the second day. After 3 weeks, 87 magnitude 3.0 and larger aftershocks had occurred. (Ref. 74, 574, 579, 594, 595, 596, 606, 607.) 184 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Ground failure along the San Andreas fault zone, causing slumping and cracking of Hazel Dell Road, north of Watsonville, California, during the October 18, 1989 (Oct. 17 PST), Santa Cruz Mountains (Lorna Prieta) earthquake. EARTHQUAKES IN CALIFORNIA 185 M, 4A mama“ ‘7 H H t House on Rebecca Drive, Boulder Creek, California, destroyed by the October 18, 1989 (Oct. 17 PST), Santa Cruz Mountains (Loma Prieta) earthquake. 186 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 124° 122° 120° 118° 116° Redding o 40° ' o \ . Lovelock NEVADA 38° ‘ San Francisco I I CALIFORNIA Bishop 0 Santa Cruz Fresno ’0 7 O / 4 I O 36° 0 Bakersfield Sama Maria \ 0 Los Angeles 34° 0 EXPLANATION \/ * Epicenter V||| Intensity 8 | 0 100 KILOMETERS E l—.—_| b FIGURE 24.—Isoseismal map for the Santa Cruz Mountains (Loma Prieta), California, earthquake of October 18, 1989. This map is a simplified version of figure 1 in reference 574 of table 1. COLORADO 108° 106° 104° 102° WYOMING NEBRASKA . . (D 0 Craig 0 Sterling 40° 0% Denver I , COLORADO E Grand Junction 0 o W 0 Colorado Springs 32> U) > (/2 38° C? A U Durango O o 0 Trinidad EXPLANATION OKLA. < Magnitude/Intensity % o 2.9—4.4/VI E 0 4-5'4-9 NEW MEXICO 36° -3: O 5.0-5.4/VI TEXAS 5.5-5.9 O o 100 KILOMETERS O 6.0-6.4 ;_1_J Earthquakes in Colorado with magnitudes 2 4.5 or intensity 2 VI. 187 188 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) COLORADO [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m s (°) (°) (km) m., Ms M (1,000 km2) 1871 10 40.5 N 108.5 W — 487 -— — — — VI 487 —— 1882 11 08 0130 40.5 N 105.5 W — 487 — — 6.20Mf,KRK —— VII 273 485 1891 12 21 40.5 N 108.0 W — 273 — — — — VI 273 -— 1913 11 11 2155 38.1 N 107.7 W — 487 —— —- — — VI 487 14 1944 09 09 041220 39.0 N 107.5 W -— 266 —-— —-— —— — VI 38 19 1955 08 03 063942 38.0 N 107.3 W — 273 -— -- — — VI 28 5 1960 10 ll 08 05 30.5 38.3 N 107.6 W 049 33 — — 5.50mi, BRK — VI 33 39 1962 02 05 14 45 51.1 38.2 N 107.6 W 025 266 — — 4.70ML GOL — V 35 — 1962 12 04 17 49 59.4 39.8 N 104.7 W 033 266 —- — 3.20ML GOL — VI 35 12 1962 12 05 1348004 39.9 N 104.6 W 033 266 —- -- 3.80ML GOL — VI 35 16 1965 02 16 22 21 43.7 39.9 N 105.0 W 005 74 — -— 3.00ML GOL -— VI 75 l 1965 09 14 224624.1 39.9 N 104.6 W 005 266 —- -— 3.60ML GOL — VI 75 3 1965 09 29 18 59 56.1 39.8 N 105.1 W 005 266 — — 3.50ML GOL — VI 75 4 1965 11 21 040228.7 39.8 N 104.8 W 005 266 — — 3.80ML GOL ——- VI 75 7 1966 10 03 02 26 02.3 37.4 N 104.1 W 010 266 — — 4.60ML GOL — VI 81 45 1966 11 14 2002 35.9 39.9 N 104.7 W 005 266 -- -- 3.50ML GOL — VI 81 4 1967 04 10 1900255 39.94 N 104.75 W 005 266 —— —— 4.30Mn HER — VI 40 16 1967 04 27 1724423 39.91 N 104.77 W 005 266 4.5 — 3.8OML GOL — VI 40 4 1967 08 09 13 25 06.2 39.9 N 104.7 W 005 74 5.3 — 4.90m, NUT — V11 40 50 1967 11 27 050924.6 39.87 N 104.88 W 005 274 5.2 — 4.60mi, NUT — VI 40 56 1979 01 06 0158 55.3 38.96 N 105.16 W 005 262 — —— 2.90ML GS — VI 262 11 1981 04 02 16 10 06.4 39.91 N 104.95 W 009 325 4.3 — 3.80ML GS — VI 325 6 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1871. October. Lily Park, Moffat County, Colo. An avalanche of rock cascaded from the high cliffs of the canyon walls at Lily Park. The ground heaved and fell. It is possible that the date of this earthquake is Nov. 9, 1871. (Ref. 487.) 1882. Nov. 8 (Nov. 7). Near Denver, Colo. This earthquake probably was the largest event to occur in Colorado in the period of historic record. It caused minor damage in Colorado and southern Wyoming and was felt slightly in Utah and Kansas (see fig. 25). The location of this earthquake is very uncertain and has been postulated to have occurred in western Colorado or southern Wyoming. In Denver, electricity was cut off after an iron bolt that connected an engine-driving pulley was broken in two at the electric power building; another bolt was bent out of shape. Buildings trembled violently and residents ran out of doors. Plaster fell and win— dows broke as far north as Laramie, Wyo., and plaster fell from the ceiling of a building at the Uni- versity of Colorado in Boulder. Observers also reported that the walls of the railroad depot in Louis— ville were cracked, that timbers cracked in a house at La Porte, and that walls of one house were cracked severely and plaster fell near Thompson, Colo. An aftershock on Nov. 8 was reported to be almost as strong as the main shock in Laramie and Denver. (Ref. 27 3, 283, 440, 487, 488, 499.) 1891. Dec. Lily Park, Moffat County, Colo. The earth was convulsed by waves that rolled at intervals of a few seconds. Thousands of tons of boul- ders rolled down Fitzpatrick's Cliff. A house moved, calendars and pictures on the walls oscillated, dishes rattled, and people ran outside. A cow was knocked against a house. (Ref. 273, 487, 488.) 1913. Nov. 11. Near Ridgway, Ouray County, Colo. Damage at Ridgway included damage to the school ceiling and broken dishes. The shock was reported as strong at towns near Ridgway, including Montrose, Ouray, and Telluride; rocks rolled down cliffs at Ouray. Three shocks were reported. (Ref. 38, 487, 488.) EARTHQUAKES IN COLORADO 114° 112° 110° 108° 106° 189 104° 102° 100° 93° l W YOMING 42° SOUTH DAKOTA NEBR ASK A 4U” G dJ l' I "o" ""m" COLORADO 38° KANSAS 36° 200 KLMTERS ‘——EIX—P-L—ANATION *7 Epicenter V|| Intensity 7 OKLAHOMA TEXAS FIGURE 25.—Isoseismal map for the Colorado earthquake of November 8, 1882. This map is a simplified version of figure 1 in reference 499 of table 1. 1944. Sept. 9 (Sept. 8). Near Basalt, south- west Eagle County, Colo. Walls and chimneys cracked at Basalt; bricks fell from chimneys; and rocks rolled onto the road. A strongly built log house was moved slightly out of line at Riland. (Ref. 17, 38, 266, 487, 488.) 1955. Aug. 3 (Aug. 2). Lake City, Hinsdale County, Colo. Residents at Lake City reported cracks formed in a chimney and in the ground; one chimney fell. Also felt at Ouray, west of Lake City; Silverton (San Juan County), southwest of Lake City; and Creede (Mineral County), southeast of Lake City. (Ref. 28, 273, 487.) 1960. Oct. 11. Near Montrose, Colo. At Mon- trose, southeast of Grand Junction, a foundation cracked in three places in a house, and all cupboards loosened from walls. Damage at nearby towns con- sisted of a cracked chimney at Ophir, cracked and broken windows at Placerville and Powderhorn, fallen plaster at Lake City, and cracked walls at Telluride. (Ref. 33, 487.) 1962. Dec. 4. Near Denver, Colo. At Dupont, a picture window broke and a bed moved 15 cm from the wall. At Irondale, windows broke at a school, electrical wall outlets were left hanging by their wires, and brick tiles loosened. (Ref. 35, 266, 487.) 1962. Dec. 5. Near Denver, Colo. This earth- quake caused cracks in plaster and a wall in the Derby-Dupont area, about 13 km northeast of Den- ver. Plaster cracked in the Derby area. (Ref. 35, 266, 487.) 1965. Feb. 16. Near Denver, Colo. At North- glenn, a large crack formed in one house. At Com- merce City, a washer moved from the wall and furnishings shifted. (Ref. 74, 75, 487.) 1965. Sept. 14. Near Denver, Colo. Plaster cracked and dishes and windows broke at Denver; chimneys and plaster cracked at Broomfield; and plaster cracked in the Commerce City—Derby area. Felt from 40 km south of Denver northwest to Boulder. (Ref. 75, 266, 487.) 1965. Sept. 29. Near Denver, Colo. Plaster and windows cracked at Commerce City, a refrigerator 190 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Cracks in highway overpass pillar in the Denver, Colorado, area caused by the August 9, 1967, earthquake. (Photograph by the Denver Post.) EARTHQUAKES IN COLORADO was moved several inches at Northglenn. The shock was felt from Denver northwest to Boulder and Ned- erland. (Ref. 75, 266, 487.) 1965. Nov. 21 (Nov. 20). Near Denver, Colo. The earthquake broke many windows at Northglenn and Thornton and cracked plaster at Commerce City (one window also broke), Hudson (fallen plaster), and Louisville. (Ref. 7 5, 266, 487.) 1966. Oct. 3 (Oct. 2). Near Trinidad, Las Ani‘ mas County, Colo. Minor damage reported in Las Animas County includes cracks in houses at Aguilar and Segundo, cracks in plaster and windows at Trinchera, and broken windows and cracks in plaster at Trinidad. Felt over a large area of southeast Colo- rado and northeast New Mexico. Magnitude 3.6 Ms NUT (Ref. 81, 263, 266, 487.) 1966. Nov. 14. Near Denver, Colo. A slight earthquake in the Denver area cracked plaster and lengthened old cracks in Commerce City and knocked merchandise from shelves in a supermarket. (Ref. 81, 266, 487 .) 1967. Apr. 10 Near Denver, Colo. In the Denver—Commerce City region, plaster cracked and fell, windows broke, and a house foundation cracked. North of Denver, at the Rocky Mountain Arsenal, 118 small windows were broken; at Boulder, walls cracked at a high school. Water pipes broke at one Commerce City residence, and cracks in a parking lot were reported in the Derby area of Commerce City. Minor damage occurred in several other towns in the area, including Brighton, Golden, Lafayette, Lake- wood, Thornton, and Westminster. (Ref. 40, 266, 487 .) 1967. Apr. 27. Near Denver, Colo. This earth- quake caused slight damage in Commerce City and Boulder. Plaster cracked and nails were forced out of walls at Commerce City, and walls and a tile ceiling were cracked at Boulder. (Ref. 40, 266, 487.) 191 1967. Aug. 9. Near Denver, Colo. The main damage occurred in Northglenn, a northern suburb of Denver, but minor damage occurred in many area towns. At Northglenn, concrete pillars were damaged at a church; foundations, concrete floors, and walls cracked; windows broke; and tile fell at a school. At one residence, a piano shifted about 15 cm and a television set overturned. Some bricks fell from a chimney in downtown Denver, damaging a car. This was the largest of a series of earthquakes in the northeast Denver area that were believed to be induced by pumping of waste fluids into a deep dis- posal well at the Rocky Mountain Arsenal. The C010- rado School of Mines recorded more than 300 earthquakes from this zone during 1967. Felt north to Laramie, Wyo., south to Pueblo, west to Vail, and east to Sterling. Magnitude 4.4 MS NUT (Ref. 40, 74, 263, 487.) 1967. Nov. 27 (Nov. 26). Near Denver, Colo. Damage occurred mainly in the suburban area of northeast Denver, at Commerce City. It consisted chiefly of cracked plaster, enlargement of existing cracks, and loss from fallen merchandise in stores. Masonry walls and basement floors in the area also were cracked. Felt north to Laramie, Wyo., south to Pueblo, west to Glenwood Springs, and east to Ster- ling. (Ref. 40, 263, 274, 487.) 1979. Jan. 6 (Jan. 5). Cripple Creek, Teller County, Colo. Plaster cracked and furniture shifted at Cripple Creek, west of Colorado Springs. Also felt in Florissant and the nearby area. Magnitude 3.3 Mn TUL. (Ref. 262, 487.) 1981. Apr. 2. Near Denver, Colo. At Thornton, cracks formed in plaster and concrete-block walls. At Commerce City, many large cracks occurred in plas- ter walls. Magnitude 4.5 MI] TUL. (Ref. 325, 487 .) r. 1 \ . .k , ._ » y 1 y , ,E J- i: , Ll Stil, I; :11: 1 . , , .. \ . K. V 1 . k N a P h . ‘ . , y . h ‘ v . ,.. .. ‘ g . _. .‘ 42° 41° CONNECTICUT 73° 72° MASSACHUSETTS th C. E Hartford 8 ° m M a g CONNECTICUT r > a 3 Moodu.s . U E Q Norwich / W 25 KILOMETERS J/OL—J—J EXPLANATION Magnitude/Intensity o 4.5-4.9/VI O l5.0-5.4/VI Earthquakes in Connecticut with magnitudes 2 4.5 or intensity 2 VI. 193 194 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) CONNECTICUT [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1568 41.5 N 72.5 W — 126 — —— — 4.85IOH VI 126 —- 1791 05 16 1300 41.5 N 72.5 W — 78 — —— — — VII 78 —— 1845 10 26 23 15 41.2 N 73.3 W — 78 —- — — — VI 76 — [Reference (Refi) numbers given in parentheses at the end of each description refer to sources of data in table 1.] 1568. Date unknown. Moodus—East Haddam, Middlesex County, Conn. Ref. 126 assigns MM intensity VI to this earthquake. The original source of the intensity data is the Massachusetts Historical Society Collection, 4th series, v. 6, 1863, by R. Will— iams. (Ref. 126.) 1791. May 16. Near Moodus, Middlesex County, Conn. The region around East Haddam, on the Connecticut River northeast of New Haven, has been the scene of a series of local disturbances since this country was settled. The region southeast of Middletown has been referred to in Indian tradi- tion as Morehemoodus, or “place of noises.” The first reported earthquake began on May 16 with two heavy shocks in quick succession. Stone walls were shaken down, tops of chimneys were knocked off, and latched doors were thrown open. A fissure several meters long formed in the ground. In a short time, 30 lighter shocks occurred, and more than 100 continued during the night. Reported felt at Boston, Mass., and New York City, NY. (Ref. 38, 76, 78.) 1845. Oct. 26. Near Stamford, Fairfield County, Conn. The shock was severe in Fairfield County, Conn. At Stamford and Weston, sections of a stone fence were damaged; at Huntington, books were thrown from a table; and at Greenfield Hill, milk pans were thrown down. Also felt in New Jer- sey and New York. (Ref. 76, 78.) 40° 39° DELAWARE 76° 75° 74° PENNSYLVANIA /[ / Philadelphia Wilmington NEW JERSEY Q f $4 Q A? \/ a 3 Cape May > a: DELAWARE EXPLANATION 2 |ntensity 4 O VII ’ Laurel ‘g/é 0 J SJO KILOMETERS Damaging earthquake in Delaware, intensity 2 VI. 195 196 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) DELAWARE [See table 1 for hypocenber and intensity references and table 2 for definitions of magnitude source codes. Leader (—-) indicates information is not available] Origin Hypocenter Magnitude Intensity Date “"10 (UTG) Latltude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo D: h m 3 (°) (°) (km) m. Ms M (1,000 km?) 1871 10 09 14 40 39.7 N 75.5 W — 38 — — — — VII 38 — [Reference (Ref) number given in parentheses at the end of area, Chimneys toppled and windows broke in north- each description refer to sources of data in table 1. Magnitude em Delaware at Wilmington. Damage also was values are described 1n the Introductlon, and codes are defined in reported at New Castle (10 km south of Wilmington) t bl 2. a e ] , and at Oxford, Pa. (about 40 km west of Wilmington). 1871. Oct. 9. New Jersey—Delaware border Also reported felt in New Jersey. (Ref. 38.) 30° 28° 26° 88° 86° FLORIDA 84° 82° ALABAMA Pensacola EXPLANATION Intensity ow < GEORGIA k 5 E Y‘ > O ‘2. Tallahassee . *3: Jacksonville ‘8 \ O n F) o 12 O 04¢ 0» 47 o 6:190 Orlando 0 FLORIDA o 1 \Fort Myers 100 KILOMETERS Miami Damaging earthquakes in Florida, intensity 2 VI. 197 198 SEISMICITY OF THE UNITED STATES, 1568-1989 (REVISED) FLORIDA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MM| Ref Felt area Yr Mo Da h m 3 (°) (°) (km) "1., Ms M (1.000 kmz) 1780 02 06 30.4 N 87.2 W — 101 — — — — VI 101 — 1879 01 13 04 45 29.5 N 82.0 W — 38 — — —- — VI 38 258: [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1.] 1780. Feb. 6. Northwest Florida. Regimentals and arms racks fell from walls in many barracks; everything in the rooms was moved; doors were sprung. Chimneys were thrown together causing fires. Neighboring houses clashed together, and peo- ple buried in the ruins cried for help. This event occurred during a “fearful” storm that was accompanied by violent thunder and lightning and raging seas. Possibly a hurricane. (Ref. 101.) 1879. Jan 13 (Jan. 12). Near St. Augustine, St. Johns County, Fla. Plaster was shaken down and articles were thrown from shelves at St. August- ine and, to the south, at Daytona Beach. At Tampa, a trembling motion was preceded by a rumbling sound. Felt from a line joining Tallahassee, F1a., to Savan- nah, Ga., on the north to a line joining Punta Rassa and Daytona Beach, Fla., on the south. Two shocks occurred, each lasting 30 seconds. (Ref. 38, 101, 134.) 34° 32° 30° 86° GEORGIA 84° 8 2o 80" TENNESSEE /—/ NORTH CAROLINA Chattanooga I f 2/\ o O U 0 SOUTH CAROLINA Atlanta 0 EXPLANATION 0 Augusta Magnitude/Intensity g o 3.6-4.4/VI 4.5-4.9 < O m 5 < GEORGIA Columbus Savannah % :5 D O V Id t E . a osa £3 & % a’ fig 0 100 KILOMETERS V N‘V—\ FLORIDA \ /§ \ \ Earthquakes in Georgia with magnitudes 2 4.5 or intensity 2 VI. 199 200 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) GEORGIA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (~-) indicates information is not available] Origin Hypoconter Magnitude Intensity Date time (UTO) Latitude Longltudo Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1875 11 02 02 55 33.8 N 82.5 W — 38 — —- 4.30Mfa SC — VI 38 65 1903 01 24 01 15 32.1 N 81.1 W —— 38 — — 4.10Mf. SC —- VI 38 26 1914 03 05 20 05 33.5 N 83.5 W — 38 —— — 4.50Mfa SC — V 135 246 1976 02 04 19 53 53.0 34.971N 84.702W 014 349 — — 3.60Mn DG — VI 49 8 1984 10 09 11 54 26.2 34.775N 85.193W 015 370 — — 4.00Mn GS 4.22GT V1 370 8 1986 07 11 14 26 14.8 34.937N 84.987W 013 562 3.7 — 3.80M“ GS — VI 562 13 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1875. Nov. 2 (Nov. 1). Northern Georgia. The earthquake was strong enough to move a mirror back and forth from the wall and to shake doors and win- dows. Felt from Spartanburg and Columbia, SC, to Atlanta and Macon, Ga., and from Gainesville (north- east of Atlanta) to Augusta, Ga. Several aftershocks were reported. (Ref. 38, 211, 473.) 1903. Jan. 24 (Jan. 23). Near Savannah, Bryan County, Ga. The highest intensity was reported at Tybee Island, Ga., east of Savannah, on the Atlantic Ocean. Houses were shaken strongly in that area. (Ref. 38.) 1976. Feb. 4. Northern Georgia, south of Conasauga, Tenn. Near Conasauga in the Lake Ocoee Dam area of Polk County, cracks formed in masonry, chimneys, and a concrete-block building. Also felt at several towns in northern Georgia. Mag- nitude 3.0 Mn BLA. (Ref. 49, 349.) 1984. Oct. 9. Near Ringgold, Catoosa County, Ga. The most serious damage occurred a few km south of Ringgold, where cracks formed in plaster and sheetrock walls, a house foundation, and exterior brick-veneer walls. One tractor plow was overturned. Light damage also was reported at Chickamauga, LaFayette, Summerville, and Trenton, Ga., and at Chattanooga, Tenn. Also felt in Alabama and Tennes- see. Magnitude 4.2 Mn SLM, 3.8 MD TEC. (Ref. 370.) 1986. July 11. Northwest Georgia, near Chat- tanooga, Tenn. Damage reported at Cohutta, Ga., near the Tennessee border, southeast of Chattanooga, consisted of cracks in a house foundation, chimneys, and outside brick walls. Slight damage also was reported at Dalton and Tunnel Hill, Ga., and Chatta- nooga and Turtletown, Tenn. Felt in northern Geor- gia, southeastern Tennessee, and southwestern North Carolina. Magnitude 3.8 MD GT. (Ref. 562.) 161° 159° HAWAII 157° 155° 153° 23 a? Q“ Honolu|u° 1:27 o EXPLANATION Magnitude/Intensity o 4.5-5.4 o 5.5-5.9/VI O 6.0-6.4/VII O 6.5-6.9 21° 19° 200 KILOMETERS _J HAWAII Earthquakes in Hawaii with magnitudes 2 4.5 or intensity 2 VI. 201 202 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) HAWAII [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (__) indicates information is not available] Origin Hypocenter Magnitude lntenelty Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1823 06 08(1) 19. 25 N 155.0 W — 500 — — — — IX 500 — 1834 02 20 0430 19. 25 N 155.0 W — 405 — -— — — VI 405 — 1838 12 12 23 30 19.25 N 155.0 W — 405 — — — — VI 405 — 1840 02 02 0000 19. 25 N 155.0 W — 405 — — — — V 405 —- 1841 04 08 1015 19. 25 N 155.0 W — 405 -— — —— — VI 405 — 1844 02 19 0500 19. 25 N 155.0 W — 405 -— — — -— V 405 — 1848 07 09 1445 19. 25 N 155.0 W -— 405 — — — — V 405 — 1857 07 30 1130 19. 25 N 155.0 W — 405 — — — -— V 405 — 1859 11 21 12 50 20.0 N 156.0 W -— 423 — — — — V 423 —- 1860 07 19 02 30 19.25 N 155.0 W — 405 -— — —- — V 405 -— 1861 06 02 0700 19.25 N 155.0 W — 405 — — — — V 405 — 1861 12 05 22 20 21.0 N 157.0 W — 423 — — — VI 423 —- 1868 03 29 0015 19.0 N 155.5 W — 406 — — 7.00Mf.WY —- VIII 406 — 1868 04 03 02 25 19.0 N 155.5 W — 38 — ——- 7.90Mf.WY — X 406 — 1868 04 04 1057 20.5 N 156.5 W — 406 — — — -— VII 406 — 1868 05 25 1030 19.0 N 155.5 W — 405 — — — -— V 405 — 1868 07 25 0910 19.0 N 155.5 W — 405 — —- — — V 405 — 1868 11 17 08 30 19.0 N 155.5 W —- 405 — —— — — V 405 — 1869 02 19 10 30 19.0 N 155.5 W — 405 — — — — V 405 -— 1869 02 22 1210 19.0 N 155.5 W — 405 -— — — — V 405 — 1869 08 15 14 30 19.0 N 155.5 W — 405 —— -— — — V 405 — 1870 03 22 0700 19.0 N 155.5 W — 405 — -— — V 405 —— 1870 08 07 14 43 20.5 N 157.0 W —- 500 -— — 6.00Mf.WY — V 500 — 1871 02 20 0842 20.8 N 157.0 W 015 422 — — 7.00MfI COX —- VIII 422 — 1871 09 13 1045 19.25 N 155.0 W — 405 ——- — — — VII 405 —— 1872 04 22 03(X) 19.25 N 155.5 W — 500 — — — — V 500 — 1874 05 15 2215 19.25 N 155.0 W -— 405 — — — -— V 405 — 1874 12 29 16 30 19.25 N 155.0 W — 405 — — — — V 405 -— 1875 11 23 2200 19.25 N 155.0 W — 405 —-— — —- V 405 — 1877 05 31 14 50 19.25 N 155.0 W — 405 — — 6.25Mf. Wy — VI 405 —— 1879 05 16 0800 19.25 N 155.0 W — 405 — — — — V 405 —— 1879 11 04 19 25 19.25 N 155.0 W — 405 —- — — — V 405 — 1880 09 24 0145 19.25 N 155.0 W -- 405 — —- —— — V 405 — 1880 09 25 14 30 19.25 N 155.0 W — 405 — — —— — V 405 — 1881 04 22 0100 21.0 N 157.0 W — 423 —- — — —— V 423 — 1881 09 13 21.0 N 156.0 W — 463 — — — — V 463 — 1881 09 30 15 23 19.5 N 156.0 W — 463 —- — 6.00Mf.Wy — V111 463 — 1885 01 13 1629 21.0 N 156.0 W -— 423 — — 6.(X)Mf. Wy — VI 423 — 1887 01 24 0957 19.25 N 155.50 W —- 500 — — 6.00M“ Wy — VIII 500 — 1888 08 20 1805 19.25 N 155.0 W — 405 — -— —— — V 405 — 1890 08 07 0940 19.25 N 155.0 W — 405 — —— — -— VI 405 — 1894 12 03 1400 19.25 N 155.0 W — 405 — — — —— Felt 405 — 1895 12 09 0934 21.0 N 157.0 W — 423 — —- —- — V 423 — 1896 09 13 15 30 19.25 N 155.0 W — 405 — — 6.00Mf. Wy — V 405 — 1904 04 04 1809 19.25 N 155.0 W — 463 —— — — —- V 463 — 1904 06 04 2257 21.0 N 156.0 w 272 — — — — v 272 — 1905 O5 04 0200 19.25 N 155.0 W — 405 — —— — — V 405 —- 1908 09 21 0631 19.0 N 155.0 W — 412 — -— 6.80M. ABE — VI 405 — 1912 10 13 1600 20.5 N 155.5 W —- 423 — — — — V 423 —- 1913 09 08 2208 19.0 N 155.5 W --— 38 — —— — — V 38 — 1913 10 25 1128 19.0 N 155.5 W 38 — — — —- V 38 — 1914 03 30 0634 21.0 N 157.0 W — 417 — — — — Felt 417 — 1918 06 14 2143 19.0 N 155.5 W — 417 — — — — V 417 — EARTHQUAKES IN HAWAII HAWAII—Continued 203 [See table 1 for hypocenber and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnltude lntenelty Date tlme (UTc) Latitude Longitude Depth Ref USGs Other Moment MMI Ref Felt area Yr Me De h m 3 (°) (°) (km) m. M, M (1,000 km!) 1918 11 02 100110 19.4 N 155.3 W — 265 — —- 6.20Mf. Wy —- V11 38 — 1919 01 29 0322 19.0 N 155.5 W — 417 — — ~— —- V 38 — 1919 09 15 0350 19.0 N 155.5 W — 38 — — 6.10Mf.Wy —- VII 38 — 1923 01 14 125925 19.0 N 155.5 W — 417 — — — — V1 417 — 1923 12 26 0516 21.0 N 157.0 W —— 417 — — — — IV 417 — 1924 08 20 1650 19.25 N 155.55 W — 500 — —— 5.00Mf. Wy — V 500 — 1924 09 11 0333 19.0 N 155.5 W -— 445 — — — — V 416 — 1926 02 07 2159 21.0 N 157.0 W —— 218 — — —— — V 218 1926 02 28 1711 19.0 N 155.5 W —— 408 — — — — V 408 1926 03 20 0903 20.5 N 155.5 W — 423 -— — 6.00M“ Wy — V 423 — 1926 04 22 1503 19.5 N 155.5 W — 408 — — — — VI 218 — 1927 03 20 152142 20.5 N 155.25 W — 218 — — 60MfIWy — V 408 — 1927 08 03 2012 19.0 N 155.5 W —- 218 — -— — — VI 218 — 1929 09 26 045056 19.75 N 156.0 W -— 258 — — 5.60 GR — V11 38 —— 1929 09 27 2120 19.75 N 156.0 w — 408 — —- — — VI 408 — 1929 09 28 17 38 19.75 N 156.0 W — 408 — — — — V11 38 — 1929 09 29 0148 19.75 N 156.0 W — 408 —— — — — VI 408 — 1929 09 30 22 25 19.75 N 156.0 W —— 408 — -— — — VI 408 — 1929 10 06 075131 19.75 N 156.0 W — 258 — -— 6.50M. GR — V11 38 —- 1930 05 26 0647 19.4 N 155.4 W — 500 — —— 4.70Mf.WY —- V 50) — 1932 07 08 083049 19.4 N 155.3 W 010 408 — — — -- V 408 — 1935 01 02 17 17 19.418N 155.283W 004 8 —— -- 5.90Mf. Wy — V 408 — 1935 06 28 193005 19.50 N 155.25 W —— 258 — — 5.60M. GR — V1 408 -— 1935 10 01 1028 19.635N 155.434W — 418 — — — — IV 408 — 1935 11 21 1141 19.516N 155.518W — 418 — — 5.60Mf. Wy — V 408 — 1938 01 23 0832 43 21.0 N 156.0 W — 258 — — 6.75M. GR — VII 11 — 1939 05 15 2057 31 19.367N 155.133W 016 266 — — -- — VI 408 — 1939 07 14 14 21 19.318N 155.116W — 418 — — 5.50Mf. Wy — V 500 -- 1940 06 17 10 26 47 20.4 N 154.7 W — 265 — — 6.00M. GR — V"l 13 — 1940 06 17 1817 20.5 N 155.25 W -— 408 — —- — — V 408 — 1940 06 17 2309 20.5 N 155.25 W -- 408 -- — — — V 408 -— 1940 07 16 031733 20.5 N 155.0 W —- 258 — -— 5.60M. GR — V 408 — 1940 09 02 084442 21.0 N 155.25 W —- 258 — -— 5.60M. GR —— IV 408 ~— 1941 09 25 17 48 38 19.5 N 155.5 W — 258 — — 6.00M. GR — VII 38 — 1941 11 16 2011 20.0 N 155.8 W — 408 — —— -— -— V 38 — 1941 11 18 13 26 20.0 N 155.8 W -- 408 — -— — — V 38 — 1943 11 11 02 52 19.0 N 155.5 W — 408 — — - — V 408 — 1944 12 27 141140 19.5 N 155.5 W — 258 — — 5.60M. GR — VI 38 — 1945 05 19 1218 19.5 N 155.5 W — 408 — — — — V 38 — 1948 06 28 1141 21.2 N 157.9 W 005 421 — — 4.80Mf.UH - V1 421 — 1949 05 02 15 02 19.5 N 155.7 W — 22 — -- — — V 38 — 1950 05 30 011615 19.5 N 156.0 W — 258 — — 6.25M. GR — V1.1 408 — 1951 04 23 0052 23 19.2 N 155.5 W — 418 — — 6.50M. PAS — VII 24 —- 1951 08 21 1056 57.5 19.483N 155.967W — 408 — —- 6.90M. GR — V111 419 -— 1951 09 16 114251 19.32 N 155.42 W — 481 — — — — V 481 — 1951 11 08 193412 19.192N 155.720W -— 409 — — — — VI 481 ~— 1952 03 18 03 58 19.125N 155.033W — 408 -— — — -— V 408 — 1952 04 07 070951 21.0 N 157.0 W 060 25 — — — — IV 238 — 1952 05 23 221226 19.483N 155.983W 010 408 — -— 6.00M. PAS — VI 238 — 1953 01 15 12 05 19.317N 155.433W 024 408 — — 5.20M. BRK — V 408 — 204 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) HAWAII—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude lntenslty Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI net Felt area Yr Mo Da h m 9 (°) (°) (km) m., Ms M (1.000 km?) 1953 08 22 0547 19.75 N 155.8 W — 408 — — —— — V 408 — 1954 03 30 l64002.0 19.380N 155.025W 009 418 — — 6.00Ms PAS — VI 410 —— 1954 03 30 18 4156.0 19.353N 155.020W 009 418 — — 6.50UknPAS -— VII 410 —— 1954 07 03 215235 19.4 N 155.2 W 012 408 — — 5.40ML HVO — VI 408 — 1955 03 08 0821261 19.335N 154.997W 000 482 —- — 5.40ML HVO — IV 408 — 1955 03 28 02 02 20 19.4 N 155.3 W — 408 —— — — — VI 408 — 1955 04 01 1424255 19.407N 155.305W 010 482 -- — 5.20ML HVO — V 38 — 1955 08 07 171744 20.0 N 155.8 W 040 408 —— — —— — V 38 —- 1955 08 14 1228000 19.313N 155.285W 029 482 — — 5.70ML HVO —— VI 28 —- 1956 05 14 075336 20.283N 155.283W 020 418 — -— 4.50ML HVO — V 38 — 1956 10 16 104455 19.667N 156.467W 025 418 — —— 5.50M; HVO — V 38 —— 1957 07 04 1053 59 19.8 N 155.7 W 015 418 — — 4.50ML HVO —- IV 30 —-— 1957 07 26 114030 20.250N 156.083W 005 418 — —— 4.60ML HVO — IV 30 — 1957 08 18 104156 21.800N 155.467W 010 418 — —— 5.60ML HVO — V 38 — 1958 12 27 191724 19.783N 155.117W 045 418 — —— 4.50ML HVO — III 31 — 1959 02 20 060028 19.350N 155.150W 005 32 — —- 4.50ML HVO — III 32 — 1960 01 19 0426 49.2 19.320N 155.670W 007 418 — — 4.50ML HVO — III 33 —- 1960 12 25 12 56 27.8 19.222N 155.764W 001 418 -- — 4.50ML HVO — III 33 — 1961 01 21 11 39 36.8 19.225N 155.666W 010 418 —— — 4.60ML HVO — III 34 — 1961 07 23 1524155 19.377N 155.282W 026 418 — — 4.60ML HVO — V 34 — 1961 09 23 0301333 19.320N 155.113W 004 418 — — 4.50ML HVO —— V 34 — 1961 09 25 0528535 19.302N 154.998W 009 418 — — 4.50ML HVO — V 34 — 1962 02 11 020048.3 19.224N 154.398W 003 418 — — 4.50ML HVO — — —— — 1962 06 28 042714.2 19.399N 155.454W 010 418 — — 6.10ML HVO — VI 35 — 1962 07 25 0348158 19.540N 155.961W 002 418 — —— 4.70ML HVO — V 35 — 1963 01 08 19 39 45.0 19.390N 155.218W 031 418 -— — 4.60M; HVO -- V 36 — 1963 08 26 18 49 18.1 19.375N 155.370W 006 418 4.4 — 4.70ML HVO — IV 36 — 1963 09 21 1624206 19.428N 155.823W 006 418 4.6 — 4.70ML HVO — IV 36 - 1963 10 23 2024069 19.376N 155.416W 009 418 5.0 — 4.60ML HVO — V 36 —— 1964 09 18 10 25 29.1 19.315N 155.115W 005 37 4.8 —- 4.90ML HVO —- IV 37 — 1964 10 ll 100643.6 18.856N 156.517W 006 418 5.3 — 5.30M], HVO — V 423 — 1964 12 03 0828410 19.405N 155.277W 025 418 4.7 — 4.50ML HVO — V 37 -— 1964 12 10 11 53 44.6 19.266N 155.139W 008 418 5.1 -— 4.60ML HVO — III 37 — 1965 02 13 2306296 18.754N 155.314W 015 418 -— — 4.60ML HVO — IV 75 — 1966 08 19 15 21 39.5 18.537N 155.087W 051 418 — — 4.60ML HVO — D1 81 — 1966 09 05 16 33 21.9 19.353N 155.437W 008 81 4.7 — 4.50ML HVO — IV 81 — 1967 07 22 07 3410.1 20.753N 156.121W 008 418 — -— 4.60ML HVO —— II 40 — 1968 02 22 19 20 40.3 19.223N 156.297W 005 418 — — 4.50ML HVO — —— — — 1968 04 28 1408 59.0 19.375N 155.298W 030 41 4.7 — 4.50ML HVO — IV 41 ~- 1969 05 10 01 33 28.0 19.359N 155.073W 013 418 4.9 — 4.30ML HVO —— IV 42 — 1969 11 10 0512128 19.187N 155.542W 033 418 3.7 — 4.60ML HVO —- III 42 — 1969 ll 24 19 12 21.6 19.731N 156.099W 002 418 3.8 — 4.70ML HVO — III 42 — 1970 09 21 11 26 36.5 19.332N 155.203W 011 418 -— ——- 4.50ML HVO —-— IV 43 — 1970 10 25 19 55 29.1 21.146N 156.612W 011 418 4.5 — 4.80ML HVO —- IV 43 —- 1971 08 01 18 52 39.5 18.402N 154.545W 007 418 4.8 — 4.60ML HVO — — — — 1971 08 16 01 35 09.1 19.367N 155.278W 034 418 4.5 — 4.80ML HVO — IV 44 — 1971 12 28 011151.8 19.262N 155.372W 005 418 — — 4.70ML HVO —— III 44 —- 1971 12 29 02 59 12.0 19.248N 155.382W 008 418 -— — 4.60ML HVO — IV 44 — 1971 12 29 11 38 43.1 19.249N 155.363W 007 418 -— — 4.60ML HVO — III 44 —— 1972 02 29 2208239 19.360N 156.351W 008 , 418 4.9 — 4.90ML HVO — IV 45 — 1972 07 14 19 36 57.7 19.033N 155.330W 038 418 — — 4.50ML HVO — III 45 — 1972 09 05 11 3133.8 19.331N 155.206W 010 418 4.4 —- 5.00M], HVO -— IV 45 — EARTHQUAKES IN HAWAII 205 HAWAII—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo D: h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1972 12 23 190452.7 19.589N 155.926W 015 418 .4.9 —— 5.10ML HVO — V 45 — 1972 12 23 2043 07.0 19.578N 155.936W 015 418 — —— 4.60ML HVO — IV 45 — 1973 04 23 0707531 19.963N 154.672W 032 418 4.2 —— 4.80ML HVO -— IV 46 —- 1973 04 26 20 26 30.6 19.903N 155.130W 048 464 6.0 6.1 6.20ML HVO —- V111 46 — 1973 10 09 11 53 45.3 19.338N 155.267W 033 418 4.8 —— 4.60ML HVO —- IV 46 — 1973 12 13 0425 56.1 19.374N 155.292W 035 418 4.4 — 4.60ML HVO — IV 46 — 1974 01 12 1604 34.2 19.332N 155.120W 009 418 4.8 -— 4.70ML HVO — III 47 — 1974 06 19 15 05 42.6 19380N 155.422W 010 418 5.1 — 4.70ML HVO — V 47 -— 1974 08 28 0749 41.0 19.328N 155.205W 010 418 4.8 -— 4.50ML HVO — III 47 — 1974 11 30 1354238 19.442N 155.416W 008 418 5.1 5.5 5.40ML HVO — IV 47 — 1974 12 16 0917 29.8 19.406N 155.434W 009 418 5.0 — 4.70ML HVO — V 47 — 1974 12 25 17 47 49.4 19348N 155.280W 032 418 4.5 — 4.60ML HVO —— IV 47 — 1974 12 31 2240484 19.305N 155.366W 006 418 5.5 5.2 5.40ML HVO —— V 47 — 1975 01 01 12 41 11.1 19.217N 155.356W 005 418 4.7 —- 4.60ML HVO — IV 48 — 1975 01 01 13 18 59.6 19.059N 155.899W 010 74 4.5 — — — Felt 74 — 1975 01 01 13 20 54.5 19475N 155.580W 010 74 5.1 5.3 — — Felt 74 — 1975 01 01 1344363 19.071N 155.854W 010 74 4.7 —— 4.90M; HVO — Felt 74 ~— 1975 01 02 13 2743.4 19.232N 155.391W 009 418 4.5 42 4.90ML HVO — V 48 — 1975 01 03 1732495 19.207N 155.364W 010 418 4.7 — 4.90M], HVO — V 48 — 1975 01 05 01 32 05.5 19.247N 155.373W 007 418 5.1 5.3 4.90ML HVO —- V 48 — 1975 03 30 0056 26.5 19.283N 155.374W 006 418 — -— 4.60MD HVO — — — —- 1975 05 22 08 32 58.4 20.288N 155.657W 012 418 4.4 — 4.70ML HVO — V 48 — 1975 05 28 1202088 18.641N 154.273W 042 418 4.6 —— 5.10MB HVO -— — — — 1975 07 08 0047 42.6 19.536N 155.504W 003 418 3.9 — 4.70ML HVO — IV 48 — 1975 11 06 1205 28.4 19.343N 155.313W 019 418 4.4 — 4.50ML HVO — V 48 — 1975 11 29 13 35 40.7 19.362N 155.039W 002 418 5.8 5.1 5.90ML HVO — VI 48 — 1975 11 29 1447 40.1 19.341N 155.004W 009 418 6.0 7.1 7.20Ms PAS 7.45AND VII] 48 — 1975 11 29 18 4400.2 19.145N 155.252W 005 418 4.9 — 4.60ML HVO — — — — 1975 11 30 0615 27.4 19.419N 155.373W 012 418 . — — 4.50M], HVO — -— — — 1976 01 15 22 59 26.2 19.413N 155.295W 018 418 4.8 — 4.50ML HVO — V 49 —— 1976 01 29 20 19 56.6 19.373N 154.988W 010 418 4.5 — 4.70ML HVO — IV 49 — 1976 02 21 05 51 17.4 20.267N 155.990W 021 418 4.9 40 5.00ML HVO — VI 49 — 1976 04 02 18 14 06.7 19.342N 155.106W 010 418 4.5 — 4.50ML HVO — V 49 — 1976 04 21 18 13 35.9 18.816N 155.032W 012 418 — -— 4.50ML HVO — — —- — 1976 05 24 0924078 20.995N 156.362W 020 418 —- — 4.90MD HVO — V 49 — 1976 12 18 1401007 19.330N 155.115W 010 418 5.0 — 4.80ML HVO — V 49 — 1977 01 14 23 2642.5 19.329N 155.119W 010 418 4.2 — 4.70ML HVO — IV 39 — 1977 01 22 22 36 28.5 20.940N 160.260W 033 74 4.7 . —— 5.10ML HVO — —— — — 1977 02 04 0120599 19.347N 155.074W 010 418 4.5 — 4.50ML HVO — IV 39 -- 1977 04 21 0449 23.2 19.326N 155.325W 012 418 — — 5.00ML HVO — V 39 —- 1977 06 06 0942191 19.362N 155.081W 009 418 4.8 —- 5.10ML HVO — V 39 -— 1977 09 07 23 5106.9 19.373N 155.322W 031 418 — —- 4.50ML HVO -—- 111 39 — 1979 03 06 1507585 19.520N 155.270W 027 418 5.0 4.3 4.70ML HVO —- V 489 — 1979 03 10 13 55 14.6 19.334N 155.111W 010 418 4.8 — 4.50ML HVO -— IV 262 — 1979 03 22 0646598 20.100N 155.841W 016 418 4.6 —— 4.50ML HVO — V 262 —- 1979 03 28 0730098 20.090N 155.835W 012 418 4.4 — 4.90ML HVO — V 262 -- 1979 03 30 0906396 20.608N 158.862W 010 299 4.7 3.9 5.50ML HVO — V 262 —- 1979 08 14 12 51 42.2 20.814N 156.290W 024 418 4.1 —- 4.50ML HVO — V 262 — 1979 09 22 07 59 37.6 19.347N 155.071W 009 418 5.7 4.8 5.50ML HVO — VI 262 — 1980 01 20 0128486 19.312N 155le 027 418 — -— 4.60ML HVO — V 300 — 1981 01 12 141810.6 19.356N 155.305W 031 418 4.4 — 4.50M]. HVO — V 325 — 1981 01 14 0420165 19.368N 155.324W 029 418 4.5 — 4.80MB HVO — V 325 ~- 1981 03 05 1409398 21.017N 156.988W 010 74 5.0 — 5.10ML HVO —— VI 325 — 1981 03 06 0243 36.4 21.159N 156.910W 000 418 4.5 -- 4.50ML HVO — 111 325 ~- 1981 08 10 1940350 19.306N 155.359W 004 418 4.7 — 4.50ML HVO — IV 325 —- 206 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) HAWAII—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude , Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m s (°) (°) (km) mb Ms M (1,000 km?) 1981 11 10 1302566 19.343N 155.211W 010 418 .3 - 4.90Mp HVO — V 325 — 1982 01 21 21 52 41.2 19.230N 155.592W 010 418 .4 49 5.40ML HVO — VI 350 —— 1982 01 21 22 29 13.9 19.218N 155.552W 014 418 .6 4.8 5.40ML HVO — VI 350 - 1982 05 14 16 26 31.7 20.001N 155.864W 020 418 .5 — 4.80ML HVO — V 350 — 1982 05 19 03 3619.8 19.954N 156.436W 001 418 .8 3.7 4.80ML HVO — V 350 —— 1983 03 08 1641034 19.199N 155.593W 011 418 — 4.50ML HVO — IV 360 —- 1983 03 21 0318 392 19.357N 155.050W 007 360 .9 —- 4.80ML HVO — V 360 - 1983 09 09 1630553 19.332N 155.122W 009 360 .5 5.0 5.40ML HVO — V 360 — 1983 11 16 1613001 19.429N 155.452W 011 360 .4 6.7 6.60ML HVO — VIII 360 — 1984 06 09 0334106 20.055N 157.975W 030 370 — — 5.00ML HVO — — — — 1985 02 22 0548294 19.378N 155.211W 009 371 5.0 — 4.80ML HVO — V 371 — 1985 12 12 19 01 22.9 20.578N 155.755W 025 371 4.3 — 4.70ML HVO -— V 371 — 1986 04 23 0443 51.3 19.305N 155.271W 031 562 — — 4.50ML HVO — IV 562 — 1986 04 26 17 19 46.5 20.811N 155.749W 033 562 5.1 — 4.90ML HVO — V 562 — 1987 02 04 02 22 32.7 20.053N 156.530W 010 74 5.2 4.9 5.20ML HVO 5.44HAV V 577 — 1988 03 02 08 41 56.5 19.329N 155.213W 010 74 4.9 — 4.70MB HVO — V 578 — 1988 03 25 0029 50.5 19.992N 156.454W 000 74 5.3 4.5 — — IV 578 -— 1988 03 28 03 33 40.8 19.936N 156.445W 001 74 5.6 5.1 5.30Ms BRK 5.44HAV V 578 —- 1988 04 02 0448011 19.714N 156.570W 010 74 4.7 — — — Felt 578 — 1988 06 07 1048 45.0 19.319N 155.117W 010 74 4.4 — 4.70MB HVO — V 578 -- 1988 07 04 05 38 09.3 19.221N 155.459W 011 74 5.1 ——- 5.20ML HVO -- IV 578 — 1988 07 31 1404330 18.924N 155.207W 017 74 4.5 — 4.60MD HVO — — — —-— 1989 04 04 190957.0 18.972N 155.288W 024 74 4.6 -— 4.40MB HVO — IV 579 — 1989 06 26 03 2703.9 19.362N 155.083W 009 74 5.8 6.1 6.20MB HVO 6.43 V VII 579 — 1989 12 05 22 16 58.6 21.633N 157.323W 010 74 4.0 —— 4.60ML HVO -— IV 579 —- 1989 12 28 0913 17.3 19.333N 155.212W 009 74 5.0 45 5.00ML HVO -— V 579 — INTRODUCTION as experiencing “severe” shaking. Only the All earthquakes included in the hypocenter list above are of magnitude 2 4.5 or Modified Mercalli intensity 2 VI. Those without a computed magnitude were estimated to be 2 4.5. Since the routine compu- tation of magnitudes for Hawaiian earthquakes began in about 1956, most of the earthquakes that do not have recorded magnitudes occurred before that year. Epicenters included in this table that are without magnitudes are estimated to be equivalent to a mag- nitude 2 4.5. These estimates were derived by com- paring pre-1956 felt or damage reports to reports from well-documented earthquakes in later years that had computed magnitudes. From that compari- son, two criteria emerged that defined an estimated magnitude 2 4.5 earthquake. These were: (1) reported felt on more than one island, or (2) reported earthquakes meeting one of these criteria were included in the table. Estimates of intensity also were necessary for many of the earthquakes in the hypocenter list that had a general description of the shaking but no assigned intensity. The estimates of maximum inten- sity are based on the following: (1) shaking described as severe—intensity V; (2) shaking reported island- wide on Hawaii Island—intensity IV; and (3) shaking reported felt only on parts of Hawaii Island—inten— sity III. Felt areas were not computed in Hawaii. Reliable estimates are not possible owing to the small land area of that State. [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] EARTHQUAKES IN HAWAII 1823. June (date unknown). Kaimu, Hawaii. A strong earthquake threw down a 4-ft-wide by 6-ft- high stone wall, caused large fissures and sand blows in the ground, and damaged a native dwell- ing. (Ref. 500.) 1834. Feb. 20 (Feb. 19). Hilo, Hawaii. A heavy shock threw down stone walls and upset small jars. The undulating motion made it difficult to stand or walk. (Ref. 38, 405.) 1838. Dec. 12. Hilo, Hawaii. This earthquake threw down stone walls and cracked plaster. The strong motion made it difficult to walk. (Ref. 405.) 1841. Apr. 8. Hilo, Hawaii. Plaster cracked and fell to the floor in every room of a house. Water was splashed out of a bucket. (Ref. 405.) 1861. Dec. 5. Honolulu, Hawaii. Plaster fell from the ceilings of several houses, and people rushed into the streets. (Ref. 423) 1868. Mar. 29 (Mar. 28). Island of Hawaii. This is a foreshock of the Apr. 3 event. At Kahuku, a stone house was destroyed, the chimney of the Mis- sion parsonage was thrown down, and the walls of the stone church were cracked. At Kona, stone walls were thrown down, masses of rock were thrown off the cliff at the bay, stone buildings were damaged, and the cisterns of the Kona Plantation were cracked. At Waiohinu, walls were shaken down, and the stone church was cracked from top to bottom. Also slightly felt at Hilo. (Ref. 406, 500.) 1868. Apr. 3 (Apr. 2). Near south coast of Hawaii. This major earthquake caused 77 deaths (tsunami, 46; landslide, 31). It knocked almost all wooden houses off their foundations in the Keiawa, Punaluu, and Ninole areas. In those areas, straw houses supported by posts in the ground reportedly were “torn to shreds.” At Kau, the more substantial houses and every stone wall were thrown down. At Waiohinu, a large stone church collapsed within 10 seconds of the onset of shaking. The shock “ruined” the few stone buildings in Hilo and shook down almost every wall. Brooks became muddy. At Kealakekua, strong trees were bent backward and forward “like reeds in a storm.” Ground waves as much as 0.6 m from ground to crest were observed at Kohala. The motion was so violent at Ulupalakua that it was difficult for people to stand. Reports from Keaiwa and Kiolakaa suggest that vertical accelera- tions larger than 1 g may have occurred. Extensive surface effects were observed in the epi— central region. Ground fissures extended from Pahala to Kilauea. At Kohuku, a fissure about 5 km long was reported. A volcanic eruption took place from that fissure a few days later, on Apr. 7. 207 Landslides, which occurred beyond Hilo as far as Waipio and Hamakua, buried 10 houses in the area. A mass of earth as much as 3 km wide and 9 m thick swept down the hillside at Kapapala, carrying with it trees, animals, and people. Thirty-one people were killed. Along the Puna coast from Kapoho to Apua, the land subsided in places as much as 2 m. At Kaimu, trees stood about 2.5 m deep in sand and water. The plain at Kalapana sank about 2 m, and water stood as much as 1.5 m deep over 8 hectares (20 acres) of formerly dry land. A tsunami that struck the Kau-Puna coast added to the devastation. The waves, which were most destructive at Honuapo, Keauhou, and Punaluu. At Keauhou (now Keauhou Landing) the water rose 12—15 m, destroying all the houses and warehouses and drowning 46 people. At Hilo, the height of the wave was about 3 m, and at Kealakekua, 2 m. The tsunami also was observed on Maui and Oahu. Also felt on Lanai, Maui, Oahu, and Kauai (about 560 km from the epicenter). (Ref. 38, 406, 500, 570, 610.) 1868. Apr. 4. Near the island of Hawaii. This earthquake was described as “almost as noticeable” as the main shock on Apr. 2. Dishes were shaken from shelves on Kauai. It was “severe” at Honolulu on Oahu. (Ref. 406, 423.) 1871. Feb. 20 (Feb. 19). Near Lanai, Hawaii. This major earthquake caused severe damage on the islands of Lanai, Molokai, and Maui, and minor dam- age on Hawaii and Oahu. It was felt throughout the islands. On Lanai, in the Palawai Valley, a large part of the Pali Kaholo bluff fell into the sea, and enormous fragments broke from the towering ocean walls between Manele Bay and Kamaiki Point. Masses of the red basalt were torn from the turrets of Puupehe, located on the southeast coast of Lanai. Huge boul- ders were hurled from the mountainsides, and ravines were filled with debris of rocks and trees. “Several great clefts opened” on different parts of the island. On Molokai, in the Pukoo area, the earth opened for a distance of several meters; stone houses in the area cracked in every direction. A 1.5-m-deep hole opened in the ground at Pukoo. At Kaluaaha, a small addition on the northwest corner of the old stone Mission house was thrown down and a part of the east gable end crashed down through the veranda roof below. Stone walls fell in every direction. In one place on the shore, a hole about 0.6 m in diameter and 5.5 m deep was formed by the sinking earth. 208 On Maui, at Lahaina, all adobe and stone houses were cracked and some were damaged so severely that they were uninhabitable. The old Mission church was damaged, and its walls were cracked. All fence walls reportedly fell to the north. A stone building and the courthouse were damaged. The main road to Lahaina cracked open for several meters. Close to the pier, the earth cracked open for a length of 14.6 m. Damage was much less severe on other parts of Maui—stone walls were thrown down at Kaeleku, Kapueokahi, and Wailuku; cliffs collapsed at Keanae, Koali, Muole, Pukuila, and Wailua. (Ref. 422.) 1871. Sept. 13. Hilo, Hawaii. A severe earth- quake knocked down walls. (Ref. 405.) 1877. May 31. Hilo, Hawaii. A severe and long- lasting earthquake damaged walls and threw objects to the floor in a house. (Ref. 405.) 1881. Sept. 30. Kona, Hawaii. Many buildings and cisterns were shattered at Kona. Stone houses were damaged severely, and several kilometers of stone-wall fencing was destroyed. Every movable object in houses was jumbled and thrown together. It was described as a severe and destructive earth- quake. The shaking at Hilo also was violent. (Ref. 405, 407, 463.) 1885. Jan. 13. Island of Maui, Hawaii. The main earthquake, which caused some damage at Kahului, Maui, was felt severely at Honolaa and Heeia, Hawaii. Also felt at Honolulu. (Ref. 405, 423.) 1887. January 24. Kau District, Hawaii Island. Many houses were moved several inches from their foundations. Water tanks were thrown down and broken. Contents of homes and stores were thrown about and broken. Six aftershocks were felt in the following half hour. (Ref. 405, 500). 1890. Aug. 7 (Aug. 6). Hilo, Hawaii. Stone walls were knocked down. In some houses, tables and pianos were moved 15 cm from the wall. Small objects were thrown down in almost every room in one house. (Ref. 405.) 1908. Sept. 21 (Sept. 20). Hilo, Hawaii. An earthquake caused some damage in stores and a warehouse. It threw down vases, crockery, and pic- tures, and stopped clocks. It caused the water in the rivers and in Hilo harbor to rise 1.2 In. (Ref. 405, 412, 610.) 1918. Nov. 2. Mauna Loa, Hawaii. Water tanks and stone walls were damaged at Kapapala Ranch. The earthquake was felt strongly at Hilo and Kona. (Ref. 38, 265.) 1919. Sept. 15 (Sept. 14). Kilauea, Hawaii. Chimneys fell and walls cracked in the Kau section. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Slight damage was reported at Hilo. Felt on Maui and Oahu. (Ref. 38.) 1923. Jan. 14. Island of Hawaii. This strong earthquake shook down stone walls and caused some slight damage at Hilea. It was felt on Oahu and throughout Hawaii Island. (Ref. 417.) 1926. Apr. 22. Island of Hawaii. At Hilo, one building shook about 20 cm off its foundation. Unsta- ble objects were overturned. Felt widely over the island. (Ref. 218, 408.) 1927. Aug. 3. Hilo, Hawaii. Slight damage occurred at Hilo. Felt throughout the island. (Ref. 38, 218.) 1929. Sept. 26 (Sept. 25), Sept. 27—30. Kona, Hawaii. The strongest shock of a series occurred on Sept. 26. This earthquake generally was felt throughout the inhabited Hawaiian Islands. Walls fell in the Kona district, and many houses were damaged. Water tanks, underground pipes, and fences throughout the Kona district were demol- ished. Aftershocks occurring on Sept. 27, 28, 29, and 30 added greatly to the damage to tanks, masonry, stone fences, chimneys, roadways, and weak build- ings on slopes. Also felt on Maui and Oahu Islands. (Ref. 38, 258, 408, 500.) 1929. Sept. 28. Island of Hawaii. At Hilo, a church was cracked severely and a street was dam- aged. Strongly felt. Also see the description for events on Sept. 26, 1929. (Ref. 38, 408.) 1929. Oct. 6 (Oct. 5). Holualoa, Hawaii. Walls fell and houses were displaced on their foundations at Holualoa. Road fills were cracked and embank- ments overthrown at the road spurs in North Kona; telephone poles were tipped over throughout North Kona. Water tanks in Kealakekua were burst or thrown off their foundations, and some weak struc- tures collapsed. At Puuwaawaa Ranch, unbraced foundation posts fell over, masonry in the main house basement was partly thrown down, new “avalanches” fell in the gulches of Puuwaawaa hill, boulder fences were generally collapsed, and a chimney stump was broken for the second time. Also felt on Lanai, Maui, and Oahu. (Ref. 38, 258, 408, 500.) 1935. June 28. Island of Hawaii. Some damage occurred at Hilo. Generally felt throughout the island of Hawaii. (Ref. 258, 408.) 1938. Jan. 23 (Jan. 22). North of island of Maui, Hawaii. This strong earthquake, which was felt throughout the islands, caused property damage estimated at $150,000 on Maui. Several landslides occurred throughout the island, some chimneys fell, walls were cracked, and pipelines were damaged. Two large oil tanks were shattered at Hana. Ranches on southern Maui sustained heavy damage to water EARTHQUAKES IN HAWAII tanks and stone walls. Walls collapsed from Ohia to Mapulehu. The Olinda Reservoir was cracked severely, and the steel storage dam on the Wailuku- Kahului line was damaged. Many severe cracks formed in roadbeds throughout Maui. At Kula, cracks as wide as 3.8 cm formed in the Haleaka road. On Molokai, at Mapulehu, cracks 5 to 7.5 cm in width and as much 30.5 m in length formed on the east Molokai road. Minor damage also occurred on the islands of Kauai, Lanai, Oahu, and northern Hawaii. Flashes of light were observed in the sky before and during the earthquake. (Ref. 11, 258, 408, 500.) 1939. May 15. Island of Hawaii. Slight dam- age to masonry structures and plaster occurred at Hilo. Generally felt over the island of Hawaii. (Ref. 266, 408.) 1940. June 17, 10 26 UTC. North of island of Hawaii. At Kaunakakai, on Molokai, glass was cracked, vases overturned, and water spilled from containers; on Maui, sharp shocks broke medicine bottles and stopped clocks; on Hawaii, dishes fell from shelves in Hilo. Residents were awakened on the islands of Hawaii, Kauai, Lanai, Maui, Molokai, and Oahu. Loose objects rattled violently. (Ref. 38, 258, 500.) 1941. Sept. 25. Island of Hawaii. Felt sharply throughout Hawaii Island. At Pahala, roadfills cracked, shoulders along roadways failed, pipes were sprung, plaster cracked, and goods fell from shelves and broke. At the Kapapala Ranch, several stone walls were partly thrown down and two Windows and many dishes were broken. Many earthslides from the walls of Halemaumau caused large dust clouds; boul- ders shook loose from steep slopes at the head of Wood Valley and on Hilina Pali. An old crack in a building reopened at Hilo. Also felt on Oahu at Honolulu. (Ref. 38, 258, 500.) 1944. Dec. 27. Island of Hawaii. Near Hilea, stone fences were thrown down. At Pepeekeo and Naalehu, objects toppled from shelves. Also felt on Oahu. (Ref. 38, 258, 408.) 1948. June 28. Off island of Oahu, Hawaii. This sharp earthquake caused minor damage on Oahu. Four large plate-glass windows broke in down- town Honolulu; fluorescent lamps displaced from their sockets; plaster cracked in at least 20 buildings; and one chimney cracked. At the Fort Shafter mili- tary installation, a 21-m-long crack formed in the wall of the new barracks. A landslide blocked Kame- hameha Highway in Kipapa Gulch, and another landslide occurred on Moanalua Road at Red Hill. Several sidewalks in Kaimuki were cracked severely. 209 Also felt slightly on the islands of Hawaii, Kauai, and Molokai. (Ref. 38, 421.) 1950. May 30 (May 29). Kona, Hawaii. This widely felt earthquake damaged water tanks and stone walls in Kona. At Captain Cook, Machado’s store shifted about 2.5 cm from its foundation and four large water tanks split open. Cracks 2.5 cm wide were observed along the highway from Honaunau to Captain Cook, and shoulders gave way. Residents at Hilo reported broken chinaware. (Ref. 258, 408, 500.) 1951. Apr. 23 (Apr. 22). Near Kilauea caldera, Hawaii. This strong earthquake generally was felt throughout the island of Hawaii and by many resi- dents on Maui and Oahu. It caused slight damage on Hawaii, including broken windows and dishes and a broken water pipe. The roadbed between the Volcano House and Kilauea Overlook settled, and much dam- age was sustained by roads in the National Park. Small earth slips occurred in road cuts between Kilauea caldera and Hilo and north of Hilo along the Hamakua coast. Minor cracks formed in the highway at the northeast rim of Kilauea caldera. Cracks in the soil, apparently caused by lurching, formed at several places north and east of Kilauea caldera. Sur- face faulting was not observed. (Ref. 24, 418, 500.) 1951. Aug. 21. Near Napoopoo, Hawaii. This earthquake probably was caused by movement on the Kealakekua fault. It inflicted property damage that extended from Holualoa on the north to Honuapo on the southeast, a distance of 80 km. Damage was most severe in the central Kona district, along a 16- km stretch from Captain Cook to Hookena. Here, several houses, churches, and a school building were damaged severely, and about 200 water tanks were demolished or damaged beyond repair (mainly owing to damage to footings). Many stone walls were thrown down. Roads were partly blocked by small rock slides; road pavement and shoulders were cracked badly; and telephone communications and electric power were disrupted. Tombstones were shifted, rotated, or overturned in many cemeteries in the area. The earthquake was felt strongly throughout the island of Hawaii and slightly on Maui and Oahu (at Honolulu, about 290 km from the epicenter). Many aftershocks, all of lower intensity, occurred through September 1951. A small tsunami was observed at Hilo, Honolulu, and the Kona Coast area (maximum at Napoopoo—0.9 m). Residents of Naalehu and Pahala reported bright flashes of white light at the time of the earthquake. (Ref. 408, 419, 481, 610.) 1951. Nov. 8. Island of Hawaii. At 'Kahuku Ranch headquarters, 15 km north of South Point, on the southern part of Hawaii Island, stone walls were 210 damaged extensively and dishes were thrown from shelves. Felt throughout the island. (Ref. 409, 481.) 1952. May 23. Island of Hawaii. Slight damage reported in the central Kona district included cracks in pavement, landslides from roadcuts, damaged water tanks, broken dishes and windows, and over- turned tombstones. Dishes were broken as far dis- tant as Naalehu, about 60 km southeast of the epicenter. Felt throughout the island and by some residents on Maui. (Ref. 238, 408.) 1954. Mar. 30, 16 40 and 18 41 UTC. Island of Hawaii. The foreshock at 16 40 UTC collapsed sev- eral domestic water tanks at Kalapana and Opi- hikao. During the stronger shock 2 hours later, extensive damage occurred in the Hilo and Puna dis- tricts. In Hilo, several chimneys and stone walls were thrown down, plaster cracked, and windows broke. Between Kalapana and Opihikao, stone fences were thrown down, people driving automobiles were dis- turbed, and some residents found it difficult to walk or stand. Also felt on Maui and Oahu. (Ref. 410, 418.) 1954. July 3. Island of Hawaii. This strong earthquake, widely felt over the southern part of the island, caused minor damage at Hilo. Many heavy rockfalls occurred in the area of Halape during and after the earthquake. (Ref. 408.) 1955. Mar. 28 (Mar. 27). Hawaii Volcanoes National Park. This earthquake broke water lines and cracked houses in the residential area of Hawaii Volcanoes National Park. It also opened cracks across the Mamalahoa Highway, east of park headquarters. (Ref. 408.) 1955. Aug. 14. Island of Hawaii. At a farm about 64 km southwest of Hilo, walls were cracked and dishes were knocked from shelves. Felt through- out the island of Hawaii and on Kauai, Maui, and Oahu. (Ref. 28, 408, 482.) 1962. June 28 (June 27). Island of Hawaii. This earthquake, which occurred near the Kaoiki fault system, caused the most severe damage to houses at Kapapala. Paint on walls was chipped, large kitchen appliances were moved several centi- meters, and loose china fell from shelves. Damage reported at Hilo includes cracks in walls, plaster, and windows, and broken dishes. Landslides occurred at Kawalii Gulch near Laupahoehoe, on Kealakekua Bay, and in the remote Waipio Valley on the northern end of the island. Also felt slightly on Maui and Oahu. One report of this earthquake came from the North Kohala district, a region where earthquakes are not commonly felt. More than 1,500 aftershocks were recorded in the next 3 days, and intense aftershock activity continued for several SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) weeks. Magnitude 5.75 Mg BRK, 5.25—5.5 Ms PAL. (Ref. 35, 411, 418.) 1973. Apr. 26. Near northeast coast of island of Hawaii. This damaging earthquake was felt from the east coast of Hawaii Island through the main islands of Kahoolawe, Kauai, Lanai, Molokai, and Oahu, a distance of about 595 km. Property damage in and near Hilo was estimated at $5.75 million, and 11 people were injured. Damage to buildings, roads, and utilities led authorities to declare a state of emergency. Ground effects, mainly landslides but including ground cracks induced by lateral displacement and local sub- sidence, were severe locally. Subsidence damaged the main wharf in Hilo, and landslides damaged roads and structures over a large area. It was reported that 17 houses in the Hilo area were shaken from their foundations and that five col- lapsed. One structure in downtown Hilo collapsed, and the outside walls of an apartment building—a two-story concrete-block structure—were torn loose at two ends. Tombstones and chimneys overturned in several towns; water pipes and tanks were damaged. Several schools sustained damage, and four were closed temporarily. At Papaikou, the roof on the Kalaniaonaole School dropped 7—10 cm, and its ceil- ing was warped. Magnitude 6.3 MS PAS, 6.1 Ms BRK. (Ref. 46, 418, 423, 464.) 1975. Nov. 29, 13 35 UTC. Island of Hawaii. Campers at Halape saw dust clouds rising from rock- falls that the earthquake sent crashing down the face of Puu Kapukapu. Felt strongly in Hilo and Puna. (Ref. 48, 418.) 1975. Nov. 29, 14 47 UTC. Southeast coast of island of Hawaii. The largest earthquake in more than a century (since April 2, 1868) struck Hawaii on the morning of Nov. 29, killing two people, injuring several, and inflicting property damage estimated at $4.1 million in Hawaii (including damage caused by the tsunami). It was accompanied by a damaging tsu- nami, massive ground movements, hundreds of after- shocks, and a brief, small-volume volcanic eruption. The earthquake was felt throughout Hawaii Island, and on Lanai, Molokai, and Oahu. Most of the buildings in the epicentral area sus- tained little or no structural damage from ground shaking. Structural and nonstructural damage in Hilo, 45 km north of the epicenter, was slight to moderate but was more extensive than elsewhere on the island. Structural damage on the southeast part of the island included minor cracks, floor-to-wall separa- tions a few millimeters wide, and bowing of walls in EARTHQUAKES IN HAWAII Hilo at a hospital, schools, and libraries. Floor sec- tions dropped 5 to 10 mm in some of the buildings; hotel, apartment, and commercial buildings sustained structural and equipment damage] A dam- age survey of the area revealed that slight to moder- ate structural damage was sustained by five churches (Hilo, 4; Opihikao, 1), 11 commercial build- ings (Hilo, 10; Mountain View, 1), and 80 private dwellings (Hilo, 51; Puna, 23; Hamakua, 2; Kau, 3; and Kona, 1). Five poorly constructed or old houses were demolished (Hilo, 4; Kau, 1). Houses shifted on their foundations at Kalapana, Kurtistown, Pahoa, and Hawaiian Paradise Park. Water tanks were destroyed at Opihikao, Pahoa, and Volcano. The summit and south flank areas of Kilauea Vol- cano were displaced by vertical and horizontal move- ments of several meters, forming many ground cracks and faults. Roads in Hawaii Volcanoes National Park were damaged by extensive ground cracking. Landslides occurred on Coast Road. Fault displacements resulted in widespread subsid- ence (locally as much as 3.5 m near Halape), leaving coconut palms stranded in the sea and almost sub- merging a small nearby island. Inland, an almost continuous zone of ground cracking and faulting, having vertical offsets as much as 1.5 m, occurred along the Hilina fault system over a 25-km2 area. To the south and southwest of this zone of maximum faulting, vertical displacements of as much as 0.5—1.0 m were common along other faults. A large part of the coastal area between Cape Kumukahi and Punaluu subsided during or soon after the earthquake. A leveling survey of the bench marks near the Keauhou tide gage (2 km east of Hal- ape) indicated that the coast subsided about 3.5 m. The tsunami generated by this major earthquake consisted of five or more distinct waves in some places. The only locally generated tsunami in Hawaii this century to be destructive, it killed two people at Halape, where it was about 7.9 m high, and caused property damage estimated at $1.2 million at Punaluu, Honuapo, Kaalualu Bay, Hilo, and Kailua— Kona. At Punaluu (7.6 m), 30 km southwest of Hal- ape, several wood—frame houses were flattened or washed off their foundations; nearby county park facilities were damaged severely, and buildings at the Seamountain Resort sustained heavy nonstructural damage. Tsunami damage also was severe at Honu- apo (6.6 m), 6 km southwest of Punaluu. The highest wave reached a maximum height of 14.6 m above the postsubmergence shoreline, 1.5 km east of Halape. The tsunami was recorded in Alaska, California, 211 Japan, Okinawa, Samoa, and on Johnston and Wake Islands. (Ref. 48, 418, 453, 501, 610.) 1976. Feb. 21 (Feb. 20). Island of Hawaii. This minor earthquake caused damage to walls at Kawaihae. Also felt on Maui and Oahu. (Ref. 49, 418.) 1979. Sept. 22 (Sept. 21). Island of Hawaii. In the Hilo area, several hundred houses were damaged and several businesses lost merchandise. Founda— tions were damaged; water lines ruptured; and win- dows broke. At Reeds Island, a fireplace and house foundation sustained damage. (Ref. 262, 418.) 1981. Mar. 5. Near island of Molokai, Hawaii. The pipe that carries water from Waikolu Valley to Kalaupapa sustained four breaks and some cracks. Underground water pipes cracked near Kalaupapa on Molokai. Also felt on Hawaii, Lanai, Maui, and Oahu. (Ref. 74, 325.) 1982. Jan. 21, 21 52 and 22 29 UTC. Island of Hawaii. The first earthquake caused widespread minor damage in the Kau area; two small landslides occurred in Laupahoehoe Gulch. At Pahala, rock walls fell and chimneys cracked. The second shock, 37 minutes later, was not as strong, but it caused a rockfall in Kaawali Gulch that injured one person. Both shocks also were felt on Maui and Oahu. (Ref. 350, 418.) 1983. Nov. 16. Island of Hawaii. This earth- quake, the most destructive in Hawaii since a magni- tude 7.1 event occurred there in 1975, caused heavy property damage on the island of Hawaii and injured six people. The Small Business Administration reported 35 commercial buildings sustained varying degrees of damage, 317 houses had minor damage, and 39 houses had major damage. Unanchored chim- neys fell. Roads, bridges, and other government facil- ities also were damaged. At Volcano, many houses and garages were moved off their foundations, causing extensive damage to ceilings and walls. Highways in the area were cracked severely and were closed temporarily Ele- vated water tanks were thrown down; water tanks on gravel bases were moved as much as 5 cm, and some had their roofs damaged or knocked off by sloshing water. Three chimneys collapsed. Moderate damage on Hawaii Island also occurred at Hawaiian Volcano Observatory, Hilo, Kipapala Ranch, Kaumana, Kilauea Military Camp, and Wood Valley. Landslides and ground cracking occurred in many areas on southern Hawaii Island. The most severe ground failures were on Crater Rim Drive, a road around Kilauea crater. The road extended near the edge of the crater wall in several places, and a 212 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Ground failure on Crater Rim Drive, around Kilauea crater on the island of Hawaii, caused by the November 16, 1983, earthquake. (Photograph by J .D. Griggs.) section of the road fell into the crater. In other areas, cracks as much as 1—1.5 m wide and 3—6 m deep formed in the road. Also, many sections of trails in Hawaiian Volcanoes National Park collapsed into the main caldera of Kilauea Volcano. At South Point and Kealakekua Bay, parts of the cliffs fell into the ocean. Felt on Kauai, Lanai, Maui, Molokai, and Oahu. (Ref. 360.) 1989. June 26 (June 25). Near Kalapana, Puna District, Hawaii. This strong earthquake injured five people in the Puna area and destroyed five houses. Additional structural damage to resi- dential property in the County of Hawaii included major damage to 10 houses and minor damage to 100 houses. Many of the houses sustained cracks in walls, ceilings, and concrete pads, and slight shift- ing of their foundations. Total damage to property was estimated at $1 million (Robert Y. Koyanagi, oral commun, Hawaiian Volcano Observatory, Aug. 10, 1989.) Damage to structures in the Puna area included the collapse of at least five houses in Kaimu, Kala- pana, and Royal Gardens. Ground cracks were observed across the coast road in Kalapana, and landslides were reported in Puna and along the Hamakua coast between Honokaa and H110. Only slight damage to houses was reported atHilo. Power outages occurred in the Hilo, Kau, and Puna districts. A small tsunami was recorded on tide gauges at Hilo, Honuapo, and Kapoho. The main shock was felt on Maui, Oahu, and Hawaii Islands. Several aftershocks occurred. (Ref. 74, 579.) EARTHQUAKES IN HAWAII 213 Chimney in Volcano, Hawaii, toppled by the November 16, 1983, earthquake. (Photograph by the Hawaii Tribune-Herald, Ltd.) 48° 46° 44° 42° 118° 110° CANADA UNITED STAT o EXPLANATION z Coeur 'Alene O . Magnitude/Intensity S C) O 4.1-4.4/VI E O 4.5-4.9/Vl a Q 5.0-5.4/Vl <3: 0 5.5-5.9/vu MONTANA O 6.0-6.4 Lewiston O 7.0-7.4 i/ 0 100 KILOMETERS l__l__l IDAHOC0 Z . 8 0 Chain 1 ‘1 ’33 O O O O I, 002) Q.) S O E 2 O 0 C0 C) Pocatello Boise. o g 0 @ V NEVADA UTAH r“? Earthquakes in Idaho with magnitudes 2 4.5 or intensity 2 VI. 215 216 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) IDAHO [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De 1'] m 8 (°) (°) (km) mb Ms M (1,000 km?) 1884 11 10 0850 42.0 N 111.3 W — 298 —— -- -— — V11 52 15 1905 11 11 2129 42.9 N 114.5 W — 38 — — — — V11 38 — 1913 10 14 2300 45.2 N 116.7 W —— 56 — — — — VI 56 — 1916 05 13 02 26 44.2 N 116.5 W — 498 — —— 5.30UknPAS — V11 38 130 1917 12 12 1050 43.0 N 111.3 W -— 38 — — 5.30UknJON — V 272 21 1924 11 25 0710 42.5 N 111.5 W — 38 — — — — VI 218 52 1928 09 05 05 36 42.1 N 115.2 W — 54 —- — 5.20UknJON — — —- -— 1937 11 19 005020 42.1 N 113.9 W — 54 — — 5.40Mx SJG — IV 10 — 1942 11 01 18 5006 48.1 N 116.6 W — 266 — — —— — V 15 65 1944 07 12 19 3020.7 44.412N 115.063W 010 354 — — 6.10M; GR —- VII 17 153 1945 02 14 0301113 44.607N 115.087W 010 354 —-- — 6.00U1mPAS — VI 18 128 1947 09 25 013430 44.3 N 115.4 W -— 20 — — 4-70Mx JON — VI 259 — 1957 12 19 0625 47.5 N 116.0 W — 38 — — —— — VI 30 @ 1960 08 07 162716.2 42.4 N 111.5 W 049 266 — —- — -— VI 33 2 1963 01 27 1524438 44.190N 114.528W 011 354 — —— 4.80Mn DW — VI 36 15 1963 09 11 0208437 44.177N 114.615W 008 354 4.9 — 4.80M“ DW — VI 36 9 1963 09 12 0623 48.9 44.181N 114.621W 009 354 4.4 — 4.70Mn DW — IV 36 — 1963 10 17 01 22 07.7 44.4 N 114.7 W 030 74 4.7 --— — — — — — 1969 04 26 1041531 44.058N 114.444W 018 354 4.9 — 4.90Mn DW — VI 42 23 1969 09 19 13 3315.0 42.99 N 111.43 W 005 74 4.5 — 4.90ML GS — — —— -— 1975 03 28 02 3106.0 42.06 N 112.52 W 005 298 6.1 6.0 6.00M; UU 6.13BAS VIII 48 160 1975 03 29 13 01 19.9 42.03 N 112.52 W 007 298 4.7 —- 4.70ML UU 4.93BAS V 48 -- 1977 11 27 0925 55.6 44.537N 116.276W 009 354 4.2 — 4.40Mn DW — VI 39 24 1978 10 24 2030593 42.55 N 111.84 W 007 240 4.2 -- 4.10ML UU — VI 240 5 1978 10 29 1346456 44.866N 114.243W 012 354 4.2 — 4.70Mn DW — V 240 25 1978 11 30 0653 40.1 42.11 N 112.49 W 004 240 4.6 —— 4.70ML UU -— V 240 18 1982 10 14 04 10 24.3 42.59 N 111.43 W 007 350 4.6 —— 4.70ML UU — VI 350 13 1983 10 28 1406065 43.974N 113.916W 014 354 6.2 7.3 7.20ML BRK 6.95ED IX 360 855 1983 10 28 151407.7 44.127N 113.968W 010 360 4.3 — 4.60ML UU — — — —- 1983 10 28 19 51 25.0 44.045N 113.918W 013 354 5.4 5.1 5.80ML UU 5.58ED Felt 360 — 1983 10 29 232911.8 44.244N 114.055W 010 354 5.4 5.0 5.80ML UU 5.48ED Felt 360 — 1983 10 29 23 39 05.4 44.241N 114.109W 011 354 5.5 5.0 5.40ML UU 4.71GM Felt 360 —- 1983 10 30 0124513 44.089N 113.977W 013 360 4.3 — 4.80ML UU 4.36GM —- -- — 1983 10 30 01 59 02.0 44.200N 114.056W 016 360 4.2 — 4.70ML UU 4.18GM — — — 1983 11 06 2104487 44.140N 113.963W 011 360 4.3 — 4.60ML UU 4.16GM 111 360 — 1984 01 24 2107 57.5 44.047N 114.442W 010 370 4.5 -— 4.60ML MMT — IV 370 15 1984 08 22 0946302 44.467N 114.008W 010 370 5.0 5.1 5.80ML UU — V 370 173 1985 02 06 19 3419.4 44.551N 114.176W 010 371 4.7 — 4.80Mp BU —— V 371 15 1985 03 17 0656 17.1 44.553N 114.182W 010 371 4.5 — 4.70Mp BU — V 371 15 1986 09 26 2248 57.9 44.043N 114.756W 005 562 4.6 — 4.50ML GS — IV 562 —- 1988 01 10 23 22 19.5 44.840N 114.377W 005 74 4.8 -— 4.40ML GS —- 111 578 — 1988 07 14 17 3133.0 44.456N 114.083W 005 74 4.9 4.1 —— -— IV 578 110 1988 11 19 200053.1 42.007N 111.477W 005 74 5.0 -- 4.30MLUU —— Felt 578 —- [Reference (Ref) numbers given in parentheses at the end of each Paris, about 100 km southeast of Pocatello, near the description refer to sources of data in table 1. Magnitude values are _ -W - I, I knocked down chim- described in the Introduction, and codes are defined in table 2.] Idaho Utah yomlng borde ' t neys and shook stock from shelves in Richmond, Utah, about 125 km north of Salt Lake City. In an 1334- NOV- 10. Paris, Franklin County, Idaho. area north of Ogden, Utah, the tremor shook a Utah The earthquake damaged houses considerably in and Great Northern Railroad train. Also reported felt EARTHQUAKES IN IDAHO at Salt Lake City, Utah, and Franklin, Idaho. (Ref. 52, 298.) 1905. Nov. 11. Near Shoshone, Lincoln County, Idaho. Cracks formed in the walls of the courthouse and schools in Shoshone, and plaster fell from ceilings in almost all the buildings. Felt from Salt Lake City, Utah, to Baker, Oreg. (Ref. 38.) 1913. Oct. 14. North-central Idaho. A tremor broke windows and dishes in the area of Idaho and Adams Counties. (Ref. 56.) 1916. May 13 (May 12). Boise, Idaho. The earthquake wrecked several brick chimneys at Boise and sent residents rushing into the street. The shock was described as “Violent” at Emmett, 40 km north of Boise, and at Weiser, 96 km west of Boise. Reclama- tion ditches in the area were damaged. Pressure in a new gas well increased noticeably immediately after the shock. Also felt in western Montana and eastern Oregon. (Ref. 38, 272, 498.) 1924. Nov. 25. Near Wardboro, Franklin County, Idaho. A slight earthquake in Franklin County on this date broke windows at Wardboro, cracked ceilings at Montpelier, and displaced furni- ture at Geneva and Montpelier. (Ref. 38, 218.) 1944. July 12. Near Sheep Mountain, south- west Idaho. This earthquake apparently was most severe in the area of Fontez Creek, near Sheep Mountain, Idaho, where buildings were shaken so severely that occupants thought the structures were falling apart. A new cabin set on concrete piers was displaced on its foundation. Along Seafoam Creek, rocks and boulders were thrown down the hillside. Cracks about 30.5 In long formed in the ground in the Duffield Canyon trail along Fontez Creek. Cracks 2.5 to 7.5 cm wide extended for several meters in a continuous break near Seafoam. A sec- tion of the Rapid River Canyon wall (near Lime Creek) fell into the river. Also felt in Montana, Ore- gon, and Washington (see fig. 26). Seventeen shocks were reported felt, the first of which was the stron- gest. (Ref. 17, 354.) 1945. Feb. 14 (Feb. 13). Idaho City, Boise County, Idaho. This tremor broke dishes at Idaho City and cracked plaster at Weiser, northwest of Boise in Washington County. Also felt in Montana, Oregon, and Washington. (Ref. 18, 354.) 1947. Sept. 25 (Sept. 24). Boise, Ada County, Idaho. Several large cracks formed in a well- constructed brick building at Boise, but damage gen- erally was slight. (Ref. 20, 259.) 1957. Dec. 19 (Dec. 18). Northern Idaho. Timbers fell and mine walls collapsed at the Galena Silver mine near Wallace, Shoshone County. (Ref. 30, 38.) 217 1960. Aug. 7. Near Soda Springs, Caribou County, Idaho. Southeast of Pocatello and about 14 km east of Soda Springs, cracks formed in plaster and a concrete foundation at a ranch. (Ref. 33, 266.) 1963. Jan. 27. Clayton, Custer County, Idaho. Plaster and windows cracked at Clayton, northeast of Boise. Large boulders rolled down a hill at Living- ston Camp, about 22 km south of Clayton. Several aftershocks were felt in the area. (Ref. 36, 354.) 1963. Sept. 11 (Sept. 10). Central Idaho. Plas— ter fell in buildings at Redfish Lake, south of Stanley in Custer County; a vvindowpane was broken at a fire station in Challis National Forest. (Ref. 36, 354.) 1969. Apr. 26. Ketchum, Blaine County, Idaho. Cracks formed in concrete floors of struc- tures in Warm Springs and Ketchum. Plaster was cracked at Livingston Mill, 20 km south of Clayton. (Ref. 42, 354.) 1975. Mar. 28 (Mar. 27). Eastern Idaho. In the Ridgedale area of the sparsely populated Poca- tello Valley, this earthquake shifted several ranch houses on their foundations and toppled many chim- neys. At Malad City, 20 km northeast of the epicen- ter, about 40 percent of the chimneys on old buildings were damaged. Total property damage was estimated at $1 million. Geologists observed one zone of ground fractures—about 0.6 km long and 5 cm wide—in the south~central section of the valley. The shock trig- gered many snow avalanches northeast of the val- ley. Fourteen aftershocks ranging in magnitude from 3.8 to 4.7 were located through Mar. 31. Felt in parts of Colorado, Idaho, Nevada, Utah, and Wyoming. (Ref. 48, 298.) 1977. Nov. 27. Cascade, Valley County, Idaho. Property damage was reported only at Cas- cade, a few kilometers east of the epicenter, near Cascade Dam. The tremor cracked foundations and sheetrock walls, separated ceiling beams, and left water muddy in wells and springs. Also felt in Ore- gon. (Ref. 39, 354.) 1978. Oct. 24. Southeast Idaho. Cracks formed in plaster and a concrete foundation at Thatcher in Franklin County. This earthquake was felt mainly in Bannock and Franklin Counties of southeast Idaho, and at Plymouth, Utah, south of Pocatello, Idaho. (Ref. 240.) 1982. Oct. 14 (Oct. 13). Near Soda Springs, Caribou County, Idaho. In the Soda Springs area, about 45 km southeast of Pocatello, bricks fell from chimneys and cracks formed in the foundation of a house and in interior drywalls. Also felt in Utah and Wyoming. (Ref. 350.) 1983. Oct. 28. Borah Peak, Custer County, Idaho. The Borah Peak earthquake is the largest ever 218 48° >\ WASHINGTON Walla Walla 46° 7,._._.__._ OREGON 44° 42° .......... _ SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 116° 114° 112° 110° Kalispell. \. 1. ‘K S < ‘\ '\ L. \. L. v \. Lx-P MONTANA NEVADA Twin Falls IDAHO EXPLANATION * Epicenter VII Intensity 7 100 KILOMETERS FIGURE 26 ~—Isose1smal map for the southwest Idaho earthquake of July 12, 1944. Isoseismals are based on intensity estimates from data listed in references 17 and 259 of table 1. recorded in Idaho—both in terms of magnitude and in amount of property damage. It caused two deaths in Challis, about 200 km northeast of Boise, and an esti- mated $12.5 million in damage in the Challis-Mackay area. A maximum MM intensity IX was assigned to this earthquake on the basis of surface faulting. Vibrational damage to structures was assigned inten- sities in the VI to VII range (see fig. 27.) Spectacular surface faulting was associated with this earthquake—a 34-km—long northwest-trending zone of fresh scarps and ground breakage on the southwest slope of the Lost River Range. The most 52° 48° 44° 40° EARTHQUAKES IN IDAHO 219 124° 120° 116° 112° 108° 104° I l I l . l I PrInce George l\ ALBERTA I I.\ . ! \'\ Edmonton | \_1 l BRITISH COLUMBIA -I I .V\. I Saskatoon k. . O 3 | HEWAN \q I SASKATC '\ l 0 ‘ ‘ § .\ Calgary 'I Y} c " . I \ Kaml ' ' . 0 oops \I\, Regina \. \ II-lV | ! l Vancouver 1 l .. \ ‘ \ — ._.._ ' I " . . \ "‘ ‘— , .............. - CANADA ‘ - — " \ f .............. L ........ —_ ........... ~ —— '_‘ \ 1&6“; T ! UNITED STATES \ . . I Havre O . | o I Libby Saame WASHINGTON ' l V X“ I i lI-IV I ‘\. 5 \ \ I“ . O \.K_ ‘ Helena MONTANA . o . I l - - \. V / Mules CRY s I. ._A ——————————— - I' Q) l u. Forum: \-a"'""\.-—«-\"" \I J \ ' Pendleton \ j o . I / n. ' _ . \ ——————————— / VI l ~— _ g -- . ! / \ .. \J \I ‘DAHO VII-IX i OREGON 3‘" A I I! VI UMackaY I ‘ Boise I Jackson i I . . WYOMING o oaspef V Lakeview I Pocatello . ________________ o I ! 'T— ——- __._I‘ ________________ _ ..... _ ‘_._l I l ! CA I ' UFORNIA I II-IV | ! __ _— —— — '""‘ . ReddIng I : O l I | Salt Lake City | NEVADA l l EXPLANATION -' ' UTAH ! * I. Reno I l COLORADO Epicenter ' ‘ IX Intensny 9 o 200 KILOMETERS : II i l—___J \. . \. l l \ 1 ‘ FIGURE 27.——Isoseismal map for the Borah Peak, Idaho, earthquake of October 28, 1983. This map is a simplified version of figure 28 in extensive breakage occurred along the 8-km zone between West Spring and Cedar Creek. Here, the ground surface was shattered into randomly tilted reference 360 of table 1. blocks several meters in width. The ground breakage was as wide as 100 m and commonly had four to eight en echelon scarps as high as 1—2 m. The throw 220 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Fault scarp more than 1.8 m in height, northwest of Mackay, Idaho, caused by the October 28, 1983, earthquake. EARTHQUAKES IN IDAHO 221 Brick walls of the old Custer Hotel, in Mackay, Idaho, damaged by the October 28, 1983, earthquake. (Photograph by the Idaho Falls, Idaho, Post-Register.) on the faulting ranged from < 50 cm on the southern- most section to 2.7 m south of Rock Creek at the western base of Borah Peak. Other geologic effects included rockfalls and land- slides on the steep slopes of the Lost River Range, water fountains and sand boils near the geologic fea- ture of Chilly Buttes and the Mackay Reservoir, increase or decrease in flow of water in springs, and fluctuations in well water levels. A temporary lake was formed by the rising water table south of Dickey. The most severe property damage occurred in the towns of Challis and Mackay, where 11 commercial buildings and 39 private houses sustained major damage and 200 houses sustained minor to moderate damage. At Mackay, about 80 km southeast of Challis, most of the commercial structures on Main Street were damaged to some extent; building inspectors condemned eight of them. Damaged buildings were mainly of masonry construction, including brick, con- crete block, or stone. Visible damage consisted of severe cracking or partial collapse of exterior walls, cracking of interior walls, and separation of ceilings and walls at connecting corners. About 90 percent of the residential chimneys were cracked, twisted, or collapsed. At Challis, less damage to buildings and chimneys was sustained, but two structures were damaged extensively: the Challis High School and a vacant concrete-block building (100 years old) on Main Street. Many aftershocks occurred through 1983. Also felt in parts of Montana, Nevada, Oregon, Utah, Washington, Wyoming, and in the Provinces of Alberta, British Columbia, and Saskatchewan, Can- ada. (Ref. 354, 360, 608.) 42° 40° 92° ILLINOIS 90° 88° WISCONSIN /-L-\/‘ HQIW O IOWA Rock Island 0 ILLINOIS Chicago k/ EXPLANATION Magnitude/ Intensity C 4.0-4.4/Vl O 4.5-4.9/V| O 5.0-5.4 O 5.5-5.9 38° MISSOURI 0 Springfield 0 INDIANA 100 KILOMETERS Mm KENTUCKY Earthquakes in Illinois with magnitudes 2 4.5 or intensity 2 VI. 223 224 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) ILLINOIS [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m 3 (°) (°) (km) m, Ms M (1,000 km?) 1804 08 20 20 10 42.0 N 87.8 W — 105 -—- — 4.40Mf, SC —- VI 105 78 1838 06 O9 14 45 38.5 N 89.0 W —- 113 — -— 5.20M“ SC —— VII 113 500 1857 10 08 1000 38.7 N 89.2 W — 113 —- — 4.90Mf. SC —— VII 113 200 1876 09 25 06 38.5 N 87.8 W — 105 —- -- 4.50Mf. SC — VI 105 150 1876 09 25 06 15 38.5 N 87.8 W — 353 — — 4.80Mf. SC — VII 529 150 1881 05 27 41.3 N 89.1 W — 105 — —— 4.60M“ SC — VI 105 181 1882 09 27 10 20 39.0 N 89.5 ‘ W — 113 — —- 4.40Mfa SC — VI 38 1(1) 1883 04 12 08 36 37.0 N 89.2 W —— 38 — —- — — VI 173 — 1887 08 02 18 36 37.2 N 88.5 W —- 529 — — 4.90Mfa SC — VI 529 450 1891 09 27 0455 38.25 N 88.50 W — 302 — —— 5.20Mf. SC VII 302 560 1903 02 09 00 21 37.8 N 89.3 W —— 105 — — 4.90Mf, SC — VH 529 202 1905 08 22 05 08 37.2 N 89.3 W — 529 — 4.80M“ SC — VI 529 375 1909 05 26 14 42 41.6 N 88.1 W — 529 —— 5.10Mfa SC — VII 38 430 1909 07 19 04 34 40.2 N 90.0 W — 38 -— — 4.80Mf, SC — VII 38 121 1912 01 02 16 21 41.5 N 88.5 W — 38 — — 4.50Mf, SC — VI 38 150 1917 04 09 20 52 38.1 N 90.2 W — 113 — — 5.10Mfa SC — VII 529 408 1922 03 22 222910 37.4 N 89.4 W —— 529 -—- — 480an SC — VI] 529 135 1922 03 23 02 22 37.4 N 89.4 W — 529 — —— 4.60Mfa SC — VI 529 175 1922 11 27 03 31 37.8 N 88.5 W —-— 105 — -—- 4.80Mf. SC — VII 529 130 1934 11 12 14 45 41.5 N 90.5 W — 149 — — 4.00Mf. SC — VI 38 13 1939 11 23 15 14 52.0 38.180N 90.137W 0(X) 349 —- — 4.60Mf. SC — V 38 440 1947 06 30 04 23 53 38.4 N 90.2 W — 20 — — 420an SC —— VI 38 40 1953 09 11 18 26 28 38.8 N 90.1 W — 105 — —— 4.00Mf. SC — VI 26 15 1955 04 09 13 01 23.3 38.232N 89.785W 011 349 — —— 4.30M“ SC —— VI 28 54 1958 11 08 02 41 12.6 38.436N 88.008W 005 349 —-- -—- 4.40Mf. SC —- VI 31 75 1965 08 14 13 13 56.9 37.226N 89.307W 001 349 — 3.80Mn SLM 3.44S'1'T VII 75 1 1968 11 09 17 01 40.5 37.911N 88.373W 021 349 5.3 —— 5.50Mn SLM 5.27HRN VII 490 1473 1972 09 15 05 22 15.9 41.645N 89.369W 011 349 3.7 — 4.50Mn DG 4.03S'I'I' VI 45 230 1974 04 03 23 05 02.8 38.549N 88.072W 014 349 4.5 — 4.70Mn DG 4.36S'I'I' VI 47 400 1984 06 29 07 58 29.3 37.700N 88.470W 002 370 —- — 4.10Mn GS —- VI 370 7 1987 06 10 23 48 54.8 38.713N 87.954W 010 74 4.9 5.1 5.20Mn SLM 4.961011 VI 592 433 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1804. Aug. 20. Fort Dearborn (Chicago), Ill. The earthquake was felt at the south end of Lake Michigan and at Fort Wayne, Ind. (about 320 km from the epicenter). (Ref. 38, 105, 353.) 1838. June 9. Southern Illinois. Several cata- logs place the epicenter of this earthquake near St. Louis, Mo., because of a report of a chimneys being thrown down at St. Louis and because it was “severely felt” at St. Charles, Mo. Although reported effects do not support an intensity of VII, that intensity is assigned because of the similarity of the distribution of intensity to that of the earthquake of Oct. 8, 1857. Felt reports recorded at common points are one-half to one unit of intensity higher for the 1857 earthquake. Also felt in Illinois, Indiana, and Kentucky. Magnitude M5 5.7 Mfa BAR. (Ref. 113, 353, 529.) 1857. Oct. 8. Southern Illinois. This severe earthquake was centered in the Mississippi River valley between St. Louis, Mo., and Centralia, Ill. At Centralia, the first of three reported shocks threw down chimneys; at St. Louis, it moved furniture, EARTHQUAKES IN ILLINOIS dislocated bricks, and felled plaster. The largest buildings rocked and articles fell from mantles. Reports indicate that the Mississippi River was in tumult. Felt in many towns in Illinois, along the Mis- sissippi River south of Hannibal, Mo., in western Kentucky, and in parts of Indiana and Iowa. (Ref. 105, 109, 113, 353, 529.) 1876. Sept. 25, 06 and 06 15 UTC. Wabash River valley. These earthquakes were felt most strongly between Friendsville and Mt. Carmel, Ill., and Evansville, Ind. They were described as “heavy” at Friendsville. The second shock threw down chim- neys at Vincennes, Ind., alarmed residents at Evans- ville, Ind., and caused slight damage at Louisville and Owensboro, Ky. They were felt from St. Louis, Mo., to Indianapolis, Ind., and Louisville, Ky. (Ref. 38, 105, 353, 463, 529.) 1881. May 27. La Salle, 111. Before daybreak, a shock in the southwest part of La Salle, about 90 km northeast of Peoria, formed six parallel fissures that were traceable for 183 m in a northwest-south- east direction. Walls, foundations, and furnaces in bottle and glass factories cracked in many places. (Ref. 105, 463.) 1882. Sept. 27. Southern Illinois. A chimney was cracked severely at Greenfield, Green County, Ill., and a crack in the wall of a building was wid- ened considerably at Salem, Marion County. People were awakened and small objects were displaced throughout the area. The felt area extended from Mexico, Mo., to Vlncennes, Ind., and Henderson, Ky., in an east-west direction, and from Springfield to Pickneyville, Ill., in a north-south direction. (Ref. 38, 113, 353, 463.) 1883. Apr. 12. Cairo, Pulaski County, 111. A strong local earthquake rattled windows for 30 sec- onds and awakened everyone in Cairo, in southern Illinois near the Kentucky-Missouri border. People were injured slightly in the collapse of an old frame house. (Ref. 38, 105, 173, 463.) 1887. Aug. 2. Southern Illinois. This severe shock broke windows at Cobden, Ill., cracked brick walls at Jonesboro, Ill., and Russellville, Ky., and loosened some plaster at Nashville, Tenn. Also felt in Indiana and Missouri and as far south as Huntsville, Ala. Magnitude 4.7 Mfa BAR. (Ref. 38, 529.) 1891. Sept. 27 (Sept. 26). Near Mount Vernon, Jefferson County, Ill. Several chimneys were top- pled at Mount Vernon, and the ceiling and sidewalls of the Methodist Church were damaged. Chimney damage also was reported at Browns and Nashville, Ill., and Cloverport, Ky. Plaster was knocked down at Jerseyville, Murphysboro, and Warsaw, 111. Also felt in all or parts of Indiana, Iowa, Kentucky, Missouri, 225 Ohio, and Tennessee (see fig. 28). Magnitude 5.8 mb BAR. (Ref. 302, 353, 529.) 1903. Feb. 9 (Feb. 8). Mississippi River val- ley. This earthquake threw down chimneys in Jack- son County at Grand Tower and Murphysboro, Ill., and damaged chimneys east of Murphysboro, at Carterville and Harrisburg, Ill. It was strongly felt from Jeffersonville, Mo., to Louisville, Ky., and from Cairo, Ill., to Hannibal, Mo. (Ref. 38, 105, 353, 529.) 1905. Aug. 22 (Aug. 21). Southern Illinois. Chimneys were shaken down at Cairo, Pulaski County, Ill., and, about 40 km southwest, at Sikeston, Mo. Chimneys also were broken or partly collapsed at nearby Charleston, Mo., and, about 175 km southeast, at Clarksville, Tenn. The earthquake was felt most strongly along the Mississippi and Ohio River valleys, including parts of Arkansas, Illi- nois, Indiana, Kentucky, Mississippi, Missouri, and Tennessee (Ref. 109, 353, 529.) 1909. May 26. Aurora, Kane County, III. This earthquake has been related to the La Salle anticline in the Illinois Basin. Many chimneys fell, a stove overturned, and gas line connections broke at Aurora, west of Chicago. Several chimneys were downed at Forreston, Naperville, Streator, Triumph, and Troy Grove, and one fell at Waukegan. Brick walls cracked at Bloomington, and sidewalks, cracked and many chimneys were damaged at Freeport. At Platteville, Wis, about 130 km northwest of Chicago, an old building was cracked; houses were jostled out of plum at Beloit, Wis, about 240 km northwest of Chicago. Felt from Missouri to Michigan and Minne- sota to Indiana. Magnitude 5.1 Mfa BAR. (Ref. 38, 105, 353, 529.) 1909. July 19 (July 18). Between Havana and Petersburg, Ill. Chimneys were demolished on more than 100 buildings in Menard County at Petersburg, northwest of Springfield. At a farm west of Peters- burg, 20 windows broke and bricks pushed out above the doors. Fallen chimneys also were reported north- west of Springfield at Davenport, Iowa, and west of Springfield at Hannibal, Mo. Several newspaper articles describe this earthquake but do not report property damage. (Ref. 38, 105, 353, 529.) 1912. Jan. 2. Near Aurora, Freeport, Morris, and Yorkville, Ill. The highest intensity was reported at those towns in Kane, Stephenson, Grundy, and Kendall Counties, respectively. Slight damage to chimneys was reported at Batavia and Geneva, Ill., north of Aurora, in Kane County. Two distinct shocks were observed at some places. The stronger shock also was felt in parts of Indiana, Iowa, Kentucky (Fulton County), and Wisconsin. (Ref. 38, 105, 353, 529.) 226 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 96° 94° 92° 90° 88° 86° 84° 82° \ l .3. ________________ i 2 i’ 5 _________________ _ <( <( 0: ~ \. g ‘71? / WIS 9 ‘< l E MICH. 0: (g ‘- —'\" ~ \ l; . 3,5 x’ "L - _ :32, - . .L: Dem“ o IOWA n K \ " 42 / ‘.\ 7 ‘ I . .’ . ' Des Momes ./ Chicago —- _/ <3 l-IV 'l / Peoria l _____________ __ {.1 "2' v l 40° - -_.‘.' A I :5 l W l‘: \ lLL. I \ l. Kansas City '\ J ~ l \\. l (, KANS. ‘~"‘- V 5 St. Louis,“ ,- MO . '1 38° \\ \ \ . \ «it 1 l- _____________ l _____ I _____ - ______ ' \ 3 .3 Nashville 36° ‘1‘ 3’ O \ j , \ 3 . I " EXPLANATION . \ '1’. / / I . ) _ * Eplcenter Little Rock .’_‘.__7._._ _.,_.). ______________ \ ______ V|| Intensity 7 - o ‘5" i ‘ ARK "j I 34° ' .7’ MISS ALA. 5 150 KILOMETERS L__—__l C .' \ ‘\ Atlanta FIGURE 28.-—Isoseismal map for the southern Illinois earthquake of September 27, 1891. Isoseismals are based on intensity estimates from data listed in references 302 and 529 of table 1. 1922. Mar. 22. Southern Illinois. This strong earthquake knocked down 25 chimneys at Illmo, Scott County, Mo., and sent people rushing out of stores. Dishes fell from shelves at Carbondale, Ill. Also felt in Kentucky and Tennessee. (Ref. 529.) 1922. Mar. 23 (Mar. 22). Southern Illinois. At Illmo, Mo., south of Cape Girardeau in Scott County, the earthquake knocked down “many more chimneys” (see above description of the main shock on Mar. 22). The shock was “violen ” at Belleville, 111., and “severe” at J onesboro, Ill. Stovepipes were downed at Cape Girardeau, Mo., and people were knocked off their feet. Also felt at Evansville, Ind. (Ref. 529.) 1917. Apr. 9. Southern Illinois in the Missis- sippi River valley. At St. Louis, Mo., several chim- neys were knocked down, Windows were broken, and people were thrown to the pavement. At Granite City, Mo., buildings shifted on their foundations. At DeSoto, Mo., in Jefferson County, bricks fell from chimneys and the walls of several buildings were cracked. Many windows were broken and buildings rocked at Ste. Genevieve and St. Mary, Mo., south of St. Louis near the Illinois border. Heavy rumbling preceded and accompanied the earthquake in places. Felt from Kansas to Ohio and from Wisconsin to Mis- sissippi (see fig. 29). (Ref. 38, 113, 353, 529.) EARTHQUAKES IN ILLINOIS 227 96° 94° 92° 90° 88° \‘ WIS \ i .1" . E !\ Madison :ch '\. 9 \‘\ ....... —. E IOWA \-\ g ’—‘ . 42° _" \\‘ ~ ~ ‘1 / jl \\ Chicagov._._. . - ._,_ 0 I ll \ I I. Des Molnes / (.J/ \ l I. NEBR. / f \~ i ! / \i \! l / ~/ !\ i .7 ___________ _..~\ j/J II \ l \/ ILL. l l 400 _ ___________ P-\ I l ". l l - l .lndianapolis l . . \ i e . I' i "w Kansas City “ (l. ' \ - V «j\'\ ‘ um IV v \ . ; Salnt LouisQ”Vl f) / MO. '/ /( / l v . 38° ; I , 'j’lifiv.‘ U,"‘\.LJ _ _ _\ .,._7_._._._._._ / Na.shvllle 36° TENN. ARK. \ Little Rock \ ._._...._.—._¢\: I 0 \ .I l 0 150 KILOMETERS gr? ll 34° w 3, i I ’ EXPLANATION 3 MISS‘ '- ALA. <73 . ‘k Epicenter {)3 l - .‘(. I V| Intensity 6 .7 i FIGURE 29.—Isoseismal map for the southern Illinois earthquake of April 9, 1917. Isoseismals are based on intensity estimates from data listed in references 272 and 529 of table 1. chimney flue was demolished and stovepipes fell at Harrisburg, 8 km southwest of Eldorado. Generally felt in southern Illinois, western Indiana, northern 1922. Nov. 27 (Nov. 26). Near Eldorado, Saline County, Ill. The earthquake broke several windows and downed chimneys at Eldorado. One 228 Kentucky, eastern Missouri, and western Tennessee. (Ref. 105, 109, 353, 529.) 1934. Aug. 20 (Aug. 19). Mississippi River valley near the Illinois-Missouri border. In the area near Charleston, Mississippi County, Mo., chim- neys were thrown down or lost bricks, windows were broken, and plaster was cracked. Destructive inten— sity covered an area of 600 km2, including Charles- ton, Mo., Arlington and Wicklifi'e, Ky., and Cairo and Mounds, Ill. Felt north to Alton, 111.; east to Paducah and Marion, Ky.; south to Paris and Ripley, Tenn., and Coming and Paragould, Ark.; and west to Poplar Bluff and Greeneville, Mo. (Ref. 7, 38, 149, 149, 353.) 1934. Nov. 12. Near Rock Island, Ill. In Rock Island and Moline, Ill., and Davenport, Iowa, bricks fell from a few chimneys and pendulum clocks stopped. In Rock Island, a stucco cornice was dis- lodged from St. Joseph's School; some loose plaster was shaken from ceilings in the men's dormitory at Augustana College, and loose bricks were shaken from a few buildings. (Ref. 7, 38, 129, 149, 353.) 1947. June 30 (June 29). Waterloo-Dupo, Ill., area, south of St. Louis, Mo. At St. Louis, several chimneys were toppled and a sidewalk was cracked. (Ref. 20, 38, 105, 353.) 1953. Sept. 11. Southwest Illinois. At Roxana, north of East St. Louis, in Madison County, cracks formed in a concrete-block foundation and in plaster. Also felt in eastern Missouri. (Ref. 26, 105, 353.) 1955. Apr. 9. West of Sparta, Randolph County, H1. Concrete foundations and plaster walls were cracked at Evansville, Ill. (about 20 km west of Sparta), and at Lemay, University City, and Webster Groves, Mo. Also felt in Kentucky and Missouri. Magnitude 4.5 Mfa B . (Ref. 28, 349, 353.) 1958. Nov. 8 (Nov. 7). Southeast Illinois, near the Indiana border. laster fell at Dale (Hamilton County) and Albion (E wards County), and a base- ment wall cracked at aunie (White County). Also felt in Indiana, Kentuc y, and Missouri. Magnitude 4.5 Mfa BAR. (Ref. 31, 38‘ 105, 349, 353.) 1965. Aug. 14. Southwest Illinois. This strong local earthquake at Tainms (Alexander County) downed chimneys, cracked\walls, muddied water, and knocked stock from shelves. (Ref. 75, 349, 353.) 1968. Nov. 9. Southern Illinois. This was the strongest felt earthquake in southern Illinois since the 1895 Missouri event. Property damage in the area consisted mainly of fallen bricks from chimneys, broken windows, toppled television aerials, and SEISMICI'I'Y OF THE UNITED STATES, 1568—1989 (REVISED) cracked or fallen plaster. In the epicentral area, near Dale, Hamilton County, MM intensity VII was char- acterized by downed chimneys, cracked foundations, overturned tombstones, and scattered instances of collapsed parapets. Most buildings that sustained damage to chimneys were 30 to 50 years old. A large two-story brick house near Dale, Ill., sustained several thousand d01- lars damage. About 10 km west of Dale, near Tuck- ers Corners, a concrete and brick cistern collapsed. A large amount of masonry damage occurred at the City Building at Henderson, Ky., 80 km east-south- east of the epicenter. Moderate damage to chimneys and walls occurred in several towns in south-central Illinois, southwest Indiana, and northwest Kentucky. Felt over all or parts of 23 States (see fig. 30): from southeast Minnesota to central Alabama and Georgia and from western North Carolina to central Kansas. People in multistory buildings in Boston, Mass. and southern Ontario, Canada, felt the earthquake. Mag- nitude 5.2 Ms NTT, 5.5 mb NUT, 5.38 M JOH (Ref. 41, 263, 349, 353, 490.) 1972. Sept. 15 (Sept. 14). Northern Illinois. Cracks in chimneys, tombstones, elevated water tanks, and plaster occurred at Amboy (Lee County), south of Rockford. Chimney and plaster cracks were observed at Holcomb, northeast of Amboy, in Ogle County. Also felt in Indiana, Iowa, Michigan, Minne- sota, Missouri, Ohio, and Wisconsin. Magnitude 3.3 Ms NTT, 4.4 mb NUT. (Ref. 45, 263, 349, 353.) 1974. Apr. 3. Southeast Illinois. Minor dam- age, generally in the form of cracked and broken chimneys, occurred in Wabash County. At West Salem, a few chimneys and tombstones were shaken down and other chimneys were damaged. Slight damage occurred at many towns in Indi- ana and Illinois. Also felt in Arkansas, Iowa, Kentucky, Michigan, Missouri, Ohio, Tennessee, Virginia, and Wisconsin. Magnitude 4.7 MB SLM. (Ref. 47, 349, 353.) 1984. June 29. Southern Illinois. At Harris- burg, in Saline County, one house sustained struc- tural damage. Also felt in western Kentucky and southeast Missouri. Magnitude 3.8 M11 SLM. (Ref. 370.) 1987. June 10. Near Olney, Richland County, Ill. Minor damage in the form of cracks in chimneys, hairline cracks in plaster and drywall, and cracks in house foundations was reported in EARTHQUAKES IN ILLINOIS 229 City Building in Henderson, Kentucky, damaged by the November 9, 1968, southern Illinois earthquake. (Photograph by the Gleaner Journal.) several towns in Illinois and Indiana. The most serious damage was observed at Olney, 111., where chimneys toppled and bricks fell from chimneys; at West York, Ill. (about 60 km northeast of Olney), where chimneys were broken at their rooflines; at Evansville, Ind. (about 100 km southeast of Olney), where underground pipes were damaged and large cracks formed in sidewalks and streets; and at Lou- isville, Ky. (about 200 km southeast of Olney), Where one downed chimney and widespread minor damage were reported. Felt over a large area of the United States, includ- ing all or parts of 17 States—from Illinois east to Pennsylvania and West Virginia, west to Kansas and Nebraska, south to Alabama and Georgia, and north to Minnesota, Wisconsin, and southern Ontario, Can- ada. This was the largest earthquake in the area in 19 years—since Nov. 9, 1968. (Ref. 74, 577, 583, 592.) SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 230 100° 95° 90° 85° 80° (, LAKE SUPEHIO..H\II N. DAK I r ‘ ............... .I I \ \‘\ Marquette (9° <3 M'NN (" “'13 0 as“? 45° ‘1 ' - é .3; S o I i U J I . AK \ -. ‘ - St. P I l- 1 . I 1”. wns. 3 \C Huron I \I ; MICH. 1m ‘ \. I: I x I _,_.__ ._._ Y; .................. I :2 I5: ._,\I . . ”I g ’ “‘«s’ Q I-III 3 3:5 I ”N:— — ------- . - \_ Detrout . Idle NEBR' I IOWA / I Chicago ,_ —. . .._ — \ J II "J. I . PA. I C | I I (V‘- _I a”) IV I I III 40° -‘. ~._.~ _ ._ '\ Y ILL. I IND. II OHIO . . ’7’ I h. ‘ "9"".‘1; ‘ Columbus ) II// {‘\~ ./~' - I Kansas City ‘\_ V I ( I/ KANs I ,. |V\ L. I Mr ' ' St. LouIs 7 V w \r- -’\. f W. VA. / I MO. \, fivr \\ I. I Q\ I ' f' VA- - \ KY‘ . _ . - ........... I VI3 If. VII r/ V v -I ‘ '_ ““ I ' "q / __. .._.—w— 7 I . _ ..... 4' .——-——- J:-—-”"' I Tulsa -— — —._._ _ _ _ . A- IJ-M . ._....—I I I O I. I~ Ngshwue f-/ N. C. I OKLA. I_ c. ./-' ' I TENN. /-—’ 350 I a“) I/_’_\____... \. -—x k ' 1 — T" ————#I ’- '\, \V I I \. "- \'\ “I \~—'\ I O ' MI I AIlanIa -\. I MISS‘ I \ * EXPLANATION I” ————————————— . ALA. -\ J * Epicenter TEX. I I GA. K 00 V“ Intensity 7 I. Jackson I .I \. . I to K I. I é o 300 KILOMETERS - I . Y 9—”; I I ............. . c / "7 i I- L._ / v FIGURE 30.—Isoseismal map for the southern Illinois earthquake of November 9, 1968. This map is a simplified version of figure 3 in reference 490 of table 1. INDIANA 88° 86° 84° 42° / MICHIGAN 40° 38° EXPLANATION Magnitude/Intensity O 4.0-4.4/Vl Q 4.5-4.9 O 5.0-5.4 ILLINOIS M \ / INDIANA 0 South Bend 0 Fort Wayne OHIO O D. Terre Haute Indianapolis 0 Vincennes 0 Louisville O Evansville A KENTUCKY 0 100 KILOMETERS Earthquakes in Indiana with magnitudes _>. 4.5 or intensity 2 VI. 231 232 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) INDIANA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTc) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 kma) 1827 07 05 1130 38.0 N 87.5 W — 529 —— —-— 4.80Mf, SC — VI 353 430 1827 08 07 04 30 38.0 N 88.0 W — 529 — -— 4.80MfI SG — V 529 — 1827 08 07 07 38.0 N 88.0 W — 105 — — 4.70Mf. BAR —— V 105 — 1887 02 06 22 15 38.7 N 87.5 W —- 38 — — 4.60M“ SC — VI 529 170 1891 07 27 02 28 37.9 N 87.5 W — 38 —- — 4.10Mf, SC —— VI 38 22 1899 04 30 02 05 38.5 N 87.4 W — 529 — — 4.90Mf, SC —-—- VII 38 179 1909 09 27 0945 39.8 N 87.2 W —— 529 -—- — 5.10Mfa SC -— V11 38 377 1921 03 14 12 15 39.5 N 87.5. W — 113 — — 4.40Mf. SC — VI 529 89 1925 04 27 0405 38.2 N 87.8 W — 529 — —— 480an SC — VI 67 325 [Reference (Ref) numbers given in parentheses at the end of Greencastle, Putnam County, northeast of Terre each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1827. July 5. Near New Harmony, Posey County, Ind. The earthquake cracked a brick store at New Harmony, Ind., and “greatly alarmed” some people. It was described as violent at New Madrid, Mo., and severe at St. Louis. It also alarmed many at Cincinnati, Ohio, and Frankfort, Ky. Magnitude 4.8 Mfa BAR. (Ref. 105, 353, 529.) 1887. Feb. 6. Near Vincennes, Knox County, Ind. This shock was strongest in southwest Indiana and southeast Illinois. Plaster was shaken from walls at Vincennes, Ind., and west of Terre Haute, at Mar- tinsville, 111.; a cornice reportedly fell from a building at Huntington, Ind. It was felt distinctly at Evans- ville, Ind., but only slightly in the outskirts of St. Louis, Mo. Also reported felt at Louisville, Ky. (Ref. 38, 105, 353, 529.) 1891. July 27 (July 26). Evansville, Vander- burgh County, Ind. A strong local earthquake dam- aged a wall on a hotel, broke dishes, and overturned furniture at Evansville. The shock also was strong near Evansville at Mount Vernon and Newburgh, Ind., and at Hawesville, Henderson, and Owensboro, Ky. Magnitude 3.8 Mfa BAR. (Ref. 38, 105, 529.) 1899. Apr. 30 (Apr. 29). Near Vincennes, Knox County, Ind. Brick walls cracked and several chim- neys fell at Vincennes, and the tops of many chim- neys were shaken down at Princeton in Gibson County. Toppled chimneys also were reported at Haute. The shock was “heavy” at J effersonville, near Louisville, Ky. Also felt in Illinois and Kentucky. Magnitude 4.6 Mfa BAR. (Ref. 88, 105, 353, 529.) 1909. Sept. 27. Wabash River valley, between Terre Haute and Vincennes, Ind. At Terre Haute (Vigo County), two chimneys were thrown down, plaster was cracked, and pictures were shaken from walls. At Covington, north of Terre Haute in Foun- tain County, a few chimneys were downed and win- dows were broken. Chimneys were “jarred loose” south of Vincennes at Princeton, Ind., one chimney was shaken to pieces at Olivette, Mo. (a suburb of St. Louis), and a brick wall was shaken down at St. Louis, Mo. Also reported felt in Arkansas, Illinois, Iowa, Kentucky, Ohio, and Tennessee (see fig. 31). Magnitude 4.8 Mfa BAR. (Ref. 38, 105, 353, 529.) 1921. Mar. 14. Near Terre Haute, Vigo County, Ind. This earthquake broke windows in many buildings and sent residents rushing into the streets at Terre Haute. Small articles were over- turned at Paris, 111., about 35 km northwest of Terre Haute. Magnitude 4.4 Mfa BAR. (Ref. 113, 529.) 1925. Apr. 27 (Apr. 26). Wabash River valley, near Princeton, Gibson County, Ind. Chimneys were downed at Princeton and at Carmi, 111., 100 km southwest; chimneys were “broken” at Louisville, Ky. Crowds fled from the theatres at Evansville, Ind. The felt area includes parts of Indiana, Illinois, Kentucky, Missouri, and Ohio. Magnitude 4.8 Mfa BAR. (Ref. 67, 105, 218, 353, 529.) EARTHQUAKES IN INDIANA 233 96° 94° 92° 90° 88° 86° 84° 82° 44° ‘ I x I 2 ' _ ) WIS. \ “ LAKE HURON I Milwaukee LAKE MICH/GAN 42° O Coiumbus Indianapolis - ’ <' ._l 6 EXPLANATION * Epicentet _ V|| Intensity 7 ! I 34° \_ \. I . . ~.\L o 450 KILOMETERS'( - '\ . I I _ - . ”'1 J gs I ‘ FIGURE 31.—Isoseismal map for the Wabash River valley, Indiana, earthquake of September 27, 1909. Isoseismals are based on intensity estimates from data listed in reference 529 of table 1. . . \\ y ‘ . . , w, . , . , ‘, N A WWW .r-g-wwmw ! \ KANSAS .S N zammnmufi .8 may N wwwdficmmfi £15 mumcam E mmxmzufipmm .lJ’. \¢.¢.m.m O >=wc2c>O~ zo: O Bommflw .02 o o O 58:33 O O WMUDHZWM m8/\\f/MWVJW o .8 ® 855me w=_>m_:o._ d w=_>m:m>m_ 207241: .<> .3 US~Em< $.06 O 3.3 O :mc$c < rrJ © 0 Gloucester 0 O PittSfield MASSACHUSETTS Boston 0 E I ‘9, oSprin f‘ Id x % Ie ‘I r g %‘ 0 g H a > E 3 CONNECTICUT LL} Z Falmouth J 455’“ grim: EXPLANATION y Magnitude/Intensity '/ o 3.2-4.4/VI 0 /VI O /VII 0 50 KILOMETERS 0 /VIII Damaging earthquakes in Massachusetts, intensity 2 VI. 249 250 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) MASSACHUSETTS [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGs Other Moment MMI Ref Felt area Yr Me Be h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1627 42.6 N 70.8 W — 126 — — -— —- VI 76 — 1638 06 11 07 46.5 N 72.5 W - 76 — — — —-- IX 76 —— 1663 02 05 2230 47.6 N 70.1 W - 76 — —— — —- X 76 1900& 1727 11 10 0340 42.8 N 70.8 W — 38 — — — —- VII 78 2968: 1744 06 14 15 15 42.6 N 70.9 W — 78 —- — — -- VI 78 157& 1755 11 18 091135 42.7 N 70.3 W — 78 —— — — -—— VIII 78 1000& 1761 03 12 0715 42.7 N 70.3 W — 78 —— — — — V 78 1278: 1766 02 02 42.0 N 68.0 W -— 76 -— — -- — VI 76 — 1800 12 25 41.9 N 71.1 W -— 76 — — -- — ”VI 76 — 1817 10 05 16 45 42.5 N 71.2 W — 38 -— — -- — VI 78 558: 1847 08 08 1500 41.7 N 70.1 W — 78 — -— —— —— VI 76 348: 1963 10 16 15 30 59.7 42.401N 70.422W 014 349 — — 3.90Mn ST 3.40ST VI 36 18& 1963 10 30 22 36 57.9 42.7 N 70.8 W — 36 —- — 3.20ML WES 2.588T VI 36 6& [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1.] 1627. Date unknown. Essex, Mass. This local earthquake at Essex, about 40 km northeast of Boston, was reported to be as violent as the shock of June 11, 1638 (see description below). (Ref. 59, 76, 126.) 1638. June 11. Probably in the St. Lawrence River valley, Canada. Tops of chimneys were thrown down and dishes were knocked from shelves in the Salem—Lynn area, north of Boston, and at Ply- mouth, on the coast about 55 km southeast of Bos— ton. At Plymouth, people had to hold on to posts to keep from falling. Ships near the coast reportedly were shaken. Also felt in Connecticut and Rhode Island. Aftershocks continued for 20 days. (Ref. 38, 59, 76.) 1663. Feb. 5. St. Lawrence River valley region, Canada. This major earthquake caused vast landslides along the St. Maurice, Batiscan, and St. Lawrence Rivers. The earthquake was felt sharply in New England. On the shores of Massachusetts Bay, the tops of chimneys were broken on houses and pewter was jarred from shelves. (Ref. 38, 59, 76.) 1727. Nov. 10 (Nov. 9). Northern Cape Ann region, east of Newbury, Essex County, Mass. At Newbury, many stone walls and chimney bricks were shaken down, and almost all tops of chimneys were knocked off. Considerable changes occurred in the flow of water in springs and, in some springs, changes occurred in the character of the water. “Some firm land became ua ire and marshes : q, were dried up.” The rise and fall of the ground made it difficult to walk, and houses shook and rocked as if they would fall apart. Sand blows were reported near Spring Island. Felt from the Kennebec River in Maine to the Delaware River on the New York— Pennsylvania border and from ships at sea to the “extreme western settlements.” Aftershocks occurred in the area for several months. The strongest after- shock (MM intensity V) occurred in the Newbury area on Dec. 28, 1727, and Jan. 4 and Feb. 10, 1728 (local dates). (Ref. 38, 59, 78.) 1744. June 14. Southern Cape Ann, Mass., region (near Salem, Essex County, Mass.). Bricks were shaken from several chimneys in Boston and other towns, and pieces of stone fence were thrown down in the country. Many persons were alarmed at Newbury and Ipswich, Mass. The shock was reported from Falmouth, Me., to New York City. Several after- shocks occurred. (Ref. 38, 78.) 1755. Nov. 18. East of Cape Ann, Mass. This earthquake caused the heaviest damage in the region around Cape Ann and Boston. At Boston, much of the damage was confined to an area of infilled land near the wharfs. There, about 100 chimneys were leveled with the roofs of houses, and many others (1,200 to 1,500) were shattered and partly thrown down. Some chimneys, which were broken off below their tops, tilted dangerously 3 or 4 cm; others were twisted or partly turned. The gable ends of several brick buildings (12 to 15) were thrown down, and the roofs of some houses were damaged by the fall of chimneys. Stone fences were thrown down through- out the countryside, particularly on a line extending EARTHQUAKES IN MASSACHUSETTS from Boston to Montreal. New springs formed, and old springs dried up. At Scituate (on the coast south- east of Boston), Pembroke (about 15 km southwest of Scituate), and Lancaster (about 40 km west of Bos- ton), cracks opened in the earth. Water and fine sand issued from some of the ground cracks at Pembroke. The earthquake generated a tsunami that left ves- sels aground and fish on the banks after the water withdrew from St. Martin’s Harbor in the West Indies. When the water flowed back into the harbor, it rose about 2 m higher than normal and inundated the low-lying lands. This earthquake was reported from Halifax, Nova Scotia, south to the Chesapeake Bay in Maryland and from Lake George, N .Y., east to a ship 320 km east of Cape Ann. The location of the ship is thought to be near the epicenter, because the shock was felt so strongly that those onboard believed the ship had run aground. Several aftershocks occurred. (Ref. 59, 78, 502.) 1761. Mar. 12. East of Cape Ann, Mass. This earthquake is included in the list of magnitude 2 4.5 or intensity 2 VI events based on the large felt area documented on land from the estimated offshore loca- tion. While no damage was documented the large felt area and strong shaking indicates that this event is as large or larger than a magnitude 4.5 earthquake. 1766. Feb. 2. Off the coast of Massachusetts. This shock was felt throughout Massachusetts, Rhode Island, and other parts of New England. It was reported that the earthquake was “accompanied by a remarkable meteor.” Note: Existing felt reports do not substantiate the MM intensity VI published in ref. 76 for this earthquake and the one in 1800 (see next paragraph), but an intensity of that level proba- bly was assigned because the shocks were felt over such wide areas. (Ref. 59, 76.) 251 1800. Dec. 25. Eastern Massachusetts. A severe shock was felt at Boston and Concord, Mass; Newport, RI; and elsewhere (see 1766 description above). (Ref. 59, 76.) 1817. Oct. 5. Northeast Massachusetts. Walls were thrown down at Woburn, in Middlesex County, according to ref. 59. Ref. 78 states that the “walls” referred to by ref. 59 possibly were stone fences, characteristic of rural New England pasture land, rather than house walls. Such walls were constructed of glacial boulders piled loosely on top of each other to form a stone fence. Felt in Connecticut, Massachu- setts, New Hampshire, New York, and probably Rhode Island and Vermont. (Ref. 38, 59, 76, 78.) 1847. Aug. 8. Near Harwich, Barnstable County, Mass. A section of “the plastering” was thrown down at the Harwich Baptist Church; mirrors hanging on the wall were broken at Nantucket (south of Hyannis) and Sandwich (northeast of Hyan- nis). In the Yarmouth area, northeast of Hyannis, glass was broken and crockery shook from shelves. Felt throughout eastern Massachusetts. (Ref. 76, 7 8.) 1963. Oct. 16. Near the coast of Massachu- setts. Slight damage at Somerville, north of down- town Boston, consisted of fallen plaster, cracks in walls, and fallen stones from building foundations. Also felt in Maine, New Hampshire, and Rhode Island. (Ref. 36, 38, 349.) 1963. Oct. 30. Northeast of Peabody, Essex County, Mass. Slight damage occurred at Framing- ham, Peabody, and Swampscott. At Framingham, in Middlesex County, southwest of Boston, 3 m of stone foundation on a 155-year-old house collapsed. North- west of Boston, at Peabody, cracks in wall plaster and a sidewalk occurred; and southeast of Peabody, at Swampscott, basement stairs were thrown out of alignment. Also felt in New Hampshire. (Ref. 36, 38.) 46° 44° 42° MICHIGAN O. Houghton O 4.5-4.9 90° 88 86° 84° 82° 0’ / KE SUPERIOR EXPLANATION LA P Magnitude o 4.0-4.4 0 4° 100 KILOMETERS INDIANA ‘; u z: :3. C. % w J g % WISCONSIN 5 % MICHIGAN A an Cf 3: x} Mwaukee< Grand Rapids K Detroit ILLINOIS / O JLAKE ERIE OHIO Earthquakes in Michigan with magnitudes 2 4.5 or intensity 2 VI. 253 254 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) MICHIGAN [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (-—) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (we) Latitude Longitude Depth Ref uses Other Moment MMI Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1905 07 27 00 20 47.24 N 88.45 W — 326 —- — 4.50Mfa SC — VII 38 40 1906 05 26 14 42 47.10 N 88.64 W —— 336 —- — 4.20Mfl| SC — V11] 38 2 1947 08 10 02 46 41.3 41.928N 85.004W 002 349 — — 4.60Mll BAS — VI 20 158 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1905. July 27 (July 26). Calumet, Houghton County, Mich. This earthquake was associated with unstable geological conditions induced by min- ing operations in the area. The shock downed many chimneys and broke plate glass Windows at Calu- met, in northwest Michigan. Accompanied by a ter- rific explosion, the shock was felt throughout the Keweenaw Peninsula in Michigan and as far east as Marquette. Magnitude 4.5 Mfa BAR. (Ref. 38, 326, 353.) 1906. May 26. Houghton, Mich. At the Atlantic mine, near Houghton (about 20 km southwest of Cal- umet), rails were twisted and a notable sinking of the earth was observed above the workings of the mine. These effects were not observed elsewhere. About 50 shocks were reported. Magnitude 3.6 Mfa BAR. (Ref. 38, 336, 353.) 1947. Aug. 10 (Aug. 9). Southern Michigan. Damage was heaviest in the area southeast of Kalamazoo at Athens, Bronson, Goldwater, Colon, Matteson Lake, Sherwood, and Union City. Chimneys were damaged, windows and plaster were broken, and brick cornices were downed. Also felt in Indiana, Illinois, Ohio, Wisconsin, and Ontario, Canada. (see fig. 33). Magnitude 4.7 Mfa BAR. (Ref. 20, 349, 353.) 44° 42° 40° 38° 90° 88° EARTHQUAKES IN MICHIGAN 86° 84" 255 82° 80° WISCONSIN 0 Madison ’ .r 3*” MICHIGAN \ ‘s \I '\ C A. \. .\I - 1 Cadillac fig —— —.— \ .. 2 \ A ‘. r . \ . . .. - 5 UNITED 5““ WW9 " n i ! Cleve|and | | ' < ! z I 3 . > I ILLINOIS «l EL" K INDIANA f. i ,— —-— ‘— ~ I j l \\ . . -" ! ~_ Muncie \! 18—1—4 ‘ ° " ' ~ Columbus ( l— . ! J ,. k / ! .f I fix . .J EXPLANATION ' ! .1 . 1 )'\.—r- ./ * EpIcenter . '\ L. . ( . I ' \ ( m VI lmensny 6 ' k' I I I ...I K- K r‘ ('-'v'/ fi'\r'\ ["7 - A j . 'r~ \'\ (J WEST VIRGINIA 0 100 KILOM_ETERS .J .V "i .1" J M] KENTUCKY 'I \ -~ ’ ‘i - r?! i ‘- FIGURE 33.—Isoseisma1 map for the southern Michigan earthquake of August 10, 1947. Isoseismals are based on intensity estimates from data listed in reference 20 of table 1. . . i . V / X \ ._ ._ ., . . , . y A , « x15, , amfiwwm 48° 46“ 44° 98° 96° 94° 92° 27" o 100 KILOMETERS CANADA ' t—J——’ UNITED STATEN/fl Baudette [it Y~ & gXO <2 309$ D a 1% m vb %‘ 0 z . Duluty / / MINNESOTA O \ A . V Alexandria O EXPLANATION E3 Magnitude/Intensity & O 4.0-4.4/VI < St. Paul 0 O 4.5-4.9/Vl Q m S 8 \ WISCONSIN IOWA ’x MINNESOTA 90" Earthquakes in Minnesota with magnitudes 2 4.5 or intensity 2 VI. 257 258 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) MINNESOTA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (..) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTc) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo D: h m 8 (°) (°) (km) ml, Ms M (1,000 km?) 1860 46.0 N 94.8 W — 105 -— — — —- VI 272 ~--— 1917 09 03 21 30 46.3 N 94.5 W — 38 —— — 4.30Mf. SC — VI 38 48 1975 07 09 14 54 21.3 45.498N 96.100w 008 349 5.0 — 4.60M“ DG 4.29HRN VI 48 75 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1860. Date unknown. Long Prairie, Todd County, Minn. Little is known about the effects of this earthquake. MM intensity V1 is assigned to the shock because it is described as “a harder shock” than that on Sept. 3, 1917. Ref. 272 describes an earthquake on a Sunday afternoon between the years 1865 and 1870. The above reports probably refer to an earthquake between 1860 and 1870. (Ref. 105, 272.) 1917. Sept. 3. Staples, Todd County, Minn. The earthquake was most severe at Staples, a railway village on the north edge of Todd County, where chimneys toppled and many windows were broken. The shock also cracked the wall of a brick building, the concrete floor in the city clerk's office, and concrete sidewalks. Several courses of bricks were dislodged from a chimney at Brainerd, east of Staples, and a chimney was thrown down near Lincoln, south of Staples. Also observed in Minne- apolis, 190 km southeast of Staples. (Ref. 38, 105, 272, 491.) 1975. July 9. Western Minnesota. The earth- quake caused minor damage to walls and founda- tions of basements in Stevens County around Morris. Also felt in Iowa, North Dakota, and South Dakota. Magnitude 4.8 M11 SLM. (Ref. 38, 48, 349.) 34° 32° 30° 92° MISSISSIPPI 90° 88° EXPLANATION )5 TENNESSEE Magnitude/Intensity O 4.0-4.4/VI O 4.5-4.9/VI ARKANSAS ' 0““ O 0 Greenville MISSISSIPPI 0 Jackson VWVHVTV LOUISIANA O 100 KILOMETERS 0C> Gulfport :13, Earthquakes in Mississippi with magnitudes 2 4.5 or intensity 2 VI. 259 260 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) MISSISSIPPI [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (--) indicates information is not available] Orlgln Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m 8 (°) (°) (km) mb Ms M (1,000 kmz) 1931 12 17 03 36 33.8 N 90.1 W — 4 — — 4.60Mf. SC — VI 4 175 1967 06 04 16 14 12.6 33.552N 90.836W 006 349 3.8 — 4.40M“ DG 4.28HRN VI 40 54 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1931. Dec. 17 (Dec. 16). Charleston, Talla- hatchie County, Miss. Several chimneys were thrown down at Charleston, and the walls and foun- dation of the Agricultural High School were cracked. Minor damage to chimneys also occurred at ’I‘illatoba and Water Valley; several buildings were damaged slightly and plaster fell at Belzoni. Also felt in Ala- bama, Arkansas, and Tennessee. (Ref. 4, 105.) 1967. June 4. Near Greenville, Washington County, Miss. A few instances of cracked plaster were reported at Greenville. One person near the epi- center observed a crack in his lawn about 0.5-1.3 cm wide and 12 m long. Also felt in Arkansas, Louisiana, and Tennessee. A slight aftershock was observed in the Greenville area on June 29. Magnitude 4.5 Mn BAR, 3.0 Ms NUT, 4.5 mb NUT.. (Ref. 40, 263, 349.) MISSOURI 95° 94° 92° 90° 4 IOWA EXPLANATION N EBR. Magnitude/Intensity o 3.6-4.4/VI 40° 0 4.5-4.9/Vl _____ O 5.0-5.4 O 5.5-5.9 O 7.0-7.4 Kansas City MISSOURI _ ILLINOIS St. LOUIS o KANSAS Jefferson City 38° 0 o 0 Springfield 0 New C OKLAHOMA ARKANSAS 2 36° 0 100 KILOMETERS Earthquakes in Missouri with magnitudes 2 4.5 or intensity 2 VI. 261 262 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) MISSOURI [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (__) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Me D: h m 9 (°) '(°) (km) m. Ms M (1,000 m2) 1812 01 23 1500 36.3 N 89.6 W — 301 — —— 7.10Mf.NU 7.55NLI X1 473 5000 1812 02 07 0945 36.5 N 89.6 W — 301 — — 7.40Mf,NU 7.88NLI XII 473 5000 1812 11 09 22 36.5 N 89.6 W — 143 -—- — — — VI 143 — 1895 10 31 1108 37.0 N 89.4 W -—- 38 —— -— 5.90M“ SC — VIII 527 2037 1902 01 24 1048 38.6 N 90.3 W — 38 — —- 4.50Mfll SC — VI 38 130 1903 11 04 1818 36.5 N 89.5 W — 529 —- — 4.60Mf. SC — VI 38 168 1903 11 04 1914 36.5 N 89.8 W — 529 — — 5.10Mfa SC -— VII 529 340 1909 10 23 0710 37.0 N 89.5 W —— 38 —— -— 4.50Mf. BAR — V 38 125 1915 12 07 18 40 36.0 N 90.0 W -- 529 — — 4.50M“ BAR — V 109 120 1924 01 01 0305 36.0 N 90.0 W —— 529 — — 4.50Mf. SC —- VI 529 150 1934 08 20 0047 27 36.95 N 89.2 W —— 38 — — 4.70Mf. SC — VII 38 85 1955 01 25 07 24 39.1 36.073N 89.827W 008 349 — — 4.40Mf. SC — VI 28 85 1956 ll 26 04 12 43.3 36.914N 90.387W 001 349 —- — 4.30M}; SC — VI 29 70 1962 02 02 0643 30.0 36.374N 89.511W 004 349 —— — 4.30M“ BAR 4.22HRN VI 35 90 1963 03 03 17 30 10.6 36.642N 90.050W 009 349 —— -— 4.80Mn DG 4.64HRN VI 38 208 1965 10 21 0204391 37.479N 90.944W 007 349 5.1 — 4.80Mn DG 4.59HRN VI 75 420 1967 07 21 09 14 48.8 37.440N 90.443W 012 349 3.9 — 4.30Mn S'I'I' 4.03HRN VI 40 53 1974 05 13 0652187 36.739N 89.357W 004 349 4.3 — 3.60Mfa SC — VI 47 2 1975 06 13 2240275 36.543N 89.682W 009 349 4.3 3.90Mn DG 3.73HRN VI 48 13 1977 01 03 22 56 48.5 37.583N 89.714W 005 349 —— — 3.60Mn DG — VI 39 6 1987 09 29 0004 57.2 36.840N 89.210W 005 74 4.6 4.50Mn GS — V 577 35 1989 04 27 16 47 49.8 36.006N 89.768W 010 74 4.6 — 4.30Mn GS —-— VI 579 57 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1812. Jan. 23. New Madrid, Mo. This is the third principal shock of the 1811—12 sequence. The first earthquake of this series on Dec. 16, 1811, was located in northeast Arkansas. It is difficult to assign intensities to the principal shocks that occurred after 1811 because many of the published accounts describe the cumulative effects of all the earth- quakes. Using the Dec. 16 earthquake as a standard, however, a comparison between it and the shock on Jan. 23 indicates that the intensities were about equal at similar locations. The meizoseismal area was characterized by general ground warping, ejec- tions, fissuring, severe landslides, and caving of stream banks. Magnitude 8.4 Msn NLI. (Ref. 143, 301, 353, 473, 529.) 1812. Feb. 7. New Madrid, Mo. This is the fourth and largest earthquake of the 1811—12 series. Several destructive shocks occurred on Feb. 7, the last of which equaled or surpassed the magnitude of any previous event. The town of New Madrid was destroyed. At St. Louis, many houses were damaged severely and their chimneys were thrown down. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe land- slides, and caving of stream banks. Magnitude 8.8 Msn NLI. (Ref. 114, 143, 301, 353, 473, 529.) 1812. Nov. 9. New Madrid, Mo. This earthquake caused “much motion to furniture” at Cape Girardeau, about 75 km north of New Madrid. (Ref. 143.) 1895. Oct. 31. Near Charleston, Mississippi County, Mo. This is the largest earthquake to occur in the central Mississippi River valley since the 1811- 12 series in the area of New Madrid, Mo. Structural damage and liquefaction phenomena were reported along a line from Bertrand, Mo., in the west to Cairo, 111., in the east. Many sand blows were observed in an area southwest of Charleston, Mo., and south of Bertrand, M0. Isolated occurrences of sand blows also were reported north and south of Charleston. The most severe damage occurred in Charleston, Puxico, and Taylor, M0,; Alton and Cairo, 111.; Prince- ton, Ind.; and Paducah, Ky. The earthquake caused EARTHQUAKES IN MISSOURI 100° 95° 90° 263 45° NEBR. 40° \. 'x. I , // Washing‘on .r -7 . Oklahoma cny\ i 35° -’ ° \ l i \ .\ ‘ TX. 30° EXPLANATION fir Epicenter V||| Intensity 8 Q 200 KlOMETERS FIGURE 34.—Isoseismal map for the Charleston, Missouri, earthquake of October 31, 1895. Isoseismals are based on intensity estimates from data listed in references 527 and 529 of table 1. extensive damage (including downed chimneys, cracked walls, shattered windows, and broken plas- ter) to school buildings, churches, private houses, and to almost all the buildings in the commercial section of Charleston. East of Charleston, at Cairo, Ill., few buildings escaped at least the loss of a chimney or a broken window. The courthouse, library, and a church at Cairo sustained extensive damage, and the brick walls of many buildings in the downtown section were cracked badly. Other damage included a cracked pier on the Illinois Central Railroad bridge over the Ohio River and downed chimneys at Gadsden, Ala; Evansville and New Waverley, Ind.; Covington, Spottsville Depot, and Uniontown, Ky.; St. Louis, Mo.; and Memphis, Tenn. Minor damage to property occurred throughout the region. Felt from Chatham, Ontario, Canada, to New Orleans, La., and from Washington, DC, to Wichita, Kans., an area that includes 23 States (see fig. 34). Magnitude 6.7 Ms,n NTL. (Ref. 38, 109, 113, 353, 366, 527, 529.) 1902. Jan. 24. Near St. Louis, Mo. 'IVvo distinct earthquakes were felt in western Illinois, Kansas, and Missouri. The shocks were particularly severe in the western part of St. Louis. A street car conductor 264 stated that the Eads Bridge swayed perceptibly. Felt from Leavenworth, Kans., and Kansas City, Mo., to Springfield, Ill. (Ref. 38, 105, 109, 353.) 1903. Nov. 4, 18 18 and 19 14 UTC. Near Charleston, Mississippi County, Mo. Two earth- quakes occurred on this date, the second of which was the strongest. The first shock which damaged chimneys at New Madrid, Mo., was felt in Arkansas, Illinois, Kentucky, Mississippi, and Tennessee. Dur- ing the second shock at 19 14 UTC, chimneys were downed at Cape Girardeau and New Madrid, Mo. Minor damage also was reported at Malden, Mo., Oxford, Miss., and Quincy, Ill. This earthquake was felt over an area similar to that of the first shock but also was reported in Indiana. Magnitude 4.9 Mfa BAR (first shock); 4.7 Mfa BAR (second shock). (Ref. 38, 105, 109, 353, 529.) 1924. Jan. 1 (1923, Dec. 31). Missouri. A few plate-glass windows were broken at Osceola (Missis- sippi County), Ark., and a few windowpanes were broken at Little Rock, Ark. Also felt in Illinois, Ken- tucky, Missouri, and Tennessee. Magnitude 4.6 Mfa BAR. (Ref. 529.) 1955. Jan. 25. Mississippi River valley, near Finley, Tenn. Windows were shattered and plaster walls and ceilings were cracked in southeast Mis— souri and western Tennessee (in Dyer County at Fin- ley). Windows cracked northwest of Finley at Hayti, Mo. Felt from Lepanto, Ark., north to Paducah, Ky., and east to Birmingham, Ala. Also felt in southern Illinois and northern Mississippi. Magnitude 4.5 Mfa BAR. (Ref. 28, 349, 353.) 1956. Nov. 26 (Nov. 25). Wayne County, Mo. Minor damage in the form of shattered windows and cracked walls was reported at Grubville, Richmond Heights (suburb of St. Louis), and St. Louis; a con- crete porch was cracked at Sturdivant. The felt area includes parts of Arkansas, Illinois, Kentucky, Mis- souri, and Tennessee. Magnitude 4.3 Mfa BAR. (Ref. 29, 38, 349, 353.) 1962. Feb. 2. New Madrid, Mo., near Catron and Marston. At Catron, two water pipes broke and walls and plaster cracked; at Marston, chimneys were damaged and windows cracked. Also felt in parts of Arkansas, Illinois, Kentucky, and Tennessee. Magnitude 3.5 Ms NUT, 4.3 mb NUT. (Ref. 35, 38, 263, 349, 353.) 1963. Mar. 3. Near Poplar Bluff, Butler County, Mo. Minor damage in the form of fallen and cracked plaster; cracks in foundations, walls, side- walks, chimneys, and windows; fallen bricks from SEISMICITY OF THE UNITED STATES, 1568-1989 (REVISED) chimneys; and damaged water lines occurred in many towns in southeast Missouri. In addition, cracks in plaster and walls occurred in several towns in Arkansas, Illinois, Kentucky, and Tennessee. Also reported felt in parts of Indiana, Kansas, and Missis- sippi. (see fig. 35). Magnitude 4.7 Mn BAR, 4.1 Ms BAR, 4.8 mb NUT, 4.1 Ms NUT, 4.66 M JOH. (Ref. 38, 263, 349, 353.) 1965. Oct. 21 (Oct. 20). Eastern Missouri. Plaster was knocked down at St. Louis, northeast of the epicenter. Minor damage also occurred at Augusta (cistern cracked), Illmo (basement floor cracked), Pacific (sewer vent line cracked), and Rey- nolds (bricks fell from flue). Minor cracks in plaster, walls, and windows were reported from several towns in Illinois, Iowa, and Kansas. Also felt in Kentucky, Nebraska, Oklahoma, and Tennessee. Magnitude 4.9 Mb NUT, 4.1 MS NUT. (Ref. 75, 263, 349, 353.) 1967. July 21. Near Poplar Bluff, Butler County, Mo. Plaster fell at Poplar Bluff, and plaster cracked north of Poplar Bluff at Elvins and Freder- icktown. Felt mainly in southeast Missouri and southern Illinoi s. Magnitude 4.3 Mn BAR, 2.8 MS BAR. (Ref. 40, 349, 353.) 1974. May 13. New Madrid, Mo., region. The City swimming pool at East Prairie, northeast of New Madrid, was “badly damaged,” and plaster was cracked in several buildings. Also felt in Arkansas, Illinois, Kentucky, and Tennessee. Magnitude 4.1 Mn SLM. (Ref. 47, 349.) 1975. June 13. New Madrid, Mo., region. Damage was slight at Lilbourn, southwest of New Madrid, where plaster cracked and fell. Furniture overturned and broke at nearby Marston. Also felt in Arkansas, Kentucky, and Tennessee. Magnitude 4.3 MB SLM. (Ref. 48, 349.) 1977. Jan. 3. Cape Girardeau, Mo., region. Plaster cracked and small objects fell at Old Apple— ton, about 35 km north of Cape Girardeau. Also felt in Illinois. Many aftershocks were felt on Jan. 3. Magnitude 3.4 Mn SLM. (Ref. 39, 349.) 1989. Apr. 27. Near Steele, Pemiscot County, Mo. At Steele, near the Arkansas-Missouri-Tennes- see border in southeast Missouri, large cracks formed in exterior walls of a brick building and plaster and drywall sustained hairline cracks. Chimneys, plaster, and drywall were cracked at nearby Hayti, and items fell from shelves in stores. Felt in parts of Arkansas, Illinois, Kentucky, Missouri, and Tennessee. Magni- tude 4.2 Mn SLM. (Ref. 74, 579.) 94° EARTHQUAKES IN MISSOURI 92° 90° 88° 265 86° 40° '\.v Kansas Clly III-IV I I I KANSAS I I I 38° I I I I I I I - ._._._._._I I I I I— ------- I I 36° I I I OKLAHOMA | 34° . Peoria f Saint LDlflS - 0) MISSOURI ILLINOIS I : INDIANA I IndIanapohs O KENTUCKY TENNESSEE I I I I I ARKANSAS R I Lime Rock . ff I I I I t". I j //" MISSISSIPPI I ALABAMA I J) I' . ’ IDD KILOMETERS r( EXPLANATION II Kan»- (- * Epicenlsv I TEXAS I _J VI Inlansily 5 I " l data listed in reference 36 of table 1. FIGURE 35.———Isoseisma1 map for the southeast Missouri earthquake of March 3, 1963. Isoseismals are based on intensity esimates from n ‘ A y ‘ , \ . ‘lu . . ( . V ‘ , 4 , .. , ‘, . . , ‘ ‘ .\ . . / MONTANA .S N 36:85 28 m4“ N 335?.me £15 98332 E mmxmififimm V .l] mmm—hm—EOAE on: O E!!! oonwB $291!}; m __x.x\m.~.ms O m! m” g o :22 O H M ___>$.w.o.m O W W ._>B.m.m.m O O O O $3.93“. 0 S .2323 o mOEEm >:mc£:_\wuzgcmas_ __ o . ZO_._.N 36:85 .8 may N mowBEMNE FEB mxmmfioz E moxmsgfimw m o O / o > m C N 9 Yvon O 3.: 0 53-2 0 $923 meDom >:m:2c_\mu3_cmas_ 0 5.5-5.9/VII E O 6.0-6.4 N ' O O 6.5 6.9 2 O 7.0-7.4 > < > 7.5-7.9 0 100 KILOMETERS L_L_J Earthquakes in Nevada with magnitudes 2 4.5 or intensity 2 VI. 283 284 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NEVADA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 kmz. Leader (--) indicates information is not. available] Origin Hypocenter Magnitude Intensity Date time (we) Latitude Longitude Depth Rot uses Other Moment MMI Rel Felt am Yr Mo Da h m 8 (°) (°) (km) ' mb Ms M (1,000 km?) 1857 09 03 0305 39.3 N 120.0 W -- 368 —— — 6.00MuDMG —- V 368 ~— 1860 03 15 1900 39.5 N 119.5 W — 368 -— — 6.30ML.DMG —— VI 368 —— 1868 05 30 0510 39.3 N 119.7 W — 368 — — 5.80ML‘DMG — VII 54 190 1869 12 27 0155 39.4 N 119.7 W — 368 — — 6.10MuDMG — VII 368 180 1869 12 27 1000 39.1 N 119.8 W — 368 — —- 5.90MuDMG — VII 368 — 1872 03 23 2141 40.0 N 117.5 W — 54 — — 5.50Mf. SIG — VI 38 31 1872 11 12 39.0 N 117.0 W — 521 — — 6.00MuELL -— Felt 54 129 1873 11 05 1700 40. N 118. W — 54 — — 5.50MfI SIG — Felt 54 -— 1875 04 02 0200 39.5 N 115.8 W —-- 54 — — -- — VI 54 — 1877 07 10 0710 39.3 N 120.0 W —— 54 —— — 5.00Mf. SIG —— IV 54 — 1887 06 03 1048 39.2 N 119.8 W — 54 — — 6.30MuDMG — VIII 368 — 1888 01 30 0635 39.0 N 120.0 W —— 54 — — 4.50Mf. SIG —— V 54 -— 1894 11 18 10 49 39.2 N 119.5 W —- 54 — — — — VI 56 — 1896 01 27 2101 39.1 N 119.8 W -— 54 -— — — — VI 54 ~— 1897 05 15 1904 39.3 N 119.7 W -— 54 -— — -— -— V 54 — 1901 07 26 22 20 40.8 N 115.7 W — 54 — — 5.00Mf. SIG — VII 54 9 1903 39.5 N 118.1 W — 54 — —— — — VI 328 — 1910 11 07 17 20 37.5 N 117.0 W —— 54 ——- — — -— VI 56 —— 1910 11 19 0225 38.0 N 118.0 W — 54 — -— ——- —— Felt 56 — 1910 ll 21 23 23 38.0 N 118.0 W — 54 —- — -— — VII 56 -— 1910 11 22 0605 38.0 N 118.0 W —— 54 — — — —— Felt 56 — 1914 02 18 18 17 39.5 N 119.8 W — 54 — — 6.00Mf. SIG — VI 38 42 1914 04 24 08 35 39.5 N 119.8 W -— 54 —— — 6.40Mf. SIG -— VII 56 260 1915 10 03 0149 40.5 N 117.5 W — 54 — -— — — V 327 — 1915 10 03 0652 48.0 40.5 N 117.5 W -— 258 — — 7.70M, ABl 7.14WAL X 56 788 1916 02 03 05 0304 41.0 N 117.8 W -— 54 — —— 5.90Mf. SIG — V 272 278 1916 08 03 134919 41.5 N 116.5 W -- 54 — —— 5.60Mx SIG — IV 272 — 1916 08 03 14 22 38 41.5 N 116.5 W — 54 — —— 5.80Mx SIG —— Felt 56 — 1916 08 04 041252 41.5 N 117.0 W 54 —- — 5.00Mx SIG — Felt 54 — 1916 10 11 05 4909 41.5 N 116.5 W —- 54 —— — 5.00Mx SIG — Felt 56 — 1917 03 28 111600 41.6 N 117.8 W — 54 —- — 4.70UanON — IV 315 — 1917 04 11 18 59 55 40.0 N 118.0 W — 54 —— — 5.10Mx SIG — III 272 — 1925 08 21 111357 38.0 N 118.3 W — 54 — — 4.80Mx SIG -- V 56 — 1928 03 26 162607 38.3 N 117.5 W — 54 — —— 4.70Mx SIG — Felt 54 — 1928 04 17 103915 39.50 N 119.83 W —- 324 — — 4.50Mx SIG — IV 1 —- 1929 09 10 2001 41.2 N 116.8 W — 54 — — 4.60Mx SIG -— IV 54 —- 1930 04 09 215647 39.25 N 120.“) W — 324 — — 4.30Mx SIG —- VI 3 49 1930 04 12 12 5640 39.25 N 119.17 W -— 324 — — 4.50Mx SIG — VI 3 30 1932 12 21 061005 38.75 N 118.0 W — 258 — — 7.20M, GR — X 38 795 1932 12 22 074930 38.75 N 118.0 W — 315 —- — 4.50UanIG — Felt 315 — 1932 12 22 103415 38.75 N 118.0 W —— 315 —— — 4.90Mx SIG — Felt 315 — 1932 12 23 2006 38.75 N 118.0 W —- 315 — — 4.50UanIG — — — — 1932 12 24 124049 38.8 N 118.0 W —— 54 —— — 5.00Mx SIG — Felt 54 — 1932 12 25 035445 38.8 N 118.0 W — 54 — — 5.50Mx SIG — Felt 356 — 1932 12 25 18 36 35 38.8 N 118.0 W — 54 — — 4.50Mx SIG —- Felt 54 — 1932 12 26 0503 38.75 N 118.0 W — 315 — —— 5.30Mx SIG — Felt 356 — 1932 12 28 0307 55 38.8 N 118.0 W — 54 —- — 4.60Mx SIG — Felt 54 — EARTHQUAKES IN NEVADA NEVADA— Continued 285 [See table 1 for hypocenter and iniensity references and tab1e 2 for definitions of magnitude source codes. @, felt area is less than 1,000 km2. Leader (--) indicates information is not available} 07191" Hypocenter Magnitude Intensity Date time (UTO) Latitude Longltudo Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo Da h m 3 (°) (°) (km) mh Ms (1.000 101.2) 1932 12 29 062028 38.8 N 118.0 W — 54 — 5.20Mx SIG Felt 54 1932 12 29 0638 03 38.8 N 118.0 W — 54 -— — 5.00Mx SIG — Felt 54 — 1932 12 29 064508 38.8 N 118.0 W — 54 — — 5.00Mx SIG -— Felt 54 1932 12 30 04 17 52 38.8 N. 118.0 W -— 54 — —— 4.60Mx SIG -—- Felt 54 — 1932 12 30 160310 38.8 N 118.0 W — 54 — —- 4.60Mx SIG — Felt 54 — 1932 12 31 17 30 38.6 N 117.9 W — 54 — -— 4.60Mx SIG — — -—- — 1933 01 02 154408 38.8 N 118.0 W — 54 -— — 4-50Mx SIG — -— — — 1933 01 02 170644 38.8 N 118.0 W — 54 —— — 4.70Mx SIG — -- — — 1933 01 04 010115 38.8 N 118.0 W — 315 — — 5.10Mx SIG — Felt 54 — 1933 01 05 0650 20 38.75 N 118.00 W — 258 -— —- 5.70M, GR — Felt 356 — 1933 01 06 130556 39.0 N 117.8 W — 54 -— — 5.10Mx SIG — —— -- — 1933 01 06 13 33 39.0 N 118.0 W —- 54 — — 4.50Mx SIG -— — — -— 1933 01 11 17 29 38 38.9 N 117.8 W — 54 — ——- 5.20Mx SIG — — — — 1933 01 17 010208 38.8 N 118.0 W —- 315 -— — 4.80Mx SIG — -— — — 1933 01 29 135111 38.5 N 118.0 W — 54 — —— 5.00Mx SIG — — —— — 1933 02 13 220845 38.7 N 117.9 W — 265 — 5-50Mx SIG — IV 6 — 1933 03 12 204420 38.8 N 117.6 W — 54 — —— 5.00Mx SIG — IV 54 — 1933 04 07 001756 38.0 N 118.0 W — 54 — -— 4.50Mx SIG — —- —— — 1933 04 30 161650 39.8 N 118.1 W — 315 — — 4.50Mx SIG — —- — — 1933 05 09 094625 38.5 N 117.9 W — 54 — — 5.10Mx SIG — III 54 — 1933 06 04 14 08 22 38.50 N 118.16 W 016 324 -- — 5.20Mx SIG —- V 6 — 1933 06 11 08 34 31 38.8 N 117.5 W —- 315 —— — 5.20Mx SIG — IV 54 —- 1933 06 25 2045 27.0 39.08 N 119.33 W — 324 — — 6.10M; GR — V11 6 175 1933 07 17 205714 39.2 N 118.15 W -- 315 — —-— 4.60Mx SIG — — — —— 1933 07 21 02 55 38.45 N 118.16 W — 324 — 4.70Mx SIG — IV 6 -— 1933 07 21 0307 38.42 N 118.16 W — 324 — — 4.70Mx SIG — Felt 324 —- 1933 10 27 10 58 54 38.9 N 117.6 W — 6 —- — 5.50Mx SIG —— V 6 — 1934 01 30 1923 29 38.3 N 118.4 W — 38 -- — 5.50M; CPR —- V11 54 —- 1934 01 30 201631 38.28 N 118.36 W — 324 — 6.50M; CPR — VIII 7 205& 1934 01 30 2034 38.3 N 118.4 W - 315 — — 4.50Mx ION — Pelt 7 — 1934 01 30 210423 38.3 N 118.4 W — 54 — — 4.90Mx SIG — IV 7 — 1934 01 30 23 39 38 38.3 N 118.4 W — 324 -— 5.40Mx SIG — Felt 7 —- 1934 01 31 002422 38.3 N 118.4 W -— 54 —- ——- 5.00Mx SIG — Felt 266 —— 1934 01 31 03 54 49 38.3 N 118.4 W —— 54 —- 5.00Mx SIG — Felt 7 — 1934 01 31 142639 38.3 N 118.4 W — 54 — — 4.60Mx SIG — Felt 266 — 1934 02 01 110054 38.3 N 118.4 W — 54 — —— 5.00Mx SIG — IV 7 -— 1934 02 01 1118 51 38.50 N 118.25 W — 324 — — 5.20Mx SIG — V 7 — 1934 02 01 114554 38.3 N 118.4 W — 54 — -— 5.40Mx SIG — V 7 — 1934 02 01 121023 38.3 N 118.4 W — 54 — — 4.50Mx SIG -— — — — 1934 02 01 13 2045 38.3 N 118.4 W — 54 -— — 4.50M; SIG — — — — 1934 02 01 18 3444 38.3 N 118.4 W — 54 — — 4.50Mx SIG — — —- — 1934 02 03 16 31 38.3 N 118.4 W —- 54 -- — 4.50ML PAS — -— — — 1934 02 09 0920 34 38.3 N 118.4 W — 54 --— -— 5.50ML PAS — IV 7 — 1934 02 10 131346 38.3 N 118.4 W — 54 — — 4.50Mx SIG —- -- — — 1934 02 12 220054 38.3 N 118.4 W —- 54 — —— 4.70Mx SIG — —— — — 1934 02 16 015453 38.3 N 118.4 W -— 54 — -— 4.80Mx SIG — — — —- 1934 02 20 05 36 59 38.3 N 118.4 W — 54 —— 4.80Mx SIG — — — — 1934 03 13 162019 38.0 N 118.0 W — 7 — — 4.70Mx ION — V 315 —- 286 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NEVADA— Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 kmz. Leader (--) indicates information is not. available Origin Hypocenter Magnitude Intensity Date time (UTG) Letltude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m 8 (°) (°) (km) mb Ms M (1,000 kmz) 1934 03 19 1040 57 38.35 N 117.88 W — 54 —— —- 4.50Mx ION — IV 7 —— 1934 03 28 0937 37.3 N 116.6 W — 54 -— —— 4.50Mx SIG — — —— — 1934 03 30 1626 37.67 N 115.33 W 016 292 — -— 4.90Mx ION — — -— —- 1934 03 31 001148 38.1 N 116.3 W — 54 —- -— 4.50Mx SIG —- —- — —— 1934 04 02 0805 38.0 N 118.0 W — 324 — — 4.50ML PAS — — -— 1934 04 15 1209 38.0 N 115.0 W -— 54 —— —— 5.00Mf.WOO — — — 1934 04 21 23 22 39.0 N 117.0 W — 54 — — 4.50ML BRK — —- — — 1934 04 22 1124 38.0 N 118.0 W — 54 -— — 4.60Mx SIG — — — — 1934 12 04 0617 46 38.4 N 118.5 W — 54 —- -- 4.50Mx SIG — — — — 1935 01 21 0008 49 38.5 N 117.9 W — 54 — — 4.60Mx SIG -— —- — — 1936 01 14 052911 39.5 N 117.5 W -— 54 -— — 4.60Mx SIG — IV 54 — 1936 01 30 18 32 38.0 N 118.0 W — 324 — -— 4.50ML BRK — — — —- 1936 02 27 0040 41.0 N 119.0 W — 54 — — 4.50ML BRK — — — — 1936 03 26 22 43 40 39.1 N 117.9 W — 54 -— — 4.50Mx SIG — IV 54 — 1936 07 02 1629 39.2 N 117.5 W —- 324 — — 5.00Mfa WOO --— Felt 324 — 1936 09 07 1148 36.0 N 114.8 W — 54 —- — 4.50UanIG — IV 54 — 1936 09 21 07 31 40.25 N 117.38 W — 315 — — 4.50ML PAS — IV 54 — 1936 09 22 10 39 07 40.43 N 117.28 W — 315 -— — 4.70Mx SIG — — — —- 1937 02 19 090910 38.3 N 118.3 W — 10 ——- — 5.00ML BRK — V 10 29 1937 02 19 2306 38.0 N 118.0 W — 10 — -— 4.50ML BRK — IV 259 — 1937 04 25 0427 48 39.0 N 117.0 W — 10 — — 4.50ML BRK — V 10 37 1937 05 25 053520 41.5 N 119.8 W — 54 —-— — 4.60Mx ION — -— — — 1937 06 18 0907 26 41.25 N 120.0 W — 324 — — 5.25M3 GR — V 10 75 1937 08 19 070515 38.1 N 118.2 W — 54 — -— 4.60Mx SIG — V 10 ~- 1938 07 28 003830 37.6 N 115.8 W 016 266 — — 4.50ML PAS —— —— — -— 1938 07 31 10 3707 38.3 N 115.8 W -— 266 -- —— 4.50ML PAS — — —— — 1938 11 01 135320 39.0 N 116.0 W — 54 —- 4.50ML PAS — —— -— — 1939 01 11 2200 39.0 N 119.2 W — 324 — —— 5.50M“ W00 —- V1 12 24 1939 04 28 2159 39.0 N 117.0 W — 324 — — 4.50ML BRK — — -— — 1939 05 04 2044 46.8 35.967N 114.817W —- 292 — —— 5.00ML PAS -— VI 12 18 1939 05 11 1804 38.58 N 117.83 W —— 324 — — 5.50ML BRK — VI 12 115 1939 05 11 20 59 30 38.58 N 117.83 W —— 266 — — 4.70Mx SIG — Felt 259 1939 05 13 02 4906 38.58 N 117.83 W — 266 — — 4.80Mx SIG —-— — — 1939 05 17 181848 38.58 N 117.83 W —— 266 -- — 4.50Mx SIG — — — 1939 06 21 1128 30 38.6 N 117.8 W — 12 — — 4.50ML BRK —- — —— — 1940 03 10 18 01 54.0 37.0 N 115.0 W 016 292 — — 5.00M“ WOO —— IV 54 — 1940 03 11 000630 37.0 N 115.0 W 016 292 — — 4.50ML PAS — Felt 54 — 1940 04 07 08 42 37.0 N 115.0 W 016 292 — —— 4.50ML PAS — IV 259 —— 1940 07 08 100445 38.58 N 117.83 W — 13 — — 4.50ML BRK — IV 259 —— 1941 07 18 03 53 42 40.0 N 119.0 W —— 324 —— —— 5.00ML BRK -— Felt 14 -— 1941 08 29 130953.0 41.5 N 118.5 W — 258 — — 5.50M; GR — Felt 54 — 1942 07 11 164156 38.5 N 117.1 W — 266 — — 5.00ML BRK — IV 15 — 1942 07 11 1645 38.5 N 117.1 W —— 15 — — 4.50Ukn SIG — IV 15 —— 1942 08 18 215524 38.6 N 118.5 W — 16 — — 5.00ML BRK — VI 15 8 1942 12 03 094442 39.7 N 119.3 W — 324 —— — 5.50ML BRK — VI 15 57 1943 08 09 05 3004 38.2 N 118.2 W — l6 — —— 5.50ML BRK -— VI 16 92 1945 09 18 22 39 40.6 N 116.5 W — 54 — —— 5.10ML PAS —— IV 54 — 1946 01 15 22 3156 40.50 N 117.25 W -—- 54 — — 5.10Ukn SIG — — — — 1946 03 17 144553 38.3 N 117.9 W —— 324 —- -— 5.00ML BRK —— V 19 31 1946 04 27 021824 38.5 N 118.0 W — 54 —- — 4.70ML PAS — —— — — 1948 03 28 18 26 20 39.0 N 119.9 W — 21 -— — 4.60ML BRK — III 54 — 1948 11 02 16 4808 35.98 N 114.78 W — 259 — —- -- — VI 21 @ EARTHQUAKES IN NEVADA NEVADA— Continued 287 [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @. felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Rot Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1949 01 02 22 03 54 38.7 N 119.0 W — 22 —-— — 4.50ML BRK — IV 259 — 1949 07 18 153105 39.7 N 119.8 W — 324 — — 4.50M]. BRK — — — —— 1950 10 17 0354 33 39.60 N 116.69 W — 324 — — 4.50M; BRK — — — — 1950 10 23 081246 39.5 N 117.5 W —— 324 —- — 4.50ML BRK —— — — — 1951 01 22 151453 39.08 N 119.95 W — 324 — — 4.80ML BRK — V 24 —— 1951 06 16 055256 37.08 N 117.08 W 016 292 — —- 4.50ML PAS —- — — — 1952 05 09 153132 39.42 N 119.78 W — 324 — —- 5.10ML BRK —— VI 25 8 1952 05 24 041515.0 36.1 N 114.7 W‘ 016 292 — -- 4.90M], PAS — VI 25 — 1952 11 13 005516 38.5 N 118.5 W — 324 — — 4.80ML BRK — — — — 1952 11 18 040408 39.8 N 117.7 W — 324 — — 4.60ML BRK — — — — 1953 08 09 220002 37.5 N 114.5 W — 54 — —- 4.50ML REN — — — — 1953 09 26 03 3429 39.53 N 119.98 W — 324 — -- 5.30ML BRK — V1 26 41 1954 07 02 104313 38.17 N 116.37 W -— 324 —— — 4.90ML BRK — 111 27 —- 1954 07 06 ll 13 20 39.42 N 118.53 W - 324 —- —— 6.80ML BRK 6.20ELL IX 27 347 1954 07 06 11 1804 39.42 N 118.53 W — 324 — — 5.50M]. BRK — Felt 27 — 1954 07 06 112655 39.42 N 118.53 W —- 324 —— —— 4.80ML BRK — Felt 27 —- 1954 07 06 114100 39.42 N 118.53 W — 324 -- — 4.50ML BRK —- Felt 27 ~— 1954 07 06 114900 39.42 N 118.53 W — 324 — — 5.70ML BRK — Felt 27 — 1954 07 06 125359 39.42 N 118.53 W — 324 — — 4.50ML BRK —- Felt 27 —- 1954 07 06 131511 39.42 N 118.53 W — 324 — — 5.20ML BRK -— — — — 1954 07 06 13 36 01 39.42 N 118.53 W —— 324 —— —— 4.50ML BRK — Felt 27 — 1954 07 06 145515 39.42 N 118.53 W — 324 — — 4.50ML BRK — — — — 1954 07 06 220741 39.3 N 118.5 W —— 324 -— — 6.00ML BRK 6.228AW VII 259 -— 1954 07 07 061108 39.42 N 118.53 W — 324 — —- 4.60ML BRK — — — — 1954 07 08 0213 55 39.42 N 118.53 W —- 324 -— — 4.80M], BRK —— IV 27 — 1954 07 08 040819 39.42 N 118.53 W — 324 —-— — 4.50ML BRK - —— -— — 1954 07 08 125510 39.42 N 118.53 W — 324 -— — 4.70ML BRK —-— V 27 — 1954 07 08 193157 39.42 N 118.53 W — 324 — —- 5.30ML BRK — V 27 — 1954 07 09 085003 39.42 N 118.53 W — 324 — — 4.90ML BRK — IV 27 — 1954 07 10 012220 39.42 N 118.53 W — 324 —- — 4.60ML BRK — — — — 1954 07 11 070400 39.42 N 118.53 W — 324 — — 4.60ML BRK — -— -— — 1954 07 11 095812 39.42 N 118.53 W — 324 —— — 4.60M], BRK — — —- — 1954 07 12 101706 39.42 N 118.53 W — 324 —— — 4.50ML BRK -- —— — — 1954 07 12 160525 39.42 N 118.53 W — 324 — ——- 4.60ML BRK — IV 27 — 1954 07 20 001138 38.2 N 116.4 W —— 324 -—- — 5.00ML BRK — — — -— 1954 07 30 020010 39.42 N 118.53 W — 324 — — 5.10ML BRK — Felt 54 —— 1954 07 31 172414 39.42 N 118.53 W -— 324 — — 4.50ML BRK — — — — 1954 08 02 1018 53 39.42 N 118.53 W — 324 —— —- 5.40ML BRK -—— V 27 -— 1954 08 03 212454 39.42 N 118.53 W —— 324 — — 4.70ML BRK — Felt 54 — 1954 08 05 050308 39.42 N 118.53 W — 324 — — 4.70ML BRK —- Felt 54 ~— 1954 08 24 05 51 32 39.58 N 118.45 W —— 324 — — 6.80ML BRK 655$AW 1X 27 490 1954 08 24 05 5746 39.58 N 118.45 W —— 324 — — 5.20ML BRK — Felt 54 — 1954 08 25 021713 39.58 N 118.45 W — 324 — — 4.80M], BRK — — -— — 1954 08 25 2221 10 39.58 N 118.45 W — 324 — — 4.70ML BRK — -— — — 1954 08 26 125615 39.58 N 118.45 W — 324 — — 4.60ML BRK — — —- — 1954 08 29 034106 39.58 N 118.45 W — 324 — —- 4.70ML BRK — — — — 1954 08 29 035805 39.58 N 118.45 W — 324 — —— 4.80ML BRK — —- — — 1954 08 31 22 20 32 39.58 N 118.45 W —- 324 — —— 5.80ML BRK 5.80ELL VII 27 -— 1954 09 01 051846 39.58 N 118.45 W — 324 — —- 5.50M; BRK — Felt 27 — 1954 09 09 092105 39.58 N 118.45 W —— 324 -—- — 4.90M]. BRK — Felt 54 —— 1954 12 16 110711 39.283N 118.117W 015 358 -— — 7.20M], BRK 7.25H'H'I‘ X 27 61X) 1954 12 16 111134 39.8 N 118.1 W 040 358 -— — 7.10ML BRK 69OSAW X 27 — 1954 12 16 11 50 36 39.28 N 118.12 W —— 324 —— — 5.00M], BRK — — — —- 288 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NEVADA— Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 km2. Leader (--) indicates information is not. available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m 3 (°) (°) (km) mb Ms M (1.000 me) 1954 12 16 1157 30 39.28 N 118.12 W —— 324 -—- — 5.00ML BRK — — — — 1954 12 16 131503 39.28 N 118.12 W — 324 — — 5.00ML BRK — — — ~— 1954 12 16 141657 39.28 N 118.12 W — 324 —— — 5.80M], BRK — —— — — 1954 12 16 142410 39.28 N 118.12 W —- 324 — — 5.30ML BRK — IV 27 — 1954 12 16 150942 39.28 N 118.12 W — 324 —— -— 5.10M; BRK — — — — 1954 12 16 214843 39.28 N 118.12 W — 324 — — 4.50ML BRK — — — — 1954 12 17 101526 39.28 N 118.12 W —- 324 — — 4.50ML BRK —- -— — — 1954 12 17 10 33 29 39.28 N 118.12 W — 324 — —- 4.70ML BRK -—- — — — 1954 12 17 20 2706 39.28 N 118.12 W — 324 —— — 5.00ML BRK — — — -— 1954 12 18 0145 36 39.28 N 118.12 W — 324 —— — 4.70ML BRK — — — — 1954 12 20 17 36 47 39.28 N 118.12 W — 324 —— — 5.00M; BRK — Felt 27 — 1955 01 01 121354 39.0 N 118.0 W — 54 — —-— 5.10ML BRK — — — — 1955 01 05 08 2040 39. N 118. W — 54 — —— — —- V 54 — 1955 01 09 091050 39.0 N 118.0 W — 28 — — 5.00ML BRK -- — — — 1955 01 11 102140 39.0 N 118.0 W -—— 54 — — 4.70ML BRK — -—- ——- — 1955 01 19 021010 39.35 N 118.25 W — 324 —— —- 4.60ML BRK —— IV 28 — 1955 01 25 232646 39.0 N 118.0 W —- 54 — — 4.70ML BRK — — — — 1955 02 11 1612 32 39.47 N 118.10 W — 324 — — 4.70ML BRK —- —— — — 1955 02 19 23 5007 39.3 N 117.8 W — 324 — — 4.80ML BRK — — — — 1955 03 08 200517 39.20 N 118.55 W —- 324 — — 4.50ML BRK - —- -— — 1955 03 11 142316 39.3 N 118.1 W —- 324 — — 4.50M; BRK — — — — 1955 03 13 084104 39.57 N 118.05 W -— 324 — — 4.60ML BRK — — — — 1955 03 14 18 23 47 39.42 N 118.25 W —-— 324 -—- — 4.70ML BRK — — — — 1955 05 08 10 38 31 38.933N 118.117W — 324 —- —- 4.50ML BRK — — — —- 1955 05 30 2128 26 39.42 N 118.00 W — 324 — — 4.50ML BRK — —- — — 1955 06 08 122211 38.88 N 118.17 W — 324 — — 4.50ML BRK — —— — —— 1955 06 19 192000 38.97 N 118.25 W — 324 —- —- 5.20ML BRK —- — — — 1955 06 19 192516 39.0 N 118.5 W --— 324 — — 5.00ML BRK — —— -— — 1955 08 08 1035 35 38.33 N 118.67 W — 324 — —— 5.20ML BRK -- V 28 23 1955 09 29 05 40 51 39.22 N 118.20 W — 324 — — 4.50ML BRK —— — — —— 1955 11 02 061517 39.50 N 118.05 W — 324 — — 4.60ML BRK -- —-— -— ~— 1955 11 21 20 25 33 39.42 N 118.08 W — 324 — — 5.50ML BRK — — — — 1955 12 22 12 0507 38.98 N 118.70 W — 324 —— — 4.80M; BRK -— —— —— — 1955 12 22 120654 38.98 N 118.70 W — 324 —— — 4.60M], BRK -— — — —— 1955 12 31 13 5104 39.00 N 118.03 W — 324 —— —— 4.50ML BRK -— — — —— 1956 03 08 072620 39.03 N 118.07 W — 324 — — 4.60ML BRK — V 29 — 1956 07 06 03 3135 38.45 N 118.62 W — 324 — — 4.90M; BRK —- IV 29 — 1956 07 26 095317 39.55 N 118.45 W — 324 — — 5.10ML BRK ~— V 29 — 1956 ll 16 08 2610 41.03 N 116.45 W —- 324 —— —- 4.70ML BRK — — —— -—- 1956 12 31 17 37 45 38.25 N 118.93 W — 324 — -— 5.00ML BRK — VI 29 15 1956 12 31 17 3924 38.28 N 118.97 W — 324 —— — 5.10ML BRK — VI 29 15 1957 10 17 101409 39.28 N 118.43 W — 324 — — 4.60ML BRK — IV 30 —- 1958 01 04 17 2734 38.9 N 115.5 W — 324 —- —— 4.50ML BRK — — — —— 1958 04 19 090102 36.0 N 114.8 W — 54 — — — — VI 31 1959 03 23 071020 39.60 N 118.02 W — 324 — -— 6.30ML BRK —— VI 32 170 1959 05 21 17 5140 39.47 N 118.12 W —— 324 — —— 4.80ML BRK — — —— — 1959 06 23 14 3500 39.08 N 118.82 W —- 324 — — 6.10ML BRK — VI 32 105 1959 06 23 150434 39.1 N 118.8 W —- 324 — — 5.50ML BRK —- V 32 — 1960 01 26 041736 38.0 N 116.5 W — 33 — —-— 4.90ML BRK — — — — 1961 07 04 045600 40.90 N 118.40 W — 324 — — 5.40ML BRK — V 34 26 1961 07 04 110911 40.13 N 118.60 W — 324 5.00ML BRK IV 34 — 196108 04 1656091 39.2 N 117.4 W 012 324 4.50ML BRK EARTHQUAKES IN NEVADA NEVADA— Continued 289 [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 km2. Leader (--) indicates information is not availableJ Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Me D: h m 3 (°) (°) (km) ml, Ms M (1,000 km?) 1962 04 25 0848582 38.5 N 118.1 W 025 35 — — 4.60ML BRK — V 35 ~— 1962 07 20 0902100 39.5 N 118.2 W 033 266 — —— 4.70ML BRK — V 35 35 1962 09 07 2319128 41.3 N 116.7 W 033 266 — -— 4.60ML PAS -— — — — 1962 12 15 063459.8 40.7 N. 117.5 W — 266 — -— 4.90M; BRK —— — —— — 1963 03 25 0928430 36.0 N 114.8 W 019 266 4.3 -— 4.90ML PAS — VI 36 45 1964 03 22 1630552 38.8 N 118.7 W 016 266 4.5 — 5.50ML BRK — V 37 28 1964 10 23 13 57 10.6 38.5 N 118.4 W 026 266 5.0 — 5.30ML BRK — V 37 —— 1964 10 30 19 03 12.3 37.7 N 118.0 W 020 266 4.4 — 4.50ML BRK — VI 37 — 1965 04 13 13 14 22.1 38.9 N 117.7 W 033 266 4.6 — 4.60ML BRK — — — — 1966 01 28 18 0009.1 41.6 N 118.2 W 020 266 4.4 — 4.80ML BRK — III 81 — 1966 04 02 1248 38.8 38.4 N 118.2 W 009 266 4.0 — 4.80ML BRK — VI 81 —- 1966 08 16 1802329 37.46 N 114.15 W 007 298 5.6 — 5.60ML UU 5.31DOS V 81 66 1966 08 16 1950095 37.4 N 114.2 W 033 266 4.6 — 4.50ML PAS — — — — 1966 08 17 2307 58.9 37.3 N 114.1 W 033 266 4.9 — 5.50ML BRK — Felt 81 — 1966 08 18 06 15 01.3 37.3 N 114.2 W 034 266 4.2 — 4.50ML PAS —- —— — — 1966 08 18 0915 37.5 37.3 N 114.2 W 033 266 4.6 — 5.00ML PAS — IV 81 — 1966 08 18 17 35 06.4 37.4 N 114.2 W 033 266 5.2 — 5.00M]. PAS — IV 259 — 1966 08 19 1051379 37.438N 114.191W 007 298 4.2 — 4.70ML UU —- — — -- 1966 08 22 08 27 30.2 37.3 N 114.2 W 033 266 4.3 — 4.60ML BRK — — - — 1966 09 04 112318.1 37.4 N 114.2 W 033 266 4.2 — 4.80ML BRK — —— — — 1966 09 22 18 56 41.0 37.3 N 114.2 W 033 266 4.5 — 5.30ML PAS — Felt 81 —— 1966 09 22 18 57 36.5 37.4 N 114.2 W 033 74 5.3 — 5.50M; PAS — V 81 — 1966 09 22 19 59 39.8 37.3 N 114.2 W 033 266 4.4 — 4.50ML PAS — — — — 1966 09 23 11 56 09.4 37.3 N 114.1 W 033 266 4.5 —- 4.50ML PAS — — — -— 1966 10 02 15 3941.2 37.3 N 114.2 W 033 266 4.5 — 4.50ML BRK — — -— — 1966 10 22 17 16 26.4 40.6 N 116.3 W 032 266 4.5 — 5.10ML BRK — V 81 -- 1966 10 25 16 39 32.9 37.3 N 114.2 W 033 266 4.4 — 4.90ML BRK -—- — — — 1966 10 26 15 17 38.6 37.3 N 114.2 W 033 266 4.3 — 5.10ML BRK — — — — 1967 02 16 15 05 54.3 37.42 N 114.18 W 033 266 4.8 —- 4.80ML BRK — — —— — 1967 05 07 18 01 35.7 37.040N 115.012W 015 74 4.7 — 5.13ML PAS — IV 40 — 1968 01 30 15 2005.6 41.0 N 117.4 W 018 74 4.5 — -— — V 41 9 1968 02 06 0041380 38.02 N 118.35 W — 324 4.6 —- 4.90ML BRK — V 41 21 1968 02 06 0348108 38.00 N 118.37 W — 324 4.4 -— 4.50ML BRK — Felt 41 — 1968 05 22 13 21 55.7 38.6 N 116.2 W 013 74 5.1 — 4.90ML BRK — Felt 41 — 1968 05 29 114107.1 39.07 N 118.05 W 003 324 4.9 — 4.90ML BRK —- — — — 1968 07 06 140240.0 41.1 N 117.4 W — 324 5.1 — 5.50ML BRK — V 41 25 1970 03 28 093844 38.95 N 116.40 W — 324 4.5 — 4.50ML BRK — — —— -— 1971 12 08 1718 56.0 37.615N 115.288W 008 292 4.8 — 4.70ML PAS — V 44 34 1972 12 09 024445.7 38.676N 115.639W 010 74 4.4 — 4.60ML BRK — — —— — 1973 03 02 11 28 42.3 41.831N 118.546W 005 74 4.2 — 4.60ML BRK — — —— ~- 1973 03 03 03 0003.3 41.810N 118.457W 005 74 4.7 — 4.60ML BRK -— — — — 1978 02 14 0435 24.0 39.63 N 117.18 W 005 240 4.4 — 4.80ML BRK — IV 240 — 1978 03 05 2246 18.2 38.94 N 118.03 W 005 240 4.0 — 4.60M], BRK -— V 240 —— 1978 05 23 05 47 55.4 40.868N 117.257W 011 74 4.1 — 4.60ML BRK — V 240 — 1979 12 31 08 27 52.5 38.460N 118.428W 008 401 4.2 -— 4.80ML BRK — V 262 — 1980 04 08 00 13 41.8 39.499N 119.178W 005 74 — — 4.70ML BRK — V 300 21 1980 09 04 13 3909.4 38.083N 118.570W 001 401 4.0 — 4.60ML BRK -— V 300 21 1980 09 04 21 03 34.1 38.113N 118.560W 010 401 4.9 — 4.90ML BRK —- III 300 — 1980 09 06 0727 52.3 38.078N 118.572W 007 401 4.1 — 4.60M], BRK — Felt 300 — 1980 09 07 0130428 38.083N 118.575W 007 401 4.4 — 5.10ML BRK —— Felt 300 — 1980 09 07 0436 38.2 38.083N 118.600W 010 401 4.9 5.0 5.50ML BRK — V 300 56 1980 09 07 0648106 38.093N 118.570W 005 401 — — 4.70ML BRK — Felt 300 — 1980 09 07 0648 30.6 38.093N 118.570W 005 401 4.7 4.4 5.30ML BRK — Felt 300 — 290 SEISMICITY OF THE UNITED STATES, 1568-1989 (REVISED) NEVADA— Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. (I), felt area is less than 1,000 km2. Leader (..) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MMI Ref Felt area Yr Mo De h m 3 (°) (°) (km) m, Ms M (1,000 km?) 1980 09 08 0426198 38.045N 118.600W 008 401 -— — 4.60ML BRK — IV 300 —- 1980 09 16 042441.1 38.047N 118.567W 007 401 4.2 — 4.70ML BRK — IV 300 — 1980 11 11 10 19 03.0 38.040N 118.590W 005 401 — -— 4.70ML BRK —- III 300 — 1980 12 28 22 58 09.8 38.157N 118.360W 005 401 4.6 — 5.00ML BRK — IV 300 10 1981 01 28 2008 50.7 38.202N 118.335W 015 401 4.5 — 4.60ML BRK -— IV 325 — 1981 04 28 2254499 38.058N 118.587W 010 401 4.2 — 4.60ML BRK — IV 325 — 1982 01 28 22 51 02.1 38.54 N 118.07 W 005 350 — — 4.60ML BRK — V 350 — 1982 04 15 21 52 09.1 38.052N 118.568W 007 401 4.5 — 5.10ML BRK — IV 350 45 1982 09 24 07 4024.6 37.870N 118.140W 017 401 5.0 4.6 5.50ML BRK — V 350 50 1982 12 28 190624.8 38.028N 118.418W 008 401 4.7 —- 4.90ML BRK — IV 350 -- 1984 02 16 11 14 58.8 39.858N 117.556W 002 475 4.8 — 5.20ML BRK — IV 370 — 1984 02 17 1203 55.8 38.854N 119.630W 012 475 4.1 — 4.60Mp REN — V 370 — 1986 11 01 19 23 38.3 38.712N 119.540W 017 562 — — 4.60ML BRK 4.37BRK V 562 15 1987 07 28 18 55 11.5 38.385N 118.168W 013 74 4.3 —— 4.60ML BRK — IV 577 —— 1987 07 29 03 52 32.1 38.378N 118.137W 014 74 4.4 — 4.50ML BRK — Felt 74 — 1988 09 19 02 56 31.7 38.461N 118.342W 009 74 4.5 — 5.30ML BRK — V 578 24 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1860. Mar. 15. Near Carson City, Ormsby County, Nev. Rockslides were reported between Pyr- amid Lake and Carson City. Merchandise was shaken from shelves at Carson City. Also reported felt in parts of California and Utah. (Ref. 358, 368.) 1868. May 30, 05 10 UTC (May 29). Near Vir- ginia City, Storey County, Nev. Brick buildings were cracked and bricks were shaken down at Vir— ginia City. Plaster fell in almost all brick buildings. (Ref. 54, 368.) 1869. Dec. 27, 01 55 UTC (Dec. 26). Near Vir- ginia City, Storey County, Nev. Masonry walls were damaged severely in Virginia City and at Washoe City, 5 km west. Plaster fell at Mokelume Hill, and a stone chimney fell at Spring Gulch. Minor damage also was reported in Calaveras County in California. (Ref. 368.) 1869. Dec. 27. Western Nevada aftershock. Considerable damage occurred at Carson City, Day- ton, Genoa, Steamboat, and Virginia City. Damage also was reported at Downieville and Oroville, Calif. It is difficult to separate the damage caused by this shock from that of the main shock at 01 55 UTC, Dec. 27. (Ref. 38, 368.) 1872. Mar. 23. Austin, southern Lander County, Nev. Plaster fell in the Austin Courthouse. The earthquake was described as a Violent shock. (Ref. 38, 54.) 1875. Apr. 2 (Apr. 1). Near Eureka, Nev. One building was seriously damaged at Eureka. (Ref. 54.) 1887. June 3. Near Carson City, Ormsby County, Nev. The ground was reported to have been uplifted about 10 m north of Carson City (at Dead- man’s Ranch). Large fissures opened and spouted water and sand near Cradlebaugh’s Bridge. The water level at Shaw’s Hot Springs, near Carson City, dropped several centimeters a few weeks before the earthquake, and the water dried up after the shock. At Carson City, chimneys were reported to be in “bad condition” and brick and stone walls were cracked. At Genoa, houses were shifted on their foundations and bricks were thrown down. (Ref. 54, 368.) 1894. Nov. 18. Near Virginia City, Storey County, Nev. Some walls were damaged, plaster cracked, and windows broke at Virginia City. Many aftershocks occurred. (Ref. 54, 56.) 1896. Jan. 27. Near Carson City, Ormsby County, Nev. A large crack formed in the side of a government building in Carson City; plaster fell in the County Building. (Ref. 54, 56.) 1901. July 26. Near Elko, Nev. A brick school- house and other buildings were damaged at Elko. A series of heavy shocks was reported. (Ref. 54, 56.) 1903. Fall. Near Wonder, Churchill County, Nev. Interviews with long-time residents of the area establishes (With a fair degree of certainty) the date EARTHQUAKES IN NEVADA as the fall of 1903 for this uncataloged earthquake in Churchill County. Evidence also suggests that as much as 19 km of surface faulting may have occurred on the Gold King fault as result of this shock. At the Stephens dwelling, about 8 km north- east of Wonder, an adobe house was damaged (prob- ably by this earthquake) and its roof required repair. (Ref. 54, 328.) 1910. Nov. 7. Southeast of Goldfield, in Nye County, Nev. A few dishes and windows were bro- ken at Goldfield. (Ref. 54, 56.) 1910. Nov. 21., Esmeralda County, Nev. The watchman’s car was thrown from the track at Tonopah Junction; windows were broken. A succes- sion of shocks occurred at the same time as a loud, rumbling noise. (Ref. 54, 56.) 1914. Feb. 18. Near Reno, Washoe County, Nev. Plaster cracked and a few bricks were thrown from chimneys at Reno and nearby Virginia City. Windows were broken at Sparks, and the shock was severe at Verdi. Also felt in California. (Ref. 38, 54, 56.) 1914. Apr. 24. Near Reno, Washoe County, Nev. This earthquake probably originated northeast of Reno. Many chimneys were toppled throughout Reno, including four that fell on buildings at the Uni- versity of Nevada. The shock was described as “severe” about 25 km east of Reno, at Hazen. Also felt in California. Magnitude 5.5 Ms ELL, 5.0 MLa DMG. (Ref. 54, 56.) 1915. Oct. 3 (Oct. 2). Pleasant Valley, Nev. This earthquake occurred along a fault on the east- ern side of Pleasant Valley, which lies about 64 km southeast of Winnemucca, in the north-central part of Nevada. The epicentral region was almost unin- habited, and, therefore, property damage was less than might have been expected. Damage was con- fined mainly to an area within 80 km of the fault in Humboldt, Lander, and Pershing Counties, including the towns of Battle Mountain, Kennedy, Lovelock, Winnemucca, and several ranches in Pleasant Valley. Four main scarps—the China Mountain, Tobin, Pearce, and Sou Hills—developed in a right-stepping en echelon pattern. The combined length of the scarps was 59 km, the average vertical displacement 2 m, and the maximum displacement (which occurred on the Pearce scarp) 5.8 m. Several northwest-strik- ing segments of the scarps had a right-lateral compo- nent of displacement, generally less than 1 m. At Kennedy, two adobe houses were destroyed, mine tunnels collapsed, and concrete mine founda- tions were cracked. At Winnemucca, adobe buildings generally were damaged, and several multistory brick buildings lost their coping and parts of upper 291 walls; many chimneys were demolished above the rooflines. In addition, water tanks were thrown down at Battle Mountain, Kodiak, Lovelock, and Parran. Damage occurred on several ranches at the southern end of Pleasant Valley: an adobe house was shaken down; a masonry chicken house and a hog pen were destroyed; and houses were displaced from their foundations. One of the most striking effects of this earthquake was the large increase (and decrease) in the flow of springs and streams throughout northern Nevada. Cracks formed in unconsolidated materials for con- siderable distances. Felt from the State of Oregon to southern California and from the Pacific coast to beyond Salt Lake City, Utah. (see fig. 40). Two fore- shocks and many aftershocks occurred. Magnitude 7.3 mb ABE, 7.75 Mg GR, 7.6 Ms CFR. (Ref. 56, 258, 327, 589.) ' 1930. Apr. 9. Near Lake Tahoe, Douglas County, Nev. At the southeast end of Lake Tahoe, chimneys were damaged. Plaster was cracked at Tahoe. Also felt in California. (Ref. 3, 324.) 1930. Apr. 12. Fernley, Lyon County, Nev. Chimneys and dishes broke at Fernley; plaster cracked at Fallon, southeast of Fernley, and objects fell from shelves. Also felt in California. (Ref. 3, 324.) 1932. Dec. 21 (Dec. 20). Cedar Mountain, Nev. This major earthquake originated in an uninhabited desert region of western Nevada, near Cedar Moun- tain, and therefore caused minimal property loss. ’IVvo cabins, one of stone and the other of adobe, were destroyed, and ore-treating plants and mines were damaged. The main shock was strong at Fallon, Mina, Luning, Tonopah, and at many other Nevada towns. Many chimneys were downed in Mineral County, at Luning and Mina. In addition, walls fell and cracks formed in the ground at Luning. Extensive and complicated faulting occurred over an area 63 km long and 6 to 14.5 km wide in the valley between Gabbs Valley Range and Pilot Peak on the west and Paradise Range and Cedar Moun- tains on the east, northeast of Mina. In this area, 60 en echelon rifts as much as 6 km in length and 122 m in width were found. The rifts consisted of zones of fissures that commonly revealed vertical displace— ment, and in several places showed horizontal dis- placement. Boulders were shaken from cliffs and hillsides in many places; large landslides occurred; and the flow of ground water either increased or decreased in some springs and wells. Felt from the Rocky Mountains to the Pacific Ocean and from San Diego to southern Oregon. (see fig. 41). One foreshock and many aftershocks occurred. Magnitude 7.3 Ms CFR. (Ref. 38, 258, 356.) 292 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 124° 122° 120° 118° 116° 114° 112° 110° 46° ‘ 1' S‘ A MONT. I . L .2 V, " I \. __ .— \. _ _ _ ~~--" " I. I “I ~ 4"fo '\ IDAHO 4"“ I 440 \ \ I \ I I \ I \ I I WYO. VPocatello I \ I I 420 . ‘\ J ’ l’ I . ._ ..... _ _ ___________ _ ............. I ._._._. 1-.-. _'\’I .' I I I . I I I I . I ......... — , I . I. I I Wirnemucca I O i * i Salt Lake City I 40° I V)I(II- I? I I I . I I UTAH l Reno ‘ NEVADA I I \ VI I / .\I \/ I / CALIFORNIA \'\ I / 33° '\~ V I \ / I / \ | Fresno \A\ I 7—— . \ ' .\ / . _ ‘ I 36° “ IV \, Las Vegas ~1\ ./ / 1“ I \ \ / / X I ARIZONA \ ‘ .— I / -\I- EXPLANATION \- * Epicenter \ X Intensity 10 .\') 34° 4/ Los Angeles I o 150 KILOMETERS I L\\\ I Phoenix I———'———I' I FIGURE 40.— Isoseismal map for the Pleasant Valley, Nevada, earthquake of October 3, 1915. Isoseismals are based on intensity estimates form data listed in references 272 and 327 of table 1. EARTHQUAKES IN NEVADA 293 124° 122° 120° 118° 116° 114° 112o 110° 44° T4 - F I 1' Boise 1 1 . OREGON l '. WYOMING i IDAHO I ! i ' i § i ‘ 42° . . | ‘-.-._._._. __|§Ia_rnath Falls ! m - ''''' ' — .— — .—..—._L._ _. . ._._._\._._._._._. _. ' / ! 3 ! l / ! . L. ' _ ' __ ______ ! ! I Salt Lake City Elk.o I I we .I ! I ! | \ i \ \ I UTAH ! \ San Francisco 36° ’9 '7 / 0/ /o 0o ARIZONA <6 '7 1 34° Los Angeles Ph ' Q B oemx \ \ San Diego \ ....--— ~- 32° - \ _ _ WEED ., Sr EXPLANATION ME*’CF"‘~TE\3__ o 100 KLOWTEH * Epicenter ' \ _ ~ ________ X Intensity 10 /\ FIGURE 41.— Isoseismal map for the Cedar Mountain, Nevada, earthquake of December 21, 1932. Isoseismals are based on intensity estimates from data listed in references 5, 259, and 356 of table 1. 294 1933. June 25. Western Nevada. Many chim- neys were downed southeast of Reno, at Virginia City, and in Lyon County, at Wabuska and Yerington. A church was damaged severely at Virginia City, and a wall separated from the rest of courthouse building at Yerington. Water spurted from cracks that formed in the ground at Yerington. Minor damage occurred in many nearby towns. Also felt in California. (Ref. 6, 324.) 1934. Jan. 30, 19 23 UTC. Excelsior Moun- tains, Nev. A strong foreshock of the damaging earthquake at 20 16 UTC downed chimneys and broke windows and dishes southeast of Hawthorne, at Mina (Mineral County). Also felt in California. (Ref. 38, 54, 335.) 1934. Jan. 30, 20 16 UTC. Excelsior Moun- tains, Nev. This strong earthquake centered in an uninhabited area having few structures, and damage therefore was slight. At Mina (Mineral County), a few chimneys were broken and a small section of a brick wall fell. At Marietta, two walls of an adobe cabin collapsed; at Candelaria, a stone cabin was partly destroyed; and at the Silver Dike mine in the eastern part of the Excelsior Mountains, a rockslide destroyed a pipeline and a pumphouse. Fissures formed in alluvium; landslides occurred; and changes in the flow of springs were observed. Fissures in alluvium, mainly related to slumping rather than to primary faulting, were found in three places: above Pepper Spring, south of Garfield Flat; on the northwest side of Teel's Marsh; and at the Endowment mine, about 5 km north of Marietta. The average trend of the fissures was N. 10° W., and the length about 30.5 m. One graben was 6 m wide and, on its west side, was a slump hole about 0.6 m deep. At the Endowment mine, two fissures—one 6 m long and the second 30.5 m long—formed in the bed of the wash about 122 m beyond the end of the fault. An earthquake scarp about 1.4 km long developed on one of the faults 5 km north of Marietta, on the southern side of the Excelsior Mountains. This scarp had a maximum height of 12.7 cm, and the fissures were as wide as 7.6 cm. It appears that this was the surface expression of the movement that caused the earthquake. Several landslides occurred, and boulders rolled down slopes throughout the Excelsior Mountains. The shock also was felt throughout central Nevada and central California as far as the west coast. Mag— nitude 6.3 Ms GR. (Ref. 7, 324, 335.) 1939. Jan. 11. Near Gardnerville, Douglas County, western Nevada. Damage was slight at Gardnerville, where cracks formed in plaster, and at SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Hudson, where dishes broke. Also felt in California. (Ref. 12, 324.) 1939. May 4. Near Boulder City, Clark County, southern Nevada. At Boulder City, about 15 km southeast of Las Vegas, plaster cracked and fell. In the Hoover Dam area, large rocks rolled onto roadways and made some of them impassable. A heavy dust cloud noted south of Hoover Dam proba- bly resulted from landslides. Plaster was cracked in several houses in Mohave City and Oatman, Ariz. Also felt in California. (Ref. 12, 292, 343.) 1939. May 11. Northeast of Mina in Nye County, Nev. At Rawhide, vases were overturned and trees and bushes were shaken strongly. Plaster was cracked at Yerington. Felt north to Lovelock, south to Beatty, east to Eureka, and west to Yosemite National Park, Calif. Magnitude 5.5 Ms GR. (Ref. 12, 38, 324.) 1942. Aug. 18. Near Mount Montgomery, Min- eral County, Nev. Dishes fell at Mount Montgomery, in southern Mineral County, and lath on veneer board panels cracked loose. Also felt in California. (Ref. 15, 16.) 1942. Dec. 3. Near Reno, Washoe County, Nev. At Reno, plaster was cracked in several build- ings, and a heavy safe was shifted several centime- ters. Rocks fell onto the highway in Truckee Canyon, east of Sparks. Also felt in California. (Ref. 15, 259, 324.) 1943. Aug. 9 (Aug. 8). Excelsior Mountains, Nev. Plaster and walls were cracked at Dyer (Esmer- alda County) and at Fallon (Churchill County), 80 km northeast. Also felt in California. Several after- shocks were recorded. (Ref. 16.) 1948. Nov. 2. Hoover Dam, Nev., area. South- east of Las Vegas, rocks rolled onto the highway leading to Hoover Dam and fell from canyon walls upstream and downstream from the dam. Dust clouds from landslides also were observed. At nearby Boulder City, some minor cracking of plaster occurred. (Ref. 21, 259.) 1952. May 9. Near Carson City, Ormsby County, Nev. New cracks formed in four State build- ings at Carson City. Plaster and knickknacks fell at Virginia City, about 20 km north. Also felt in Califor- nia. (Ref. 25, 324.) 1952. May 24 (May 23). Near Boulder City, Clark County, Nev. Slight damage occurred south- east of Las Vegas, at Boulder City (cracks in plaster and foundations) and at Whitney (cracks in walls). (Ref. 25, 292.) 1953. Sept. 26 (Sept. 25). Near Reno, Washoe County, Nev. 'IVvo chimneys toppled at Reno, and plaster cracked in buildings throughout the EARTHQUAKES IN NEVADA northwest part of town. Much damage occurred to plaster at the University of Nevada in the Mackay School of Mines Building. Slight damage also was reported in California. (Ref. 26, 324.) 1954. July 6, 11 13 UTC. Fallon-Stillwater area, Churchill County, Nev. In Fallon, the town nearest the epicenter, several old and poorly built concrete-block structures and unreinforced brick structures were damaged severely, and many brick chimneys fell. Several people were injured at the Naval Auxiliary Air Station, about 8 km southeast of Fallon, when the shock knocked heavy steel lock- ers onto them. ’IVVO areas outside Fallon that also sustained damage were the Lone Tree district to the south and the Stillwater district to the east. Ground motion and surface breakage were heavier in Stillwater. Canals and drainage systems of the Newlands Rec- lamation Project near Fallon were damaged exten- sively. Many box-type culverts were damaged or collapsed. Failure of the Coleman Diversion Dam cut off irrigation water to most of the project. Paved highways in the Fallon-Stillwater areas set- tled, cracked, and buckled in several places. One of the largest ground movements occurred in the Lone Tree area. One road dropped about 90 cm for a dis- tance of several hundred meters and lurched about 90 cm horizontally toward a canal. In the Lone Tree and Stillwater areas, canal banks settled as much as 0.9 m, and bottoms of canals were raised as much as 0.6 m. The main zone of ground fractures was observed on the east edge of Rainbow Mountain in the Still- water Range, about 24 km southeast of Fallon. This earthquake and the large shock on Aug. 24 (see description below) resulted in surface evidence of faulting for about 40 km. This break is referred to as the Rainbow Mountain fault. Vertical displace- ment was evident along about two-thirds of the fault; the west side uplifted everywhere with respect to the east side. Scarps as high as 30 cm or more formed, and small grabens developed in places. Horizontal displacement was not found. The quake was also felt in California, Idaho, Oregon, and Utah (see fig. 42). Magnitude 6.6 Ms CFR, 6.3 Ms ELL. (Ref. 27, 324, 575.) 1954. July 6, 22 07 UTC. Fallon-Stillwater area, Churchill County, Nev., aftershock. US. Highway 50 settled to the extent that it had to be filled and resurfaced about 8 km southeast of Salt Wells. Many observed a large cloud of dust rising in that area, probably a result of landslides. Little addi- tional damage to structures was reported from 295 Fallon. Also felt in California. Magnitude 6.4 Ms CFR. (Ref. 27, 38, 259, 324.) 1954. Aug. 24 (Aug. 23). Fallon-Stillwater area, Churchill County, Nev. Ground surface movement was increased several centimeters at the break of the main fault of July 6, 1954 (11 13 UTC), along the east edge of Rainbow Mountain. Displace— ment owing to this shock was much more continu- ous than that of July 6, probably as a result of the larger relative movement (76 cm compared to 30 cm on July 6). The ground breakage extended north for about 18 km to the region southeast of Carson Sink. Only vertical movement was observed, however. Except for the Lovelock area, where this earthquake considerably damaged the Rogers Dam, damage to buildings, roads, and irrigation facilities occurred in the same general areas as for the shock on July 6. Also felt in California, Idaho, Oregon, and Utah (see fig. 43). Magnitude 6.8 Ms CFR, 6.9 Ms ELL. (Ref. 27 , 324.) 1954. Aug. 31. Dixie Valley, Churchill County, Nev. A series of violent, earthquakes generated addi- tional landslides in the Stillwater Range northeast of Stillwater. In West Lee Canyon, everything in one cabin was overturned, including the stove. Magni- tude 6.3 Ms CFR. (Ref. 27, 324.) 1954. Dec. 16, 11 07 UTC. Dixie Valley—Fair- view Peak area, Churchill County, Nev. The pop- ulation was sparse in the epicentral region of this earthquake, and few man-made structures existed. Damage to structures, therefore, was minor despite the geologic and seismographic evidence of a major earthquake. The earthquake was accompanied by offsets along many faults in four main zones of a north-trending belt 96 km long by 32 km wide. Minor geologic effects included changes in flow of springs and wells, formation of craters and water fountains, landslips and landslides, mudflows, and rockfalls. The fault displacements mainly were along normal faults in the following areas: (1) west of Dixie Valley, (2) southeast of Dixie Valley, (3) east of Fairview Peak, and (4) east of Stingaree Valley. The maximum strike-slip component was 3.6 m of right-lateral movement at Fairview Peak, and the maximum ver— tical-slip component was 3.6 m at Bell Flat. Heavy furniture was displaced at Frenchman Sta- tion, about 11 km west of major surface faulting, but damage to buildings was negligible. Differential set- tlement of about 10 cm that occurred under a wood- frame store resulted in minor cracking of the build- ing. Damage at Fallon, about 48 km west of the near- est major surface break, was limited to a few toppled chimneys. Hundreds of aftershocks occurred. The 296 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 116° 114° 112° , I | ! g IDAHO | I I . UTAH 124° 122° 120° 1 18° OREGON O 42 ______________________________ “9' Redding 0 40° NEVADA 38° CALIFORNIA 0 Fresno 36° \_/ EXPLANATION Q—‘_—190 KILOMETER * Epicenter |X Intensity 9 ARIZONA FIGURE 42.— Isoseismal map for the Fallon—Stillwater, Nevada, earthquake of July 6, 1954. Isoseismals are based on intensity estimates from data listed in references 27, 259, and 575 of table 1. main earthquake also was felt in Arizona, California, Idaho, Oregon, and Utah (see fig. 44). Magnitude 7.1 Ms ABE, 6.9 mb ABE, 7.1 MS CFR. (Ref. 27, 358, 505.) 1954. Dec. 16, 11 11 UTC. Dixie Valley— Fairview Peak area, Churchill County, Nev., aftershock. See above description of the main earth- quake at 11 07 UTC on Dec. 16. Because damage from the two earthquakes cannot be separated, they are treated as one event. Magnitude 6.8 MS CFR. (Ref. 27, 358.) 1956. Dec. 31, 17 37 UTC. Near Hawthorne, Mineral County, Nev. 'IVvo moderate earthquakes (the second one at 17 39 UTC) cracked US. High- way 95, south of Hawthorne, and split Highway 50, near Frenchman Station. Also felt in California. (Ref. 29, 324.) 1956. Dec. 31, 17 39 UTC. Near Hawthorne, Mineral County, Nev. See above description of the earthquake at 17 37 UTC, Dec. 31, 1956. (Ref. 29, 324.) 1958. Apr. 19. Boulder City area, Clark County, Nev. This minor earthquake cracked plas- ter, broke dishes, and overturned books and pictures at Boulder City. (Ref. 31, 54.) EARTHQUAKES IN NEVADA 297 124° 122° 120° 118° 116° 114° 112° F '\ MONT. i '\ '__ ...... .1 \\ ."\ | .’ s -5 ‘4‘ 4’ \ F‘\.r\' m— 4 .6 1 44° 5., I Z l OREGON j 1 I i . IDAHO l 9 1 B ‘. Medford ‘. 0 ° 1 42 - _,____ _ _|V_‘ _ _ _ ..... T" i l i 1.. (2,“ Salt Lake CIW Heading 0 Elko 0 40° 38° v SanFrancis \ \ ' 1 °° CALIFORNIA ‘\. ' 7 III . o \. T“ \. i ._..— __ “o \. 1v 1; o 0 Fresno \~\ ! ‘3“ \/\_/\ "-1" a \ O 7 \/—\ ,\ L, 36 1 h‘, . 7“ Las Vegas‘ '\. 1 \.\ '\ ARlZ. EXPLANATION \\ .5 ‘z ' I 0 100 KILOMETERS * Epicenter 1' IX Intensfly 9 FIGURE 43.— Isoseismal map for the Fallon-Stillwater, Nevada, earthquake of August 24, 1954. Isoseismals are based on intensity esti- mates from data listed in references 27, 259, and 575 of table 1. 1959. Mar. 23 (Mar. 22). Dixie Valley area, Churchill County, Nev. Plaster cracked at Carson City and Frenchman Station, and the top of a new addition to the State printing office was damaged. A field investigation in Dixie Valley revealed no sign of fresh cracking on the Fairview Peak fault Where it crosses US. Highway 50, the Dixie Valley Road northward to Horse Creek Road, nor the Horse Creek Road; fresh cracking was not noted on the extension of the Gold King fault at the south edge of Dixie Val- ley. Also felt in California. (Ref. 32, 259, 324.) 1959. June 23. Near Schurz, northeast Min- eral County, Nev. This was the main shock of a series of four moderate earthquakes. Chimneys 298 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Fault scarp in the Fairview Peak area, Nevada, formed by the December 16, 1954, earthquake. (Photograph from the National Geophysical Data Center, NOAA.) twisted and cracked at Schurz, and a garage attached to a frame house separated 5 cm from the house. A new roadbed, about 8 km west of Schurz, was cracked; plaster cracked and knickknacks fell at Genoa. Some residents reported minor rockslides in the adjacent mountains. Also felt in California. (Ref. 32, 324.) 1963. Mar. 25. Near Boulder City, Clark County, Nev. Considerable minor damage—mainly cracked and fallen plaster and broken dishes—— occurred at Boulder City. Several rockslides were observed in the Boulder City area. Power was inter- rupted for 20 minutes at Hoover powerplant and dam, and one generator possibly was misaligned. Also felt in Arizona, California, and Utah. (Ref. 36, 259, 266.) 1964. Oct. 30. Dyer area, Esmeralda County, Nev. A series of earthquakes occurred along the Cali- fornia-Nevada border, all of which were preceded by a roaring noise. The strongest shock (at 19 03 UTC) cracked a concrete-block foundation and a window at Dyer. (Ref. 37, 259, 266.) 1966. Apr. 2. South of Luning, Mineral County, Nev. This earthquake separated two parts of an old building at Luning. Small objects shifted and fell. (Ref. 81, 266.) EARTHQUAKES IN NEVADA 299 124° 122° 120° 118° 116° 114° 112° 110° "' ' “s MONT. _ ' \. ,_,_._. — - I \ l' j “W (K, | J ! '5. ”vi \- Corvallis {I 1. r‘! | 44° 3. 1 I OREGON VJ . IDAHO WYOMING 42° ' —-—.— ._ . Reading 0 40° NEVADA 38° San Francisco CALIFORNIA Fresno 0 36° \ o ‘\ '1 ’4 \_ \. , x 1. o \J o 1. o , \.‘ «7 -‘ ARIZONA ’L N. 34° .4; Q N I . p \LL‘o‘sAngeIes : ’1' EXPLANATION a E g. * Epicenter \ ‘1 r. uNIJgiffl‘F-s-m t ......-—---"‘ MEXICO 'L Yuma “\- o 100 KILDNETERS ‘ N" I—s___l X Intensity 10 32° FIGURE 44.— Isoseismal map for the Dixie Valley—Fairview Peak, Nevada, earthquake of December 16, 1954. Isoseismals are based on intensity estimates from data listed in references 27 and 259 of table 1. ‘ \ \ . . . x‘ ._ . V ; ‘ . ‘ a, 4 ~ w u < . ,. i y . . “5&3, . «Marin rmww‘fifi‘ . , , ,.u..»f.x NEW HAMPSHIRE 72° 71° 45° 44° 43° 73" EXPLANATION Magnitude/Intensity O 3.2-4.4/Vl Q 4.5-4.9 H O 5.0-5.4 5.5-5.9 CANADA V UNITED STATES 0 Berlin. MAINE $0 $ VERMONT g) g (9 fi o g] Laconia O o O 0 Concord A Portsmouth 0 Keene rrJ MASSACHUSETTS 0 50 KILOMETERS L_l_._l F Earthquakes in New Hampshire with magnitudes 2 4.5 or intensity 2 VI. 301 302 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NEW HAMPSHIRE [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only. Leader (--) indicates information is not available] Origin Hypocenter Magnitude * Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1.000 km2) 1732 09 16 16 00 45.5 N 73.6 ‘ W — 76 —— -- —- —- IX 76 — 1810 11 10 02 15 43.0 N 70.8 W — 78 -— —— — ——- VI 76 218: 1925 10 09 13 55 43.7 N 71.1 W — 76 —— —— 4.00Mf. SC —- VI 38 18 1940 12 20 07 27 26.2 43.872N 71.370W 010 349 — —- 5.50M,l ST 5.258T VII 13 3568: 1940 12 24 13 43 45.0 43.908N 71.283W 008 349 — — 5.50M,I ST . 5.60ESM VII 13 — 1964 06 26 1104490 43.405N 71.680W 001 349 — — 3.20M“ DG -— VI 37 12 1973 06 15 01 09 05.1 45.307N 71.119W 012 349 4.8 --— 5.00Mn STR 4.48HRN VI 46 182& 1977 12 25 15 35 54.0 43.185N 71.658W 012 349 ~—— -— 3.20Mn WES -— VI 39 3 1982 01 19 00 14 42.7 43.51 N 71.62 W 007 350 4.5 -— 4.50Mn BLA — VI 350 127 1988 10 20 13 09 50.1 44.539N 71.158W 005 74 —— -— 3.90Mn GS — VI 578 17 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1732. Sept. 16. St. Lawrence River valley, Canada. An earthquake that was violent in Mont- real, Canada, also damaged houses at Piscataqua, N.H., in eastern Rockingham County. In Montreal, the shock damaged 300 houses, cracked walls, knocked down chimneys, and caused one death. Felt slightly at Boston, Mass, and Annapolis, Md. (Ref. 38, 59, 76.) 1810. Nov. 10 (Nov. 9). Between Portsmouth and Hampton, Rockingham County, N.H. The earthquake broke windows at Portsmouth, and caused earth noises like a heavy explosion. Felt from Concord, N.H., east to the coast and from Portland, Me., south to Charlestown, Mass. (Ref. 38, 76, 78.) 1925. Oct. 9. Eastern New Hampshire, near Lake Winnipesaukee. One chimney fell from an old colonial house at Sandwich, N.H., in Carroll County north of Laconia. Chimneys also were knocked down at Cornish, Me., about 60 km east of Sandwich, N.H. This severe shock broke windows in Carroll County at Ossipee, Sandwich, and Tuftonboro, N.H., and cracked a concrete sidewalk at Meredith, north of Laconia. Items were knocked from shelves and resi- dents were frightened in many towns in the area. Felt to the north at Bethlehem (northern Grafton County), to the southwest at Keene (Cheshire County), and to the east at Portland, Me. (Cumber- land County). (Ref. 38, 76, 78, 218.) 1940. Dec. 20 and Dec. 24. Near Ossipee Lake, Carroll County, N.H. The first earthquake and one of about the same intensity on Dec. 24 are described together. Their epicenters lie in the same general region west of Whittier, N.H. Although the second shock was of less duration, it was somewhat more intense than the first. However, the first shock undoubtedly weakened structures, which resulted in more severe damage from the second earthquake. The town of Tamworth, on the edge of the Ossipee Mountains in central Carroll County, sustained the most damage. Old houses and chimneys in need of repair were most commonly damaged. Some chim- neys were thrown down, and 20 others were dam- aged. Also, reports indicate that well water remained muddy for several days and that many cracks formed in the crusty snow. Other minor damage included cracked walls, broken water pipes, fallen plaster, and broken furniture. At the Riverside Cemetery at Whittier, about 3 km south of Tamworth, five monuments were displaced. In the nearby towns of West Ossipee and Chocorua, many old chimneys in need of repair were damaged, and water in wells became muddy. At Wonalancet, 8 km northwest of Tamworth, the foundation of an old house (constructed of heavy timber) was damaged when it shifted about 30 cm. Heavy furniture, includ- ing a kitchen stove, moved several centimeters across the floor. Minor damage occurred at several towns in Maine, Massachusetts, New York, and Vermont (see fig. 45). Reports of the shock also were received from Con- necticut, New Jersey, Pennsylvania, and Rhode Island, as well as from Montreal and Quebec, Can- ada. Several small aftershocks occurred over the next several months. Magnitude 5.6 MS GR (both), 5.44 M JOH (Dec. 20), 5.62 M JOH (Dec 24). (Ref. 13, 38, 349, 506.) 1964. June 26. Near Warner, Merrimack County, N.H. Plaster fell at Meriden, and trees and bushes were shaken lightly. Slight damage also was reported at Bradford, Merrimack County, N.H., and at Springfield, Vt. (Ref. 37, 38, 349.) EARTHQUAKES IN NEW HAMPSHIRE 80° 78° 76° 74" 303 72° 70° 68° 46° s unnsgfijf‘l CANAD' u CANADA _/ UNITED STATE / 44° Fvedm‘fim" ‘uw 42° PENNSYLVANIA 40°- ' Hamom CONNECTICUT DELAWARE EXPLANATION * Epicenter n 100 KILOMETERS V“ Intensity 7 FXGURE 45.—— Isoseismal map for the New Hampshire earthquake of December 20, 1940. Isoseismals are based on intensity estimates from data listed in references 13 and 506 of table 1. 1973. June 15 (June 14). Quebec—New Hamp- shire border area. Cracks formed in the road sur- face in the area about Montpelier, Vt.; chimneys and grocery stock were damaged at Woburn, Quebec. The earthquake cracked plaster and broke windows in Quebec Province and in the States of Maine, Massachusetts, New Hampshire, New York, and Ver- mont. Also felt in Connecticut and Rhode Island. Magnitude 4.49 M JOH. (Ref. 46, 349.) 1977. Dec. 25. Near Concord, Merrimack County, N.H. The earthquake cracked plaster and windows in Concord. Felt over a small area of south- central New Hampshire. Magnitude 3.1 Mn PAL. (Ref. 39, 349.) 1982. Jan. 19 (Jan. 18). Near Laconia, Belknap County, N.H. Damage, mainly cracks in chimneys and walls, occurred in Drury and Westford, Mass; Ashland, Bristol, Danbury, Laconia, and North Stratford, N.H.; and several towns in northeast Massachusetts and central Vermont. Other damage, widely reported in the area, included cracked plaster and broken merchandise and knick- knacks. Also felt in Quebec, Canada and in the States of Connecticut, Maine, New York, and Rhode Island. Magnitude 4.7 MD WES. (Ref. 350.) 1988. Oct. 20. Near Berlin, Coos County, N.H. Minor damage at Berlin included cracked chimneys and house foundation, hairline cracks in interior walls, and displaced tombstones. At nearby Milan, interior walls sustained hairline cracks in plaster and drywall, and a house foundation was cracked. Felt over a small area of northwest Maine, northern New Hampshire, and northeast Vermont. (Ref. 74, 578.) ,5355 i J: 3:5.33 1,, 9 mm)“ w Visa v ix , l _ a _“ j , , . . r EL\\‘\\\ \‘ww ‘ ‘ 1 |‘\\\, , 1 ‘ 1}. ‘Q “.~ \{.‘ ‘1».[l ‘\ I ‘ ‘ _ ‘ , , V » . / ‘ , _ ‘ ‘ ‘ / ‘ _ ‘ , . ; x _ . _ . . _ \ , . ‘ , 1 . \ u, , , . ‘ , ‘ ‘ n , , x , , . , , n , 2 , ‘ 1 ‘ \ , w \ w / , ‘ . , » , ~ .. . , , , , ,, 1 , . ~ ‘ , m ‘ . , ‘ fl ‘ . y , \ , . ‘ . _ H ‘ /. ‘ ‘ / . by? a.“ J u 41° 40° 39° 76° NEW JERSEY 75° 74° 73° { EXPLANATION NEW YORK Magnitude/ Intensity CONN. o 2.4-4.4/Vl 5.0-5.4/VII o . /\ Sussex fl / \ A V o N k 0/ 8W8: M PENNSYLVANIA O {M Trenton £2; (3 co :2“ j / ’5 Philadelphia 3 % 5L7 Y” 2 av /_\ Q — % II Y. 34 V (K Atlantic City Y” LU a a: < B “3—1 < >~ A L/ SE a Cape May 2 0 50 KlLOMETERS / Earthquakes in New Jersey with magnitudes 2 4.5 or intensity 2 VI. 305 306 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NEW JERSEY [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. 8:. land area only; @, felt area is less than 1,000 km2. Leader (-~) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo D: h m 8 (°) (°) (km) mu Ms M (1,000 km?) 1783 ll 30 03 50 41.0 N 74.5 W — '76 — -- 5.30Mf. SET — VI 76 —- 1895 09 01 1109 40.75 N 74.5 W —-— 369 — — 4.10Mf. SC — VI 38 30 1927 06 01 12 20 40.3 N 74.0 W -- 38 — — -- — VII 38 20& 1957 03 23 19 02 31 40.6 N 74.8 W 010 77 ——- — 3.80Mfa SC — VI 30 7 1976 03 11 2107 20.4 40.96 N 74.37 W 004 49 —— — 2.40M“ PAL —- VI 49 @ 1976 04 13 15 3913.6 40.84 N 74.05 W 001 317 —— — 3.10Mn PAL — VI 49 @ [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1783. Nov. 30 (Nov. 29). West of New York City, N.Y. This earthquake was felt from New Hamp- shire to Pennsylvania. A foreshock at 02 00 UTC on Nov. 30 and an aftershock at 07 00 UTC were reported only in New York and in Philadelphia, Pa. (Ref. 76.) 1895. Sept. 1. Near High Bridge, Hunterdon County, N.J. This earthquake knocked articles from shelves and rocked buildings in several towns in New Jersey, Pennsylvania, and New York. At Asbury Park, N.J., plaster was knocked from walls. At Phila- delphia, Pa., windows were broken and crockery was overturned. Felt from Falls Church, Va., and Wash- ington, D.C., to Connecticut. Magnitude 4.3 Mfa SET. (Ref. 38, 272, 369.) 1927. June 1. Near Asbury Park, Monmouth County, N.J. Several chimneys were downed, bricks fell from chimneys, and articles fell from shelves in an area from Asbury Park north to Long Branch, in northeast Monmouth County. Also, part of a ceiling fell at Long Branch, and plaster fell from walls and ceilings at Fairhaven, northwest of Long Branch. Many accounts of broken crockery and fallen plaster were reported from Westchester County, NY. Three shocks were felt along the New Jersey coast from Sandy Hook to Toms River. (Ref. 38, 218.) 1957. Mar. 23. Long Valley area, Morris County, N.J. At Long Valley (about 55 km west of Newark), walls were cracked and plaster fell to the floor. Chimneys cracked and windows and dishes broke at Lebanon (about 18 km southwest of Long Valley), and one chimney cracked and a well curb broke in the Hamden area (5 km southwest of Leba- non). (Ref. 30, 38, 77.) 1976. Mar. 11. Pompton Lakes area, Passaic County, N.J. Slight damage occurred about 35 km northwest of Newark, at Pompton Lakes (cracks in ceiling, fallen plaster), at nearby Kinnelon (cracks in plaster and windows), and north of Jersey City, at Ridgefield (cracks in ceiling). Felt in Bergen, Morris, and Passaic Counties in northeast New Jer- sey. (Ref. 49.) 1976. Apr. 13. Near Ridgefield, Bergen County, N.J. An earthquake slightly larger in mag- nitude than that on Mar. 11, 1976, centered in the same general area. Residents in Ridgefield, about 13 km north of Jersey City, reported that plaster was knocked to the floor. The shock was felt widely in the area. (Ref. 49, 317.) 110° 108° NEW MEXICO 106° 104° 102° 36° 34° 32° 30° 7% UTAH COLORADO E A . v o F . Raton OKLA. armington O o 9 (5 Santa Fe o 0 Albuquerque 0 2: EW MEXICO O Clovis. E G” a: Socorro o E x > a: Las Cruces 0 U ITED STATES MEXICO \ EXPLANATION Magnitude/Intensity o 3.8-4.4/Vl O 4.5-4.9 O 5.0-5.4/vr 0 100 KILOMETERS O 5.5-5.9/vu Earthquakes in New Mexico with magnitudes 2 4.5 or intensity 2 VI. 307 308 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NEW MEXICO [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1.000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr MODE h m 3 (°) (°) (km) mb Ms M (1,000 kmz) 1855 04 20 05 34.0 N 107.0 W — 269 — —- — — VI 269 — 1869 04 18 13 34.0 N 107.0 'W -— 38 — — — — VII 38 — 1869 04 20 34.0 N 107.0 W — 270 — — — — VI 270 — 1878 06 14 36.5 N 104.9 W — 463 — — —- — VI 463 —- 1893 04 08 0320 34.5 N 106.8 W — 270 —— — — —— VI 255 — 1893 0907 34.5 N 106.8 W — 255 —— — — — V11 38 —— 1897 34.0 N 107.0 W —— 38 — —- —— — VI 38 — 1906 07 12 1215 34.0 N 107.0 W — 38 —-— — — —- VII 257 104 1906 07 12 13 05 34.0 N 107.0 W —— 270 — — —— — VI 270 -— 1906 07 16 1900 34.0 N 107.0 W — 38 — -— — -- VII 257 104 1906 11 15 1215 34.0 N 107.0 W — 38 — —— — - VII 257 205 1918 05 28 1130 35.5 N 106.0 W — 84 — -- — —— VII . 38 25 1931 02 05 0448 35.1 N 106.6 W — 4 — — — — VI 38 @ 1935 02 21 0125 34.5 N 106.8 W — 38 — — -— — VI 38 — 1935 12 16 18 34.7 N 106.8 W —— 270 -— — —— — VI 270 — 1935 12 18 05 33 18 34.7 N 106.8 W —— 38 -— -— — — VI 270 5 1935 12 20 10 30 34.7 N 106.8 W — 270 —— —- — VI 270 — 1938 09 17 172017 33.3 N 108.5 W --— 277 — — 4.90M“ TAG — VI 38 21 1938 09 20 05 3900 33.3 N 108.5 W — 277 — — 4.30M“ TAG — VI 259 —— 1938 09 29 23 34 57 33.3 N 108.5 W -- 277 — —— 4.80Mn TAG — VI 259 20 1938 11 01 082606 33.3 N 108.5 W —- 277 — —— 3.80M,l TAG — VI 11 — 1938 11 02 08 59 58 33.3 N 108.5 W —- 277 —— -— 4.30M“ TAG — VI 259 — 1938 11 27 0012 39 33.3 N 108.5 W — 277 —— — 4.60Mn TAG — V 11 —— 1939 01 20 1217 20 33.3 N 108.5 W —— 277 — —— 3.70Mn TAG — VI 259 — 1939 06 04 01 1910 33.3 N 108.5 W — 277 — — 4.60M“ TAG -— VI 259 — 1947 11 06 1650 35.2 N 106.3 W — 259 —— —- — — VI 259 @ 1960 07 23 1415 34.35 N 106.85 W — 261 —- — — — VI 33 8 1961 07 03 0706 34.10 N 106.95 W — 261 — -- -— — VI 34 — 1966 01 23 01 56 38.1 36.98 N 107.02 W 003 264 5.1 —— 5.10mb NUT 4.98HDP VII 81 27 1970 01 12 1121 15.1 35.89 N 103.40 W — 261 3.5 — 3.30M; NMI —— VI 43 10 1970 11 28 0740118 35.10 N 106.61 W — 261 4.5 — 3.80M; GS — VI 43 3 1971 01 04 07 39070 35.10 N 106.60 W — 261 4.7 -— 3.50ML NMI — VI 44 2 1973 12 24 022014.9 35.26 N 107.74 W 018 74 4.4 —— 4.10ML GS — VI 46 20 1976 01 05 0623 33.9 35.817N 108.212W 040 470 5.0 — 4.60ML GS — VI 49 115 1977 03 05 0300553 35.748N 108.222W 044 470 4.6 — 4.20ML GS — VI 39 51 1983 03 02 23 22 19.4 34.302N 106.892W 008 360 4.1 —-— 4.10ML GS — VI 360 4 1985 08 16 14 56 52.9 34.130N 106.832W 007 371 —- —— 4.10ML GS — VI 371 4 1989 ll 29 0654385 34.455N 106.891W 013 74 4.6 —— 4.70MB NMI —— V 579 28 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1855. Apr. 20 (Apr. 19). Socorro area, N. Mex. The earthquake almost destroyed two houses at Socorro, about 110 km south of Albuquerque. The earth trembled; houses shook; and horses were frightened. (Ref. 269.) 1869. Apr. 18. Socorro area, N. Mex. Socorro Springs (at the base of Socorro Mountain) changed flow and became muddy, and its flow was diminished for many weeks. Some houses were damaged consid- erably at Socorro, about 110 km south of Albuquer- que. Seven severe shocks occurred from Apr. 18-20. (Ref. 38, 270, 446.) 1869. Apr. 20. Socorro area, N. Mex. This severe aftershock cracked the walls of the church at EARTHQUAKES IN NEW MEXICO Socorro, about 110 km south of Albuquerque. Near Socorro, the hot springs spouted water “hotter than ever and of a reddish color.” (Ref. 27 0, 446.) 1878. June 14. Cimarron, Colfax County, N. Mex. Windowpanes were broken by an earthquake at Cimarron, about 55 km southwest of Baton. (Ref. 463.) 1887. May 3. Northern Sonora, Mexico. Chim- neys were thrown down in Albuquerque, N. Mex. See the Arizona chapter for a complete description of this damaging earthquake. (Ref. 38, 343, 471, 494, 497.) 1893. Apr. 8 (Apr. 7). Belen, Valencia County, N. Mex. This was the strongest of a series of shocks Apr. 6—8. It damaged almost all the houses in and around Belen and threw several entirely down. The earthquake was not felt farther south than Sabinal. The effects for these earthquakes were taken from two reports, one not indicating any damage and the other as described above. The assigned intensity is lower than the above damage would indicate. (Ref. 255, 270.) 1893. Sept. 7. Los Lunas, Valencia County, N. Mex. Five shocks threw down a score of old adobe buildings already weakened by previous earthquakes in Los Lunas. At Sabinal, a spring formed in a place that always had been dry and barren. The central area of the State was subjected to tremors for a period of three months, the most severe occurring on Sept. 7. (Ref. 38, 255.) 1897. Date unknown. Socorro area, N. Mex. This violent tremor overturned chairs and small objects at Socorro, about 110 km south of Albuquer- que. The motion was so strong that one person could not walk. (Ref. 38, 270.) 1906. July 12, 12 15 UTC. Socorro area, N. Mex. About 110 km south of Albuquerque at Socorro, an earthquake threw down several chimneys, knocked plaster from the walls of many adobe houses and the courthouse, and hurled shelf goods, book cases, and dishes to the floor. The entire business block, extending from the plaza along the north side of Manzanares Avenue, was damaged heavily. A two- story brick house, one of the buildings most severely damaged, was abandoned because its walls were cracked badly and thrown out of plumb. Nearby, one of the walls of another cottage was damaged so severely that the occupants moved outside to a tent. Many other residences sustained damage to walls and furniture. Many boulders rolled onto the branch railroad leading to Magdalena, west of Socorro, breaking one rail and many ties. Fissures formed in the ground near the Santa Fe depot in Socorro, and waves were seen on the ground surface. The earthquake shook 309 residents of Carthage, Kelly, Magdalena, San Anto- nio, San Marcia], and other towns as far nortl. as Albuquerque and as far south as Silver City (Grant County). Tremors were felt daily from July 2, 1906, well into 1907. (Ref. 38, 257, 270.) 1906. July 12, 13 05 UTC. Socorro area, N. Mex. This earthquake at Socorro, about 110 km south of Albuquerque, was described as almost as severe as the first tremor on July 12 (12 15 UTC). (Ref. 270.) 1906. July 16. Socorro area, N. Mex. Described as slightly stronger that the July 12 event, an earth- quake caused additional damage in the form of downed chimneys, cracked houses, and damaged brick gables at Socorro, about 110 km south of Albu- querque. Many residents left their houses and lived in tents. The Socorro Hotel, a brick structure, was abandoned because of severe damage. The brick post office had a bulging wall, and its southeast corner was “thrown out.” Three chimneys on the Socorro County Courthouse were destroyed, and two were downed at the high school. At San Marcia], the shock knocked down a few chimneys, cracked a few houses, and broke windows. At San Antonio, the earthquake caused plaster to fall, broke windows, and cracked most houses. This shock was reported felt at Raton, about 390 km northeast of Socorro, and Douglas, Ariz., 400 km southwest. (Ref. 38, 257, 270.) 1906. Nov. 15. Socorro area, N. Mex. This earthquake, which increased the property damage already sustained at Socorro, was described as the most severe shock of the year. Four rebuilt chimneys were shaken off the Socorro County Courthouse, and two others were cracked severely. Plaster fell at the courthouse, and a cornice on the northwest corner of the two-story adobe Masonic Temple was thrown onto its first floor. Several bricks fell from the front gable on one house. Plaster was shaken from walls in Santa Fe, about 200 km from the epicenter. Felt over most of New Mexico and in parts of Arizona and Texas. (Ref. 38, 257, 270, 272.) 1918. May 28. Near Cerrillos, Santa Fe County, N. Mex. Many chimneys and plastered ceil- ings fell at Cerrillos, about 35 km south of Santa Fe. A “heavy” break in the surface of the earth occurred at the edge of town. Glass was shaken from several windows. People in the street were thrown off their feet. Plaster was knocked down at Santa Fe, and adobe walls were cracked at Stanley, southwest of Cerrillos. (Ref. 38, 84, 270, 272.) 1931. Feb. 5. (Feb. 4). Albuquerque, Berna- lillo County, N. Mex. Bricks and adobe walls cracked at Albuquerque, chimneys cracked, and part of one chimney fell. Large rocks rolled into the 310 streets from sand hills about the city. Across the river and south of town, two adobe houses were dam- aged severely. (Ref. 4, 38, 270.) 1935. Feb. 21 (Feb. 20). Near Bernardo, Socorro County, N. Mex. Coping on a building cracked at Bernardo, and walls and plaster cracked. Adobe and concrete buildings sustained damage. (Ref. 8, 38.) . 1935. Dec. 16. Belen, Valencia Count , N. Mex. Plaster fell, small cracks formed in buildings, and dishes broke at Belen. This is one of a series of 81 earthquakes that were felt from Dec. 13, 1935, to Jan. 4, 1936. (Ref. 270.) 1935. Dec. 18 (Dec. 17). Belen, Valencia County, N. Mex. Plaster fell throughout the city of Belen, objects were shaken from shelves, and sev- eral brick and adobe buildings sustained cracks. (Ref. 38, 270.) 1935. Dec. 20. Belen, Valencia County, N. Mex. A large locomotive shook on the Santa Fe tracks at Belen, and switch engines were rocked hard enough to alarm engineers and firemen. (Ref. 270.) 1938. Sept. 17. Southwest New Mexico, near the Continental Divide. This shock was strongest in Graham County, Ariz., at Clifton and Duncan, and in the southern part of Catron County, N. Mex. At Duncan, Ariz., plaster and walls cracked and bottles fell from shelves. At a Forest Service ranger station near the head of the west fork of the Gila River in New Mexico, one chimney cracked, plaster fell, and trees and bushes were shaken strongly. This was the first of a series of earthquakes that occurred through July 1939. Magnitude 5.5 Ms GR. (Ref. 8, 38, 277, 343.) 1938. Sept. 20 (Sept. 19). Southwest New Mexico aftershock. An aftershock of the Sept. 17 earthquake cracked old adobe walls and knocked others down at Duncan, Ariz., in southeast Gra- ham County. The tremor disrupted telephone ser- vice for hours, displaced furnishings in houses, and overturned vases. The main shock also was felt in Graham County, Ariz., at Clifton, Morenci, and Safford; in northern Cochise County, at San Simon; and at several towns in New Mexico. Many small shocks were reported from Sept. 17—20. (Ref. 11, 259, 277, 343.) 1938. Sept. 29. Southwest New Mexico after- shock. This aftershock of the Sept. 17 earthquake was strongest at Clifton (Graham County), Ariz., where about a large amount of plaster fell from a ceiling in one house. Felt in Graham and Cochise Counties, Ariz., and at several towns in New Mexico. (Ref. 259, 277, 343.) SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 1938. Nov. 1. Southwest New Mexico after- shock. Another aflsershock of the Sept. 17 earth- quake cracked plaster and chimneys at Cliff (Grant County), N. Mex. Rocks fell in the mountains near Buckhorn, northwest of Cliff. Also felt in Arizona. (Ref. 11, 277, 343.) 1938. Nov. 2. Southwest New Mexico after- shock. Another aftershock of the Sept. 17 earth- quake cracked chimneys at White Creek Ranger Station near Cliff (Grant County). Also felt in Ari- zona. (Ref. 259, 277, 343.) 1939. Jan. 20. Southwest New Mexico after- shock. Walls were cracked in Grant County, at Gila, by an aftershock of the tremor on Sept. 17, 1938. (Ref. 259, 277.) 1939. June 4 (June 3). Southwest New Mex- ico aftershock. The last damaging aftershock of the Sept. 17, 1938, earthquake cracked plaster at Duncan, Ariz., in southeast Graham County. (Ref. 259, 27 7.) 1947. Nov. 6. San Antonito area, Bernalillo County, N. Mex. This local earthquake cracked a fireplace and plaster at Zamora Ranch and shook dishes from shelves at San Antonito. (Ref. 259.) 1960. July 23. Near Lajoya, Socorro County, N. Mex. A weak adobe wall toppled and some adobe buildings were cracked at Lajoya. Canned goods fell from shelves and people ran outdoors at nearby Ber- nardo. (Ref. 33, 261.) 1961. July 3. Socorro area, N. Mex. Plaster cracked in adobe buildings at Socorro, about 110 km south of Albuquerque. (Ref. 34, 261.) 1966. Jan. 23 (Jan. 22). Near Dulce, Rio Arriba County, N. Mex. This earthquake affected to some extent almost every house in Dulce and dam— aged chimneys throughout the area. Property dam- age was estimated at about $200,000. The earthquake was caused by normal faulting on a fault striking approximately north-northwest, that proba- bly had its maximum activity in Miocene time. Dis- tribution of aftershock epicenters suggests that the main shock triggered aftershock activity on adjacent faults. The aftershock activity continued in the area for a year. Property damage was most severe at the Dulce Bureau of Indian Affairs School and dormitory com- plex and the Dulce independent schools. Much plas- ter fell from ceilings in the dormitories, and several brick walls sustained vertical fractures that extended from ground to roof. Brick walls in the steam—heating plant were displaced from vertical alignment as much as 3 cm, and two boilers (each weighing 10 tons) were displaced about 0.6 cm at their bases. EARTHQUAKES IN NEW MEXICO Also, an 18-m-high smokestack buckled, and only guy wires prevented it from falling. Huge masses of shale and sandstone fell down the slopes from nearby Dulce Point. In addition, several small cracks formed in fill across the frozen roads in the Dulce area, but there was no evidence of ground displacement or fissuring. Also felt in southern Colo- rado. Magnitude 4.6 Ms NUT. (Ref. 38, 81, 263, 264, 533.) 1970. Jan. 12. Amistad area, Harding County, N. Mex. Part of a ceiling fell at Amistad, and some adobe bricks in a wall crumbled at the public school gymnasium. Plaster fell at nearby Nara Visa. Also felt at Texline, Tex. (Ref. 43, 261.) 1970. Nov. 28. Near Albuquerque, Bernalillo County, N. Mex. This minor earthquake cracked plaster, a garage floor, and a concrete-block wall and broke windows. One resident reported that the roof of a barn collapsed; another said a roof air condi- tioner fell through a skylight. (Ref. 43, 261, 364.) 1971. Jan. 4. Near Albuquerque, Bernalillo County, N. Mex. Considerable minor damage at Albuquerque included cracked windows and plaster in buildings and fallen merchandise in markets. An old adobe building sustained both interior and exte- rior cracks. Slight damage also occurred at nearby Alameda and Corrales. (Ref. 44, 261.) 1973. Dec. 24 (Dec. 23). Grants area, Cibola County, N. Mex. Plaster cracked and fell, cracks formed in an exterior wall, and paneling on walls pulled apart at Grants. Walls and chimneys were cracked at Laguna, about 50 km southeast of Grants. (Ref. 46, 74.) 311 1976. Jan. 5 (Jan. 4). Near Crownpoint, McK- inley County, N.Mex. Damage, which generally was minor, consisted mostly of cracks in plaster and dry- wall in several Colorado and New Mexico towns and at Leupp, Ariz. At Cahone, 0010., a chimney was cracked. Also felt in Utah. This earthquake and that on Mar. 5, 1977, are two of the largest ever observed in New Mexico out- side the Rio Grande rift and within the Colorado Plateau. They occurred in the southern part of the San Juan Basin (known as the Chaco slope), a region that historically has had a low level of seis- micity. (Ref. 49, 470.) 1977. Mar. 5 (Mar. 4). Near Crownpoint, McKinley County, N. Mex. Fences displaced slightly at Crownpoint, and existing cracks in walls widened considerably south of Crownpoint, at Pre- witt. Also felt in Arizona and Colorado. See descrip- tion above for the earthquake on Jan. 5, 1976. (Ref. 39, 470.) 1983. Mar. 2. Near Socorro, N. Mex. At San Acacia, plaster cracked in both exterior and interior walls of adobe buildings, dishes were broken, and stock was thrown from store shelves. The shock also was strong in Socorro County at Bosque, Lajoya, and Socorro. (Ref. 360.) 1985. Aug. 16. Near Socorro, N. Mex. At Socorro, about 110 km south of Albuquerque, cracks formed in sidewalks, plaster, windows, and the foun- dation of a brick building. Also, a few glassware items were broken. This earthquake was felt only at a few towns in the area. Magnitude 4.3 Mn TUL. (Ref. 371.) NEW YORK 80° 78° 76° 74° 72° EXPLANATION Magnitude/Intensity O 2.9-4.4/Vl O 4.5-4.9/Vl O 5.0-5.4/vu 46° 0 5.5-5.9 O 6.0-6.4 Massena A CANADA 1 v Q o U. s. o O O O E 5 440 A fl 9 3 [Ev ONTARIO O E < O I ? NEW YORK B Buf alo . LU Syracuse 0 2 Ch Albany 0 / MASS 42° 0 Elmira f CONN. 0 47 A PENNSYLVANIA fi 0‘3EA 1‘0 100 KILOMETERS Afi A1L 40° Earthquakes in New York with magnitudes 2 4.5 or intensity 2 VI. 313 314 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NEW YORK [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. &, land area only; @. felt area is less than 1,000 kmz. Leader (..) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTG) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr MoDa h m 8 (°) (°) (km) mb Ms M (1.000km2) 1737 12 19 0345 40.8 N 74.0 W — 76 — -—- -— — VII 76 — 1853 03 12 0730 43.7 N 75.5 W — 76 — — —— — VI 76 — 1855 02 07 0430 42.0 N 74.0 W — 76 — -— — VI 76 — 1857 10 23 2015 43.2 N 78.6 W — 76 — — 4.30Mfll SC — VI 76 65 1867 12 18 0800 44.7 N 75.2 . W — 126 — —- 4.30Mf. SC —- VI 126 65 1877 11 04 0656 44.5 N 74.0 W — 38 —- — 4.90Mf. SC — VII 38 200 1878 02 05 16 20 40.8 N 73.9 W — 141 — — — -— VI 463 -— 1884 08 10 1907 40.6 N 74.0 W — 76 — — 5.50Mf. SET —- V11 76 540& 1897 05 28 0316 44.5 N 73.5 W —- 126 — —— 4.70Mf. SC — VI 76 225 1914 02 10 18 31 44.98 N 76.92 W —- 76 — —— 5.20Mf. SC — V11 76 518 1916 02 03 0424 43.0 N 74.0 W — 126 — — 4.10Mf.I SC — VI 272 21 1928 03 18 15 20 44.5 N 74.3 W — 38 — — 4.10ML EPB — VI 38 31 1929 08 12 11 24 48.7 42.910N 78.402W 009 349 —- — 5.20Mn ST 4.69ST VIII 77 880 1931 04 20 1954306 43.471N 73.785W 005 349 -—- — 4.70M“ ST -— VII 4 70 1934 04 15 0258 13.0 44.7 N 73.8 W — 77 — —— 4.50ML EPB — VI 126 21 1935 11 01 0603 34.2 46.87 N 79.05 W 001 349 —— —— 6.20M; GR 5.59ST VII 77 2590 1944 09 05 0438 45.7 44.958N 74.723W 012 349 — —— 5.80Mn ST 5.52ST V111 17 1095 1944 09 05 08 5106.0 44.999N 74.652W 001 349 — — 4.50Mn BAS — — — — 1966 01 01 13 23 39.0 42.842N 78.249W 000 349 4.7 —— 4.60Mn STR 4.26HRN VI 81 26& 1967 06 13 1908 55.5 42.837N 78.234W 001 349 3.9 — 4.40Mn STR 4.071-IRN VI 40 6 1974 06 07 19 45 35.7 41.595N 73.951W 003 349 — — 2.90Mn DG 2.86ST VI 47 @ 1975 06 09 18 39 22.7 44.874N 73.651W 011 349 — — 3.50Mn ST 3.28ST VI 48 13 1983 02 26 19 59 35.4 41.552N 73.663W 007 360 — — 2.90Mn GS — VI 360 4 1983 10 07 10 18 46.1 43.938N 74.258W 013 360 5.1 —- 5.10ML PAL 4.88SOM VI 360 634 1985 10 19 1007403 40.983N 73.829W 006 371 3.6 -— 4.00ML PAL — VI 371 31 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1737. Dec. 19 (Dec. 18). New York City area, N.Y. Several chimneys were knocked down and bells were rung in New York City. It was felt in Boston, Mass, Philadelphia, Pa., and New Castle, Del. (Ref. 38, 59, 76.) 1853. Mar. 12. Near Lowville, Lewis County, N.Y. Machinery was knocked down at Lowville, about 100 km northeast of Syracuse. Also felt in Canada. (Ref. 59, 76.) 1855. Feb. 7 (Feb. 6). Hudson River valley area. This event was felt to the east as far as Springfield, Mass. Ref. 444 reports that this was a nontectonic event (a cryoseism) which was caused by freezing action in ice, ice-soil, and ice-rock materials. The intensity VI in the hypocenter list above was taken from ref. 76 but could not be documented with damage descriptions. (Ref. 76, 444.) 1857. Oct. 23. Near Buffalo, Niagara County, N.Y. Crocks fell from shelves at Buffalo; bells rang and walls vibrated and surged. A man sitting on a chair was thrown to the ground. Felt from Warren, Pa., to Port Hope on Lake Ontario, and in the Mont- real, Canada, region. (Ref. 38, 76.) 1867. Dec. 18. Northern New York. This earth- quake was described as “quite severe” at Hammond (St. Lawrence County). The earthquake awakened residents at Ogdensburg (St. Lawrence County) and Syracuse (Onondaga County), N.Y., Burlington, Vt., and Hamilton, Ontario. Felt from Whitehall, N.Y., near the Vermont—New York border, to Belleville, Ontario, and Sackville, New Brunswick. (Ref. 38, 59, 126, 591.) 1877. Nov. 4. Northern New York. Effects of the shock were most severe along the St. Lawrence River and Lake Champlain. In that area, chimneys EARTHQUAKES IN NEW YORK 315 82° 80° 78° 76° 74° 72° 70° \ V ' o \._ Ottawa ‘5. \. ° F; 44° ! i gr : ," I Toronto I" I’ v... _.L.‘K?.2"!Tfl*.’9_...-' : ;" I " / i. 1 3i , Buffalo / I 420 - . "JV; 1an— .\-.‘ — ' fl, ''''''' — ——————————— / l 0‘9va ‘ II-lll IV I l PENN 0H0 x1 \ H Pittsburgh \ 40° ./'i l . J '-- — .r ....... :1 _ _ ’ I ./‘-~» ' f- . {a (' ‘t ('1' L1- ('1. . ,I'K. MD. .I' 4.- .r’ “ -’~ L ,.! w. VA. {I'V-d ' Wasmg‘OR'. }“ C . pd \ harleston ( 38° ‘- r \ '\ KY. - ./ X g VA ./' I. ,~-‘ \ EXPLANATION , ’ ~, AI...“ .7. - * Epicenter VII Intensity 7 _._._ -—-,..‘_‘._ TENN. / _'—“ - — —-— — — ._._._._._.£°.rfi).k 36° "A- 0 100 KILOMETERS N. c. FIGURE 46.— Isoseismal map for the New York City, New York, earthquake of August 10, 1884. Isoseismals are based on intensity estimates from data listed in references 369, 463, 518, and 529 of table 1. were downed, crockery was overturned, and ceilings were cracked. As far southwest as Auburn, N.Y., win- dowpanes were damaged. Felt from Pembroke, Ontario, to Trois-Rivieres, Quebec, on the north; to Boston, Mass, Providence, R.I., Hartford, Conn., and Auburn, N.Y., on the south. (Ref. 38.) 1878. Feb. 5. Flushing, Queens County, N.Y. A severe shock broke Windows and crockery and shook houses at Flushing. (Ref. 141, 463.) 1884. Aug. 10. Near New York City, N.Y. This severe earthquake affected an area roughly extend- ing along the Atlantic Coast from southern Maine to central Virginia and westward to Cleveland, Ohio (see fig. 46). Chimneys were knocked down and walls were cracked in several States, including Connecti- cut, New Jersey, New York, and Pennsylvania. Many towns from Hartford, Conn., to West Chester, Pa., reported fallen bricks and cracked plaster. Property damage was severe at Amityville and Jamaica, N.Y., where several chimneys were “over- turned” and large cracks formed in walls. Two chim- neys were thrown down and bricks were shaken from other chimneys at Stratford (Fairfield County), Conn; water in the Housatonic River was agitated 316 violently. At Bloomfield, N.J., and Chester, Pa., sev- eral chimneys were downed and crockery was bro— ken. Chimneys also were damaged at Mount Vernon, N.Y., and Allentown, Easton, and Philadelphia, Pa. Three shocks occurred, the second of which was most violent. This earthquake also was reported felt in Vermont, Virginia, and Washington, DC. Several slight aftershocks were reported on Aug. 11. (Ref. 38, 76, 369, 463.) 1897. May 28 (May 27). Northeast New York. This earthquake was reported as severe, but little damage occurred. Felt in Massachusetts, New Hamp- shire, New York, and Vermont. Also felt in Canada. (Ref. 38, 76, 126.) 1914. Feb. 10. Ontario, Canada. A strong earthquake near Lanark, Ontario, broke water pipes at Canton (St. Lawrence County), N.Y., caused a cave-in at Binghamton (Broome County), and cracked the road at nearby Johnson City. Objects were thrown from shelves and walls at Albany and Syra- cuse. Also felt in Connecticut, Massachusetts, and Pennsylvania. Magnitude 5.5 Ukn EPB. (Ref. 38, 76.) 1916. Feb. 3 (Feb. 2). Schenectady, N.Y. A dis- tinct earthquake at Schenectady (northwest of Albany) broke windows and dishes, threw people out of bed, and shook houses. Residents within a 40-km radius of Schenectady felt the shock. (Ref. 272.) 1928. Mar. 18. Saranac Lake, Essex County, N.Y. Dishes fell from shelves at Saranac Lake, and at Malone, about 60 km north, people rushed from their houses. The shock was widely felt in northeast New York and probably in adjacent Canada. (Ref. 1, 38.) 1929. Aug. 12. Attica, Wyoming County, N.Y. The earthquake was strongest in eastern Attica and the region to the east. In Attica, 250 chimneys were thrown down, several brick buildings were damaged, and a crack formed in the railroad embankment near the railroad station. East of town, almost every mon- ument was knocked over in the Brainerd Cemetery. West of Attica Reservoir, several wells went dry and a crack formed in the bottom of one well. Several chimneys also fell a few km north of Attica, at Bata- via, and at Warsaw, 20 km southeast; only slight damage occurred at other towns. It was felt from New Hampshire to Michigan and from Maryland to northern Ontario (see fig. 47). Magnitude 4.4 MS NLI, 4.9 M JOH. (Ref. 2, 38, 77, 349.) 1931. Apr. 20. Lake George area, Warren County, N.Y. The most severe damage occurred at Warrensburg, a few kilometers north of Lake George, where several chimneys were thrown down and a church spire twisted. Minor damage also occurred at Glens Falls, Luzerne, and Lake George. Although Widely felt, the shock was not as strong in the SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Catskills to the south as it was at equal distances in other directions. (Ref. 4, 349.) 1934. Apr. 15 (Apr. 14). Adirondack Moun- tains area, N.Y., near Lake Champlain. The earthquake was strongest in the Lake Champlain region, near Beekmantown (where a house shifted off its foundation); a few kilometers south at Keeseville; and at Saranac Lake (northern Essex County). Also felt in Vermont and at Montreal, Can- ada. (Ref. 7, 77, 126.) 1935. Nov. 1. Quebec-Ontario border, Can- ada. Heavy damage occurred in Timiskaming area, Canada. In the United States, chimneys and plaster sustained minor damage at Cortland, N.Y., about 50 km south of Syracuse. Felt in eastern Maine, south to Washington, DC, and west to Wisconsin, includ- ing 17 States and three Canadian Provinces. Magni- tude 5.9 Ms NLI. (Ref. 38, 77, 349.) 1944. Sept. 5 (Sept. 4). Between Massena, N.Y., and Cornwall, Ontario, Canada. This severe earthquake was felt from Canada south to Maryland and from Maine west to Indiana (see fig. 48). It caused property damage estimated at $2 million at Massena and Cornwall. Many chimneys in that area required rebuilding, and several structures were unsafe for occupancy until repaired. Residents of St. Lawrence County reported that many water wells went dry. At Massena, in northern St. Lawrence County, 90 percent of the chimneys were destroyed or damaged and house foundations, plumbing, and masonry were damaged severely. Similar effects were reported at Cornwall. Cracks formed in the ground at Hogans- burg, and brick-masonry and concrete structures were damaged. Chimneys were downed in several towns in New York, including Fort Covington, Keeseville, Malone, Norfolk, Ogdensburg, and Wad- dington. Magnitude 5.6 MS NLI, 5.77 M JOH. (Ref. 17, 77, 194, 349, 533.) 1966. Jan. 1. Near Attica, Wyoming County, N.Y. Chimneys and walls were damaged slightly at Attica and 10 km south, at Varysburg. In addition, plaster fell at the Attica State Prison, and its main smokestack was damaged. Felt in western New York, northwest Pennsylvania, and southern Ontario, Can- ada. (Ref. 81, 105, 349.) 1967. June 13. Near Attica, Wyoming County, N.Y. At Attica, plaster fell, chimneys cracked, and fluorescent light fixtures were damaged. At Alabama, about 30 km north of Attica, ceiling tile fell in a church. This shock was felt over a small area of western New York. Magnitude 3.0 Ms NLI. (Ref. 38, 40, 349.) EARTHQUAKES IN NEW YORK 317 86° 84° 82° 80° 78° 76° 74° 72° 70° / \ ° \ Fraserdale / l \ / \ \ \ 48° ll-lll o o 46 m 0 0 Ottawa QBMPA..- _ .— — m a IV /../""‘\JNTTED STATES -. 3% f. 44° .3 / '3 I / ! LAKE...2NT£E'.Q_.,/" / MCH ,' Ix" VI-VIII I 3 l I! Attica .- ‘./’ \ Detroit p& I ’3 V o " alE H,- 42 LAKE/E," i . I. "‘-.____, . . \ -" - "‘ ““‘ i V\ ‘ ._. - g i ! g l i, \ Cleveland i i \ ' I \ (-4: OHIO \ 3., 40° \z! .t‘ I f L_ _. . ._. _.v \ ~_'_'_'_'._j?__ "\ " “f i 136% 4‘ V EXPLANATION '\_ (4 L/ if. f‘IBaItimore F“ . - , Y' ,5 V i“ * Epicenter \' x r'\ .—. V I 44° . I I A ta. Q ~ . VI VT‘ \/ ‘- ‘ \ : To onto _.... ,,- n r, N i ll-Ill / ,-‘-—" ....... - = {,L K5 ONTARIO Ny_ ! I: NH / : I V . § 0 V i ’i‘ J / : ‘- Syracuse lrw—‘L" ""41 / I .f‘ I 805“)" “/7" . “ ""' ’ ' .. R. ‘1’! th __________ ! id ‘- .i— ' ! E | A, : COY‘N- I A 7K. .5 , \x , 3 {I .)— M New Y0“ / o .. 40 ) “Ix; NJ. _. / “x . , ~ ’, e _ _._.__._ — ' O , ,«J - . 1"- / o I /~' h. "( Baltmore L ,1 _/ \ 15's. 1 / ,) ~ L No. 1 ‘ , . . x w, VA. A; ' " I / p‘ .I' E K» 380 (K. II -. r , - r _," I". a Ivy) VA EXPLANATION 0 150 none-ens * I er ____4 v||| Intensity 8 “ ‘1E®“"__ _.« ._._._._. .—-~,..-._._._. .1311": FIGURE 48.—— Isoseisma] map for the Massena, New York, earthquake of September 5, 1944. Isoseismals are based on intensity estimates from original US. Coast and Geodetic Survey questionnaires and from references 17 and 77 of table 1. 1974. June 7. Wappingers Falls area, Dutch- ess County, N.Y. Windows were broken in the area, and a bookcase toppled in one house. More than 100 aftershocks were recorded through June 13. Magni- tude 3.8 Mn PAL. (Ref. 47, 349.) 1975. June 9. Northern New York. A chim- ney and fireplace were cracked at Beekmantown, on Lake Champlain north of Plattsburgh. About 35 km east of Beekmantown, at Fairfax, Vt., slight damage also was reported. Felt in southern Quebec, Canada, and in Massachusetts, New Hampshire, New York, and Vermont. Magnitude 4.2 Mn PAL. (Ref. 38, 48, 349.) 1983. Feb. 26. Near Lagrangeville, Dutchess County, N.Y. Slight damage to property was reported at two towns in Dutchess County. At Lagrangeville, chimneys and a house foundation were cracked; at Pawling, a few buildings were dam- aged and a church wall was cracked. The shock was felt only in western Connecticut and southeast New York. Magnitude 3.0 Mn PAL. (Ref. 360.) 1983. Oct. 7. Blue Mountain Lake area, Hamilton County, N.Y. At Blue Mountain Lake, EARTHQUAKES IN NEW YORK 319 86° 82° 78° 74° 70° 66° K .' / / +4-- r l I . \ ® I / K I ,\\ K 60% . . . 48° . K lMatheson l K \ K O58 Q l ' J a“ ‘- sz' K K 7 ! 36%, K \ K K K K ... ./" K ~ ' a so» -’ 4.!“ $9.) our. K I K K! ||-m K 0U ‘ 1 $7?” K“. N.8 2 K / ‘5»th l. ‘l ‘ ’3, Quebec [he i 46° .- l K /‘.\ n Ki. .M‘ ‘ .: . , \- ——l—K——/ . if 7+A 7 V, ' - K I {t K be K '\ ”._, \ ' / l MAINE K \- K \ / \ o f ' ._“" K 1,. “ IV KOttawa _.._.._.._ '— 1; 3‘ J K‘ K K g, 6 l Bangor. p K ‘ a 44° , ‘ _, ‘ a 0 - “Ex VI 6 fl Iii V v K w “L ‘ . r l ' 1' K QUE/9.1 Blue Mtn Lak- ,A x N‘ H‘ 1 K H! x e' K K \J g I l. / K K ‘KRoch t . - I K K eser “#NIV KWV/Q— __ \I K K 42° [I @ MASS. 1‘ BostonK K ___'_______ _ ._. __ A \‘ l v iR.|.' ,\‘l ' l ‘ I, t K K 5 CONN. . - j a, K ' - L a K ' ; fiv’ K ,3 K . l/ K 00 K 40° K J/T/” EXPLANATION «\0 K * Epicenter 3% VI Intensity 6 v’\ 100 KLOMETERS FIGURE 49 —- Isoseismal map for the Blue Mountain Lake, New York, earthquake of October 7, 1983. This map is a simplified vers1on of figure 37 in reference 360 of table 1. one old chimney collapsed, about 20 tombstones slid or rotated, and some minor cracks formed in plaster walls. Several landslides were reported. Light dam- age also occurred at several other towns in the area, but the most common effects were cracked chimneys, broken dishes or glassware, and overturned or fallen objects. Although this earthquake caused only minor damage, it was felt over a wide region (see fig. 49), including two Provinces in Canada and 12 States. Magnitude 5.3 Mn BLA, 5.1 Mn SLM, 4.89 M JOH. (Ref. 360.) 1985. Oct. 19. Southeast New York. Windows were broken at Newburgh, NY. (about 140 km south of Albany), and Glenville, Fairfield County, Conn. Plaster and drywall also were cracked and glassware was broken in Newburgh. Light damage was sus- tained at a few towns in Connecticut, New Jersey, and New York. Felt over a large area of Connecticut, Massachusetts, New Jersey, New York, and Pennsyl- vania. A moderate aftershock was felt in Connecticut, New Jersey, and New York on Oct. 21 (10 37 UTC). Magnitude 4.0 MD WES. (Ref. 371.) NORTH CAROLINA .3 N SEGBE 8 may N 335592: fits «£3pr £3 Z 5 moxmswsfimm “ .l] <~OMOMO =>\v.m-o.m O wmm—HMEOAE 00—. _>\§.m.m o >2wc2£$u==amu§ V W zo:w:w< as O l\ A <~Z~O~E> c mmmmmzzme fl wMUDHZmM h om: own avm own com 321 322 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NORTH CAROLINA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m s (°) (°) (km) m, Ms M (1.000 me) 1861 08 31 1022 36.1 N 81.1 W — 55 — — 5.00Mf,I SC — VI 38 784 1916 02 21 23 39 35.5 N 82.5 W — 272 — -— 520an SC — VII 67 6(1) 1926 07 08 0950 35.9 N 82.1 W —— 71 —— — —— — VII 68 @ 1957 05 13 14 2451.1 35.799N 82.142W 005 349 — — 4.00Mfll SC — VI 132 16 1957 07 02 0933 01 35.6 N 82.7 W 007 155 — — 3.70Mf. SC — VI 132 3 1957 11 24 200617 35.0 N 83.5 W —- 30 — — 3.90Mf. SC — VI 132 12 1981 05 05 2121567 35.327N 82.422W 010 339 -- — 3.50M“ BLA - VI 325 10 [Reference (Ref) numbers given in parentheses at the end of 1957, May 13. Near Woodlawn, McDowell each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1861. Aug. 31. Near Wilkesboro, Wilkes County, N.C. Bricks were shaken from chimneys, doors were jarred open, and clocks stopped running at Wilkesboro, about 85 km west of Winston-Salem. Felt along the Atlantic Coast from Washington, D.C., southward to Charleston, SC, and Columbus, Ga., and westward to Cincinnati, Ohio, Louisville, Ky., and Gallatin, Tenn. Magnitude 5.1 Mfa NUT. (Ref. 38, 55, 508.) 1916. Feb. 21. Near Waynesville, Haywood County, N.C. Tops of chimneys were thrown to the ground; windowpanes were broken in many houses; and people rushed into the streets at Waynesville. At Sevierville, Tenn., about 70 km northwest of Waynes- ville, bricks were shaken from chimneys. In Wear’s Cove, about 16 km southwest of Sevierville, the flow of water in springs increased and in places water became muddy. Minor damage was reported in west- ern Tennessee at Athens, Knoxville, Maryville, Mor- ristown, and Newport, Tenn; at 'I‘ryon, N.C.; and at Bristol, Va. Also reported felt in Alabama, Georgia, Kentucky, South Carolina, and West Virginia (see fig. 50). (Ref. 67, 71, 272, 508, 600.) 1926. July 8. Southern Mitchell County, N.C. A sharp local earthquake in Mitchell County caused minor damage—one downed chimney, cracks in chim- neys and foundations of houses, broken water pipes and glassware, and shifting of houses on foundations. Ground cracks also were reported. Damage was con- fined to an area about 1 km long and 275 m Wide. Town names were not mentioned in any of the accounts on this event. (Ref. 68, 71, 218, 508.) County, N.C. A sprinkler pipe was shaken loose at a factory at Woodlawn, and books fell from library shelves. Slight damage to plaster occurred at several towns in the area. Old cracks in a wall were enlarged at Busick, near Mt. Mitchell in southern Yancey County. The shock was strong in other towns in Burke and McDowell Counties and was reported felt at two towns in South Carolina. Magnitude 4.1 Mfa DG. (Ref. 30, 132, 349, 508.) 1957. July 2. Buncombe County area, N.C. Minor damage reported in western North Carolina included cracks in walls and plaster at Asheville, cracks in retaining wall at Marshall, damaged chim- neys and cracks in plaster at Swannanoa, and cracks in plaster at Weaverville. Also reported felt in Hay- wood and Madison Counties, N.C., and at Flag Pond, Tenn. (Ref. 38, 132, 155, 508.) 1957. Nov. 24. Northwest Jackson County, N.C. At Hartford, Tenn. (about 70 km southeast of Knoxville), slight damage to buildings included a crack in one wall and a kitchen that was separated from the rest of the house. The earthquake shifted furniture in Jackson County, at Cherokee and Sylva, N.C., about 50 km south of Hartford, Tenn. Also felt in South Carolina. Magnitude 4.0 Mfa BAR. (Ref. 30, 132.) 1981. May 5. Near Hendersonville, Hender- son County, N.C. Cracks formed in windows and a concrete patio in Hendersonville, and one sidewalk shifted 5 cm. Cracks also occurred in drywall and a house foundation a few kilometers southeast of Hendersonville, at Zirconia. Water in several wells became muddy in the Dana area. Also felt in South Carolina, Tennessee, and Virginia. Magnitude 3.3 MD TEC. (Ref. 325, 339.) 38° 36° 34° 32° 30° EARTHQUAKES IN NORTH CAROLINA 84° 320 80° 78° OHIO _} '. .A.J" 1. f./ l f-J -’\. 1L, MD. ' V I ‘~/ 8 J /' ‘. I V W. VA. «I. Washington ; Charleston f‘v/ :‘ O ‘ — ‘ \ - 5 VA. 0 ‘ K A“ Richmond *Ashevfie J A. g ”VA/Ii“ "b. N. C_ Raleigh r'\’ . 0 V“ Intensity 7 / / Charleston / i / 1 \ / (or ) / C; 2' ° \ I \O ,\ " EXPLANATION ‘3‘ \/ x ‘k Epicenter V 150 KILOMETERS !:sonvi||e FIGURE 50.— Isoseismal map for the Waynesville, North Carolina, earthquake of February 21, 1916. Isoseismals are based on intensity estimates from data listed in reference 272 of table 1. 48° 46° NORTH DAKOTA 104° 102° 100° .98” 96° C) CANADA UNITED STATES O Williston . Minot NORTH DAKOTA E < Z z a fi ‘6 g . Fargo H 2 Bismarck > EXPLANATION SOUTH DAKOTA Magnitude 0 100 KILOMETERS O 5.5-5.9 Earthquake in North Dakota with a magnitude 2 4.5 or intensity 2 VI. 325 326 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) NORTH DAKOTA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes Leader (--) indicates information is not available] Orlgln Hypocenter Magnitude Intensity Date time (UTO) Latitude Longltude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo D: h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1909 05 16 0415 49.0 N 104.0 W — 413 —— -— 5.50Mn EPB -— VI 413 1300 [Reference (Refi) numbers given in parentheses at the end of each description refer to sources of data in table 1.] 1909. May 16 (May 15). North Dakota— Montana—Saskatchewan border region. This mod- erate earthquake was felt widely over south-central Canada and the north-central United States, including the States of Montana and North Dakota. A retaining wall fell in Helena, southern Lewis and Clark County, Mont; plaster was cracked at Havre (northwest of Hel- ena, in Hill County). The shock also was “severe” in Dickinson (Stark County), N. Dak. Some Windows were broken and articles fell from shelves at a few towns in Saskatchewan, Canada. (Ref. 249, 413.) 84° OHIO 82° 80° J 42° 40° 38° e / MICHIGAN , A / e 3‘ / J] V i E A i» ° 0 Toledo 0 0 Cleveland '0 [Ti 2: 2 m e Lima < 0 o > < E. 2 Ce > S Q o O H I O E O 0 Columbus C) O Marietta Cincinnati 0 WEST VIRGINIA EXPLANATION ironton Magnitude/Intensity o 3.2-4.4/Vl O 4.5-4.9/Vl KENTUCKY O 5.0-5.4 0 100 KILOMETERS L—_i__l "\ Earthquakes in Ohio with magnitudes 2 4.5 or intenstiy 2 VI. 327 328 SEISMICITY OF THE UNITED STATES, 1568-1989 (REVISED) OHIO [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @. felt area is less than 1,000 kmz. Leader (..) indicates information is not available] Origin Hypocenter Magnitude Intenslty Date “"10 (UTO) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 3 (°) (°) (km) m, Ms M (1 .000 kmz) 1776 14 00 39.6 N 81.9 W -— 116 — —-— — — VI 60 — 1875 06 18 12 43 40.2 N 84.0 W — 38 —— 4.70Mfa SC VII 38 100 1884 09 19 19 14 40.7 N 84.1 W — 38 —— —— 4.80Mfa SC — VI 38 373 1900 04 09 14 41.4 N 81.9 W — 116 — — 3.40Mfa BAR — VI 105 — 1901 05 17 06 00 38.75 N 83.0 W — 584 —— — 4.20Mfa SC — VI 584 42 1926 11 05 16 53 39.1 N 82.1 W —- 38 — — 3.80Mf, SC — VII 38 l 1930 09 30 20 40 40.3 N 84.3 W —— 38 — -- 4.20Mfa BAR —-— VII 38 — 1931 09 20 23 05 03.4 40.429N 84.270W 005 349 -— —— 4.70M“ SC —- VII 38 90 1937 03 02 14 47 33.3 40.488N 84.273W 002 349 --- 5.00MfI SC —— VII 38 280 1937 03 09 05 44 35.5 40.470N 84.280W 003 349 — — 5.40Mfa SC — V111 38 390 1943 03 09 03 25 24.9 41.628N 81.309W 007 349 — — 4.50Mn BAS — VI 105 150 1952 06 20 09 38 08.6 39.640N 82.023W 009 349 — — 4.00Mfa SC — VI 38 13 1977 06 17 15 39 46.9 40.705N 84.707W 001 349 — — 3.20Mn AAM — VI 39 @ 1986 01 31 16 46 42.3 41.650N 81.162W 002 562 5.0 -— 4.90M,I SLM 4.97GS VI 562 322 1986 07 12 08 19 37.9 40.537N 84.371W 010 562 4.5 —— 4.60M“ SLM 4.39SZ VI 562 90 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1776. Date unknown. Near the Muskingum River. In the summer of 1776, an earthquake fright- ened people and animals and overthrew furniture. Duration of the shock was estimated at 2 to 3 min— utes. (Ref. 60, 116.) 1875. June 18. Western Ohio. This earthquake was most severe west of Columbus, at Urbana (Champaign County) and Sidney (Shelby County), where chimneys were thrown down and walls were cracked. Also felt in southern Illinois, southwest Indiana, northwest Kentucky, and eastern Missouri. (Ref. 38, 105.) 1884. Sept. 19. Near Lima, Allen County, Ohio. Slight damage occurred at Lima, Where the shock was “of considerable violence and caused much excitement.” Plaster was shaken from ceilings east and southeast of Columbus at Zanesville, Ohio, and Parkersburg, W. Va. Windows and dishes were bro- ken at Defiance and Norwalk, Ohio; to the west at Fort Wayne and Muncie, Ind.; to the north at Lan- sing, Mich.; and to the east at Wheeling, W. Va. Fur- niture was displaced and buildings were heavily shaken at Urbana, Ohio, in Champaign County, and at many other towns in the region. Also felt in Iowa, Kentucky, Pennsylvania, and western Ontario, Can- ada, and at Washington, DC, by workmen on top of the unfinished Washington Monument (see fig. 51). Magnitude 4.8 Mfa BAR, 5.1 Mfa SG. (Ref. 38, 60, 105, 463, 529.) 1900. Apr. 9. Berea, southeast Cuyahoga County, Ohio. ’va0 chimneys on one house toppled at Berea. This event was an explosion according to ref. 443. (Ref. 105, 116, 443.) 1901. May 17. Near Portsmouth, Scioto County, Ohio. The strongest effects of this earth- quake were reported in Scioto County, near the Ken- tucky—Ohio—West Virginia border. At Portsmouth, tops of chimneys toppled, bricks tumbled from many chimneys, and windows in several houses were shat- tered. East of Portsmouth, at Sciotoville, many chim- neys were damaged and dishes were thrown from cupboards. At Gallipolis, Gallia County, plaster in one house was shaken loose. Reported felt mainly in the area along the border of Kentucky, Ohio, and West Virginia, including Greenup and Lewis Coun- ties, Ky., and Cabell and Kanawha Counties, W. Va., to the south; Adams and Brown Counties, Ohio, to the west; Muskingum and Washington Counties, Ohio, and Wood County, W. Va., to the northeast; and Highland County, Ohio, to the northwest. (Ref. 584.) 1926. Nov. 5. Southeast Ohio, near Pomeroy, Meigs County. This earthquake toppled chimneys EARTHQUAKES IN OHIO 329 90° 88° 86° 84° 82° 80° 78° 46° “ .\ /\ \j Cheboygan{.\ y 0 ..\ «\o ‘39 /7¢ fi' \ 3 "3a / \s \ / \ I S: O 2 / l .' MICH. -‘ ,-' Buffalo V Detroit .& ENE i d‘ / Q“ L ................... l" \ iVlér’ ! ! ! | i ! I ! WIS. I 44° '\ > to Toron LAKE ONTARIO ..._ 42° ./ 40° 1.. .— .a—--—--.—’" "— '- l M M."—-(\ «‘ ' | / ! ‘\ ." Cincinnati ,/ } \l ’J I .1- /'~’ . /' [VJ / VA. 38° EXPLANATION f.’- ”3- _/'~. . t 'I‘\. \ ‘// \.\".\.’,J‘ * Epicen er «1 DJ 0 150 KILOMETERS ,/ Vl Intensity 6 y) Paducah L_._| 5" .) l _../ 1 FIGURE 51.——- Isoseismal map for the Lima, Ohio, earthquake of September 19, 1884. Isoseismals are based on intensity estimates from data listed in reference 463 of table 1. at Keno and nearby Pomeroy and overturned a 1930. Sept. 30. Near Anna, Shelby County, heating stove at Chester, west of Keno. Also, one Ohio. A brief but strong shock was felt over a wide stovepipe was knocked down at Success, and a flue area in Ohio. It was strongest at Anna, where a was downed at Bashan. Explosive earth sounds chimney at a schoolhouse toppled and plaster were reported. Felt throughout Meigs County, Ohio, cracked and fell. Brief shocks were felt at Sidney, and at Letart, W.Va. Magnitude 3.6 Mfa BAR. (Ref. about 12 km south of Anna, on Sept. 29 at 21 15 38, 105, 218.) UTC and Sept. 30 at 23 50 UTC. (Ref. 3, 38, 60.) 330 1931. Sept. 20. Anna, Shelby County, Ohio. Moderate damage occurred at Anna and in nearby towns in Shelby County. At Anna, several chimneys were downed, many chimneys were damaged, and two large cornice stones were thrown from the Luth- eran Church. At Botkins, north of Anna, the roof of the public school was pulled apart and its ceiling col- lapsed; several chimneys also were thrown down or otherwise damaged. In southern Shelby County, at Houston and Sidney, chimneys fell and walls and windows were cracked. Felt over a large part of Ohio and in eastern Indiana and northern Kentucky. Mag- nitude 4.6 Mfa BAR, 3.6 Ms BAR, 4.5 Mfa DG. (Ref. 38, 105, 349, 353, 509.) 1937. Mar. 2. Western Ohio, near Anna and Sidney, Shelby County. Damage was heaviest to brick chimneys and buildings at Anna and Sidney— many chimneys fell, walls cracked, and plaster fell. Springs and other water wells increased their flow, but output from oil and gas wells was decreased. At the Anna public school, walls of the building were cracked so severely that it was declared unsafe; two churches sustained minor damage. Chimneys also were damaged at nearby Botkins and Jackson Center and in southern Auglaize County, at Wapa- koneta. Several tombstones were rotated in three cemeteries near Anna. Plaster fell in buildings as far away as Fort Wayne, Ind., and plaster cracked at Indianapolis. Two to five shocks were felt in many places. Also felt in the States of Indiana, Kentucky, Michigan, and West Virginia, and in Ontario, Can- ada. Magnitude 4.8 Mfa BAR, 4.7 Mfa DG. (Ref. 38, 349, 353, 509, 524.) 1937. Mar. 9 (Mar. 8). Western Ohio. An earth- quake stronger than the shock on Mar. 2 centered near Anna in Shelby County. The three-story school- house at Anna was cracked severely, and the churches that were damaged in the Mar. 2 shock were further damaged. Almost every chimney was broken or twisted, and house foundations and walls were cracked. A few chimneys fell at Sidney, about 12 km south of Anna, and plaster was damaged. Subsurface changes caused by the two earthquakes included renewed activity of springs, conversion of ordinary wells to artesian wells, and an increase in the flow of other water wells; the output of both oil and gas wells was reduced. A spring at Huntsville (Logan County), dry for 8 years, began “spouting water” after the second shock, and the flow of arte- sian wells was increased at New Knoxville (about 45 km west of Huntsville). This shock was felt in upper stories of multistory buildings in Chicago and Mil~ waukee and in Toronto, Canada. Also felt in Ken- tucky, Michigan, Missouri, Pennsylvania, and West SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) Virginia. Magnitude 5.5 Ms GR, 5.0 Mfa BAR, 4.7 Ms BAR, 4.9 Mfa DG. (Ref. 38, 349, 353, 524.) 1943. Mar. 9 (Mar. 8). Lake Erie area, Ohio. An earthquake broke windows and dishes and cracked plaster in the Lake Erie area. The widely felt shock was reported in Michigan, New York, Ohio, Pennsylvania, and Canada. Magnitude 4.7 Mfa BAR. (Ref. 105, 349.) 1952. June 20. Near Zanesville, Muskingum County, Ohio. One old chimney fell and doors were thrown open at Zanesville. Felt throughout southeast Ohio. Magnitude 4.1 Mfa BAR, 4.1 Mfa DG. (Ref. 38, 105, 349, 353.) 1977. June 17. Northwest Ohio. The earth- quake caused slight damage in several towns in Mer- cer County. Plaster fell at Goldwater, and cracks formed in a sidewalk and a house foundation. Cracks in sidewalks, walls, and foundations also were reported north of Goldwater, at Celina and Rockford. It was reported only in Mercer County— from Celina south to Chickasaw, west to Fort Recovery, and north to Rockford. (Ref. 39, 349, 353.) 1986. Jan. 31. Northeast Ohio. This earth— quake caused minor property damage in several towns in northeast Ohio and northwest Pennsylva- nia; 17 people were injured in the epicentral area. Most of the damage to houses and commercial buildings occurred in Ashtabula, Geauga, Lake, Trumbull, and Wood Counties in Ohio and Crawford and Erie Counties in Pennsylvania. It mainly included fallen ceiling tiles and plaster; cracked chimneys, foundations, and brick walls; and broken windows and underground pipes. Changes in the flow of water were observed in more than a dozen wells in Lake and Geauga Counties, east of Cleveland. The changes included variations (starting, stopping) in the flow of water and sediment deposits in water. In Leroy Township, a small pond was formed from the flow of a new artesian well. Another artesian well suddenly began feeding water to an old water trough. Over the next 2 months, 13 aftershocks of magni- tude 0.5 to 2.5 were recorded in the area, and 13 more aftershocks of about magnitude 1.0 were detected through Apr. 15, 1987. The main earth- quake was felt over a large area of the Eastern United States, covering all or parts of eight States (Illinois, Indiana, Kentucky, Michigan, New York, Pennsylvania, West Virginia) and Ontario, Canada (see fig. 52). It also was reported by people on the top floors of multistory buildings in Delaware, Mary- land, New Jersey, Virginia, and Wisconsin, as well as Washington, DC. Magnitude 5.3 Mn EPB, 4.88 M JOH. (Ref. 562.) EARTHQUAKES IN OHIO 331 88° 36° 84° 82° 80° 78° 76° 74° *7 - ‘ "KW/P . Powassan "i b ( '5 0 x. K \' Ottawa N7 0 \ \ . \ Apena ‘- CANAQA_.. ”- ‘ ”/[fiTTéb—smzs r— 1 “I 'P \ / 5 2 2;“; v ./' <5 U :z ‘ GrBen Bay g 1 avg o c 24: _ 44o W'S- ,c n F»! II III . 2 ‘ J t MC” 1 f\ :/ i \/ j N ' __,_____..__.,._'.b_. , C / .-- A K a N T A I " N Y. ._.- — .I ( (' Syracuse . - —,_,_ _ * I,» ||~ll| 42° / meaw __. ___.--'_._———-'—' ‘_'—‘\\ . _ ______ \ ' ''''' 1._._ _ _ .1 i {a l j Scranton L.\ ! i w |I-ll| ,1 '\.\V I l I . . ( " ’ I m , I ’ N07 FE T . i i I Hi i g ' \ I one Pittsbugl . LL I! l . l ' Hamsbuvg \-\ Trenlon 400 I m l i . r./' ‘ ' IV . i I ,- _,J N J. l i cam.S IV-V . : ___ _ _ _ _ __{r 4 ' . V i ‘‘‘‘‘ _.__.T__._._ ————— . l m... : a , a if I f/ l ’7‘" Baltimore l (I ' ' ! ,r' _ ‘- I" IV .1" V I. i 1 \_ 6 \ DEL. é .,- ._,\_.,.J IN u-m , N. '1. J J I \z-x. "' I ,1 ! o r' ./ v-- k W. VA. _r-\ / L ----- o W " KY. ..—- Chaflesxon ( \Jv 2’ “ - ' H . s 380 ' ,J— L ! Lexngton \f _/' VA. k -" o 100 KLDNETERS XPLANAT' N '\, _,v’ 1:“ .\J t—.__l t Epicenter \. _, R‘ d V IV". ’ \_ <) . V| Intensfly 6 \4 ‘ a“ “7" \ FIGURE 52.——— Isoseismal map for the northeast Ohio earthquakes of January 31, 1986. This is a simplified version of figure 2 in reference 1986. July 12. Western Ohio. This earthquake occurred near Anna, in Shelby County—the same area where damaging shocks occurred in 1875, 1930—31, and 1937. It caused minor property damage in Shelby County, at Anna, and in Auglaize County, at Minster, New Bremen, and Saint Marys, Ohio. 562 of table 1. The damage, which was much less severe than that occurring in the earlier earthquakes, mainly of cracks in chimneys and walls, fallen bricks from chimneys, and broken windows. Also felt in parts of Indiana, Michigan, and West Virginia. Mag- nitude 4.9 Mn EPB. (Ref. 562.) consisted é um. I: , 7 . ,, ¢ r ‘ . ‘ _ , , x , W ‘ .’ y , 1 . ‘ r1. , _ V , » , u 1 ‘ l r , . _ u . .,, w w , w ‘ . \ a ‘ r _ . / / OKLAHOMA .3 N bumcwufi .8 9% N mmvsfifiwmfi firs «Eonmio fl mwxmdcfihwm mam—th—OJE oop 0 930mm; {J 33 I\ l‘ g .0222 . . . EoEEo< an mm 0 3-3 0 .231; o o 0 2:2 0 3682:3223: zo:zoo m m E m O E O 0 Bend OREGON o O 0 Grants Pass '0 o 03 O a Adel EXPLANATION Magnitude/Intensity NEVADA O 4.0-4.9/VI O 5.0-5.4/Vl O 5_5_5.9 CALIFORNIA O 60 64 0 100 KILOk‘AETERS . - . l I I Earthquakes in Oregon with magnitudes 2 4.5 or intensity 2 VI. 337 338 SEISMICITY OF THE UNITED STATES, 1568—4989 (REVISED) OREGON [See table lfor hypocenter and intensity references and tableror definitions of magnitude source codes. &, land area only. Leader (~) indicates information is not available] Origin Hypocenter Magnitude lntenslty Date timetUTc) Latitude Longitude Depth Ref uses Other Moment MM Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1892 02 04 0430 45.5 N 122.7 W —- 56 — — 5.00UknEPB —— V 56 268: 1893 03 07 0103 45.9 N 119.3 W — 53 — — 4-70ML. NQT —- VI 56 — 1896 04 02 1117 45.2 N 123.2 W —— 338 —- — 5.00UknEPB — V 56 —— 1910 08 05 013136 42.0 N 127.0 W — 258 —— — 6.80Ms GR — Felt 338 — 1914 08 22 052818 44.0 N 129.0 W — 258 —— —- 6.75Ms GR — — —— — 1917 06 10 043224 44.0 N 129.0 W -—— 258 — — 6.50Ms GR — — — — 1923 01 11 0429 42.2 N 120.3 W — 53 —- — 5.00MLaDMG — VI 56 69 1924 02 24 054510 44.0 N 127.0 W — 258 — — 5.75M; GR —- — — —- 1926 06 05 19 5024 43.0 N 127.5 W — 258 — — 6.00Ms GR — -— —- — 1928 09 11 123619 43.5 N 130.3 W — 258 — — 6.30M; GR — — -— —- 1930 07 19 02 38 45.0 N 123.2 W — 3 —— — — -— VI 3 — 1932 03 02 174048 43.0 N 131.0 W — 5 — — 6.00mb VIC — — —— —— 1932 06 20 0926 27 43.0 N 127.5 W — 338 — 5.50Ms GR — -— — — 1933 03 26 190553 43.5 N 129.0 W —— 338 — —— 5.50Ms GR — — —- —— 1936 04 30 1055 38 44.0 N 128.5 W — 53 — — 5.50M, GR — -— — — 1936 07 16 070748 45.966N 118.212W 005 260 —— — 5.75M; GR — VII 9 190 1936 09 25 12 53 35 43.0 N 129.0 W — 338 — — 6.20M, GR — — —— ——- 1936 11 05 204618 43.0 N 131.0 W — 338 — — 6.00m}, VIC — — — — 1937 11 10 071923 43.0 N 127.0 W — 258 —— — 5.75M; GR — — —- — 1938 05 28 101401 42.75 N 126.1 W -— 258 — — 6.00Ms GR -— V 11 — 1938 08 03 13 32 36 43.9 N 126.2 W — 338 —— — 5.60M; GR — — —— 1940 11 17 035630 44.8 N 130.0 W — 338 —— — 6.00m}, VIC — — -— — 1941 06 09 061724 42.8 N 126.0 W — 338 — -—- 5.25Ms GR — — — — 1941 06 09 084345 42.8 N 126.0 W — 53 — — 5.00Ms GR — —— — —— 1941 10 31 12 41(X) 43.0 N 128.5 W —— 53 — —— 5.50Ms GR —— — — —- 1941 12 29 18 37 45.5 N 122.7 W — 53 — — —— — VI 53 10 1944 03 06 200908 44.5 N 129.0 W — 258 — — 5-75M3 GR — — — — 1944 03 06 231630 44.5 N 129.0 W — 258 — — 5.75M, GR —- — —- — 1944 12 30 22 0302 43.75 N 126.75 W — 258 —- —- 5.75M; GR — — — 1945 04 11 112257 42.0 N 126.0 W — 338 —- —- 5.00UknEPB — — — 1945 09 28 222410 42.0 N 126.0 W — 258 — — 6.00Ms GR — — — — 1947 09 22 021601 43.5 N 128.0 W — 53 —- — 5.50mb VIC — — -— — 1948 05 25 151307 44.0 N 127.0 W — 258 —— — 5.50Ms GR —- — 1948 05 25 15 3202 43.5 N 127.0 W — 338 —- — 5.80ML PAS —- — — 1949 03 28 19 43 16 42.0 N 126.0 W — 266 —— -— 5.80UknEPB — — — — 1949 08 24 060714 43.5 N 127.0 W — 266 — — 5.50Ms GR —- — — — 1950 08 24 17 45 34 42.5 N 126.0 W — 266 — -— 5.60UknEPB — — — -— 1951 02 23 02 5642 44.5 N 129.5 W — 338 — -— 5.60mi, VIC — — -— — 1951 06 16 234658 44.5 N 130.0 W — 357 — —- 5.50ML BRK — — —— — 1951 06 17 094015 44.5 N 130.0 W — 258 —- —- 6.00ML BRK — —— — — 1952 08 20 15 24 59 43.0 N 127.0 W —- 357 — — 6.00ML BRK — —- --— — 1953 12 16 043212 45.5 N 122.7 W — 53 -—- — 5.00ML EPB — VI 26 9 1955 08 23 15 32 37 43.5 .N 128.0 W —— 266 —- — 6.25UknPAS — Felt 324 — 1956 01 10 123215 43.4 N 122.3 W — 324 —- —- 4.90ML BRK - — — — 1956 07 06 02 2200 42.5 N 126. W — 266 — -— 5.00ML BRK —- — —— — 1957 11 17 060029 45.3 N 123.8 W — 30 —- — 4.00ML BRK — VI 30 13& 1958 03 12 120916 42.4 N 120.0 W —— 324 —— — 4.50ML BRK — —— — —— 1959 06 02 18 4900 43.7 N 119.7 W —- 324 — —— 4.70ML BRK — — — — 1959 08 21 002817 44.8 N 124.7 W — 324 — —- 4.60ML BRK —- — — — 1959 09 26 08 2048 43.7 N 128.3 W — 324 -— — 6.10ML BRK -— —-— — ——- EARTHQUAKES IN OREGON 339 OREGON— Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. 8:, land area only. Leader (--) indicates information is not available! Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo be h m s (°) (°) (km) m, Ms M (1,000 km?) 1960 11 08 113627 44.9 N 125.2 W — 324 -— — 5.00ML BRK -— IV 53 — 1961 08 19 0456 24.1 44.7 N 122.5 W 033 266 -— — 4.50UknPAS — VI 34 18 1961 08 23 17 59 47 42.4 N 123.2 W —— 324 — -— 4.60ML BRK — — — —-— 1963 03 07 23 53 26.5 44.877N 122.738W — 324 4.6 — 4.40Mp YEL — V 36 —- 1963 12 27 02 36 21.6 45.7 N 123.4 W 033 266 4.5 — 4.10M], YEL —- VI 36 10 1964 01 28 0456 48.6 43.3 N 125.9 W 017 266 4.5 — 4.50ML BRK — — — — 1964 07 13 0647 54.1 44.7 N 129.9 W 033 266 5.5 — 5.00mi, ISC — — — — 1964 10 01 1100483 43.5 N 126.9 W 033 74 — — 5.50ML BRK — — — —- 1965 05 31 050743.4 44.1 N 128.8 W 033 266 5.5 —- 5.10m], ISC — — — 1965 06 17 11 22 54.9 43.2 N 126.0 W 033 266 4.6 — 4.50ML BRK -— — — 1965 06 20 17 23 56.8 43.1 N 126.0 W 033 266 4.6 — 4.60M; BRK — — — — 1965 06 20 1804373 42.9 N 126.1 W 033 266 5.6 — 4.70M; BRK — — -—- — 1965 07 25 08 3443.2 42.1 N 126.0 W 033 266 4.6 — —— — -— —- — 1968 05 08 1217142 43.58 N 127.89 W 030 299 6.1 — 6.10mi, ISC — — -— — 1968 05 08 2217 13.8 43.871N 128.180W 033 74 5.0 — 5.50mb ISC -— — — — 1968 05 30 0035 59.8 42.3 N 119.8 W 024 74 5.1 —— 4.70mb ISC — IV 41 — 1968 06 03 13 27 39.7 42.2 N 119.8 W 020 74 5.0 — 4.90ML BRK — V 41 — 1968 06 04 023415.7 42.3 N 119.9 W 021 74 4.7 -— 5.10ML BRK — VI 41 18 1968 06 04 062219.0 42.2 N 119.8 W 033 74 4.3 — 4.50ML BRK — Felt 41 —-— 1968 06 05 0451568 42.3 N 119.9 W 021 74 4.7 — — — Felt 41 -— 1970 ll 26 031142.8 43.776N 127.449W 014 74 5.6 5.9 6.00UknBRK — —- —- — 1972 04 08 062413.7 42.646N 126.320W 011 74 5.6 -— 4.90ML BRK — — — —— 1973 06 16 14 43 47.5 44.980N 125.774W 033 74 5.6 5.1 5.80mi, ISC — IV 46 — 1976 04 13 004717.1 45.221N 120.771W 015 74 4.5 3.3 4.80ML GS — VI 49 35 1976 12 09 0950595 44.525N 129.961W 018 74 5.3 5.5 5.20mi, ISC — — — —- 1978 02 16 120021.2 42.685N 125.890W 015 74 5.0 4.5 4.80ML BRK — —— —— — 1980 08 03 14 43 04.2 42.498N 124.560W 015 74 4.5 — 4.60mi, ISC -- — — —— 1980 12 24 13 29 15.3 42.369N 125.726W 015 74 5.2 5.3 5.00ML BRK —- —- — -- 1981 11 03 13 47 34.1 43.542N 127.706W 010 74 6.0 6.2 5.80ML BRK 6.43ED —— -— — 1985 03 13 193457.6 43.510N 127.561W 010 74 6.1 6.3 5.90m], ISC — IV 371 — 1988 08 11 08m50.6 42.023N 125.400W 010 74 4.6 ——- — — — — ~— 1988 10 23 1348 35.6 44.423N 129.455W 010 74 5.3 5.5 — 5.50HAV — — — [Reference (Ref) numbers given in parentheses at the end of Perrydale, southwest of Portland. Plasfier was each description refer to sources of data in table 1.] 1893. Mar. 7 (Mar. 6). Umatilla, Oreg. One wall of a large stone building was thrown down at Umatilla, about 75 km west of Milton-Freewater. Several shocks were felt by residents. (Ref. 53, 56.) 1923. Jan. 11 (Jan. 10). Lakeview, southern Lake County, Oreg. The shock was reported to be strongest in the Lakeview district. Plaster fell at Alturas (Modoc County), Calif. The intensity was taken from ref. 56 (Ref. 38, 53, 56.) 1930. July 19 (July 18). Near Perrydale, Polk County, Oreg. A crack formed in the roadbed near cracked at McCoy, northwest of Salem. (Ref. 3.) 1936. July 16 (July 15). Milton-Freewater, Umatilla County, Oreg. This earthquake was strongest in the area of Milton-Freewater, Where many chimneys were broken, several houses were displaced on their foundations, and cracks formed in the ground. Many capstones in area cemeteries were rotated. After the shock, water in several springs and wells started to flow again. Property damage was estimated at $100,000. Chimneys were reported dam- aged at Athena and Ferndale, Oreg., and Waitsburg and Walla Walla, Wash. 340 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 124° 122° 120° 118° 116° 114° 0" a 3‘: “c3 2 an " ..._ CANADA 00 _. .._.._.._..._ 9 m UNITED STATES mg? Kalispeu o STRA/T OF JUAN DE FUCA ‘ 48° MD ‘ 'V R Z Seattle ( / ° \ . WASH? *- C 46° . / I .. i. /-.(r-\ /.\_/"’.~ .\.\./ \ ‘f‘ Portland \ Bend 44° . \ ‘ d OREGON EXPLANATION 0 100 KILOMETEHS * Epicenter fi—A V|| Intensity 7 42°» FIGURE 54.— Isoseismal map for the Milton-Freewater, Oregon, earthquake of July 16, 1936. Isoseismals are based on intensity esti- mates from data listed in references 9, 495, and 510 of table 1. At Milton-Freewater, most chimneys were damaged and two concrete houses, about 11 km west, were at the roof level. One brick house at the penitentiary almost demolished. At nearby Umapine, one concrete was condemned as unsafe. A new house, about 6.5 house collapsed and a stucco house was damaged so km west of Milton-Freewater, was almost wrecked, badly that the family moved into the yard. The EARTHQUAKES IN OREGON Milton-Freewater school buildings were damaged, and repairs were estimated at $8,500. Most wells in the area increased or decreased their flow of water. Between the towns of Milton-Freewater and Uma— pine, many ground cracks as much as 0.6 m in width developed. The general direction of the cracks was roughly parallel to the Touchet fault. The largest earth fractures were observed about 6.5 km west of Sunnyside, near Glencove. On a hillside, an irregular area about 24 m wide was broken by cracks into blocks of several sizes and shapes. The uphill side of the area, in one cross section, dropped about 2.5 m, and the lower side displaced to the north about 2.5 m, pushing over and covering a 15-m length of rail- way fence. The largest cracks were about 0.6 m wide, but most were not more than 8 cm wide. Water was forced out of the ground in many places. Also felt in Idaho (see fig. 54). Aftershocks occurred to Nov. 17,‘ 1936. (Ref. 9, 260, 495, 510.) 1941. Dec. 29. Portland, Multnomah County, Oreg. This minor earthquake shattered a display window in downtown Portland, cracked chimneys about 50 km southwest of Portland, at Yamhill, and cracked plaster near Portland at Hillsboro and Sher- wood and north of Portland, at Woodland, Wash. (Ref. 14, 53.) 1953. Dec. 16 (Dec. 15). Portland, Multnomah County, Oreg. The shock cracked plaster and chim- neys and damaged fireplace tile slightly at Portland. A one-story building also was cracked, and a leak developed in an apartment building. In Vancouver, Wash., commercial buildings of block and concrete 341 were damaged slightly and plaster was cracked. (Ref. 26, 53.) 1957. Nov. 17 (Nov. 16). Northwest of Salem, Marion County, Oreg. Walls and plaster cracked and furnishings shifted in West Salem. Also felt in the State of Washington. (Ref. 30.) 1961. Aug. 19 (Aug. 18). Northwest Oregon. Damage was most severe at Lebanon (Linn County), where two chimneys toppled, store windows broke, and two traffic lights and five signs fell. Plaster walls were cracked at nearby Albany. Also felt in Washing- ton. (Ref. 34, 266.) 1963. Dec. 27 (Dec. 26). Northwest Oregon. Slight damage, mainly in the form of cracked plaster, occurred in Washington County, at North Plains and Timber, Greg, and in northern Cowlitz County, at Toutle, Wash. Also, furnishings and small objects shifted. A car on the Tillamook-Portland Highway swayed to the opposite side of the highway before being controlled. (Ref. 36, 266.) 1968. June 4, 02 34 UTC (June 3). Southern Oregon. Old chimneys fell or sustained cracks at Adel, in southern Lake County. Also, part of an old rock cellar fell, and the rest of the building was cracked. About 4 km northwest of Fort Bidwell, Calif, along Bidwell Creek, cracks formed in the ground, and a house foundation cracked and shifted. (Ref. 41, 74.) 1976. Apr. 13 (Apr. 12). Northern Oregon. This minor earthquake opened cracks in plaster and drywall at Dufur and Wamic, south of The Dalles, in Wasco County. Also felt in southern Washington. (Ref. 49, .'74.) . . v ‘ $1,1K\i..l1 A“ , ‘ ‘ 1 ‘ ‘ r ‘ ‘ ‘ B l: ‘ 1 if ¢L ‘V? y { ‘ l ‘ A 4:».Illl «ww1t’lv‘lfi‘il ‘ ‘ ‘ ,m . ‘ ‘ “M .. , a A. \ M , ~ . ‘ .c x J u. 1.... ., ‘2,4§_....,.X at, PENNSYLVANIA .H> N 56¢an .8 m.v N movsficmmfi HEB «mamzxnmccwm S. mmxmsufiumm L. A . . E QZM<2 <> >9 0 , m 25208.2; c 938:8: Y o E C O m o 5932:; E . T J O 959?. W E N <~Z<>A>mzzmm 0 Q m 0 coEflomo L\ _|l_ll_ m:m_\v\ __>?.m-o.m O gum—29.x 2: o .23-: C an? 5:}-3 O Aw >=wc2c<8§cm§ MMO> Bun—Z E V/ ZO_._.~ 3 EXPLANATION \ Magnitude/Intensity IOWA O 3.0-4.4/Vl O 4.5-4.9/VI NEBRASKA 42° 0 100 KILOMETERS 3 Earthquakes in South Dakota with magnitudes 2 4.5 or intensity 2 VI. 355 356 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) SOUTH DAKOTA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (0) indicates information is not available} Origin Hypocenter Magnitude Intensity Date ti"1001113) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 9 (°) (°) (km) mb Ms M (1.000 m2) 1906 05 10 0027 43.0 N 101.3 W — 105 -- -- 3.70Mf. SC -— VI 105 45 1911 06 02 22 34 44.2 N 98.2 W — 38 —-— —— 4.50Mfa BAR -— V 105 100 1922 01 02 14 50 43.8 N 99.3 W — 105 — -— —— — VI 105 — 1946 07 23 0645 44.1 N 98.6 W —— 105 — — 4.10Mfa SC — VI 38 22 1961 12 31 16 36 05.8 44.250N 100.724W 023 349 — — 4.20Mf. SC — VI 34 34 1966 06 26 11 59 43.1 44.296N 103.428W 002 349 — — 3.10Mn BAR — VI 38 3 1983 03 04 0632 18.6 44.214N 99.409W 005 360 4.4 —— 4.40ML GS —— VI 360 42 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1906. May 10 (May 9). South Dakota— Nebraska border. This earthquake was reported all along the Niobrara River valley from Rushville to ' Valentine, Nebr., and at Rosebud, S. Dak., about 100 km southwest of Pierre. Plants fell from a windowsill at Cody, Nebr. Residents of towns for 100 km in all directions felt the shock. (Ref. 105, 353.) 1922. Jan. 2. Near Winner, Tripp County, S. Dak. Chimneys were thrown down and dishes and Windows were broken at Winner, about 130 km south of Pierre. (Ref. 105.) 1946. July 23. Wessington, Beadle County, S. Dak. A series of earthquakes broke five water mains in the Wessington area, east of Pierre, and awakened sleepers at nearby Huron. Generally felt from Pierre east to De Smet and northward, including Redfield. Magnitude 4.2 Mfa BAR. (Ref. 38, 105, 353.) 1961. Dec. 31. Pierre, Hughes County, S. Dak. Cracks formed in plaster and a concrete floor at Pierre and a clothes drier was moved several centi- meters. Felt from Pierre west to Midland (Haakon County) and east to Huron (Beadle County). Magni- tude 4.3 Mfa BAR, 4.2 Mfa DG. (Ref. 34, 349, 353.) 1966. June 26. Southwest South Dakota. At Keystone (in Lawrence County, near Rapid City), well water was muddied for several hours. At Rapid City, a patio and concrete steps were cracked and objects fell from walls. Felt over a small area of southwest South Dakota. (Ref. 38, 349, 353.) 1983. Mar. 4. Near Fort Thompson, Buffalo County, S. Dak. This moderate earthquake caused minor damage at Fort Thompson (cracks in walls and ceiling), Lower Brule (cracks in reinforced concrete foundation, ceilings, and walls), and Stephan (cracks in exterior brick walls). Also felt in western Minne- sota and northern Nebraska. Magnitude 4.6 Mn TUL. (Ref. 360.) TENNESSEE H> N 36:85 .8 9v N mwvdfismma £15 33¢:st E mwxmdcfiamm <~OMOM© £wNZ O thnmhmgo O 8E5 } r HZ~O~=> W 3.3 O m _>\m.v.m.¢ O O _>\v.¢.m.m o WMODFZWM m >3wc£c .3 d . .|.l._ NEW MEXICO g M U) 0 0 Dallas 32° N o '5' P330 v'MidIand o o S TEXAS g E > Z O > A t' UNITED us m . Houston A z: o “'18 4’» ’YICO '7), 28" W 00 EXPLANATION $69 Magnitude/Intensity § (fl 0 3.8-4.4/Vl 00v 0 4.5-4.9 O 0 200 KILOMETERS 5.5-5.9 . Brownswlle Earthquakes in Texas with magnitudes 2 4.5 or intensity 2 VI. 361 362 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TEXAS [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1891 01 08 06 00 31.7 N 95.2 W — 342 -- 3.80M“ BAR -— VI 342 @ 1917 03 28 19 56 35.4 N 101.3 W — 364 -— — 3.80Mf. SC -— VI 364 5 1925 07 30 12 17 35.4 N 101.3 W —- 364 — —— 4.90MfI SC — VI 364 520 1931 08 16 ll 40 22.3 30.502N 104.575W 001 214 — — 5.80Mn NIT — VIII 4 980 1932 04 09 10 17 31.7 N 96.4 W -— 342 — — 3.90Mf. SC — VI 342 8 1936 06 20 03 24 03.5 35.3 ION 100.773W 005 349 -— —— 4.40Mf, SC -— VI 364 87 1948 03 12 04 29 06.3 36.221N 102.478W 005 349 — — 4.50M“ SC — VI 364 123 1966 08 14 15 25 53.7 32.115N 102.339W 003 349 3.4 — 4.30M“ BAR — VI 81 ~— 1974 02 15 13 33 49.2 36.399N 100.688W 000 349 4.5 — 4.50M“ DG 4.35HRN V 47 45 1978 06 16 ll 46 56.0 32.990N 100.875W 003 349 4.4 —— 4.60Mn SLM 4.48VOS V 240 52 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1887. May 3. Northern Sonora, Mexico. Chimneys were thrown down in El Paso, Tex. See Arizona section for a complete description of this earthquake. (Ref. 38, 343, 471, 494, 497.) 1891. Jan. 8. Rusk, Tex. A strong local earth- quake thre w down chimneys at Rusk, southeast of Dallas, and awakened many residents. Two distinct shocks were felt. Some researchers have questioned the authenticity of this event, suggesting that it may have been a violent thunderstorm or a tornado. (Ref. 342, 353.) 1917. Mar. 28. Panhandle area, Carson County, Tex. Ceiling plaster fell to the floor of the bank and the walls of many buildings were cracked at Panhandle, east of Amarillo. Distinctly felt in northern Carson County and southern Hutchinson County. Magnitude 3.8 Mfa BAR. (Ref. 353, 364.) 1925. July 30. Panhandle area, Carson County, Tex. ‘ Plaster fell and jars were displaced from shelves at Plemons; ground settling resulted in damage to a section of track of the Santa Fe Railroad at Cuyler. Plaster was shaken from ceilings at Guy- mon, Okla., north of Panhandle. Also felt in Colo— rado, Kansas, Missouri, and New Mexico (see fig. 56). Magnitude 4.9 Mfa BAR. (Ref. 218, 353, 364.) 1931. Aug. 16. Near Valentine, Jeff Davis County, Tex. In terms of magnitude and damage, this is the largest earthquake known to have occurred in Texas. The most severe damage was reported at Valentine, where all. buildings except wood-frame houses were damaged severely and all brick chimneys toppled or were damaged. The schoolhouse, which consisted of one section of con- crete blocks and another section of bricks, was dam— aged so badly that it had to be rebuilt. Small cracks formed in the schoolhouse yard. Some walls collapsed in adobe buildings, and ceil— ings and partitions were damaged in wood-frame structures. Some concrete and brick walls were cracked severely. One low wall, reinforced with con- crete, was broken and thrown down. Tombstones in a local cemetery were rotated. Damage to property was reported from widely scattered points in Brewster, Jeff Davis, Culberson, and Presidio Counties. Landslides occurred in the Van Horn Mountains, southwest of Lobo; in the Chisos Mountains, in the area of Big Bend; and farther northwest, near Pilares and Porvenir. Landslides also occurred in the Guad- alupe Mountains, near Carlsbad, N. Mex., and slides of rock and dirt were reported near Picacho, N. Mex. Well water and springs were muddied throughout the area. Also felt in parts of Oklahoma, New Mexico (see fig. 57), and in Chihuahua and Coahuila, Mex- ico. Magnitude 6.4 Mfa SAN, 5.8 MI] NTT, 6.4 Ms GR, 5.7 Mfa SC. (Ref. 4, 99, 124, 353, 364.) 1932. Apr. 9. Wortham, Freestone County, Tex. At Wortham, northeast of Waco, weakly mor- tared concrete bricks fell from at least four chimneys. Felt in Freestone, Hill, Limestone, McLennan, and Navarro Counties. Magnitude 3.6 Mfa BAR, 3.9 Mfa CAR. (Ref. 342, 353.) EARTHQUAKES IN TEXAS 363 106° 104° 102° 100° 98° 96° 94° 40° 38° . Woodward o o 36 34° l _, / TEX. Dallas ‘ o l i o . 32 --,—~—. _____________________ l \(37) EXPLANATION 4A9) 6’75 1") San Angelo * Epicenter O ‘73:? . VI Intensitys \ 0 100 KILOMETERS I , < FIGURE 56.—Isoseismal map for the Texas Panhandle earthquake of July 30, 1925. Isoseismals are based on intensity estimates from data listed in references 218 and 364 of table 1. 1936. June 20 (June 19). Near Pampa, Gray County, Tex. The last shock of a series of three on this date cracked the cornice of the Pampa City Hall and enlarged an existing crack. Houses were jarred strongly at nearby Borger. Slight damage also was reported in Elkhart, Kans., and Kenton, Okla. Also felt at Richards, Colo. Magnitude 4.5 Mfa BAR, 4.5 Mfa DG. (Ref. 349, 353, 364.) 1948. Mar. 12 (Mar. 11). Hartley County in northwest Texas. Cracks in walls and plaster were reported from several towns in the epicentral region, including Amarillo, Panhandle, and Perico. Slight damage to plaster also was reported in Colo- rado, New Mexico, and Oklahoma. Also felt in Kan- sas. Magnitude 4.8 Mfa BAR, 4.8 Mfa DG. (Ref. 349, 353, 364.) 1966. Aug. 14. Kermit, Winkler County, Tex. At Kermit, windows were broken and several street signs were knocked down. Plaster was cracked in one church. Also felt at Wink, Tex., and Loco Hills, N. Mex. (Ref. 81, 349, 353.) 364 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 110° 108° 106° 104° 102° 100° 98° 96° 94° ' l . I f I I "I \ UTAH I I I I- COLORADO I KANSAS I MISSOURI ..... T""‘—* _ _ _ _ _ _ ._._. I ._I_._. .._._._.—-—--—-- _.__._._A_«I_ ‘ ——————————————— .r _______ .l. .................... I ! i I_ __ ______ I . I - r- ....... _ _____________ I ‘. 36° I I I 'l ——- I — § .a / ! .Oklahoma CW :3; 1 / \ / .’ l . ; ARIZON I / . ~ —’ I . , l A z A I. Albuquerque I Amanlio I OKLAHOM g; I NEW MEXICO I I \ \ m l A A V 7- I \/ . / ' '; .’ / - g !/ ® “_“| Dallas _; I g 32° Mldland ‘\. I, V _ '-"‘UN’LEREST‘TES .! 1 A MEXICO—u— " ‘ 30° \ O Houslon ' /, // '— ‘x -. 1/ \ \. 28° / \ K I 0 / $0 \ $0 /‘ 0“ k \ _ _— / ‘ 26° 06 EXPLANATION . ( 49¢ *7 Epiceme, Monlerrey Q7 .CUI'aca" Vm lnlenslty a (46 o ’2 24° '7 mo “0051an I FIGURE 57.—Isoseismal map for the Valentine, Texas, earthquake of August 16, 1931. Isoseismals are based on intensity estimates from data listed in references 4, 124, and 342 of table 1. 42° 40° 38° UTAH 114° 112° 110° EXPLAN IDAHO ATION Magnitude/Intensity 2 o 3.2-4.4/Vl 100 KILOMETERS 5 O 4.5-4.9/vn A g___O 5.0-5.4/VI _________._.. (8" E O 5.5-5.9/vu . 0 an CD 0 O 6.0-6.4/Vlll 0 D > . Salt Lake City Vernal 63° ' O C < UTAH 9: O > O 0 E a O 8 0 © :0 Richfiel O E; O o Moab 0 o o O @0 Cedar City Q 0 ARIZONA N- MEX- 4i Earthquakes in Utah with magnitudes 2 4.5 or intensity 2 VI. 365 366 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) UTAH [See table 1 for hypocenter and intensity references and table 2 for definitions ofmagnitude source codes. @. felt area is less than 1,000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Oiher Moment MM Ref Felt area Yr Mo Da h m 3 (°) (°) (km) mb Ms M (1,000 kmz) 1876 03 22 39.5 N 111.6 W — 298 — -— -— — VI 52 3 1887 12 05 15 30 37.1 N 112.5 W —— 38 — —— —— — VI 38 — 1891 04 20 13 55 37.1 N 113.6 W — 298 —- — —— —— VI 52 3 1894 O7 18 2250 41.2 N 112.0 W —— 38 — —-— — — VI 298 —- 1900 08 01 0745 40.0 N 112.1 W — 298 —— — -- --— V11 52 — 1901 ll 14 0432 38.7 N 112.1 W —— 38 — — — — VIII 52 130 1902 ll 17 19 50 37.4 N 113.5 W —— 38 — —- — — VIII 52 —- 1902 12 05 37.4 1N 113.5 W —— 298 -— —— — — VI 52 — 1909 10 06 0241 41.8 N 112.7 W —- 298 — — — — VII 38 78 1910 01 10 1300 38.7 N 112.1 W — 298 — — — — VI 52 -- 1910 01 12 0300 38.7 N 112.1 W —- 298 — —- -— -— VI 52 — 1910 05 22 1428 40.7 N 111.8 W -— 298 — — — — VII 52 9 1914 05 13 1715 41.2 N 112.0 W — 298 —- —- — — VII 38 21 1915 07 15 2200 40.4 N 111.6 W — 52 —- — — — VI 272 13 1921 09 29 1412 38.7 N 112.1 W —- 298 —— — 5.20UknPAS — VIII 38 3 1921 09 30 0230 38.7 N 112.1 W —— 298 —— — — — VII , 38 @ 1921 10 01 1532 38.7 N 112.1 W — 298 -— — — -— VIII 38 @ 1933 01 20 13 05 37.8 N 112.8 W —— 298 —— —— — — VI 6 3 1934 03 12 15 05 40 41.7 N 1128 W — 7 — -— 6.60Ms GR 6.54DOS VIII 7 405 1934 03 12 17 29 41.5 N 1125 W — 315 —— —- 4.80Mx JON —- Felt 259 — 1934 03 12 1812 41.5 N 112.5 W —— 315 — —-— 5.10Mx JON — Felt 259 — 1934 03 12 182013 41.5 N 112.5 W —- 258 — — 6.00Ms GR 5.61DOS VII 298 165 1934 03 15 12 01 41.5 N 112.5 W — 315 — —— 5.10Mx JON — VI 259 -— 1934 03 15 13 46 41.5 N 112.5 W —— 315 — —— 4.80Mx JON — III 259 — 1934 04 07 02 16 41.5 N 111.5 W —- 7 — — 5.50Mx JON —- III 7 —— 1934 04 14 212632 41.5 N 112.5 W — 258 —— — 5.25Ms GR -- Felt 259 78 1934 05 06 080949 41.5 N 113.0 W — 258 — — 5.50Ms GR — VI 259 78 1936 09 21 0620 38.0 N 113.3 W — 298 — — 4.70Mx JON — Felt 315 —— 1942 08 30 23 08 37.7 N 113.1 W — 298 —-— — —— — VI 15 @ 1942 09 26 15 50 37.7 N 113.1 W — 298 — — —— — VI 15 @ 1943 02 22 14 20 40.7 N 112.0 W —- 265 — — -— — VI 16 26 1945 11 18 010741 38.8 N 112.0 W — 298 — —— —— — VI 18 — 1949 03 07 0650 40.7 N 111.8 W — 298 — — — — VI 259 — 1949 11 02 022938 37.0 N 113.5 W — 265 — —- 4.70UknPAS — V 22 4 1950 01 18 015551 40.5 N 110.5 W — 24 — —— 5.30UknPAS -- V 23 11 1958 02 13 225200 40.5 N 111.5 W — 31 — — — — VI 31 3 1959 02 27 221952 38.0 N 112.5 W — 32 — — — —- VI 32 4 1961 04 16 0502393 39.33 N 111.65 W — 234 — — — — VI 34 5 1962 06 05 22 2945.0 38.0 N 112.1 W 033 35 -— — 4.50ML PAS — —— — — 1962 08 30 13 35 28.7 41.917N 111.733W 010 556 —- — 5.70ML UU 5.85DOS VII 35 170 1962 09 05 160427.8 40.72 N 112.09 W 007 298 5.1 — 5.20ML UU 5.02DOS VI 35 42 1963 O7 07 19 20 39.6 39.53 N 111.91 W 007 298 4.9 — 4.40ML UU 4.97DOS VI 36 4 1966 03 17 11 47 47.4 41.66 N 111.56 W 007 298 4.4 — 4.60M; UU 5.22DOS V 81 16 1967 10 04 10 20 12.8 38.54 N 112.16 W 007 298 5.2 — 5.20ML UU 5.55DOS VII 40 74 1970 O3 29 1240403 41.66 N 113.84 W 007 298 4.6 —— 4.70ML UU —— V 43 — 1972 01 03 10 20 38.9 38.65 N 112.17 W 007 298 4.6 —— 4.4OML UU —- VI 45 5 1972 10 01 19 42 29.5 40.51 N 111.35 W 007 298 4.7 — 4.30ML UU — VI 45 6 1977 09 30 10 19 20.4 40.47 N 110.47 W 006 319 5.0 — 4.50ML CDL — VI 39 20 1978 03 O9 0630 51.9 40.76 N 112.09 W 009 298 —- —— 3.20ML UU —— VI 240 @ 1981 02 20 09 13 01.2 40.32 N 111.74 W 001 341 4.7 — 3.90ML UU —- VI 325 4 1981 04 05 0540397 37.59 N 113.30 W 001 341 4.2 — 4.60ML UU — V 325 23 1982 05 24 12 13 26.6 38.71 N 112.04 W 005 350 4.7 — 4.00ML UU —- VI 350 2 EARTHQUAKES IN UTAH 367 U TAH—Continued [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 kmz. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 3 (°) (°) (km) mb Ms M (1,000 km?) 1983 10 08 1157538 40.748N 111.993W 006 360 4.5 — 4.30ML UU — VI 360 7 1986 03 24 2240234 39.236N 112.009W 001 562 4.7 — 4.40ML UU — V 562 3 1986 03 25 0253012 39.223N 112.011W 001 562 4.5 —- 3.90ML UU — V 562 3 1987 09 25 0427 581 41.210N 113.152W 010 74 4.7 4.6 4.70ML UU — V 577 42 1987 10 26 04 16 00.9 41.203N 113.172W 009 74 4.3 — 4.80ML UU — IV 577 37 1988 08 14 2003 03.9 39.128N 110.869W 010 74 5.5 — 5.30ML UU —- VI 578 110 1988 08 18 124453.4 39.132N 110.867W 012 74 4.5 — 4.40ML UU — V 578 18 1988 11 19 1942 37.3 41.996N 111.472W‘ 006 74 4.9 — 4.80ML UU — VI 578 28 1989 01 30 040622.7 38.824N 111.614W 010 74 5.0 4.8 5.40ML UU 5.31HAV VI 579 148 1989 07 03 2244286 41.706N 112.373W 007 74 4.5 -— 4.80ML UU — V 579 4 1989 07 05 22 51 56.3 41.707N 112.371W 010 74 4.2 — 4.60ML UU — IV 579 4 [Reference (Ref.) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1876. Mar. 22. Moroni, northern Sanpete County, Utah. A local earthquake on the Thousand Lake fault cracked two buildings and sent Moroni residents running from their houses. (Ref. 52, 298.) 1887. Dec. 5. Kanab, Kane County, Utah. A local earthquake on the Sevier fault caused minor damage at Kanab, near the Arizona border. Bricks fell from chimneys, a few houses were cracked, and people who were walking were thrown to the ground. Rocks fell from nearby cliffs, causing large clouds of dust. (Ref. 38, 52.) 1891. Apr. 20. St. George, southern Washing- ton County, Utah. One chimney was thrown from a house, plaster was shaken from the walls, and dishes were broken at St. George, near the Arizona border west of Kanab. (Ref. 52, 298.) 1894. July 18. Northern Utah. Walls were cracked and dishes were shaken from tables at Ogden, north of Salt Lake City, in Weber County. Three distinct shocks were reported. (Ref. 38, 52, 298.) 1900. Aug. 1. Near Goshen, Utah County, Utah. At Goshen, southwest of Provo, dishes and a chimney were broken and plaster fell from walls. At nearby Santaquin, an adobe house was split in two and people were thrown from their beds. The mine shaft at the Mammoth mine at Santaquin was thrown out of line and the cage could not be lowered. (Ref. 52, 298.) 1901. Nov. 14 (Nov. 13). Southern Utah. An earthquake on the Tushar fault caused much damage to brick buildings and chimneys from Parowan (Iron County) on the south to Richfield (Sevier County) on the north. Extensive rockslides occurred between Beaver and Marysvale, in Piute County. Masses of fallen rock in Bullion and Cottonwood Canyons made the roads almost impassable. Water and sand were ejected from cracks that formed in the ground about 5 km east of Richfield; creeks in the area increased their flow. Many towns sustained minor damage. Aftershocks continued for several weeks. Also felt at Salt Lake City, 220 km to the north. (Ref. 38, 52.) 1902. Nov. 17. Pine Valley, Washington County, Utah. Every chimney was destroyed in Pine Valley, north of St. George, and rockslides occurred in the nearby mountains. At Santa Clara, south of Pine Valley, almost every chimney was knocked down. Buildings were damaged consider- ably at St. George; chimneys and plaster fell at Pinto. The earthquake reportedly was felt as far north as Salt Lake City. (Ref. 38, 52.) 1902. Dec. 5. Pine Valley, Washington County, Utah. Many aftershocks occurred at Pine Valley, keeping chimneys in “disrepair.” Students were dismissed from school because of the shocks. (Ref. 52, 298.) 1909. Oct. 6 (Oct. 5). Hansel Valley, Utah. The earthquake was felt by people on a northbound train approaching Logan in Cache County. Waves report- edly rolled over a bathhouse pier at Saltair, a few kilometers west of Salt Lake City. Windows were cracked at Salt Lake City. Felt from Lehi, Utah (about 25 km northwest of Provo), north to Malad 368 City, Idaho, a distance of about 200 km. West of Logan, in the Garland-Tremonton area, 30 to 60 earthquakes were reported to December 1909. A few were strong enough to throw down chimneys. (Ref. 38, 52, 298.) 1910. Jan. 10. Richfield, Sevier County, Utah. A local earthquake on the Tushar fault broke win- dowpanes at Richfield. School was dismissed at nearby Elsinore, where six severe shocks were observed. (Ref. 38, 52, 298.) 1910. Jan. 12 (Jan. 11). Elsinore, Sevier County, Utah. Located on the Tushar fault, this local earthquake shook down chimneys and destroyed merchandise on Elsinore store shelves. (Ref. 52, 298.) 1910. May 22. Salt Lake City, Utah. Many chimneys were demolished and several buildings were damaged in Salt Lake City, but well-constructed buildings were damaged little. Slight damage was reported at Bingham and Garfield. This local shock centered on the Wasatch fault. (Ref. 52, 298.) 1914. May 13. Ogden, Weber County, Utah. Some chimneys toppled, walls cracked, and plate- glass windows broke at Ogden. Dishes were broken at Salt Lake City. (Ref. 38, 52, 298.) 1915. July 15. Provo, Utah County, Utah. An earthquake that was centered on the Wasatch fault cracked a few ceilings at Provo and shook dishes from shelves. (Ref. 52, 272.) 1921. Sept. 29. Elsinore, Sevier County, Utah. Elsinore is a small town in Sevier Valley, 240 km south of Salt Lake City. After about 2 weeks of light foreshocks at Elsinore, three damaging local earthquakes occurred: two on Sept. 29 (local time) and one on Sept. 30. The first strong earthquake threw down scores of chimneys, or broke them at roof level, and fractured and displaced walls. A new two-story brick schoolhouse was damaged when a fire wall fell and several pilasters on the front of the building were dislodged. Gables of houses were “thrown out.” The front of one store building was cracked severely (it collapsed in the strong shock on Oct. 1.). Considerable damage also occurred at the nearby towns of Joseph, Monroe, and Richfield. The shocks continued from Sept. 12 to Dec. 20, 1921. (Ref. 38, 52, 298, 311.) 1921. Sept. 30 (Sept. 29). Elsinore, Sevier County, Utah. The second damaging earthquake of this series of shocks toppled many chimneys and increased the damage caused by the previous earth- quake (see paragraph above). At Monroe, about 8 km south of Elsinore, this earthquake was more destructive than the first shock on Sept. 29 at 14 12 UTC. Felt slightly at Joseph and Richfield. (Ref. 38, 298, 311.) SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 1921. Oct. 1. Elsinore, Sevier County, Utah. The third destructive shock of this series of earth- quakes at Elsinore downed chimneys that remained upright and caused additional structural damage. Heavy damage was sustained by buildings made of stone or “sun-dried brick” [adobe(?)]. Ten houses were wrecked and made uninhabitable. The store building that was cracked severely in the first shock on Sept. 29 collapsed during this earthquake. Large rockfalls occurred on both sides of Sevier Valley. Warm springs were discolored for hours. Additional damage was reported at Monroe, but the shock was only lightly felt at Joseph and Richfield. (Ref. 38, 52, 298, 311.) 1933. Jan. 20. Parowan, Iron County, Utah. A local earthquake on the Hurricane fault cracked plas- ter at Parowan and caused slight damage to brick, masonry, and concrete. Plaster also was cracked a few kilometers north, at Minersville. (Ref. 6, 52, 298.) 1934. Mar. 12, 15 05 UTC. Near Kosmo, Box Elder County, Utah. This earthquake occurred in Hansel Valley, a sparsely populated area. Two people were killed. Property damage was limited mainly to downed chimneys and cracked walls in poorly con- structed brick buildings. Chimneys were downed in several towns in the County, including Hooper, Kel— ton, Kosmo, Locomotive Springs, Monument, and Snowville. Large rockslides occurred at Aragonite, Lakeside, Monument Rock, and Snowville. An out- standing feature of this earthquake was the large quantity of water emitted from the craterlets and fis- sures that developed in the area. Most of the ground cracks that formed in the epi- central area occurred in poorly consolidated rocks on the salt flats. These cracks were traced for a dis- tance of more than 8 km. Four distinct fractures, about 1 km apart, developed across a road about 5 km north of Kosmo. The vertical displacement along the fractures ranged from about 7.5 to 25.5 cm. Pre- cise leveling surveys later revealed that areas of land sank as much as 39 cm. Horizontal displace- ment was not observed. Many springs formed in the epicentral area. Most of them developed along well-defined fractures in the salt flats where water flowed along the fissure. Notable exceptions, however, were the springs that formed in Monument Rock where water flowed at individual centers and formed mud cones. In places, large holes developed around the springs by the caving of the soft material through which the water flowed. Two such holes on the salt flats northeast of Monument Rock ranged in diameter from 2.5 to 3 m, and one was 11 m deep. Also felt in Idaho, Montana, Nevada, and Wyoming (see fig. 58). (Ref. 7, 52, 258, 533.) EARTHQUAKES IN UTAH 369 122° 120° 118° 116° 114D 112° 110o 108° 106° 104° 1 \ .‘ K. WASHINGTON ! \ N. D. Lewiston x"? 46° k 1 MONTANA .I- ------ j ‘ \_ ...... ‘ o Bozeman OREGON 44° WYOMING o Pocatello 42° ..- _ a "n‘—~__ w lg ' {A ! ' ‘ I o l'' U VIII ! Rock Springs . I ,— i / 5 i. ._._ ._._. I Salt Lake City 40° 1' I a ' ' Grand Junction “- COLORADO CALIFORNIA ‘-\ \- 38° \_ EXPLANATION'\I l * Epicenter -\ i . VIII Intensity 8 '\ i Cedar City '\ ‘ ._. ——————————— 100 KILOMETERS \_ I ............. _._._...._._.._. ‘—-'—“"‘ \. I ARIZONA NEW MEXICO \ FIGURE 58.—Isoseismal map for the Kosmo (Hansel Valley), Utah, earthquake of March 12, 1934. Isoseismals are based on intensity estimates from data listed in references 7 and 259 of table 1. 1934. Mar. 12, 18 20 UTC. Near Kosmo, Box Elder County, Utah. See description in the para- graph above for the effects of this earthquake because damage for the two shocks could not be sepa- rated. Thjs shock was reported to be slightly less severe than the first, but it was felt over a similar area of Idaho, Nevada, Utah, and Wyoming. (Ref. 258, 298.) 1934. Mar. 15, 12 01 UTC. Near Kosmo, Box Elder County, Utah. This earthquake damaged chimneys and overturned small objects in Locomo- tive Springs. It also was felt in Idaho. (Ref. 259, 298, 315.) 1934. May 6. Near Kosmo, Box Elder County, Utah. This strong earthquake apparently is an after- shock of the Mar. 12 event. A few windows were broken at Salt Lake City, and plaster was cracked at Preston, Idaho. (Ref. 52, 258, 259.) 1942. Aug. 30. Cedar City, Iron County, Utah. A 10Ca1 earthquake on the Hurricane fault shook bricks from a chimney in the northeast part of Cedar City. It knocked plaster from the walls of one house and cracked plaster at another. (Ref. 15, 259, 298.) 1942. Sept. 26. Cedar City, Iron County, Utah. A local earthquake on the Hurricane fault caused minor damage at Cedar City, including cracked walls, cracked plaster, and one broken plate- glass Window. (Ref. 15, 298.) 1943. Feb. 22. Near Salt Lake City, Utah. This earthquake, believed to be centered on the Wasatch fault, shook plaster from the wall and ceiling at the 370 Bingham High School and knocked down a chimney at Camp Kearns Air Force Training Center. The shock also cracked chimneys and broke windows and dishes at Magna and cracked plaster and windows at Salt Lake City. (Ref. 16, 259, 265.) 1945. Nov. 18 (Nov. 17). South-central Utah. Slight damage occurred in Sevier County, at Glen— wood and nearby Richfield. Chimneys and plaster were cracked and many residents were frightened. This local shock occurred on the Sevier fault. (Ref. 18, 298.) 1949. Mar. 7 (Mar. 6). Salt Lake City, Utah. A sharp local earthquake broke a pipeline, cracked walls in some houses, and broke windows at Salt Lake City. This shock, located on the Wasatch fault, also displaced furniture and tumbled dishes from shelves. (Ref. 22, 259, 298.) 1958. Feb. 13. North-central Utah. Plaster fell from ceilings and walls cracked in several build- ings in Utah County, at Provo. Plaster also fell from a wall in the student service center at Brigham Young University. Felt mainly in the region east of Utah Lake. (Ref. 31, 259.) 1959. Feb. 27. Panguitch, western Garfield County, Utah. A minor earthquake knocked plaster from ceilings, cracked walls, and broke dishes and windows at Panguitch. Felt in several towns in southwest Utah. (Ref. 32, 259.) 1961. Apr. 16 (Apr. 15). Near Ephraim, San- pete County, Utah. This earthquake caused minor damage at Ephraim and nearby towns to the north. ’va0 chimneys fell, plaster was cracked, and bottles were knocked from shelves at Ephraim; chimneys were cracked at Chester; and plaster was cracked at Mount Pleasant and Spring City. (Ref. 34, 234.) 1962. Aug. 30. Cache Valley, Utah. The earth- quake severely damaged many old, unreinforced brick buildings and other old structures on the east side of Cache Valley, Utah (from Logan to Lewiston). In Richmond (24 km north of Logan), where the most severe property damage occurred, 75 percent of the older brick chimneys collapsed and tombstones were overturned. One large church was damaged beyond repair. The walls of many houses were damaged badly, and building officials declared several houses were unsafe for occupancy. Heavy damage also occurred at Franklin, Lewiston, Logan, and Preston. Total property damage was estimated at $1 million. Mudslides were noted west of Lewiston, along the Bear River, and at Cornish. At Fairview, Idaho, two large areas of land broke loose and slid down a hill. Felt in parts of Colorado, Idaho, Nevada, Utah, and Wyoming (see fig. 59). (Ref. 35, 298, 556.) SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 1962. Sept. 5. Near Salt Lake City, Utah. Property damage occurred mainly in the area from Provo to Salt Lake City. It consisted of damaged chimneys, broken windows, minor cracks in walls and plaster, and loss from fallen stock in stores. In Salt Lake City, an outside wall of an older house fell through the ceiling; sections of interior walls and ceiling plaster fell at two other houses. Some large buildings sustained cracks in interior walls. Most of the damage to schools was superficial, consisting mainly of plaster cracks and loosened acoustical tile. Other towns reporting slight damage from this earth- quake were Draper, Lark, Magna, Morgan, and Provo. (Ref. 35, 298.) 1963. July 7. Central Utah. A minor earth- quake, felt over a small area of Juab County, caused slight damage at Levan and Nephi. Plaster fell and chimneys were cracked at Levan; plaster, walls, and chimneys were cracked at Nephi. (Ref. 36, 298.) 1967. Oct. 4. Central Utah. This earthquake caused minor damage in the Marysvale-Koosharem area. At Marysvale, in northern Piute County, brick and stone houses sustained many 'cracks in ceilings and walls; a cupboard in one house pulled away from the wall. Well water was muddied about 1.6 km north of Marysvale. Chimneys partly collapsed at Joseph, 20 km north of Marysvale, and root cellars caved in at Circleville, 30 km south of Marysvale. Rockslides were reported at Junction City, in the can- yon near Joseph, and 8 km south of Sevier. Also felt in northern Arizona. Magnitude 5.1 mb NUT, 4.7 MS NUT. (Ref. 40, 263, 298.) 1972. Jan. 3. Elsinore, Sevier County, Utah. An earthquake toppled chimneys and cracked walls at Elsinore and damaged the contents of houses con- siderably. Plaster was cracked at Central and Sevier. (Ref. 45, 72, 298.) 1972. Oct. 1. Midway, Wasatch County, Utah. This earthquake shook bricks from chimneys at Mid- way and cracked plaster at two schools. Slight dam- age (mainly cracks in plaster) also occurred at Salt Lake City, about 40 km northwest and, at Wallsburg about 15 km south. (Ref. 45, 72, 298.) 1977. Sept. 30. Northeast Utah. Damage was most severe at Mountain Home, east of Provo, in Duchesne County, where a septic system drain was broken and old mortar on a log house was cracked. There was an unconfirmed report of cracks in a stone fence and in interior plaster at Fruita and Grand Junction, 0010., more than 200 km southeast of the epicenter. A few indications of minor earth movement were found in the epicentral area two days after the shock: one possible rockfall in Rock Creek Canyon and EARTHQUAKES IN UTAH 371 116° 114° 112° 110° 108° X.-.‘ MONT. : . ('A'\I . (' ,. ,. , Q l. i 1 f\_ I' \,. .,.- - I! \J Worland 44° Twin Falls l 42° -._. . , . o Elko NEVADA 40° WYOMING o Sauna 0 100 KILOMETERS |—J——l 38° ; AH i L ............. ‘. .._.—, —————————————————————— _ gent Lake City % w Il-IV . P ' Graig i l i COLO. l EXPLANATION * Epicenter v" Intensity 7 FIGURE 59.—Isoseismal map for the Cache Valley, Utah, earthquake of August 30, 1962. Isoseismals are based on intensity estimates from data listed in references 35 and 259 of table 1. slumping of a rock slab in Farnsworth Canal, near Moon Lake. This earthquake occurred along a linea— ment that strikes N. 70° E. along the south flank of the Uinta Mountains and extends into the basin to the south. A lighter shock on Oct. 11 occurred along the same fault zone. Also felt in Idaho and Wyo- ming. Magnitude 5.1 ML GS. (Ref. 39, 319.) 1978. Mar. 9 (Mar. 8). Magna, Salt Lake County, Utah. This minor earthquake broke win- dows and cracked exterior walls, plaster, and drywall at Magna, west of Salt Lake City. (Ref. 240, 298.) 1981. Feb. 20. Orem, Utah County, Utah. A house foundation cracked at Orem, north of Provo, and hairline cracks formed in plaster and drywall. At 372 Provo, about 100 km south of Salt Lake City, a hair- line crack in a cinder-block wall was enlarged. (Ref. 325, 341.) 1982. May 24. Southwest Utah. This earth- quake was observed mainly in Sevier Valley, between Aurora and Joseph. The heaviest damage occurred at Annabella, about 25 km south of Aurora, where bricks fell from chimneys, stone or brick fences fell or were cracked, exterior walls of houses were cracked, and a garage roof was shifted 2.5 cm. Slight damage also occurred in the nearby towns of Elsinore, Glen- Wood, Koosharem, and Monroe. (Ref. 350.) 1983. Oct. 8. Northern Utah. At West Valley City (in the western suburbs of Salt Lake City), one chimney toppled, cracks formed in chimneys and plaster walls, and glassware was broken. Bricks fell from a chimney south of Salt Lake City, at Granger, and hairline cracks formed in walls of buildings at Layton and Sandy. (Ref. 360.) 1988. Aug. 14. Near Clawson, Emery County, Utah. This earthquake was felt over a wide area but caused only minor damage to property. Bricks fell from chimneys at Clawson, Elmo, Orangeville, and Sunnyside, and chimneys were cracked at Ferron and Wellington. Other reported damage included bro— ken Windows, and cracks in plaster, drywall, exterior brick walls, and foundations. This earthquake caused hundreds of rockfalls within 40 km of its epicenter. Ground cracks due to liquefaction of saturated alluvium were reported 4 km from the epicenter, and similar ground cracks SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) and a sand boil were observed in saturated alluvium 1.9 km from the epicenter. Flow of water into a spring in Tie Fork Canyon, 48 km from the epicenter, increased after the earthquake. Two foreshocks occurred on Aug. 14 at 18 58 and 19 07 UTC, and the largest aftershock caused one rockfall on Aug. 18. More than 100 aftershocks were located through Sept. 30. Felt to Brigham City, 280 km to the northwest of the epicenter; Delta, 156 km to the west; Albuquerque, N. Mex., 567 km to the south; Bluff, 233 km to the southeast; and Golden, 0010., 475 km to the east. (Ref. 74, 578, 590.) 1988. Nov. 19. Northeast of Logan, Cache County, Utah. Slight damage reported at Garden City included hairline cracks in plaster and cracks in a fireplace and in the foundation of a reinforced con- crete building. Some windows also were broken in the area. An observer at Logan reported broken pipelines and “some structural damage.” Felt over a small area of northern Utah and southeast Idaho. (Ref. 74, 578.) 1989. Jan. 30 (Jan. 29). Near Salina, Sevier County, Utah. Slight damage in the form of cracks in chimneys, walls, windows, and foundations occurred at Ferron (Emery County), Koosharem (Sevier County), and Wales (Sanpete County). In addition, underground pipes were broken at Salina, and large amounts of plaster fell from a ceiling at Wales. Felt in northern Arizona, western Colorado, eastern Utah, and southwest Wyoming. Several small aftershocks were reported. (Ref. 74, 579.) 45° 44° 43° VERMONT 73° 72° CANADA UNITED STATES . Newport B l' t ur mg on LL} 5 o Montpelier «'0’: Q, 5 I § VERMONT 5 o 2 >1 3 LL] Z EXPLANATION o Rutland Intensity 0 VI 0 100 KILOMETERS l__l____l /_r MASSACHUSETTS Damaging earthquake in Vermont, intensity 2 VI. 373 374 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) VERMONT [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt. area is less than 1.000 km2. Leader (--) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo D: h m 8 (°) (°) (km) mb Ms M (1,000 km?) 1952 01 30 04 00 44.5 N 73.2 W —— 77 —— — —— -—— VI 25 @ [Reference (Ref.) numbers given in parentheses at the end of long and 3.5 m apart were observed in the each description refertosources of data in table 1.] north end of Burlington_ Minor damage result- ing from this local shock included cracks in pave- 1952. Jan. 30 (Jan. 29). Burlington, Chit- ment, basement walls, and a gas main. (Ref. tenden County, Vt. Ground cracks about 3 km 25, 38, 77.) VIRGINIA .S N 36:35 .8 m4. N $62:ng £15 £595 3 mwxwacafiam 4%? \J 3 , . V \:.o.m o UCOEcoE AU 0 >:mc$c_\ou3_cmms_ O 20.225me n» It ,” \ o CEDHsz mm cofimmtmco a I q (14 K Emma fl 0 O . 0 ~ H _m>om EOE D OEAO 1|] \ » QZM- * Epicenter l BOIse l; IX Intensity 9 l l l l Megford 0 200 KILOMETERS l \ 42° \ _.__. | _._ _ -41 _.__ __ __ __ . FIGURE 61.—Isoseismal map for the central Washington earthquake of December 15, 1872. This is a simplified version of an unpublished map by M.G. Hopper and ST. Alger-missen. thrown to the floor; waves were observed in the Damaging intensities in Washington (MM intensity ground; and loud detonations were heard. About 3 VI) extended on the west throughout the now densely km above the Ribbon Cliff slide area, the logs on populated Puget Sound basin and on the southeast to another log cabin caved in. beyond the Hanford nuclear reactor site. The 384 earthquake also was reported in Idaho, Montana, Oregon, and Canada. Many aftershocks were observed in the area over the next 2 years. (Ref. 373, 375, 518.) 1877. Oct. 12. North of Portland, Greg. in Clark County, Washington. ’IVVo earthquakes were reported felt in northern Oregon. The first light shock occurred east of Portland, at Cascade Locks (Hood River County) at about 09 00 (local time). The second shock, about 5 hours later, was sufficiently violent at Portland to overthrow two chimneys and break windows. At the county jail, a stove was knocked from its “moorings” and thrown over. The second shock also was felt at Cascade Locks, Hub- bard, and Marshfield (18 km southeast of Portland). One report indicated that the earthquake was felt on Puget Sound and at points down the Columbia River. (Ref. 38, 53, 463, 484.) 1880. Aug. 22. Puget Sound area, Washing- ton. In Victoria, B.C., Canada, loose bricks fell and plaster was cracked. Also felt at Port Townsend and Seattle and on southern Vancouver Island. (Ref. 38, 375.) 1882. May 1 (Apr. 30). Near Olympia, Wash- ington. This severe earthquake threw down two chimneys, broke crockery, and stopped clocks on southern Puget Sound, at Olympia (Thurston County). Large trees swayed back and forth, the ground moved in a wavy motion, and people were thrown from their feet. Also felt at Fort Canby, Wash., Portland, Greg, and Victoria, B.C., Canada. (Ref. 56, 463.) 1891. Nov. 29. Near Port Angeles, Wash. One building in Seattle swayed so much that an elevator became jammed. On the east side of Seattle, Lake Washington was disturbed and the water “rolled onto the beach 2 feet above the mark of the highest water and 8 feet above the present stage.” At Port Townsend, northwest of Seattle, residents rushed from buildings, and windowpanes were broken in a hotel at Pysht (Clallam County). Also felt in Snohom- ish and Bellingham Bay. (Ref. 38, 56.) 1892. Apr. 17. Near Olympia, Washington. The shock was described as "severe" at Olympia, but "sharp" in the areas a few kilometers northeast, at Tacoma, Wash., and at Portland, Oreg., about 175 km south. People rushed into the street when buildings began to tremble in Portland. (Ref. 38, 56.) 1906. Jan. 3. Northeast Washington. At Nel— son, B.C., Canada, plaster was knocked down, arti- cles fell from shelves, and hanging pictures were displaced. TWO shocks were felt from the south boundary of Spokane County, Wash., to a point north of Bradshaw, B.C., Canada. (Ref. 38, 375.) SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 1909. Jan. 11. British Columbia—Washington border. This earthquake caused minor. damage in Whatcom and Skagit Counties. The shock cracked a sidewalk and damaged piers slightly at Anacortes, cracked walls near the Canadian border at Blaine, and cracked plaster and twisted sidewalks at Belling- ham. It was “violen ” at Crescent, Dungeness, Neah Bay, and Port Angeles. Crockery was broken at Victo- ria, B.C., Canada. Felt throughout much of British Columbia, Canada, and as far south as Portland, Oreg. (Ref. 38, 56, 375.) 1920. Jan. 24. (Jan. 23). Strait of Georgia, Northwest Washington. Windows were broken in Whatcom County, at Bellingham, and several brick walls were cracked at Bellingham and at Anacortes, a few kilometers south. Some damage to houses was reported in Canada, on Vancouver Island, and chim- neys were cracked at New Westminster. Boulders were shaken off Crown Mountain, near Vancouver, and some windows were broken in the city. (Ref. 38, 56, 374.) 1923. Feb. 12. Near Bellingham, Whatcom County, Wash. Plaster cracked at Bellingham, in western Whatcom County. Also felt at Marietta, Wash., and Victoria, B.C., Canada. (Ref. 56, 375.) 1928. Feb. 2. Startup, southern Snohomish County, Wash. Plaster and wallpaper were cracked and residents were alarmed at Startup, northeast of Seattle. A strong shake and roaring noises were reported. (Ref. 1, 38.) 1931. Apr. 18 (Apr. 17). Near Bellingham, Whatcom County, Wash. A few bricks fell from chimneys at Acme (about 25 km southeast of Bell- ingham), and wallpaper was cracked at nearby Lawrence. Felt at several towns in the area, including Vancouver and Victoria, B.C., Canada. (Ref. 4, 38.) 1931. Dec. 31. Puget Sound area, Wash. At Lilliwaup, north of Olympia, in Mason County, a new concrete wall of a store was cracked and a basin hanging on a nail was knocked down. Articles were thrown from store shelves in several towns in the area. (Ref. 4, 38.) 1932. July 18 (July 17). Near the forks of Tolt River, King County, Wash. The epicenter of this earthquake was in the wilderness east of Seattle, along the western base of the Cascade Range; there were few inhabitants and few buildings or other structures for the earthquake to affect. Fissures or other displacements of the ground were not observed in this region. Near the epicenter, on the South Fork, Tolt River, a tremendous detonation was heard and standing was almost impossible. One chimney was thrown down at EARTHQUAKES IN WASHINGTON Tolt. Some buildings were damaged north of Seattle, at Lowell and Everett; and windows were broken and standing was difficult at Farrell’s Ranch, northeast of Seattle and about 6 km east of Duvall. At cemeteries in Monroe and South Everett, several vases, small pots, and unattached statues were toppled. Felt to the east as far as Coulee City and Conconully, to the south as far as Chehalis and Centralia, and to the north as far as Bellingham, Wash., and Vancouver, B.C., Canada. The western felt limit is unknown. (Ref. 375, 496.) 1932. Aug. 6. Seattle, King County, Wash. A strong local shock demolished a few chimneys and severely damaged others at Seattle. Several slight shocks were felt in the area through early October. (Ref. 5, 38.) 1939. Nov. 13 (Nov. 12). Southern Puget Sound area, Washington. Slight damage to chim- neys, plaster, and windows occurred in towns throughout the area. Chimneys were twisted or fallen south and west of Olympia at Brooklyn, Cen- tralia, Elma, Fairfax, and Oakville, and east of Tacoma at Auburn. At Tacoma, many buildings sus- tained cracks; some chimneys were damaged; and pavement was cracked. Felt north to Canada and south to Oregon (see fig. 62). Four small aftershocks occurred in the next 9 days. (Ref. 12, 38, 258.) 1941. Apr. 7. Near Okanogan, Okanogan County, north-central Washington. An observer at Mazama, Okanogan County, reported that a stove was displaced and furniture was overturned. MM intensity V was assigned to effects at three other towns in Okanogan County: Nespelem, Okanogan, and Omak. (Ref. 14, 38.) 1943. Nov. 29 (Nov. 28). Puget Sound area, Wash. Chimneys were cracked and furniture was displaced west of Anacortes, at Richardson, San Juan County. Also felt at several other towns in the region. (Ref. 16, 38, 375.) 1944. Dec. 7 (Dec. 6). Near Aberdeen, Grays Harbor County, Wash. At Grays Harbor Junior College, at Hoquiam, a large brick chimney on top of a building rotated about 46 cm out of alignment and had to be replaced. (Ref. 17, 259.) 1945. Apr. 29. Near North Bend, King County, Wash. At North Bend, chimneys and plas- ter were cracked, and dishes, windows, and the town water main were broken. Near North Bend, at the Mount Si Ranger Station, tons of rock and earth cas- caded down the cliffs. Bricks were dislodged from a dozen or more houses in the Cle Elum area of Kitti- tas County. Minor damage occurred at several towns in the region. Felt over most of Washington and in western Idaho and northern Oregon. (Ref. 18, 20.) 385 1946. Feb. 15 (Feb. 14). Puget Sound area, Wash. Although property damage at Seattle gener— ally was moderate, it was marked by a few instances of spectacular damage (total estimate about $250,000). Structures that were most severely dam- aged included the Sears-Roebuck Building, Fisher flour mills and grain elevator on Harbor Island, Fry & Company packing plant, Seattle Port of Embarka- tion Building No. 14, and Smith Tower. Several old brick chimneys at Tacoma broke off at the roofline, and about 24 m of fire wall was knocked off the Olympia Hotel in Olympia, southwest of Tacoma. Light damage occurred at several nearby towns. Also felt in Canada and northwest Oregon. Three small aftershocks occurred through Feb. 22. (Ref. 19, 260.) 1946. June 23. Strait of Georgia, B.C., Can- ada. Heavy damage occurred in the epicentral area. The Canadian Hydrographic Department reported the bottom of Deep Bay in the Strait of Georgia sank from about 3 to 25 m. A 3-m vertical ground shift occurred on Read Island, and ground settlements as much as 30.5 m were observed at other points. In the United States, some chimneys fell at East Sound, San Juan County, Wash.; a concrete mill was damaged at Port Angeles; and buildings were dam- aged slightly at Northport, Port Townsend, and to the south as far as Olympia. At Seattle, plaster fell in the County~City Building, and a few bricks fell from the Sears-Roebuck Building. Also felt at several towns in Oregon. (Ref. 19, 38, 258.) 1949. Apr. 13. Puget Sound area, Wash. This is the largest known earthquake in the history of Washington. Its epicenter lies between Olympia and Tacoma, along the southern edge of Puget Sound. Property damage in Olympia, Seattle, and Tacoma was estimated at $25 million; eight people were killed; and many were injured. Several structures were condemned, including two schools and a church at Centralia, south of Olympia; a junior high school at Auburn, northeast of Tacoma; and a library at Chehalis, near Centralia. School buildings in widely separated towns were damaged seriously. Water spouted from cracks that formed in the ground at Centralia, Longview, and Seattle. One new spring developed on a farm at Forest. Downed chimneys and walls were reported from towns throughout the area. At Olympia, almost all large buildings were dam- aged to some extent, including eight structures on the Capitol grounds. Many chimneys and two large smokestacks fell. Public utilities sustained serious damage—water and gas mains were broken, and electric and telegraph services were interrupted. At Seattle, houses on filled ground were demol- ished, many old brick buildings were damaged, and 386 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 124° 122° 120° 118° CANADA ......................................... F ~ ......... (JfifiébEfire—s ............... Victoria Q% 48° % Seattle <- N V WASHINGTON Aberdeen > 3 4 0 Vl-Vll VI 3 Yakima o 6 46° \] '\.\ 1 V a \ \ ,.\ .—. ,1 r; \\ Portlandk.‘~\. . - ’ W'- s"? A z / / / / N ~r / \ I OREGON 44o \Eugezel EXPLANATION [J * Epicenter 0 \oo KILOMETERS l VII Intensity 7 '_—"——J l FIGURE 62.-—Isoseismal map for the northwest Washington earthquake of November 13, 1939. Isoseismals are based on intensity estimates from data listed in references 12 and 259 of table 1. chimneys toppled. One wooden water tank and the top of a radio tower collapsed. About 50 km northeast of Olympia, at Tacoma, many chimneys were knocked to the ground and many buildings were damaged. Near Tacoma, a huge section of a 73-m cliff toppled into Puget Sound shortly after the earthquake; south of Tacoma, rail- road bridges were thrown out of alignment. A 23-ton cable saddle was thrown from the top of the Tacoma Narrows bridge tower, causing considerable damage. Also felt in Idaho, Montana, Oregon, and in British Columbia, Canada (see fig. 63). Only one small aftershock occurred during the next six months. Magnitude 6.5 Ms ABE, 7.1 Ukn PAS, 7.0 Ms GR, 6.5 ML KJ. (Ref. 22, 38, 376, 460, 533.) 1950. Apr. 14. Near Langley, Island County, Wash. Plaster cracked and fell and small objects overturned at Langley. A few cracks formed in EARTHQUAKES IN WASHINGTON 387 124° 122° 120° 118° 116° 114° UNITED STATES Omak 0 48° WASHINGTON MONTANA OlilOVd 46° NVEIOO w \ Iverton o I 44 _ m ‘ Bend. I 42° EXPLANATION NEVADA 1* Epicenter VIII Intensity 8 0 100 KILOMETERS FIGURE 63.—Isoseisma1 map for the Puget Sound, Washington, earthquake of April 13, 1949. Isoseismals are based on intensity estimates from data listed in references 22 and 259 of table 1. plaster northwest of Langley, at Port Townsend, and formed in walls at Belfair (northwest Mason County) pendulum clocks stopped. Felt over a small area of and Lake Stevens; plaster cracked at Seattle (King northwest Washington. (Ref. 23, 38, 375.) County), and dishes broke at Skykomish (northeast 1954. May 15. Near Lake Stevens, Snohomish King County). (Ref. 27, 38, 266.) County, Wash. A moderate earthquake was felt 1957. Jan. 26 (Jan. 25). Northwest Washing- throughout northwest Washington. Small cracks ton. This earthquake was strongest at Clear Lake 388 (southeast of Bellingham, in Skagit County), where plaster cracked and fell at a school and a knickknack shelf was displaced. Felt over most of northwest Washington. (Ref. 30, 38.) 1957. Feb. 11. Near North Bend, King County, Wash. One chimney was cracked and knick- knacks fell at Fall City; plaster was damaged at North Bend and Snoqualmie. Observers over a small area of northwest Washington reported this earth- quake. (Ref. 30.) 1958. Apr. 12. North-central Washington. Windows and dishes were broken in some houses at Chelan and at Pateros and Winthrop, north of Chelan in Okanogan County. Rocks fell on roadways near Chelan. Moderate to loud earth noises were heard in most areas. (Ref. 31, 38.) 1958. Oct. 7 (Oct. 6). Willapa Bay, Pacific County, Wash. At a motel in Tokeland (at the north end of Willapa Bay), several cracks formed in a patio. Felt over a small area of Grays Harbor and Pacific Counties in western Washington. (Ref. 31, 38.) 1959. Aug. 6 (Aug. 5). Near Chelan, Wash. This minor shock, which was observed over most of the State, caused slight damage in a few towns. At Chelan, about 180 km east of Seattle, bricks and part of a chimney fell; at Orondo, southwest of Chelan, chimneys were cracked; and at nearby Waterville, chimneys were cracked and bricks fell from several buildings. Rocks slid down the steep hills near Chelan and Waterville. (Ref. 32, 38.) 1960. Apr. 11 (Apr. 10). Near Seattle, King County, Wash. At Seattle, a concrete wall was cracked and a wood retaining wall was damaged. Felt over a small area, mainly in western King County. (Ref. 33, 38.) 1960. Sept. 10. Puget Sound area, Washing- ton. A light earthquake cracked many concrete floors and walls in Bremerton, west of Seattle, and caused considerable plaster damage in Seattle. Felt over most of northwest Washington. (Ref. 33, 38, 266.) 1961. Sept. 17. Clark County, Washington near the Oregon-Washington border. Slight dam- age occurred at a few towns along the Columbia River. In southern Skamania County, chimneys and concrete foundations cracked at Stevenson, and an old house shifted about 2.5 cm on its foundation at North Bonneville. At Latourell Falls, Oreg., a few cracks formed in a concrete-block foundation. Felt over a small area of southwest Washington and northwest Oregon. (Ref. 34, 38, 266, 618.) 1961. Nov. 7 (Nov. 6). Clark County, Washing- ton near the north Oregon-Washington border. Minor damage occurred in the Portland, Oreg., area. Part of a chimney fell and interior lights were broken SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) at Portland; a concrete-block foundation of a service station was damaged at Glenwood, west of Portland; and windows were broken at Vernonia, north of Glen- wood. Felt over a large area of southwest Washington and northwest Oregon. (Ref. 34, 38, 266.) 1962. Nov. 6 (Nov. 5). Clark County, Wash- ington near the Oregon-Washington border. At Portland, Oreg., many chimneys were cracked severely, shaken down, or broken off. Tile ceilings were downed in several buildings; large cracks formed in walls; and plaster was knocked to the floor. Minor damage, consisting mainly of cracked plaster and chimneys and broken windows, occurred in many towns in both Oregon and Washington. Felt over a large area of southwest Washington and northwest Oregon. Magnitude 5 1/4—5 1/2 Ukn PAL, 4.9 MD YP. (Ref.35, 38, 266, 619.) 1962. Dec. 31. Near Berkley, Pierce County, Wash. Residents in several towns (mainly in Pierce County) reported cracks in chimneys and plaster. Chimneys were cracked southeast of Tacoma, at Ort- ing and Wilkeson, and walls were cracked at Buck- ley. Several rocks fell from a cut bank onto the road near Buckley. Cracks in chimneys also were reported in northern Yakima County, at Naches. (Ref. 35, 38, 266.) 1963. Jan. 24. Near Maple Valley, King County, Wash. At Maple Valley and Tacoma, cracks formed in plaster and walls and objects fell to the floor. Felt in many towns in western Washington. (Ref. 36, 38, 266.) 1964. July 14. Near Bellingham, Whatcom County, Wash. Slight damage, consisting mainly of cracks in plaster and walls, occurred at Bellingham, Custer, Nooksack, and Sumas. At Lumni Island, southwest of Bellingham, a fireplace chimney was split and mortar fell to the floor. In British Colum- bia, Canada, plaster cracked and fell at Abbotsford, and a ceiling cracked at White Rock. Loud earth noises were heard in several areas. Magnitude 3.7 Ms NUT. (Ref. 37, 38, 263, 266.) 1965. Apr. 29. Puget Sound area, Wash. This was the second largest earthquake in the history of Washington. It caused about $12.5 million in prop- erty damage and killed seven people. This shock was characterized by a rather large area of MM intensity VII and small pockets of MM intensity VIII in Seattle and suburbs and southeast of Seat- tle, in Issaquah. Pockets of high earthquake inten- sity, as typified by damage such as fallen chimneys, almost always were associated with variations in the local geology. Chimneys were damaged extensively in West Seattle, and two schools were damaged severely. The EARTHQUAKES IN WASHINGTON 389 Roof of house in Seattle, Washington, damaged by the April 29, 1965, earthquake. (Photograph from the National Geophysical Data Center, NOAA.) low-lying and filled areas along the Duwamish River and its mouth settled, causing considerable building damage. Harbor Island, at the mouth of the Duwa- mish River, was severely damaged. Slumping occurred along a steep slope near Admiral Way. A brick garage partly collapsed at Issaquah; one school was damaged extensively; and chimneys in the area sustained heavy damage. Many instances of parapet and gable failure occurred. Damage to utilities in the area was not severe. In general, damage patterns repeated those observed in the April 1949 shock, although the 1949 event was more destructive. Buildings apparently damaged in 1949 often sustained additional damage in 1965. An example is the Alki Beach section of West Seattle, where almost every chimney was knocked down in 1965. Similar damage occurred there in the 1949 earthquake. Buildings having unreinforced brick-bearing walls with sand-lime mortar were damaged most severely. Multistory buildings, however, generally had slight or no damage. Performance of wood frame dwellings almost always was excellent, and, where damage occurred, it was confined mainly to cracks in plaster or to failure of unreinforced brick chimneys at or above the roofline. Also felt in Idaho, Montana, Ore- gon, and in British Columbia, Canada. Little after- shock activity was observed. Magnitude 6.2 mb NUT, 6.4 MS NUT. (Ref. 38, 75, 263, 266, 377, 533.) 1975. Apr. 23 (Apr. 22). Puget Sound area, Wash. Slight damage occurred at Sumner, a few km east of Tacoma in Pierce County, where tar on a roof was cracked. Felt throughout the southern Puget Sound area. (Ref. 38, 48, 74.) 1976. May 16. Vancouver Island region, Can- ada. Minor damage occurred at Deming, Whatcom County, Wash., and Lake Cowichan and Victoria, BC. At Deming, cracks formed in plaster and dry- wall; at Victoria, one chimney was damaged; and at Lake Cowichan, a water line was broken. Felt over a large area of British Columbia and northwest Washington. (Ref. 38, 49, 74.) 1976. Sept. 8. Puget Sound area, Washington. Broken glassware and other minor damage were 390 reported at Tacoma, in Pierce County. Felt through- out the Puget Sound area. (Ref. 38, 49, 74.) 1978. Mar. 11. Puget Sound area, Wash. This minor earthquake cracked a rock-and—mortar wall at Crystal Mountain Ski Resort (in Mount Rainier National Park) and displaced open roof beams 1—2 cm. Felt over a moderate area of northwest Washing- ton. (Ref. 38, 240.) 1979. Mar. 11. Southwest Washington. Minor damage in Cowlitz County, at Ariel, included cracks in chimneys, exterior cinder-block walls, brick walls, and sidewalks. A few windows were cracked at Cas- tle Rock, northwest of Ariel. Felt over a small area of southwest Washington and northern Oregon. Magnitude 3.8 ML GS. (Ref. 38, 262.) 1980. May 18. Mount St. Helens, Wash., earthquake and volcanic eruption. An earth- quake occurred at 15 32 UTC, only seconds before the explosion that began the eruption of Mount St. Helens volcano. This eruption and blast blew off the top of the volcano, reducing its elevation by 396 m, killed 31 people, and caused an estimated property damage of between $0.5 billion and $2 billion. About 53 earthquakes having magnitudes larger than 4.5 were located near Mount St. Helens before the main event and eruption. No earthquakes having magni- tudes higher than 4.5 were located following the eruption. The sound from the explosion and the Vibratory effects from the earthquake were insepara- ble, resulting in a felt area that was based on both (Ref. 74, 300, 609.) 1981. Feb. 14 (Feb. 13). Southwest Washing- ton. Several towns in the area reported cracks in SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) foundations, plaster, drywall, and windows. Damage to chimneys (broken at roofline, twisted, cracked) occurred in Lewis County, at Mossyrock (near the epicenter); in Pierce County, at Graham and Kapowsin; and at Grays River, in Wahkiakum County (west of the epicenter). In Cowlitz County, about 50 km southwest of the epicenter, sidewalks were cracked at Ariel, and plaster fell at Hazel Dell. Felt over a large area of western Washington and northwest Oregon. Several aftershocks were observed in the area. Magnitude 5.2 MD WAS. (Ref. 74, 325.) 1981. Feb. 18 (Feb. 17). Central Washington. Bricks fell from chimneys in the Cle Elum area of Kittitas County. Hairline cracks in drywall as well as broken windows were reported at Puyallup, about 100 km west of the epicenter, near Tacoma. Minor damage to plaster, drywall, windows, and glassware was reported from several towns in theCle Elum area. A sharp crack or explosive-like sound was reported by some residents. Magnitude 4.2 MD WAS. (Ref. 74, 325.) 1989. May 9. Near Okanogan, Wash. This earthquake cracked chimneys, walls, and plaster at Okanogan, about 180 km northwest of Spokane. Objects fell from shelves and tables in several towns in north-central Washington. Felt in northern Okanogan County near the United States—Canadian border, west to Chelan County, south to Grant County, and east to Ferry and Lincoln Counties. (Ref. 74, 579.) 40° 38" WEST VIRGINIA 82° 80° 78° 100 KILOMETERS l___L__J PENNSYLVANIA Wheeling OHIO MD. Romney 0 o Clarksburg WEST VIRGINIA 0 Charleston VIRGINIA EXPLANATION Magnitude O 4.6 Earthquake in West Virginia with a magnitude 2 4.5 and intensity 2 VI. 391 392 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) WEST VIRGINIA [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. Leader (—-) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTO) Latitude Longitude Depth Ref USGS Other Moment MM Ref Felt area Yr Mo Da h m 8 (°) (°) (km) mb Ms M (1,000 kmz) 1969 ll 20 01 00 09.3 37.449N 80.932W 003 349 4.3 —— 4.60Mn GB 4.53HRN VI 42 300 [Reference (Ref) numbers given in parentheses at the end of old house, At Rich Creek, plaster cracked and fell each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1969. Nov. 20 (Nov. 19). Southern West Vir- ginia. Minor damage occurred in Giles County, Va., at Glen Lyn and Rich Creek, and at three towns in southern West Virginia. At Glen Lyn, a few bricks were knocked from a chimney, windows were broken, and plaster was broken from most of the walls in an and windows were broken. A cornice reportedly was shaken from one building in Henry County, at Col- linsville, Va. Windows also were broken in southern Mercer County, W.Va., at Lerona, Oakvale, and Elgood. Felt over all or parts of nine States: Geor- gia, Kentucky, Maryland, North Carolina, Ohio, South Carolina, Tennessee, Virginia, and West Vir- ginia. Magnitude 4.7 Mfa NUT, 4.54 M JOH. (Ref. 38, 263, 42, 349, 353, 508.) 44° 42° 40° 110° WYOMING 108° 106° 104° MONTANA m 0 C ...1 O OSheridan m A U i Q) o g 0 > 3 O E cglckson 9 ° WYOMING Lander. 0 Casper 3 0 % 0 U5 7°... > m 71 > 0 Rock Springs Cheyenne o EXPLANATION COLORADO Magnitude/ intensity UTAH O 4.5-4.9/Vl O 5.0-5.4/vn O 5.5-5.9 0| 100 KILOMETERS 0 6-0-6-4 0 6.5—6.9 Earthquakes in Wyoming with magnitudes 2 4.5 or intensity 2 VI. 393 394 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) WYOMING [See table 1 for hypocenter and intensity references and table 2 for definitions of magnitude source codes. @, felt area is less than 1,000 km2. Leader 1..) indicates information is not available] Origin Hypocenter Magnitude Intensity Date time (UTC) Latitude Longitude Depth Flef USGS Other Moment MM Ref Felt area Yr Mo Da h m 3 (°) (°) (km) mb Ms M (1.000 kmz) 1897 11 14 13 30 42.9 N 106.3 W -- 38 —— — — —- VI 38 — 1925 ll 18 0145 44.4 N 107.5 W —- 280 —— — — —— V 280 30 1930 06 12 0915 42.6 N 111.0 W — 3 —— —- — — VI 3 -— 1932 01 26 1013 43.5 N 110.7 W -— 5 — -— — — VI 279 3 1936 01 15 0440 44.0 N 111.0 W -— 38 — —- — — VI 38 3 1959 08 18 0756168 44.699N 110.705W 005 576 — — 6.50UknBRK — Felt 32 — 1959 08 18 08 41 47.5 44.854N 111.049W 005 576 — —- 6.00UknBRK —- VI 32 — 1959 08 18 1103 48.1 44.719N 110.850W 005 576 — -— 5.60UknBRK — Felt 32 — 1959 08 18 15 26 05.9 44.721N 110.871W 005 576 -— —— 6.50UknPAS 6.28DSR Felt 32 — 1959 08 19 040401.7 44.648N 110.840W 005 576 —- —- 6.00UknBRK 5.98DOR V 38 — 1959 08 19 19 43 47.2 44.756N 110.960W 005 576 — — 5.00UknBRK —— Felt 32 —- 1963 03 08 08 35 48.9 44.8 N 110.2 W 033 266 3.8 — —— — VI 36 @ 1963 09 24 0635 52.1 44.9 N 111.0 W 033 266 4.7 — — — V 36 — 1973 03 30 0032 56.1 44.34 N 110.34 W 001 307 4.6 — 4.60Mp GM — Felt 46 — 1973 03 31 20 33 31.8 44.35 N 110.41 W 001 307 5.1 — 4.70Mp GM — Felt 46 — 1974 06 09 0050 42.4 44.77 N 110.97 W 005 307 -— — 4.90ML GS — II 47 —— 1974 08 30 16 41 58.8 44.63 N 110.73 W 000 307 4.5 — 4.50ML GS —- V 47 — 1974 10 22 08 43 07.1 44.74 N 110.81 W 005 47 4.6 —- —- — IV 47 — 1975 06 30 18 47 57.1 44.68 N 110.61 W 003 307 4.6 —— 4.80ML GS — — — — 1975 06 30 18 54 12.7 44.68 N 110.62 W 002 307 5.6 5.9 6.40ML GS —-— VII 48 50 1975 06 30 190027.4 44.77 N 110.72 W 005 48 5.1 — 5.30ML GS — — — —— 1975 06 30 1956 33.7 44.71 N 110.52 W 005 48 4.7 — 4.50ML GS — — — ~— 1975 06 30 20 20 56.6 44.69 N 110.59 W 005 48 4.9 —— 4.60ML GS — H1 48 —- 1976 12 08 1440591 44.76 N 110.79 W 005 49 5.5 —-— 4.60ML GS — V 49 5 1976 12 09 22 36 23.7 44.77 N 110.80 W 005 49 4.5 — 5.10ML GS —— V 49 17 1976 12 19 171015.6 44.77 N 110.80 W 005 49 4.9 —- 4.50ML GS — V 49 @ 1980 02 22 10 18 27.7 44.81 N 110.90 W 000 308 4.5 —- 4.70ML GS — IV 300 — 1983 02 06 20 25 16.5 44.571N 110.643W 005 360 4.7 —- 4.50ML GS —— V 360 5 1983 12 20 22 52 23.7 43.294N 110.767W 005 360 4.5 —- — — IV 360 — 1984 05 29 20 18 29.6 44.134N 106.099W 015 522 5.0 -- 4.80M“ GDW —— V 370 56 1984 09 08 0059 31.1 44.138N 106.110W 015 522 5.1 —— 5.00Mn GDW 4.94JOH V 370 68 1984 10 18 15 3022.0 42.317N 105.735W 022 522 5.4 5.1 5.50M... GDW — VI 370 287 1984 11 03 0930 08.4 42.534N 108.919W 005 522 5.0 4.1 4.50Mn GDW — VI 370 15 1985 09 07 03 47 29.2 43.156N 110.724W 005 371 —- — 4.60ML GS —— V 371 22 [Reference (Ref) numbers given in parentheses at the end of each description refer to sources of data in table 1. Magnitude values are described in the Introduction, and codes are defined in table 2.] 1897. Nov. 14. Casper, Natrona County, Wyo. The northeast corner of the Grand Central Hotel at Casper sustained a 5- to 10-cm-wide crack that extended from the third to the first floor. The ceiling in the hotel lobby also was cracked. An almost deaf- ening noise preceded the shaking. (Ref. 38, 359.) 1930. June 12. Grover, northern Lincoln County, Wyo. A minor earthquake cracked a brick building in Grover and a concrete swimming pool north of Grover. Cracks also formed in plaster, and clocks stopped running. Slight aftershocks continued until Nov. 16, 1930. (Ref. 3.) 1932. Jan. 26. Western Wyoming. At Jackson, in southern Teton County, an earthquake cracked floors and foundations, broke plaster, and tore wall- paper. Slight damage also occurred in the nearby towns of Grovont, Kelly, and Moran. One light fore- shock was observed in the area on Jan. 25, and several minor aftershocks occurred through Jan. 28. (Ref. 5, 38, 279.) EARTHQUAKES IN WYOMING Rockslide on Virginia Cascade Road in Yellowstone National Park, Wyoming, caused by the earthquake of June 30, 1975. 1936. Jan. 15 (Jan. 14). Yellowstone National Park, Wyo. An earthquake caused extensive cracks in two chimneys at the south entrance to the park, in northwest Wyoming. (Ref. 9, 38.) 1959. Aug. 18, 08 41 UTC. Yellowstone National Park, Wyo. An aftershock of the August 17, 1959, earthquake at Hegben Lake, Mont, broke a chimney at the Old Faithful Ranger Station in north- west Wyoming. Also felt at Fairfield, Idaho. (Ref. 32, 38, 576.) 1963. Mar. 8. Yellowstone National Park, Wyo. At the winter caretaker’ s house in Canyon, large cracks separated the walls and ceilings in sev- eral rooms, and plaster cracked and fell. Aftershocks continued until Mar. 12. (Ref. 36, 266.) 1975. June 30. Yellowstone National Park, Wyo. This Widely felt earthquake downed one chim- ney in the park at Norris Junction and formed cracks 90 m long in a parking lot. Rockfalls and landslides closed or hindered traffic on many roads in the park. Two new geysers formed; the Gibbon River was mud- died; and the earth settled and cracked in the back- country. Several aftershocks occurred through early July. Also felt in Montana, Idaho, South Dakota, Nebraska, Nevada, Utah, and Washington. Magni- tude 6.1 Ukn BRK. (Ref. 38, 48, 307.) 1984. Oct. 18. Eastern Wyoming. Although this earthquake was felt over a large part of eight States (see fig. 64), only minor property damage occurred. The damage was characterized by cracked chimneys and 396 SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) 110° 108° 106° 104° 102° 100° '. | i TA MONTANA l NORTH DAKO 46° - _.__. _. _,.__.- o | Billings I l .' _ “ ' — ' — ------ —— - —~’ SOUTH DAKOTA (‘\ .' . "" ~I Pierre '- cgdy amine I ' u-m 44° '- . .l r O . I l | :5. ‘ WYOMING __ __ __ _______ - .l 7 ————— . i . Lander . Varem‘me . Douglas ! II—III IV * 42° _ _. / V VI I / / NEBRASKA I C . Rock Springs 1 ‘‘‘‘‘ — ..__ .__.__._.-._.. --1 “'l“ Kearney r i ° I I. 40° A . ‘——- ”””””””” - . v UTAH I Vzil . Denver Ii “—“I i Goodland i COLORADO I EXPLANATION . . - Grand Junction I * Eplcenter Colorado Springs I KANSAS VI lmens'ty 6 ‘ o 100 KILOMETERS - 38° I ‘- \I\fi r 1 '. FIGURE 64.—Isoseismal map for the eastern Wyoming earthquake of October 18, 1984. This is a simplified version of figure 28 in reference 370 of table 1. foundations and cracked brick and cinder-block walls at several towns, including Casper, Douglas, Guernsey, Hanna, Lusk, McFadden, Medicine Bow, Rock River, and Shirley Basin. Underground pipes were broken in Natrona County, at Casper, and in Carbon County, at Shirley Basin, about 40 km south of Casper. In addition, slight damage was reported at a few towns in Colorado, Nebraska, and South Dakota. An unusual report of structural damage to two five-story buildings was received from Golden, 0010., about 300 km south of the epicenter. This damage, which consisted of foundation failure, cracks in walls, EARTHQUAKES IN WYOMING and a gas leak, may not have been caused by the earthquake. Felt in Colorado, Kansas, Montana, Nebraska, South Dakota, Utah, and Wyoming. Mag- nitude 5.5 ML GS, 5.3 Mr1 TUL. (Ref. 370, 487, 522.) 1984. Nov. 3. Western Wyoming. At Lander, Fremont County, 50 buildings sustained cracks in 397 walls, foundations, and windows; and glass was bro- ken at the local hospital. About 30 km south of Lander, at South Pass City, cracks in windows and damage to glassware occurred, and residents had dif- ficulty walking and standing. Magnitude 4.9 ML EU, 5.1 ML GS. (Ref. 370, 522.) v, . ‘ ,H _ / . . . » TABLES 1—3 400 ' 45. 935° 99°99)?!“ 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 46. 47. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 1,—Hypocenter and intensity references [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Heck, NH, and Bodle, R.R., 1930, United States earthquakes 1928: U.S. Coast and Geodetic Survey, Serial 483, 28 p. Heck, NH, and Bodle, R.R., 1931, United States earthquakes 1929: U.S. Coast and Geodetic Survey, Serial 511, 55 p. Neumann, Frank, and Bodle, R.R., 1932, United States earthquakes 1930: U.S. Coast and Geodetic Survey, Serial 539, 25 p. Neumann, Frank, 1932, United States earthquakes 1931: U.S. Coast and Geodetic Survey, Serial 553, 26 p. Neumann, Frank, 1934, United States earthquakes 1932: U.S. Coast and Geodetic Survey, Serial 563, 21 p. Neumann, Frank, 1935, United States earthquakes 1933: U.S. Coast and Geodetic Survey, Serial 579, 82 p. Neumann, Frank, 1936, United States earthquakes 1934: U.S. Coast and Geodetic Survey, Serial 593, 99 p. Neumann, Frank, 1937, United States earthquakes 1935: U.S. Coast and Geodetic Survey, Serial 600, 90 p. Neumann, Frank, 1938, United States earthquakes 1936: U.S. Coast and Geodetic Survey, Serial 610, 45 p. Neumann, Frank, 1940, United States earthquakes 1937: U.S. Coast and Geodetic Survey, Serial 619, 55 p. Neumann, Frank, 1940, United States earthquakes 1938: U.S. Coast and Geodetic Survey, Serial 629, 59 p. Bodle, R.R., 1941, United States earthquakes 1939: U.S. Coast and Geodetic Survey, Serial 637, 69 p. Neumann, Frank, 1942, United States earthquakes 1940: U.S. Coast and Geodetic Survey, Serial 647, 74 p. Neumann, Frank, 1943, United States earthquakes 1941: U.S. Coast and Geodetic Survey, Serial 655, 41 p. Bodle, R.R., 1944, United States earthquakes 1942: U.S. Coast and Geodetic Survey, Serial 662, 44 p. Bodle, R.R., 1945, United States earthquakes 1943: U.S. Coast and Geodetic Survey, Serial 672, 47 p. Bodle, R.R., 1946, United States earthquakes 1944: U.S. Coast and Geodetic Survey, Serial 682, 43 p. Bodle, R.R., and Murphy, L.M., 1947, United States earthquakes 1945: U.S. Coast and Geodetic Survey, Serial 699, 38 p. Bodle, R.R., and Murphy, L.M., 1948, United States earthquakes 1946: U.S. Coast and Geodetic Survey, Serial 714, 48 p. Murphy, L.M., 1950, United States earthquakes 1947: U.S. Coast and Geodetic Survey, Serial 730, 62 p. Murphy, L.M., and Ulrich, FR, 1951, United States earthquakes 1948: U.S. Coast and Geodetic Survey, Serial 746, 50 p. Murphy, L.M., and Ulrich, FR, 1951, United States earthquakes 1949: U.S. Coast and Geodetic Survey, Serial 748, 64 p. Murphy, L.M., and Ulrich, ER, 1952, United States earthquakes 1950: U.S. Coast and Geodetic Survey, Serial 755, 47 p. Murphy, L.M., and Cloud, W.K., 1953, United States earthquakes 1951: U.S. Coast and Geodetic Survey, Serial 762, 50 p. Murphy, L.M., and Cloud, W.K., 1954, United States earthquakes 1952: U.S. Coast and Geodetic Survey, Serial 773, 112 p. Murphy, L.M., and Cloud, W.K., 1955, United States earthquakes 1953: U.S. Coast and Geodetic Survey, Serial 785, 51 p. Murphy, L.M., and Cloud, W.K., 1956, United States earthquakes 1954: U.S. Coast and Geodetic Survey, Serial 793, 110 p. Murphy, L.M., and Cloud, W.K., 1957, United States earthquakes 1955: U.S. Coast and Geodetic Survey, 83 p. Brazee, R.J., and Cloud, W.K., 1958, United States earthquakes 1956: U.S. Coast and Geodetic Survey, 78 p. Brazee, R.J., and Cloud, W.K., 1959, United States earthquakes 1957: U.S. Coast and Geodetic Survey, 108 p. Brazee, R.J., and Cloud, W.K., 1960, United States earthquakes 1958: U.S. Coast and Geodetic Survey, 76 p. Eppley, RA, and Cloud, W.K., 1961, United States earthquakes 1959: U.S. Coast and Geodetic Survey, 115 p. Talley, H.C., and Cloud, W.K., 1962, United States earthquakes 1960: U.S. Coast and Geodetic Survey, 90 p. Lander, J .F., and Cloud, W.K., 1963, United States earthquakes 1961: U.S. Coast and Geodetic Survey, 106 p. Lander, J .F., and Cloud, W.K., 1964, United States earthquakes 1962: U.S. Coast and Geodetic Survey, 114 p. Cloud, W.K., and von Hake, C.A., 1965, United States earthquakes 1963: U.S. Coast and Geodetic Survey, 69 p. Von Hake, C.A., and Cloud, W.K., 1966, United States earthquakes 1964: U.S. Coast and Geodetic Survey, 91 p. Coffinan, J .L., von Hake, C.A., and Stover, C.W., 1982, Earthquake history of the United States: U.S. National Oceanic and Atmospheric Administration and U.S. Geological Survey, Publication No. 41—1, revised edition, [through 1980], 258 p. Cofi‘man, J .L., and Stover, C.W., 1979, United States earthquakes 1977: U.S. National Oceanic and Atmospheric Administration and U.S. Geological Survey, 81 p. von Hake, C.A., and Cloud, W.K., 1969, United States earthquakes 1967: U.S. Coast and Geodetic Survey, 90 p. Coffman, J .L., and Cloud, W.K., 1970, United States earthquakes 1968: U.S. Environmental Science Services Administration, 111 p. von Hake, C.A., and Cloud, W.K., 1971, United States earthquakes 1969: U.S. National Oceanic and Atmospheric Administration, 80 p. Coffman, J .L., and von Hake, C.A., 1972, United States earthquakes 1970: U.S. National Oceanic and Atmospheric Administration, 81 p. Cofi‘man, J .L., and von Hake, C.A., 1973, United States earthquakes 1971: U.S. National Oceanic and Atmospheric Administration, 174 p. Coffinan, J .L., and von Hake, C.A., 1974, United States earthquakes 1972: U.S. National Oceanic and Atmospheric Administration, 119 p. Coffinan, J.L., von Hake, C.A., Spence, W., Carver, D.L., Covington, P.A., Dunphy, G.J., Irby, W.L., Person, W.J., and Stover, C.W., 1975, United States earthquakes 1973: U.S. National Oceanic and Atmospheric Administration and U.S. Geological Survey, 112 p. Coffman, J .L., and Stover, C.W., 1976, United States earthquakes 1974: U.S. National Oceanic and Atmospheric Administration and U.S. Geological Survey, 135 p. 48. 49. 52. 53. 54. 55. 56. 59. 60. 63. 67. 68. 71. 72. 74. 75. 76. 77. 78. 81. 84. 86. 96. 99. 101. 105. 109. 113. 114. 116. TABLES 1—3 401 TABLE 1.-Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Coffman, J .L., and Stover, CW, 1977, United States earthquakes 1975: U.S. National Oceanic and Atmospheric Administration and U.S. Geological Survey, 136 p. Coffman, J .L., and Stover, CW, 1978, United States earthquakes 1976: U.S. National Oceanic and Atmospheric Administration and U.S. Geological Survey, 94 p. Williams, J .S., and Tapper, M.S., 1953, Earthquake history of Utah, 1850 to 1949: Seismological Society of America Bulletin, v. 43, no. 3, p. 191—218. Berg, J .W., and Baker, C.D., 1963, Oregon earthquakes, 1841 through 1958: Seismological Society of America Bulletin, v. 53, no. 1, p. 95—108. Slemmons, D.B., Jones, AB, and Gimlett, J .I., 1965, Catalog of Nevada earthquakes, 1852—1960: Seismological Society of America Bulletin, v. 55, no. 2, p. 519-565. MacCarthy, G.R., 1964, A descriptive list of Virginia earthquakes through 1960: Elisha Mitchell Scientific Society Journal, v. 80, no. 2, p. 94—114. Townley, SD, and Allen, M.W., 1939, Descriptive catalog of earthquakes of the Pacific Coast of the United States, 1769 to 1928: Seismological Society of America Bulletin, v. 29, no. 1, p. 1—297. Brigham, W.T., 1871, Historical notes on the earthquakes of New England, 1638—1869: Memoirs Boston Society of Natural History, v. 2., p. 1—28. Bradley, EA, and Bennett, T.J., 1965, Earthquake history of Ohio: Seismological Society of America Bulletin, v. 55, no. 4, p. 745—752. Merriam, D.G., 1956, History of earthquakes in Kansas: Seismological Society of America Bulletin, v. 46, no. 2, p. 87—96. Moneymaker, B.C., 1957, Earthquakes in Tennessee and nearby sections of neighboring States 1901 to 1925: Tennessee Academy of Science Journal, v. 32, no. 2, p. 91—105. Moneymaker, B.C., 1958, Earthquakes in Tennessee and nearby sections of neighboring States 1926 to 1950: Tennessee Academy of Science Journal, v. 33, no. 3, p. 224—239. MacCarthy, G.R., 1957 , An annotated list of the North Carolina earthquakes: Elisha Mitchell Scientific Society Journal, v. 73, no. 1, p. 84—100. U.S. Coast and Geodetic Survey, Abstracts of earthquake reports for the United States, 1967 through 1973. U.S. Geological Survey, Preliminary determination of epicenters report and monthly listing, January 1961—1989 [formerly by U.S. Coast and Geodetic Survey, U.S. Environmental Science Services Administration, and U.S. National Oceanic and Atmospheric Administration]. von Hake, C.A., and Cloud, W.K., 1967, United States earthquakes 1965: U.S. Coast and Geodetic Survey, 91 p. Smith, W.E.T., 1962, Earthquakes of Eastern Canada and adjacent areas, 1534—1927: Publications of the Dominion Observatory, Ottawa, v. 26, no. 5, p. 271—301. Smith, W.E.T., 1966, Earthquakes of Eastern Canada and adjacent areas, 1928—1959: Publications of the Dominion Observatory, Ottawa, v. 32, no. 3, p. 87—121. Weston Geophysical Research, Inc., Weston, Mass., 1976, Historical seismicity of New England, prepared for Boston Edison Company, Preliminary Safety Analysis Report, Docket No. 50—471, 641 p. von Hake, C.A., and Cloud, W.K., 1968, United States earthquakes 1966: U.S. Coast and Geodetic Survey, 110 p. Woollard, G.P., 1968, A catalogue of earthquakes in the United States prior to 1925 based on unpublished data compiled by Harry Fielding Reid and unpublished sources prior to 1930: Hawaii Institute of Geophysics, University of Hawaii, Data Report No. 10, 163 p. Bollinger, GA, 1975, A catalogue of Southeastern United States earthquakes 1754 through 1974: Virginia Polytechnic Institute and State University, Department of Geological Sciences, Research Bulletin 101, 68 p. Taber, S., 1914, Seismic activity in the Atlantic coastal plain near Charleston, South Carolina: Seismological Society of America Bulletin, v. 4, no. 3, p. 108—160. Dumas, D.B., Dorman, J.H., and Latham, G.V., 1980, A reevaluation of the August 16, 1931 Texas earthquake: Seismological Society of America Bulletin, v. 70, no. 4, p. 1171—1180. Campbell, R.L., 1975, Historical sketches of colonial Florida: A facsimile reproduction of the 1892 edition, A University of Florida Book, The University of Florida Press, Gainsville, Fla. Docekal, Jerry, 1970, Earthquakes of the stable interior, with emphasis on the midcontinent, v. 2: Lincoln, Neb., University of Nebraska, Ph.D. dissertation, [available from Ann Arbor, Mich., University Microfilms Ltd.], 332 p. Heinrich, RR, 1941, A contribution to the seismic history of Missouri: Seismological Society of America Bulletin, v. 31, no. 3, p. 187—224. Nuttli, O.W., 1974, Magnitude—recurrence relation for central Mississippi valley earthquakes: Seismological Society of America Bulletin, v. 64, no. 4, p. 1189—1207. Nuttli, O.W., 1973, The Mississippi valley earthquakes of 1811 and 1812: Intensities, ground motion, and magnitudes: Seismological Society of America Bulletin, v. 63, no. 1, p. 227—248. Vanna, M.M., 1975, Seismicity of the eastern half of the United States (exclusive of New England): Bloomington, Ind., University of Indiana, Ph.D. dissertation, 176 p. 402 121. 124. 126. 129. 132. 134. 135. 136. ’ 140. 141. 142. 143. 145. 149. 155. 159. 162. 163. 167. 168. 173. 174. 179. 186. 187. 189. 190. 194. 201. 208. 211. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 1.—Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Wood, H.O., 1955, The 1857 earthquake in California: Seismological Society of America Bulletin, v. 45, no. 1, p. 47—68. Sellards, E.H., 1932, The Valentine, Texas, earthquake: The University of Texas Bulletin 3201, Contributions to Geology, p. 113—137. Chiburis, ER, 1979, Seismicity, recurrence rates, and the regionalization of the Northeast United States and adjacent Southeastern Canada: Weston, Mass, Weston Observatory, [for the US. Nuclear Regulatory Commission], NUREG/ CR—2309, 76 p. Fryxell, F.M., 1940, The earthquakes of 1934 and 1935 in northwestern Illinois and adjacent parts of Iowa: Seismological Society of America Bulletin, v. 30, no. 3, p. 213—218. Moneymaker, BC, 1972, Earthquakes in Tennessee and nearby sections of neighboring States, 1951—1970: Tennessee Academy of Science Journal, v. 47, no. 4, p. 124—132. Rockwood, C.G., 1880, Notices of recent earthquakes: American Journal of Science, v. 19, no. 112, p. 295—299. Taber, Stephen, 1915, Earthquakes in South Carolina during 1914: Seismological Society of America Bulletin, v. 5, no. 2, p. 96—99. Rockwood, C.G., 1881, Notices of recent American earthquakes: American Journal of Science, v. 21, no. 123, p. 198—202. Dutton, C.E., 1889, The Charleston earthquake of August 31, 1886, in Ninth Annual Report of the United States Geological Survey to the Secretary of the Interior 1887—1888, p. 209—628. Pomeroy, P.W., and Fakundiny, R.H., 1976, Unpublished list of earthquakes used to compile the Seismic Activity and Geologic Structure in New York and Adjacent Areas map, New York State Museum and Science Service Map and Chart Series Number 27, 2 sheets. Philadelphia Electric Company, 1970, Preliminary Safety Analysis Report, Limerick Generating Station, Units 1 and 2, Nuclear Regulatory Commission, Public Documents Room, p. 25—36. Fuller, M.L., 1912, The New Madrid earthquake: US. Geological Survey Bulletin 494. 119 p. Shaler, NS, 1869, Earthquakes of the Western United States: Atlantic Monthly, v. 24, no. 15, p. 549—659. Bradford, DC, and Dahm, C.G., 1935, The Rodney, Missouri, earthquake of August 20, 1934: Seismological Society of America Bulletin, v. 25, no. 2, p. 154—160. MacCarthy, GR, and Sinha, E.Z., 1958, North Carolina earthquakes 1957: Elisha Mitchell Scientific Society Journal, v. 74, no. 2, p. 117—121. Collins, R.H., 1874, History of Kentucky: By the late Lewis Collins (revised): Collins and Co., v. 1, 683 p. Taber, Stephen, 1913, The South Carolina earthquake of January 1, 1913: Seismological Society of America Bulletin, v. 3, p. 6—13. Bollinger, G.A., 1972, Historical and recent seismic activity in South Carolina: Seismological Society of America Bulletin, v. 62, no. 3, p. 851—864. Hopper, M.G., and Bollinger, G.A., 1971, The earthquake history of Virginia 1774—1900: Blacksburg, Va., Virginia Polytechnic Institute and State University, Department of Geological Sciences, 87 p. Willson, RE, 1926, The Montana earthquake of June 27, 1925, damage in Gallatin County: Seismological Society of America Bulletin, v. 16, no. 3, p. 164—169. Nuttli, O.W., and Herr-mann, R.B., 1978, Credible earthquakes for the Central United States, state—of—the—art for assessing earthquake hazards in the United States: US. Army, Chief of Engineers Report 12, p. 1—99. DuBois, S.M., and Wilson, F.W., 1978, A revised and augmented list of earthquake intensities for Kansas, 1867—1977: Kansas Geological Survey, Lawrence, Kans., The University of Kansas, Environmental Geology Series 2, 56 p. MacCarthy, G.R., 1958, A note on the Virginia earthquake of 1833: Seismological Society of America Bulletin, v. 48, no. 2, p. 177—180. Watson, T.L., 1918, The Virginia earthquake of April 9, 1918: Seismological Society of America Bulletin, v. 8, no. 4, p. 105—116. Watson, T.L., 1919, Earthquake in Warren and Rappahannock Counties, Virginia, September 5, 1919: Seismological Society of America Bulletin, v. 9, no. 4, p. 128—134. Bollinger, G.A., and Hopper, M.G., 1972, The earthquake history of Virginia 1900—1970: Blacksburg, Va., Virginia Polytechnic Institute and State University, Department of Geological Sciences, 85 p. Pakiser, L.C., 1976, Review of intensity of Giles County 1897 earthquake: US Geological Survey unpublished memorandum. Berkey, CB, 1945, A geological study of the Massena—Cornwall earthquake of September 5, 1944, and its bearing on the proposed St. Lawrence River Project: United States Engineer Office, Corp of Engineers, New York, p. 1—18. Armbruster, J .G., and Seeber, Leonardo, 1987, The 23 April Martic earthquake and the Lancaster seismic zone in eastern Pennsylvania: Seismological Society of America Bulletin, v. 77, no. 3, p. 877—890. Byerly, Perry, 1926, The Montana earthquake of June 28, 1925, G.M.C.T.: Seismological Society of America Bulletin, v. 16, no. 4, p. 209—265. Rockwood, C.G., 1876, Notices of recent American earthquakes—no. 6: American Journal of Science, v. 12, third series, p. 25—30. 214. 218. 228. 234. 237. 238. 240. 249. 255. 257. 258. 259. 260. 261. 262. 264. 265. 266. 269. 270. 272. 273. 274. 277. 279. 280. 281. 283. 288. 289. 292. TABLES 1—3 403 TABLE 1.—-Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Gordon, D.W., 1988, Revised instrumental hypocenters and correlation of earthquake locations and tectonics in the Central United States: U.S. Geological Survey Professional Paper 1364, 69p. U.S. Coast and Geodetic Survey, Seismological Reports, July 1924 through December 1927. Miller, H.J., 1956, The Oklahoma earthquake of April 9, 1952: Seismological Society of America Bulletin, v. 46, no. 4, p. 269—279. Cook, KL, and Smith, R.B., 1967, Seismicity in Utah, 1850 through June 1965: Seismological Society of America Bulletin, v. 57, no. 4, p. 689—718. Lawson, J .E., Luza, K.V., DuBois, R.L., and Foster, RH., 1979, Inventory, detection, and catalog of Oklahoma earthquakes: Oklahoma Geological Survey, [text to accompany Map GM—19], 15 p. Seismological Society of America, 1952, Seismological Notes: Seismological Society of America Bulletin, v. 42, no. 3, p. 271—281. Stover, C.W., and von Hake, C.A., 1980, United States earthquakes 1978: U.S. Geological Survey and U.S. National Oceanic and Atmospheric Administration, 112 p. Qamar, A.I., and Stickney, M.C., 1983, Montana earthquakes 1869—1979: Butte, Mont, Montana School of Mines, Montana Bureau of Mines and Geology Memoir No. 51, 79 p. Holden, ES, 1898, A catalogue of earthquakes on the Pacific Coast 1769 to 1897: Smithsonian Miscellaneous Collections No. 1087, 253 p. Reid, H.F., 1911, Remarkable earthquakes in central New Mexico in 1906 and 1907: Seismological Society of America Bulletin, v. 1, no. 1, p. 10—16. Gutenberg, Beno, and Richter, CE, 1954, Seismicity of the Earth and associated phenomena: New York, Hafner Publishing Company, Inc., 310 p. U.S. Coast and Geodetic Survey, Abstracts of earthquake reports for the Pacific Coast and the Western mountain region, January 1, 1934, to December 31, 1966, and 1933 abstracts from the San Francisco office, U.S. Department of Commerce. Stover, C.W., 1990, U.S. Geological Survey, recomputed hypocenters (unpublished data). Sanford, A.R., Olsen, H.N., and Jaksha, L.H., 1981, Earthquakes in New Mexico, 1849—1977: New Mexico Bureau of Mines and Mineral Resources Circular 171, 20 p. Stover, C.W., and von Hake, C.A., 1981, United States earthquakes 1979: U.S. Geological Survey and U.S. National Oceanic and Atmospheric Administration, 170 p. Herrmann, R.B., Dewey, J .W., and Park, Sam—Kuen, 1980, The Dulce, New Mexico, earthquake of 23 January 1966: Seismological Society of America Bulletin, v. 70, no. 6, p. 2171—2183. International Seismological Summary, 1913—1963, Kew Observatory, Kew, England. U.S. Coast and Geodetic Survey, Seismological Bulletin MSI 1 through MSI 316, January 1934 through May 1967. Hammond, J .F., 1966, A surgeon's report on Socorro, N. Mex., 1852: Santa Fe Stagecoach Press, 47 p. Northrop, S.A., Unpublished notes, newspaper clippings, and questionnaires, New Mexico University, Albuquerque, N. Mex. Monthly Weather Review, July 1891 to June 1924, v. 19 to 68, U.S. Department of Agriculture, Washington, DC. Hadsell, EA, 1968, History of earthquake activity in Colorado: in Geophysical and geological studies of the relationship between the Denver earthquakes and the Rocky Mountain Arsenal well, Colorado School of Mines Quarterly, v. 63, no. 1, p. 57—72. Herrmann, R.B., Park, Sam—Kuen, and Wang, Chien—Ymg, 1981, The Denver earthquakes of 1967—1968: Seismological Society of America Bulletin, v. 71, no. 3, p. 731—745. Taggart, James, and Baldwin, Frank, 1982, Earthquake sequence of 1938—1939 in Mogollen Mountains, New Mexico: New Mexico Geology, v. 4, no. 4, p. 49—52. Fryxell, Fritiof, 1933, Earthquake shocks in Jackson Hole, Wyoming: Seismological Society of America Bulletin, v. 23, no. 4, p. 167—168. Pardee, J .T., 1927, Earthquake in the Bighorn Mountains, Wyoming, November 17, 1925: Seismological Society of America Bulletin, v. 17, no. 3, p. 129—136. Tocher, Don, 1962, The Hebgen Lake, Montana, earthquake of August 17, 1959, MST: Seismological Society of America Bulletin, v. 52, no. 2, p. 153—162. Dames and Moore, 1981, Geologic and seismologic investigations for Rocky Flats Plant, report prepared for U.S. Department of Energy, v. 1, chapter 8.0, p. 80—1 to 80—18. Bollinger, GA, and Visvanathan, T.R., 1977, The seismicity of South Carolina prior to 1886: U.S. Geological Survey Professional Paper 1028—C, p. 33—42. Visvanathan, T.R., 1980, Earthquakes in South Carolina 1698—1975: South Carolina Geological Survey’Bulletin 40, 61 p. Hileman, J .A., Allen, CR, and Nordquist, J .M., 1973, Seismicity of the southern California region, 1 January 1932 to 31 December 1972: California Institute of Technology, Pasadena, 395 p. 404 294. 298. 299. 300. 301. 302. 307. 308. 310. 311. 312. 314. 315. 316. 317. 319. 324. 325. 326. 327. 328. 330. 335. 336. 338. 339. 340. 341. 342. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 1.—Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Seismological Society of America, 1951, Seismological Notes: Seismological Society of America Bulletin, v. 41, p. 243—254 and p. 389—404. Arabasz, W.J. Smith, R. B. and Richins, W.D.,1979, Earthquake studies in Utah, 1850 to 1978: University of Utah, Department of Geology and Geophysics, 552 p. Bulletin of the International Seismological Centre, 1964 to 1989, Newbury, Berkshire, United Kingdom. Stover, CW, and von Hake, C.A., 1982, United States earthquakes 1980: U.S. Geological Survey and U. S. National Oceanic and Atmospheric Administration, 182 p. Nuttli, O.W., 1979, Seismicity of the Central United States, Geology in the siting of nuclear power plants: Geological Society of America, Reviews in Engineering Geology, v. 4, p. 67—107. Street, KL, 1980, The southern Illinois earthquake of September 27, 1981: Seismological Society of America Bulletin, v. 70, no. 3, p. 915—920. Pitt, A.M., 1980, Catalog of earthquakes in the Yellowstone Park—Hebgen Lake region from November 1972 to December 1975: U.S. Geological Survey Open—File Report 80—2006, 32 p. Pitt, A.M., 1982, Catalog of earthquakes in the Yellowstone Park—Hebgen Lake region from January 1980 to September 1981: U.S. Geological Survey, unpublished data. Ryall, Alan, 1962, The Hebgen Lake, Montana, earthquake of August 18, 1959: P—waves: Seismological Society of America Bulletin, v. 52, no. 2, p. 235—271. Pack, F.J., 1921, The Elsinore earthquakes in central Utah, September 29 and October 1, 1921: Seismological Society of America Bulletin, v. 11, no. 3, p. 155—165. Pardee, J .T., 1927, The Montana earthquake of June 27, 1925, in Shorter contributions to general geology 1926: U.S. Geological Survey Professional Paper 147, p. 7—23. Jefferson, Thomas, 1774, Unpublished memorandum book for 1774: Massachusetts Historical Society. Jones, A.E., 1975, Recording of earthquakes at Reno, 1916—1951: Reno, University of Nevada, Mackay School of MinesNevada Bureau of Mines, Seismological Laboratory Bulletin, 199 p. Scott, H.W., 1936, The Montana earthquakes of 1935: Butte, Mont, Montana School of Mines, Montana Bureau of Mines and Geology Memoir No. 16, 57 p. Dewey, J .W., and Gordon, D.W., 1988, U.S. Geological Survey, unpublished data. Carver, David, Richins, W.D., and Langer, C.J., 1983, Details of the afiershock process following the 30 September 1977, Unita Basin, Utah, earthquake: Seismological Society of America Bulletin, v. 73, no. 2, p. 435—448. Bolt, BA, and Miller, RD, 1975, Catalogue of earthquakes in northern California and adjoining areas, 1 January 1910«31 December 1972: Berkeley, Calif, University of California, Seismographic Stations, 567 p. Stover, C.W., 1984, United States earthquakes 1981: U.S. Geological Survey Special Publication, 136 p. Frantti, G.E., 1983, Seismicity investigations of the southern Lake Superior Precambrian Province, [for the U.S. Nuclear Regulatory Commission], 59 p. Jones, J .C., 1915, The Pleasant Valley, Nevada, earthquake of October 2, 1915: Seismological Society of America Bulletin, v. 5, no. 4, p. 190—205. Slemrnons, D.B., Steinbrugge, K.V., Tocher, Don, Oakeshott, G.B., and Granella, V.P., 1959, Wonder, Nevada, earthquake of 1903: Seismological Society of America Bulletin, v. 49, no. 3, p. 251—265. Nuttli, O.W., 1987, The effects of earthquakes in the Central United States: Central United States Earthquake Consortium, Monograph Series, v. 1, 33 p. Callaghan, Eugene, and Gianella, V.P., 1935, The earthquake of January 30, 1934, at Excelsior Mountains, Nevada: Seismological Society of America Bulletin, v. 25, no. 2, p. 161—168. Sleep, NH, 1981, The events of February 4, 1883, Michigan, Indiana, and Illinois: Seismological Society of America, Eastern Section, Earthquake Notes, v. 52, no. 4, p. 3~9. Couch, Richard, Victor, Linda, Keeling, Kenneth, 1974, Coastal and offshore earthquakes of the Pacific Northwest between 39° and 49° 10 N. latitude and 123° and 131° W. longitude: Corvallis, Oregon State University, School of Oceanography, 67 p. Sibol, M. S. and Bollinger, G. A. 1984, Hypocenter listing from Southeastern U. S. seismic network bulletins no. 1—12: Blacksburg, Virginia Polytechnic Institute and State University, Southeastern U. S. Seismic Network Bulletin, no. 12A, 44 p. Herrmann, R.B., Langston, CA, and Zollweg, J .E., 1982, The Sharpsburg, Kentucky, earthquake of 27 July 1980: Seismological Society of America Bulletin, v. 72, no. 4, p. 1219—1239. Richins, W.D. Arabaz, W.J., Hathaway, G. M., McPherson, Erwin, Oehmich, P.J., and Sells, L. L, 1984, Earthquake data for the Utah region, January 1,1981 to December 31,1983: Salt Lake City, University of Utah, Seismograph Stations, 111 p. Carlson, S.M., 1984, Investigations of recent and historical seismicity in east Texas: The University of Texas at Austin, Master of Arts thesis, 197 p. 343. 345. 349. 350. 353. 354. 355. 356. 357. 358. 359. 360. 364. 365. 366. 368. 369. 370. 371. 373. 374. 375. 376. 377. 378. 379. 382. 383. TABLES 1—3 405 TABLE 1,—Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] DuBois, S.M., Smith A.W., Nye, N.K., and Nowak, T.A., Jr., 1982, Arizona earthquakes, 1776-1980: Tucson, University of Arizona, Bureau of Geology and Mineral Technology, State of Arizona, Bulletin 193, 456 p. Street, Ronald, 1982, A contribution to the documentation of the 1811—1812 Mississippi valley earthquake sequence: Seismological Society of America, Eastern Section, Earthquake Notes, v. 53, no. 2, p. 39—51. Dewey, J.W., and Gordon, D.W., 1984, Map showing recomputed hypocenters of earthquakes in the Eastern and Central United States and adjacent Canada, 1925—1980: US. Geological Survey, Miscellaneous Field Studies Map MF—1699, [pamphlet], 39 p. Stover, C.W., 1985, United States earthquakes 1982: US. Geological Survey Bulletin 1655, 142 p. Barstow, N.L., Brill, KG., Nuttli, O.W., and Pomeroy, RW, 1981, An approach to seismic zonation for siting nuclear electric power generating facilities in the Eastern United States: Roundout Associates, Inc., Stone Ridge, N.J., [for US. Nuclear Regulatory Commission], NUCREG/CR—1577, 315 p. Dewey, J.W., 1987, Instrumental seismicity of central Idaho: Seismological Society of America Bulletin, v. 77, no. 3, p. 819—836. Hutton, L.K., Allen, CR, and Johnson, CE, 1985, Seismicity of southern California; Earthquakes of ML 3.0 and greater, 1975 through 1983: California Institute of Technology, Division of Geological and Planetary Sciences Contribution No. 4207, 142 p. Gianella, V.P., and Callaghan, Eugene, 1934, The Cedar Mountain, Nevada, earthquake of December 20, 1932: Seismological Society of America Bulletin, v. 24, no. 4, p. 345—384. Tocher, Don, 1956, Earthquakes off the North Pacific Coast of the United States: Seismological Society of America Bulletin: v. 46, no. 3, p. 165—173. Romney, Carl, 1957, Seismic waves from the Dixie Valley—Fairview Peak earthquakes: Seismological Society of America Bulletin, v. 47, no. 4, p. 301—319. Mokler, A.J., 1923, History of Natrona County, Wyoming, 1888—1922: Chicago, Lakeside Press, R.R. Donnelley and Sons Company, p. 72—74. Stover, C.W., 1986, United States earthquakes 1983: US. Geological Survey Bulletin 1698, 197 p. Davis, S.D., 1985, Investigations of natural and induced seismicity in the Texas Panhandle: The University of Texas at Austin, Master of Arts thesis, 230 p. Oaks, S.D., and Bollinger, G.A., 1986, The epicenter of the mb 5, December 22, 1875, Virginia earthquake: New findings from documentary sources: Earthquake Notes, Eastern Section, Seismological Society of America, v. 57, no. 3, p. 65—75. Street, R.L., Couch, D., and Konkler, J ., 1986, The Charleston, Missouri earthquake of October 31, 1895: Earthquake Notes, Eastern Section, Seismological Society of America, v. 57, no. 2, p. 41—51. Toppozada, T.R., Real, GR, and Parke, D.L., 1981, Preparation of isoseismal maps and summaries of reported effects for pre-1900 California earthquakes: California Division of Mines and Geology, Open—File Report 81—118AC, 182 p. Street, KL, 1989, Personal communication, letter dated July 5, 1989, and copies of press reports from 1884 newspapers. Stover, C.W., 1988, United States earthquakes 1984: US. Geological Survey Bulletin 1862, 284 p. Stover, C.W., and Brewer, L.R., 1990, United States earthquakes 1985: US. Geological Survey Bulletin 1954, 170 p. Hopper, M.G., Algermissen, S.T., Perkins, D.M., Brockman, SR, and Arnold, ER, 1988, The December 14, 1872, earthquake in the Pacific Northwest: US. Geological Survey unpublished data. Seismological Society of America, 1920, Seismological notes: Seismological Society of America Bulletin, v. 10, no. 1, p. 45-50. Milne, W.G., 1956, Seismic activity in Canada, west of the 113th meridian 1841—1951: Publication of the Dominion Observatory, Ottawa, v. 18, no. 7, p. 119-146. Nuttli, O.W., 1952, The western Washington earthquake of April 13, 1949: Seismological Society of America Bulletin, v. 42, no. 1, p. 21—28. Algermissen, S.T., Harding, S.T., Steinbrugge, K.V., and Cloud, W.K., 1965, The Puget Sound, Washington, earthquake of April 29, 1965: US. Department of Commerce, Coast and Geodetic Survey, 51 p. Bolt, Bruce A., 1968, The focus of the 1906 California earthquake: Seismological Society of America Bulletin, v. 58, no. 1, p. 457—471. Agnew, DC, and Sieh, K.E., 1978, A documentary study of the felt efiects of the great California earthquake of 1857: Seismological Society of America Bulletin, v. 68, no. 6, p. 1717—1729. zada, T.R., Parke, D.L., and Higgins, CT, 1978, Seismicity of California 1900—1931: California Division of Mines Geology, Special Report 135, 39 p. zada, T.R., Parke, D.L., Jensen, Laurel, and Campbell, Gordon, 1982, Areas damaged by California earthquakes 0—1949: California Division of Mines and Geology, Open File Report 82—17SAC, 65 p. Richter, GE, 1958, Elementary seismology: San Francisco and London, WH. Freeman and Company, 768 p. Beal, CH, 1915, The earthquake in the Imperial Valley, California, June 22, 1915: Seismological Society of America Bulletin, v. 5, no. 3, p. 130—149. 406 384. 385. 386. 388. 389. 390. 391. 392. 393. 394. 395. 396. 397. 398. 399. 400. 401. 402. 403. 404. 405. 406. 407 . 408. 409. 410. 411. 412. 413. 414. 417. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 1.—Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Townley, S.D., 1918, The San Jacinto earthquake of April 21, 1918: Seismological Society of American Bulletin, v. 8, no. 2—3, p. 45—62. Taber, Stephen, 1920, The Inglewood earthquake in southern California, June 21, 1920: Seismological Society of American Bulletin, v. 10, no. 3, p. 129—145. Taber, Stephen, 1921, The Los Angeles earthquakes of July 1920: Seismological Society of America Bulletin, v. 11, no. 1, p. 63—79. Laughlin, Homer, Arnold, Ralph, Kew, W.S.W., 1923, Southern California earthquake of July 22, 1923: Seismological Society of America Bulletin, v. 13, no. 3, p. 105—106. Willis, Bailey, 1925, A study of the Santa Barbara earthquake of June 29, 1925: Seismological Society of America Bulletin, v. 15, no. 4, p. 255—278. Byerly, Perry, 1927, The Idria (California) earthquake of July 25, 1926: Seismological Society of America Bulletin, v. 17, no. 4, p. 203—206. Mitchell, G.D., 1928, The Santa Cruz earthquakes of October 1926: Seismological Society of America Bulletin, v. 18, no. 3, p. 153—213. Byerly, Perry, 1930, The California earthquake of November 4, 1927: Seismological Society of America Bulletin, v. 20, no. 2, p. 53—66. Dyk, Karl, 1936, The California earthquake of April 15, 1928: Seismological Society of America Bulletin, v. 26, no. 3, p. 239—244. Wood, HQ, and Richter, GE, 1931, Recent earthquakes near Whittier, California: Seismological Society of America Bulletin, v. 21, no. 3, p. 183203. Richter, GE, 1935, An instrumental earthquake magnitude scale: Seismological Society of America Bulletin, v. 25, no. 1, p. 1—32. Gutenberg, B., Richter, CE, and Wood, HQ, 1932, The earthquake in Santa Monica Bay, California, on August 30, 1930: Seismological Society of America Bulletin, v. 22, no. 2, p. 138—154. Wood, HQ, 1933, Preliminary report on the Long Beach earthquake: Seismological Society of America Bulletin, v. 23, no. 2, p. 43—56. McEvilly, T.V., Bakun, W.H., and Casady, KB, 1967, The Parkfield, California, earthquake of 1966: Seismological Society of America Bulletin, v. 57, no. 6, p. 1221—1244. Cloud, WK, Hill, D.M., Huffman, M.E., Jennings, C.W., McEvilly, T.V., Nason, R.D., Steinbrugge, K.V., Tocher, D., Unger, J .D., and Youd, TL, 1970, The Santa Rosa earthquakes of October 1969: California Division of Mines and Geology, Mineral Information Service, v. 23, no. 3, 63 p. Allen, C.R., Hanks, TC, and Whitcomb, J .H., 1973, San Fernando earthquake: Seismological studies and their tectonic implications, in San Fernando, California, earthquake of February 9, 1971: US. Department of Commerce, v. III, p. 13—21. Bulletin of the Seismographic Stations, 1973 to 1989, University of California—Berkeley. Fuis, G.S., Friedman, M.E., and Hileman, J .A., 1977, Preliminary catalog of earthquakes in southern California, July 1974—September 1976: US. Geological Survey, Open—File Report 77—181, 107 p. Reid, HR, 1912, List of strong shocks in the United States and dependencies,_in Report of the eightieth meeting of the British Association for the Advancement of Science, Seismological Investigations, p. 41—45. Gutenberg, Beno, 1956, Great earthquakes 1896—1903: Transactions American Geophysical Union, v. 37, no. 5, p. 608—614. Lyman, S.J., and family, An unpublished record of earthquakes felt at Hilo, Hawaii, from June 1833 to June 1916. Wood, H.O., 1914, On the earthquakes of 1868 in Hawaii: Seismological Society of America Bulletin, v. 4, no. 4, p. 169—203. Rockwood, CG, 1882, Notes on American earthquakes—no. 11: American Journal of Science, v. 23, 3rd series, no. 133—138, p. 257—161. The Volcano Letter, No. l—No. 529, 1925—1955, Hawaiian Volcano Observatory, Volcano House, Hawaii. Seismological Society of America, 1952, Seismological notes: Seismological Society of America Bulletin, v. 42, no. 1, p. 954108. Seismological Society of America, 1954, Seismological notes: Seismological Society of America Bulletin, v. 44, no. 3, p. 529—542. Koyanagi, R.Y., Krivoy, H.L., and Okamura, A.T., 1966, The 1962 Kaoiki, Hawaii, earthquake and its aftershocks: Seismological Society of America Bulletin, v. 56, no. 6, p. 1317—1335. Abe, Katsuyuki, and Noguchi, Shin‘ichi, 1983, Revision of magnitudes of large shallow earthquakes, 1897—1912: Physics of the Earth and Planetary Interiors, v. 33, p. 1—11. , Horner, RB, and Hasegawa, HS, 1978, The seismotectonics of southern Saskatchewan: Canadian Journal of Earth Sciences, p. 1341—1355. Bea], OH, 1914, The earthquake in the Santa Cruz Mountains, California, November 8, 1914: Seismological Society of America Bulletin, v. 4, no. 4, p. 215—219. Weekly Report and Weekly Bulletin of the Hawaiian Volcano Observatory, July 1913—December 1924, Honolulu, Hawaii. 418. 419. 420. 421. 422. 423. 424. 425. 426. 427. 428. 432. 434. 435. 436. 437. 438. 440. 442. 443. 444. 445. 446. 447. 448. 449. 450. 451. 452. 453. 454. 455. TABLES 1—3 407 TABLE 1.—Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Koyanagi, R.Y., 1988, Unpublished list of Hawaiian earthquakes, U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii. MacDonald, G.A., and Wentworth, GK, 1952, The Kona earthquake of August, 21, 1951, and its aftershocks: University of Hawaii, Pacific Science, v. 6, no. 4, p. 269—287. Tarr, R.S., and Martin, Lawrence, 1912, Earthquakes at Yakutat Bay, Alaska, in September 1899: U.S. Geological Survey Professional Paper 69, 135 p. Cox, D.C., 1986, The Oahu earthquake of June 1948, associated shocks, and the hypothetical Diamond Head fault: University of Hawaii, Environmental Center, SR:0036, 32 p. Cox, D.C., 1985, The Lanai earthquake of February 1871: University of Hawaii, Environmental Center, SR:0034, 50 p. Cox, D.C., 1986, Earthquakes felt on Oahu, Hawaii, and their intensities: University of Hawaii, Environmental Center, SR:0038, 120 p. ‘ Stover, C.W., Reagor, B.G., and Wetmiller, R.J., 1980, Intensities and isoseismal map for the St. Elias earthquake of February 28, 1979: Seismological Society of America Bulletin, v. 70, no. 5, p. 1635—1649. Abe, Katsuyuki, 1983, Determination of magnitude for large shallow earthquakes 1898—1917: Physics of the Earth and Planetary Interiors, v. 32, p. 45—59. Milne, John, 1912, Seismological investigations, List of earthquakes 1899—1903 inclusive, in Report of the eightieth Meeting of the British Association for the Advancement of Science, Seismological Investigations, p. 57—65. Taggart, J .N., 1986, Unpublished list of earthquakes in Alaska, U.S. Geological Survey, Denver, Colo. Abe, Katsuyuki, 1981, Magnitudes of large shallow earthquakes from 1904 to 1980: Physics of the Earth and Planetary Interiors, v. 27, p. 72~92. Sykes, LR, 1971, Afiershock zones of great earthquakes, seismicity gaps, and earthquake prediction for Alaska and the Aleutians: Journal of Geophysical Research, v. 76, no. 32, p. 8021—8041. . Seismological Society of America, 1923, Seismological notes: Seismological Society of America Bulletin, v. 13, no. 2, p. 82. Seismological Society of America, 1927, Seismological notes: Seismological Society of America Bulletin, v. 17, no. 3, p. 193—200. Dall, W.H., 1870, Alaska and its resources: London, Sampson, Lawson, and Marston, 627 p. Fenner, C.N., 1925, Earth movements accompanying the Katmai eruption: The Journal of Geology, v. 33, no. 1, p. 116—139. Steinbrugge, K.V., and Cloud, W.K., 1962, Epicentral intensities and damage in the Hebgen Lake, Montana, earthquake of August 17, 1959: Seismological Society of America Bulletin, v. 52, no. 2, p. 181—234. Kirkham, R.M., and Rogers, WP, 1986, An interpretation of the November 7, 1882, Colorado earthquakes: Colorado Geological Survey, Open-File Report 86—8, 36 p. Davis, ER, 1915, The earthquakes of October 7, 1915, in central California: Seismological Society of America Bulletin, v. 5, no. 4, p. 230—235. Berea Advertiser, April 13, 1900, Berea, Ohio. LaCroix, A.V., 1980, A short note on Cryoseisms: Seismological Society of America Bulletin, Eastern Section, Earthquake Notes, v. 51, no. 1, p. 15—20. Monthly Bulletin of the Hawaiian Volcano Observatory, February 1918—July 1929, Honolulu, Hawaii. Weekly New Mexican, May 4, 1869, Sante Fe, N. Mex. Tobin, D.G., and Sykes, LR, 1966, Relationship of hypocenters of earthquakes to the geology of Alaska: Journal of Geophysical Research, v. 71, no. 6, p. 1659-1667. Tobin, D.G., and Sykes, LR, 1968, Seismicity and tectonics of the northeast Pacific Ocean: Journal of Geophysical Research, v. 73, no. 12, p. 3821—3845. Rothé, J .P., 1969, The seismicity of the Earth, 1953—1965: Paris, United Nations Educational, Scientific, and Cultural Organization (UNESCO), 336 p. Rankin, D.W., ed., 1977, Studies related to the Charleston, South Carolina, earthquake of 1886—A preliminary report: U.S. Geological Survey Professional Paper 1028, 204 p. Sherbume, R.W., Algermissen, S.T., and Harding, S.T., 1969, The hypocenter, origin time, and magnitude of the Prince William Sound earthquake of March 28, 1964, in Leipold, L.E., ed., The Prince William Sound, Alaska, earthquake of 1964 and afiershocks: U.S. Department of Commerce, Coast and Geodetic Survey, p. 49—69. Cloud, W.K., and Knudsen, CF, 1967, The Fairbanks, Alaska, earthquakes of June 21, 1967: U.S. Department of Commerce, Environmental Science Services Administration, Preliminary Engineering Seismological Report, p. 33—60. 'I‘illing, R.I., Koyanagi, R.Y., Lipman, P.W., Lockwood, J .P., Moore, J .G., and Swanson, D.W., 1976, Earthquake and related catastrophic events, Island of Hawaii, November 29, 1975: A preliminary report: U.S. Geological Survey Circular 740, 33p. Engdahl, ER, 1977, Amchitka data file, 1969—1973 from seismicity and plate subduction in the central Aleutians, in Island arcs, deep sea trenches and back—arc basins: Maurice Ewing Series, v. 1, p. 259—271. Stephens C.D., Lahr, J .C., Fogleman, K.A., and Homer, R.B., 1980, The St. Elias, Alaska, earthquake of February 28, 1979: Regional recording of aftershocks and short—term, preearthquake seismicity: Seismological Society of America Bulletin, v. 70, no. 5, p. 1607—1633. 408 456. 457. 458. 459. 461. 463. 464. 465. 466. 467. 468. 470. 471. 472. 473. 474. 475. 476. 477. 479. 480. 481. 482. 483. 484. 485. 487. 488. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 1.-—Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Davies, J ., Sykes, L., House, L., and Jacob, K., 1981, Shumagin seismic gap, Alaska Peninsula: History of great earthquakes, tectonic setting, and evidence for high seismic potential: Journal of Geophysical Research, v. 86, no. B5, p. 3821—3855. Ryall, A., VanWormer, J .D., and Jones, A.E., 1968, Triggering of microearthquakes by earth tides, and other features of the Truckee, California, earthquake sequence of September 1966: Seismological Society of America Bulletin, v. 58, no. 1, p. 215—248. Stiermann, D.J., and Ellsworth, W.L., 1976, Aftershocks of the February 21, 1973, Point Mugu, California, earthquakes: Seismological Society of America Bulletin, v. 66, no. 6, p. 1931—1952. Abdypoor, Gladees, and Bischke, RE, 1982, Earthquakes felt in the State of Pennsylvania; with emphasis on earthquakes felt in Philadelphia, Pennsylvania, and surrounding areas: Philadelphia, Temple University, Department of Geology unpublished manuscript, 351 p. Balderman, M.A., Johnson, C.A., Miller, D.G., and Schmidt, D.L., 1978, The 1852 Fort Yuma earthquake: Seismological Society of America Bulletin, v. 68, no. 3, p. 699—7 09. Monthly Weather Review, Annual report of the Chief Signal Officer to the Secretary of War, June 1872 to June 1891, v. 119, U. S. War Department, Washington, D. C. Unger, J. D. and Ward, PL, 1979, A large, deep Hawaiian earthquake—The Honomu, Hawaii, event of April 26,1973: Seismological Society of America Bulletin, v. 69, no. 6, p. 1771—1781. Qamar, A, and Hawley, B., 1979, Seismic activity near the Three Forks Basin, Montana: Seismological Society of America Bulletin, v. 69, no. 6, p. 1917—1929. Bolt, B.A., McEvilly, T.V., and Uhrhammer, RA, 1981, The Livermore Valley, California, sequence of January 1980: Seismological Society of America Bulletin, v. 71, no. 2, p. 451—463. Evans, D.G., and McEvilly, TV, 1982, A note on relocating the 1963 Watsonville earthquakes: Seismological Society of America Bulletin, v. 72, no. 4, p. 1309—1316. Corbett, E.J., and Johnson, C.E., 1982, The Santa Barbara, California, earthquake of 13 August 1978: Seismological Society of America Bulletin, v. 72, no. 6, p. 2201—2226. Wong, I.G., Cash, D.J., and Jaksha, L.H., 1984, The Crownpoint. New Mexico, earthquakes of 1976 and 1977: Seismological Society of America Bulletin, v. 74, no. 6, p. 2435—2449. Sbar, M.L., and DuBois, S.M., 1984, Attenutation of intensity for the 1887 Northern Sonora, Mexico, earthquake: Seismological Society of America Bulletin, v. 74, no. 6, p. 2613—2628. Webb, TH, and Kanamori, Hiroo, 1985, Earthquake focal mechanisms in the Eastern Transverse Ranges and San Emigdio Mountains, southern California and evidence for a regional decollement: Seismological Society of America Bulletin, v. 75, no. 3, p. 737—757. Gupta, I.N., and Nuttli, O.W., 1976, Spatial attenuation of intensities for Central US. earthquakes: Seismological Society of America Bulletin, v. 66, no. 3, p. 743—751. Hauksson, Egill, and Saldivar, G.V., 1986, The 1930 Santa Monica and the 1979 Malibu, California, earthquakes: Seismological Society of America Bulletin, ’v. 76, no. 6, p. 1542—1559. Aburto, A.A., Savage, M.K., DePolo, D.M., and Delaplain, DA, 1988, Bulletin of the Seismological Laboratory, January 1983 to May 1984: Reno, Nevada, University of Nevada—Reno, McKay School of Mines, 74 p. Dehlinger, Peter, and Bolt, BA, 1987, Earthquakes and associated tectonics in a part of coastal central California: Seismological Society of America Bulletin, v. 77, no. 6, p. 2056-2073. Boyd, T.M., and Lemar—Lam, A.L., 1988, Spatial distribution of turn—of—the—century seismicity along the Alaska—Aleutian arc: Seismological Society of America Bulletin, v. 78, no. 2, p. 636—650. Engdahl, E.R., Billington, S., and Kisslinger, C., 1989, Teleseismically recorded seismicity before and after the May 7, 1986, Andreanof Islands, Alaska, earthquake: Journal of Geophysical Research, v. 94, no. B11, p. 15,48115,498. Nowroozi, A.A., 1973, Seismicity of the Mendocino Escarpment and the aftershock sequence of June 26, 1968: Ocean seismic measurements: Seismological Society of America Bulletin, v. 63, no. 2, p. 441—456. MacDonald, G.A., and Wentworth, GK, 1954, Hawaiian volcanoes during 1951: US. Geological Survey Bulletin 996—D, 216 p. MacDonald, G.A., and Eaton, J .P., 1964, Hawaiian volcanoes during 1955: US. Geological Survey Bulletin 1171, p. 139. Armbruster, J .G., and Scharnberger, OK, 1986, Lancaster earthquakes, in Journal of the Lancaster County Historical Society, v. 90, no. 2, p. 78—86. Thenhaus, PO, 1978, A study of the October 12, 1877 Oregon earthquakes: U.S. Geologcial Survey Open-File Report 78—234, 17 p. Landsberg, H., 1938, The Clover Creek earthquake of July 15, 1938: Seismological Society of America Bulletin, v. 28, no. 4, p. 237—241. Kirkham, R.M., and Rogers, WP, 1985, Colorado earthquake data and interpretations 1867 to 1985: Colorado Geological Survey Bulletin 46, 106 p. Oaks, SD, and Kirkham, R.M., 1986, Results of a search for felt reports for selected Colorado earthquakes: Colorado Geological Survey Information Series 23, 89 p. 489. 490. 491. 492. 493. 494. 495. 496. 497. 498. 499. 500. 501. 502. 503. 504. 505. 506. 508. 509. 510. 511. 512. 513. 514. 515. 516. 517. 518. 520. 521. 522. TABLES 1—3 409 TABLE 1.-—Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Stover, C.W., 1989, Reassigned intensities based on a review of the earthquake questionnaires collected by the Hawaiian Volcano Observatory, Hawaii. Gordon, D.W., Bennett, T.J., Hermann, R.B., and Rogers, A.M., 1970, The south—central Illinois earthquake of November 9, 1968: Macroseismic studies: Seismological Society of America Bulletin, v. 60, no. 3, p. 953—971. Seismological Society of America, 1917, Seismological notes, Seismological Society of America Bulletin, v. 7, no. 4, p. 138—142. Seismological Society of America, 1916, The earthquake at Volcano Lake, Mexico, November 20, 1915: Seismological Society of America Bulletin, v. 6, no. 2—3, p. 181—184. Wood, HQ, 1916, California earthquakes: Seismological Society of America Bulletin, v. 6, no. 2—3, p. 55—180. Rockwood, C.G., 1888, Notes on American earthquakes: American Journal of Science, v. 35, 3rd series, p. 110. Woodward—Clyde Consultants, 1980, Seismological review of the July 16, 1936, Milton—Freewater earthquake source region: San Francisco, Calif, Contract No. 52028 C.O.11, Task No. WCC 1 for Washington Public Power Supply, System, 58 p. Bradford, DO, and Waters, AG, 1934, The Tolt River earthquake and its bearing on the structure of the Cascade Ranges: Seismological Society of America Bulletin, v. 24, no. 1, p. 51—62. MacDonald, Bernard, 1918, Remarks on the Sonora earthquake—its behavior at Tepic, Sonora, etc.: Seismological Society of America Bulletin, v. 8, no. 1, p. 74—78. The News, Cambridge, Idaho, May 19, 1916, and June 2, 1916. Rogers, WR, and Kirkham, R.M., 1986, Contributions to Colorado seismicity and tectonics—A 1986 update: Colorado Geological Survey Special Publication 28, p. 122-132. Wyss, Max, and Koyanagi, R.Y., in press, Isoseismal maps, macroseismic epicenters and estimated magnitudes of historical earthquakes in the Hawaiian Islands, U.S. Geological Survey Bulletin. Rojahn, C., and Morrill, B.J., 1977, The Island of Hawaii earthquakes of November 29, 1975: Strong—motion data and damage reconnaissance report: Seismological Society of America Bulletin, v. 67, no. 2, p. 493—515. Brasch, EE., 1916, An earthquake in New England during the colonial period (1755): Seismological Society of America Bulletin, v. 6, no. 1, p. 26—42. Engle, H.M., 1936, The Montana earthquakes of October 1935: Structural lessons: Seismological Society of America Bulletin, v. 26, no. 2, p. 99—109. Witkind, I.J., Myers, W.B., Hadley, J .B., Hamilton, W., and Fraser, G.D., 1962, Geologic features of the earthquake at Hebgen Lake, Montana, August 17, 1959: Seismological Society of America Bulletin, v. 52, no. 2, p. 163—180. Slemmons, DB, 1957, Geological effects of the Dixie Valley—Fairview Peak, Nevada, earthquake of December 16, 1954: Seismological Society of American Bulletin, v. 47, no. 4, p. 353—375. Devlin, J .J ., Langguth, LG, and Arringdale, R.L., 1942, Macroseismic study of the New Hampshire earthquakes of December 1940: Seismological Society of America Bulletin, v. 32, no. 2, p. 67—73. Reinhold, D.J., and Johnston, AG, 1987, Historical seismicity in the southern Appalachian seismic zone: U.S. Geological Survey Open-File Report 87—433, 858 p. Westland, A.J., and Heinrich, RR, 1940, A macroseismic study of the Ohio earthquakes of March 1937: Seismological Society of America Bulletin, v. 30, no. 3, p. 251—160. Brown, B.H., 1937, The State—line earthquake at Milton and Walla Walla: Seismological Society of America Bulletin, v. 27, no. 3, p. 205—209. Haar, L.C., Fletcher, J .B., and Mueller, CS, 1984, The 1982 Enola, Arkansas, swarm and scaling of ground motion in the Eastern United States: Seismological Society of America Bulletin, v. 74, no. 6, p. 2463—2482. Eickelberg, E.W., 1936, Review of earthquakes for the past year: Seismological Society of America, Eastern Section, Earthquake Notes, v. 8, nos. 1—2, p. 95. Gordon, C.H., 1913, Earthquakes in east Tennessee: Seismological Society of America Bulletin, v. 3 p. 191—194. Rockwood, C.G., 1865, Notes on American earthquakes: American Journal of Science and Arts, v. 40, 2nd series, p. 362—366. Kisslinger, J .B., 1983, Some volcanoes, volcanic eruptions, and earthquakes in the former Russian America: Pacific Northwest Quarterly, v. 74, no. 2, p. 59-68. Cox, D.C., 1984, Probable Aleutian source of the tsunami observed in August 1872 in Hawaii, Oregon, and California: Science of Tsunami Hazards, The International Journal of the Tsunami Society, v. 2, no. 2, p. 79—94. Lawson, AG, 1908, The California earthquake of April 18, 1906: Report of the State Investigation Commission, Carnegie Institution of Washington, v. 1, 451 p. Rockwood, C.G., 1885, Notes on American earthquakes: American Journal of Science, 3rd series, v. 29, p. 425—437. Kisslinger, J .B., 1980, Unpublished translations of Russian reports from the Alaskan regions. Ellsworth, W.L., 1990, Earthquake history, 1769—1989, in R.E. Wallace, ed., The San Andreas fault system: U.S. Geological Survey Professional Paper 1515, p. 153—187. Gordon, D.W., 1989, Personal communication, U.S. Geological Survey. 410 523. 524. 525. 526. 527. 528. 529. 530. 531. 532. 533. 534. 535. 536. 537. 539. 540. 541. 542. 543. 544. 545. 546. 547. 548. 549. 550. 551. 552. 553. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 1.———Hyp0center and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Allen, M.W., 1925, Some remarks concerning Pacific Coast earthquakes: Seismological Society of America Bulletin, v. 15, no. 2, p. 135—136. Westland, A.J., S.J., and Heinrich, RR, 1940, A macroseismic study of the Ohio earthquakes of March 1937: Seismological Society of America Bulletin, v. 30, no. 3, p. 251—260. Law Engineering Testing Company, 1975, Report on evaluation of intensity of Giles County, Vlrginia, earthquake of May 31, 1897: Marietta, Ga., Law Engineering Testing Company and Burns and Roe, Inc., 94 p. Bollinger, G.A., 1977, Reinterpretation of the intensity data for the 1886 Charleston, South Carolina, earthquake, in Studies related to the Charleston, South Carolina, earthquake of 1886A preliminary report: U.S. Geological Survey Professional Paper 1028, p. 17—32. ' Hopper, M.G., and Algermissen, S.T., 1980, An evaluation of the effects of the October 31, 1895, Charleston, Missouri, earthquake: U.S. Geological Survey Open-File Report 80—778, 44 p. Espinosa, A.F., Brockman, SR, and Michael, J .A., 1986, Modified Mercalli intensity distribution for the most significant earthquakes in Alaska 1899—1981: U.S. Geological Survey Open-File Report 86—0203, map, scale 1:12,500,000. Street, R.L., and Green, RE, 1984, The historical seismicity of Central United States, 1811—1928: University of Kentucky Research Foundation, U.S. Geological Survey Contract No. 14—08—0001, 550 p. Huber, W.L., 1930, San Francisco earthquakes of 1865 and 1868: Seismological Society of America Bulletin, v. 20, no. 4, p. 261—272. Bateman, RC, 1961, Willard D. Johnson and the strike—slip component of fault movement in the Owens Valley, California, earthquake of 1872: Seismological Society of America Bulletin, v. 51, no. 4, p. 483—493. Legg, Mark, and Agnew, D.C., 1979, The 1862 earthquake in San Diego, in Earthquakes and other perils: Geological Society of America Field Trip Guidebook, p. 139—141. Coffman, J .L., 1969, Earthquake investigations in the United States: U.S. Department of Commerce, ESSA, Coast and Geodetic Survey Special Publication No. 282 [revised 1969 edition], p. 51—52. Branner, J .C., 1917, The Tejon Pass earthquake of October 22, 1916: Seismological Society of America Bulletin, v. 7, no. 9, p. 51—60. Blackweider, Eliot, 1929, A recent earthquake in the Sierra Nevada: Seismological Society of America Bulletin, v. 19, no. 1, p. 52—53. Byerly, Perry, and Wilson, J .T., 1935, The central California earthquakes of May 16, 1933, and June 7, 1934: Seismological Society of America Bulletin, v. 25, no. 3, p. 223—246. Palmer, AH, 1921, California earthquakes during 1920: Seismological Society of America Bulletin, v. 11, no. 1, p. 9—10. Kenmitzer, L.E., 1924, The Salinas earthquake of December 27, 1924: Seismological Society of America Bulletin, v. 14, no. 4, p. 230—232. Byerly, Perry, 1925, Notes on the intensity of the Santa Barbara earthquake between Santa Barbara and San Luis Obispo: Seismological Society of America Bulletin, v. 15, no. 1, p. 279—281. Dewell, H.D., and Willis, B., 1925, Earthquake damage to buildings: Seismological Society of America Bulletin, v. 15, no. 4, p. 282—304. Kirkbride, W.H., 1927, The earthquake at Santa Barbara,,California, June 29, 1925, as it affected the railroad of the Southern Pacific Company: Seismological Society of America Bulletin, v. 17, no. 1, p. 1-7. Byerly, Perry, 1927, The Eureka (California) earthquake of August 20, 1927: Seismological Society of America Bulletin, v. 17, no. 4, p. 213—217. Sparks, N.R., 1936, The Eureka earthquake of June 6, 1932: Seismological Society of America Bulletin, v. 26, no. 1, p. 13—18. Wood, HQ, 1937, The Terwilliger Valley earthquake of March 25, 1937: Seismological Society of America Bulletin, v. 27, no. 4, p. 305—312. . Sylvester, A., 1979, Earthquake damage in Imperial Valley, California, May 18, 1940, as reported by TA. Clark: Seismological Society of America Bulletin, v. 69, no. 2, p. 547—568. Trifunac, M., and Brune, Jim, 1970, Complexity of energy release during the Imperial Valley, California, earthquake of 1940: Seismological Society of America Bulletin, v. 60, no. 1, p. 137—160. Richter, C.F., Allen, C.R., and Nordquist, J .M., 1958, The Desert Hot Springs earthquakes and their tectonic environment: Seismological Society of America Bulletin, v. 48, no. 4, p. 315—337. Steinbrugge, K.V., and Moran, D.F., 1954, An engineering study of the southern California earthquake of July 21, 1952, and aftershocks: Seismological Society of America Bulletin, v. 44, no. 2B, p. 199—462. Steinbrugge, K.V., and Moran, DR, 1957, An engineering study of the Eureka, California, earthquake of December 21, 1954: Seismological Society of America Bulletin, v. 47, no. 1, p. 129—153. Cloud, W.K., 1967, Intensity map and structural damage, Parkfield, California, earthquake of June 27, 1966: Seismological Society of America Bulletin, v. 57, no. 6, p. 1161—1178. Cloud, WK, and Scott, N.H., 1968, The Borrego Mountain, California, earthquake of 9 April 1968, A preliminary engineering seismology report: Seismological Society of America Bulletin, v. 58, no. 3, p. 1187—1191. Murphy, L.M. (scientific coordinator), 1973, San Fernando, California, earthquake of February 9, 1971: Washington, D.C., U.S. National Oceanic and Atmospheric Administration, v. 13. 554. 555. 556. 557. 558. 559. 560. 561. 562. 563. 564. 565. 566. 567. 569. 570. 571. 572. 573. 574. 575. 576. 577. 578. 579. 580. 581. 582. 583. 584. 587. 588. 589. TABLES 1—3 411 TABLE 1.~—Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Clark, M.M., 1972, Surface rupture along the Coyote Creek fault, in The Borrego Mountain earthquake of April 9, 1968: U.S. Geological Survey Professional Paper 787, p. 55—86. Kachadorian, R., Yerkes, RR, and Waananen, A.O., 1967, Effects of the Truckee, California, earthquake of September 12, 1966: U.S. Geological Survey Circular 537, 14 p. Westaway, Rob, and Smith, RB, 1989, Source parameters of the Cache Valley (Logan), Utah, earthquake of 30 August 1962: Seismological Society of America Bulletin, v. 79, no. 5, p. 1410—1425. Hopper, M.G., ed., 1985, Estimation of earthquake effects associated with large earthquakes in the New Madrid seismic zone: U.S. Geological Survey Open-File Report 85—457, 186 p. McKeown, F.A., and Pakiser, L.C., eds., 1982, Investigations of the New Madrid, Missouri, earthquake region: U.S. Geological Survey Professional Paper 1236, 201 p. Seismological Society of America, 1934, Seismological notes, Seismological Society of America Bulletin, v. 24, no. 2, p. 329. Seismological Society of America, 1950, Seismological notes, Seismological Society of America Bulletin, v. 40, no. 4, p. 314. Seismological Society of America, 1951, Seismological notes, Seismological Society of America Bulletin, v. 41, no. 1, p. 63—80. Stover, C.W., and Brewer, L.R., in press, United States earthquakes 1986: U.S. Geological Survey Bulletin. Seismological Society of America, 1952, Seismological notes, Seismological Society of America Bulletin, v. 42, no. 1, p. 100—106. Seismological Society of America, 1956, Seismological notes, Seismological Society of America Bulletin, v. 46, no.2, p. 150. Sharp, K.V., 1976, Surface faulting in Imperial Valley during the earthquake swarm of January—February 1975: Seismological Society of America Bulletin, v. 66, no. 4, p. 1145—1154. Clark, M.M., Sharp, R.V., Castle, R.O., and Harsh, PW, 1976, Surface faulting near Lake Oroville, California, in August 1975: Seismological Society of America Bulletin, v. 66, no. 1, p. 1101—1110. Hansen, Gladys, and Condon, Emmet, 1989, Denial of disaster, the untold story and photographs of the San Francisco earthquake and fire of 1906: San Francisco, Cameron and Company, 160 p. Nuttli, O.W., 1983, Average seismic source.parameter relations for mid—plate earthquakes: Seismological Society of America Bulletin, v. 73, no. 2, p. 519—535. Coan, T., 1869, Notes on the recent volcanic disturbances of Hawaii: American Journal of Science, 2nd series, v. 47, nos. 139, 140, 141, p. 89—98. Nason, Robert, 1980, Damage in San Mateo County, California, in the earthquake of 18 April 1906: U.S. Geological Survey Open-File Report 80—176, 51 p. Nason, Robert, 1980, Damage in Santa Clara and Santa Cruz Counties, California, caused by the earthquake of 18 April 1906: U.S. Geological Survey Open-File Report 80—1076, 66 p. Nason, Robert, 1982, Damage in Alameda and Contra Costa Counties, California, in the earthquake of 18 April 1906: U.S. Geological Survey Open-File Report 82—63, 46 p. Stover, C.W., Reagor, B.G., Baldwin, F.W., and Brewer, LR, 1990, Preliminary isoseismal map for the Santa Cruz (Lorna Prieta), California, earthquake of October 18, 1989, UTC: U.S. Geological Survey Open-File Report 90—18, 24 p. Steinbrugge, K.V., and Moran, DE, 1956, Damage caused by the earthquakes of July 6 and August 23, 1954: Seismological Society of America Bulletin, v. 46, no. 1, p. 15—33. Dewey, J .W., 1990, Unpublished data, U.S. Geological Survey. Stover, C.W., 1992, Unpublished intensity data for 1987, U.S. Geological Survey. Stover, C.W., 1992, Unpublished intensity data for 1988, U.S. Geological Survey. Stover, C.W., 1992, Unpublished intensity data for 1989, U.S. Geological Survey. Earthquake Engineering Research Institute, 1988, The Whittier Narrows earthquake of October 1, 1987: Earthquake Spectra, v. 4, nos. 12, 409 p. Hauksson, E., Jones, L.M., Davis, T.L., Hutton, K., Brady, G.A., Reasenberg, F.A., Michael, A.J., Yerkes, R.F., Williams, P., Reagor, G., Stover, C.W., Bent, A.L., Shakal, A.K., Etheredge, E., Porcella, R.L., Bufe, C.G., Johnston, M.J.S., and Cranswick E., 1988, The 1987 Whittier Narrows earthquake in the Los Angeles metropolitan area, California: Science, v. 239, p. 1409—1412. ‘ Hauksson, E., and Jones, L.M., 1989, The 1987 Whittier Narrows earthquake sequence in Los Angeles, southern California, seismological and tectonic analysis: Journal of Geophysical Research, v. 94, no. B7, p. 9579—9589. Langer, C.J., Powers, RS, Johnston, A.O., and Bollinger, G.A., 1987, The Olney, Illinois, earthquake of 10 June 1987, A preliminary report: U.S. Geological Survey Open-File Report 87—623, p. 1—23. Valley Sentinel, Portsmouth, Ohio, Wednesday, May 22, 1901, v. 6, p. 1. Seismological Society of America, 1989, Special issue on the Elmore Ranch and Superstition Hills, California, earthquakes of 24 November 1987: Seismological Society of America Bulletin, v. 79, no. 2, 550 p. Finch, M.O., 1988, Damage to irrigation facilities in Imperial Valley, in California Geology: California Division of Mines and Geology, v. 41, no. 4, p. 85—90. Wallace, RE, 1984, Fault scarps formed during the earthquakes of October 2, 1915, in Pleasant Valley, Nevada, and some tectonic implications, in Faulting related to the 1915 earthquakes in Pleasant Valley, Nevada: U.S. Geological Survey Professional Paper 1274—A, p. A1—A33. 412 590. 591. 592. 593. 594. 595. 596. 597. 598. 599. 600. 601. 602. 603. 605. 606. 607. 608. 609. 610. 611. 612. 613. 615. 616. 617. 618. 619. 620. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 1.——Hypocenter and intensity references—Continued [Please note that numbers in this table are not sequential because these references were selected from a master list compiled for other USGS publications] Case, W.F., 1988, Geologic effects of the 14 and 18 August 1988, earthquakes in Emery County, Utah: Utah Geological and Mineral Survey, Survey Notes, v. 22, no. 1 and 2, p. 8—15. Silliman, B., and Dana, J .D., 1868, Earthquake in western New York, Vermont, and lower Canada: American Journal of Science and Arts, v. 45, nos. 133, 134, 135, p. 135. Reagor, Glen, and Brewer, LR, 1987, Preliminary isoseismal map and intensity distribution for the southeastern Illinois earthquake of June 10, 1987: U.S. Geological Survey Open-File Report 87—578, 3 p. Rymer, M.J., and Ellsworth, W.L., eds., 1990, The Coalinga, California, earthquake of May 2, 1983: U.S. Geological Survey Professional Paper 1487, 417 p. Benuska, Lee (technical ed.), 1990, Loma Prieta earthquake reconnaissance report, in Earthquake Spectra: Earthquake Engineering Research Institute, Supplement to v. 6, 448 p. Astanek, A., Bertero, V.V., Bolt, B.A., Mahin, S.A., Moehle, J .P., and Seed, R.B., 1989, Preliminary report on the seismological and engineering aspects of the October 17, 1989, Santa Cruz (Lorna Prieta), earthquake: University of California at Berkeley, Earthquake Engineering Research Center, Report No. UCB/EERC—89/14, 58 p. U.S. Geological Survey, 1990, The Lorna Prieta, California, earthquake: An anticipated event: Science, v. 247, p. 286—293. Given, D.D., Hutton, L.K., and Jones, L.M., 1987, The southern California network bulletin, July—December 1986: U.S. Geological Survey Open-File Report 87—448, p. 24~27. Given, D.D., Wald, L.A., Jones, L.M., and Hutton, L.K., 1989, The southern California network bulletin, July—December 1987: U.S. Geological Survey Open-File Report 89—323, p. A1—A6. 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Retsel, Frank, Torrance, W.T., and Weaver, HF, 1954, Report on investigation of an earth's disturbance at Wilkes-Barre, Luzerne County, Pennsylvania, U.S. Department of Interior, Bureau of Mines, Region 8, appendix 1, p. 25-33 to 25-43. Housner, G.W., and Thiel, C.C., Jr., 1990, Competing against time: Report of the Governor's Board of Inquiry on the 1989 Loma Prieta earthquake: Earthquake Spectra, Earthquake Engineering Research Institute, v. 6, no. 4, p. 681—711. Plafker, G., and Galloway, J.P., eds., 1989, Lessons learned from the Lorne Prieta, California, earthquake of October 17, 1989: U.S. Geological Survey Circular 1045, 48 p. Stein, R.S., and Bucknam, R.C., eds., 1985, Proceedings of Workshop XXV'III, on the Borah Peak, Idaho, earthquake, volume A: U.S. Geological Survey Open-File Report 85—290, 686 p. Lipman, RW, and Mullineaux, DR, 1981 (1982), The 1980 eruption of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, 844 p. Lander, J.F., and Lockridge, RA, 1989, United States Tsunamis (including United States Possessions) 1690—1988: U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Publication 41—2, 265 p. Steinbrugge, KV., 1967, Introduction to the earthquake engineering of the 1964 Prince William Sound, Alaska, earthquake, in The Prince William Sound, Alaska earthquake of 1964 and afiershocks: U.S. Department of Commerce, NOAA, Coast and Geodetic Survey, Publication 10—3, v. 2, part A, p. 1—6. Toppozada, TR, and Wong, LG, 1990, M 2 5.5 earthquakes within 100 km of Parkfield, California [abs], Seismological Society of America, Eastern Section, Seismological Research Letters, v. 61, no. 1, p. 42. Toppozada, TR, and Cramer, CH, 1978, Ukiah earthquake, 25 March 1978, Seismicity possibly induced by Lake Mendocino: California Geology, v. 31, no. 12, p. 275—281. Perrine, CD, 1899, Earthquakes in California in 1898: U.S. Geological Survey Bulletin 161, 29 p. Johnson, T.E., Ludwin, RS, and Qamar, A.I., in press, The central Cascades earthquake of March 7, 1891: Washington Geology. Rogers, G.C., and Hasegawa, H.S., 1978, A second look at the British Columbia earthuake of June 23, 1946: Seismological Society of America Bulletin, v. 68, no. 3, p. 653—675. Grant, W.C., and Weaver, 0.8., 1986, Earthquakes near Swifl: Reservoir, Washington, 1958—1963: Seismological Society of America Bulletin, v. 76, no. 6, p. 1573—1587. Yelin, T.S., and Patton, H.J., 1991, Seismotectonics of the Portland, Oregon, region: Seismological Society of America Bulletin, v. 81, no. 1, p. 109—130. Qamar, A., Rathbum, A., Ludwin, R., Crosson, RS, and Malone, SD, 1986, Earthquake hypocenters in Washington and Northern Oregon—1980: Washington Division of Geology and Earth Resources, Information Circular 82, 64 p. AAM ABE ABI A32 A83 ADK AND ARC AS BAK BAR BAS BL BLA BLT BMU BOL BOT BRK BU BUR CAR CDL CFR CON COX CWR DDA TABLES 1—3 413 TABLE 2.—Magnitude references University of Michigan, Ann Arbor. Mich. Abe. Katsuyuki. 1981. Magnitude of large shallow earthquakes from 1904 to 1980: Physics of the Earth and Planetary Interiors, v. 27. p. 72—92. Abe. Katsuyuki. and Noguchi. Shin'ichi. 1983, Determination of magnitude for large shallow earthquakes, 1898—1917: Physics of the Earth and Planetary Interiors, v. 32, p. 45—59. Abe. Katsuyuki, and Noguchi. Shin'ichi. 1983. Revision of magnitudes of large shallow earthquakes, 1897—1912: Physics of the Earth and Planetary Interiors. v. 33. p. 1-1 1. Abe, Katsuyuki, 1984, Complements to “Magnitudes of large shallow earthquakes from 1904 to 1980:” Physics of the Earth and Planetary Interiors, v. 34. p. 17—23. Adak Observatory. US National Oceanic and Atmospheric Administration. Adak Island, Aleutian Islands, Alaska. Ando. 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Roundout Associates, Inc.. repon prepared for US. Nuclear Regulatory Commission, NUCREG/CR—1577, 315 p. Basham. P.W., Weichen. DH, and Berry. ML 1979. Regional assessment of seismic risk in Eastern Canada: Seismological Society of America, v. 69. no. 5. p. 1567—1602. Baker. GE, and Langston, C.A., 1987. Source parameters of the 1949 magnitude 7.1 South Puget Sound, Washington. earthquake as determined from long-period body waves and strong ground motions: Seismological Society of America Bulletin, v. 77, no. 5, p. 1530—1557. Seismological Observatory, Virginia Polytechnic Institute and State University. Blacksburg, Va. Bolt, B.A., 1978, The local magnitude ML of the Kern County earthquake of July 21, 1952: Seismological Society of America Bulletin. v. 68. no. 2. p. 513—515. Bolt, B.A., McEvilly, T.V., and Uhrhammer, R.A., 1981. The Liverrnore Valley. California. sequence of January 1980: Seismological Society of America Bulletin. v. 71, no. 2, p. 451—463. Bollinger. 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A.M.. 1985. Centroid—moment tensor solutions for 35 earthquakes in Western North America (1977—1983): Seismological Society of America Bulletin, v. 75, no. 1, p. 23—39. Ellsworth, W.L, 1990, Historical seismicity. in Wallace. R.E.. ed., The San Andreas fault system: U.S. Geological Survey Professional Paper 1515, p 153—181. Seismological Service, Geological Survey of Canada [formerly Earth Physics Branch], Ottawa, Ont., Canada. Ebel. J.E., Somerville, P.G.. and Mclver, J .D.. 1986, A study of the source parameters of some large earthquakes of northeastern North America: Journal of Geophysical Research, v. 91, no. BS, p. 8231—8247. Frankel, Arthur, 1984, Source parameters of the ML about 5 earthquake near Anza. Califomia, and a comparison with an Imperial Valley aftershock: Seismological Society of America Bulletin, v. 74, no. 5, p. 1509—1527. Bollinger, G.A., 1979, Attenuation of the Lg phase and the determination of Mb in the Southeastern United States: Seismological Society of America Bulletin, v. 69, no. 1, p. 45—63. Gordon, D.W.. 1990, U.S. Geological Survey unpublished data. U.S. Geological Survey, Menlo Park, Calif. Geophysical Observatory, Colorado School of Mines, Golden. Colo. U.S. Geological Survey, Pasadena, Calif. Gutenberg, Beno, and Richter, CF, 1954, Seismicity of the Earth and associated phenomena: New York, Hafner Publishing Inc., 310 p. U.S. Geological Survey. Golden, Colo. Georgia Institute of Technology, Atlanta, Ga. Harvard University, Cambridge, Mass. Hanzell, SH, and Brune, J.N., 1979, The Horse Canyon earthquake of August 2, 1975—two stage stress-release processs in a strike-slip earthquake: Seismological Society of America Bulletin, v.69, no. 4, p. 1161—1173. 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HK HLS HRM HRN HRR HVO ISC JDH JLM JLQ JM JOH JON KA KAN KIR KJ KRK LB MAT MH MMT MOS MSO NLI NMI NQT NS TABLES 1—3 415 TABLE 2.—Magnitude references—Continued Hanks. T.C.. and Kanamori, H.. 1979. A moment magnitude scale: Journal of Geophysical Research, v. 84, no. B5, p. 2348—2350. Hasegawa, H.W., Lahr. J.C.. and Stephens. CD. 1980. Fault parameters of the St. Elias, Alaska. earthquake of February 28, 1979: Seismological Society of America Bulletin, v. 70, no. 5, p. 1651—1660. Hemnann. KB, 1986, Surface-wave studies of some South Carolina earthquakes: Seismological Society of America Bulletin, v. 76, no. 1, p. 1 11—121. Hen‘rnann, R.B., 1979, Surface wave focal mechanisms for Eastern North America earthquakes with tectonic implications: Journal of Geophysical Research, v. 84, no. B7, p. 3543—3552. Hemnann, R.B., Langston, C.A.. and Zollweg, J.E., 1982, The Sharpsburg, Kentucky, earthquake of 27 July 1980: Seismological Society of America Bulletin, v. 72. no. 4, p. 1219—1239. 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Kirkham, R.M.. and Rogers, W.P., 1986, An interpretation of the November 7, 1882. Colorado, earthquake: Colorado Geological Survey, Open-File Report 86—8, 36 p. Langston, C.A.. and Blum, DE. 1977. The April 29. 1965. Puget Sound earthquake and the crustal and upper mantle structure of western Washington: Seismological Society of America Bulletin, v. 67, no. 3, p. 693—711. Matsushiro Seismological Observatory. Japan Meteorological Agency. Matsushiro, Japan. Mori, Juim, and Hartzell. Stephen, 1990, Source inversion of the 1988 Upland, California, earthquake—Determination of a fault plane for a small event: Seismological Society of America Bulletin, v. 80, no. 3, p. 507—518. Montana College of Mineral Sciences and Technology. Butte, Mont. Institute of Physics of the Earth of the U.S.S.R., Moscow. University of Montana, Missoula, Mont. N uttli, O.W., 1983, Average seismic source-parameter relations for mid-plate earthquakes: Seismological Society of America Bulletin, v. 73, no. 2, p. 519—535. New Mexico Institute of Mining and Technology, Socorro. N. Mex. Noson, L.L., Qamar. A.. and Thorsen. G.W.. 1988. Washington State earthquake hazards: Washington Division of Geology and Earth Resources. Information Circular 85, p. 22. Natali, 5.0., and Sbar. M.L.. 1982, Seismicity in the epicentral region of the 1887 northeastern Sonoran earthquake, Mexico: Seismological Society of America Bulletin. v. 72. no.1, p. 181—196. 416 NU NUT PAL PAS PMR QAM REN RIC RK ROG ROT SAN SAW SC SEE SET SG SIG SLM SOM SR SRT ST SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 2.——Magnitude references—Continued Nuttli, O.W.. 1974, Magnitude—recurrence relation for central Mississippi valley earthquakes: Seismological Society of America Bulletin, v. 64, no. 4, p. 1189—1207. Nuttli, O.W., 1987, The effects of earthquakes in the Central United States: Central United States Earthquake Consortium, Monograph Series, v. 1. 33 p. Nuttli, O.W.. 1979, Seismicity of the Central United States, geology in the siting of nuclear power plants: Geological Society of America, Reviews in Engineering Geology, v. 4, p. 67—107. Nuttli, O.W., 1973, The Mississippi valley earthquakes of 1811 and 1812: Intensities, ground motion, and magnitudes: Seismological Society of America Bulletin, v. 63, no. 1, p. 227—248. Nuttli, O.W., Bollinger, G.A., and Griffiths, D.W., 1979, On the relation between Modified Mercalli intensity and body-wave magnitude: Seismological Society of America Bulletin, v. 69, no. 3, p. 893—909. Lamont-Doherty Geological Observatory. Columbia University, Palisades, N.Y. Seismological Laboratory, California Institute of Technology. Pasadena, Calif. Alaska Tsunami Warning Center, US. National Oceanic and Atmospheric Administration, Palmer, Alaska. Plafker, G.. and Thatcher, W., 1982. Geological and geophysical evaluation of the great 1899—1900 Yakutat Bay, Alaska. earthquakes [abs], in Coppersmith, K..l., and Schwartz, D.P., eds.: Chapman conference on fault behavior and the earthquake generation process, American Geophysical Union, p. 7. Qarnar, A., Rathbum, A., Ludwin R.. Crosson. RS, and Malone, SD, 1986, Earthquake hypocenters in Washington and Northem Oregon—1980: Washington Division of Geology and Earth Resources, Innformation Circular 82, 64 p. Mackay School of Mines, University of Nevada—Reno, Reno, Nev. Richter, C.F., 1935, An instrumental earthquake magnitude scale: Seismological Society of America Bulletin, v. 25, no. 1, p. 1-32. Ruff, Larry, Kanamori, Hiroo, and Sykes, Lynn, 1985. The 1957 great Aleutian earthquake [abs]: EOS, Transactions, American Geophysical Union, v. 66. no. 18, p. 298. Rogers, G.C.. 1983, Seismotectonics of British Columbia: University of British Columbia, Canada, PhD. thesis, 247 p. Rothé, J.P., 1969, The seismicity of the Earth: Paris, United Nations Educational, Scientific, and Cultural Organization, 336 p. Sanford. A.R., and Toppozada, T.R., 1974, Seismicity of proposed waste disposal site in southeastern New Mexico: New Mexico Bureau of Mines and Mineral Resources. Circular 143, 15 p. Scholz, C.H., Aviles, C.A., and Wesnousky. 5.0.. 1986, Scaling differences between large interplate and intraplate earthquakes: Seismological Society of America Bulletin, v. 76, no. 1, p. 65—70. Stover, C.W., and Coffman, J.L.. This publication. Street, R.L., 1982. A contribution to the documentation of the 181 1—1812 Mississippi valley earthquake sequence: Seismological Society of America, Eastern Section, Earthquake Notes, v. 51, no. 2, p. 39—52. Street, R.L., 1989, Personal communication. letter dated July 5, 1989. Street, R.L., and Green, R.F., 1984, The historical seismicity of Central United States, 1811—1928, University of Kentucky Research Foundation. Lexington, Ky., 550 p. Slemmons, D.B., Jones, AB. and Gimlet, 1.1.. 1965. Catalog of Nevada earthquakes, 1852—1960: Seismological Society of America Bulletin, v. 55, no. 2, p. 519—565. Saint Louis University, Saint Louis, Mo. Somerville, P.G., McLaren, J.P.. LaFevre. L.V.. Berger. R.W., and Helmberger. H.V.. 1987, Comparison of source scaling relations of Eastern and Western North American earthquakes: Seismological Society of America Bulletin, v. 77, no. 2, p. 322—346. Schell, M.M., and Ruff, LL, 1986, Southeastern Alaska tectonics: source process of the large 1972 Sitka earthquake [abs]: EOS, Transactions, American Geophysical Union, v. 67, p. 304—305. Street, R.L., 1984. Some recent Lg-phase displacement spectral densities and their implication with respect to the prediction of ground motions in Eastern North America: Seismological Society of America Bulletin, v. 74, no. 2, p. 757—762. Street, R.L., and Turcotte, F.T., 1977. A study of northeastem North America spectral moments, magnitudes, and intensities: Seismological Society of America Bulletin. v. 67, no. 3, p. 599—614. STR S'I'I‘ SZ TAG TEC TH THH TUL TW UH UPP UU VIC VOS WAL WAS WES WK WOO WY WYS YEL YP TABLES 1—3 417 TABLE 2.—Magnitude references—Continued Street, R.L., 1976, Scaling Northeastem United States/Southeasten Canadian earthquakes by their Lg waves: Seismological Society of America Bulletin, v. 66, no. 5, p. 1525-1537. Street, R.L., Herrmann, R.B., and Nuttli, O.W., 1975, Spectral characteristics of the L3 wave generated by Central United States earthquakes: Geophysical Journal of Royal Astronomical Society, v. 41, p. 51—63. Schwartz, S.Y., and Christensen. D.H.. 1988. The 12 July 1986 St. Marys, Ohio, earthquake and recent seismicity in the Anna. Ohio, seismogenic zone: Seismological Society of America, Eastern Section, Seismological Research Letters, v. 59. no. 2, p. 57—62. Taggart, James. and Baldwin. Frank, 1982. Earthquake sequence of 1938—1939 in Mogollen Mountains, New Mexico: New Mexico Geology, v.4, no. 4, p. 49—52. Center for Earthquake. Research and Information, Memphis State University, Memphis, Tenn. Thatcher, W., and Hanks, T.C., 1973, Source parameters of southern California earthquakes: Journal of Geophysical Research, v. 78, no. 35, p. 8547—8576. Thatcher, W., Hileman, J.A., and Hanks, T.C., 1975, Seismic slip distribution along the San Jacinto fault zone, southern California, and its implications: Geological Society of America Bulletin, v. 86, p. 1140—1146. Oklahoma Geophysical Observatory, Oklahoma Geological Survey. Leonard, Okla. Thatcher, W., 1975, Strain accumulation and release mechanism of the 1906 San Francisco earthquake: loumal of Geophysical Research, v. 80, no. 35, p. 4862—4880. University of Hawaii, Honolulu, Hawaii. Uppsala Seismograph Station, University of Uppsala. Sweden. Seismograph Stations, University of Utah, Salt Lake City. Utah. Victoria Geophysical Observatory, Victoria B.C., Canada. Voss, LA, and Hen-mann, RB, 1980. A surface-wave study of the June 16, 1978, Texas earthquake: Seismological Society of America, Eastern Section, Earthquake Notes, v. 51, no. 1, p. 3—14. Wallace, R.E., 1984, Fault scarps formed during the earthquakes of October 2, l915, in Pleasant Valley, Nevada, and some tectonic implications, in Faulting related to the 1915 earthquakes in Pleasant Valley, Nevada: US Geological Survey Professional Paper 1274—A, p. A1—A33. University of Washington, Seattle, Wash. Weston Observatory, Boston College, Weston, Mass. Webb, T.H., and Kanamori, Hiroo, 1985, Earthquake focal mechanism in the Eastern Transverse Ranges and San Emigdio Mountains, southern California, and evidence for a regional decollement: Seismological Society of America Bulletin. v. 75, no. 3, p. 737—757. Wood, H.O., 1947, Earthquakes in southern California with geologic relations: Seismological Society of America Bulletin, v 37, no. 3. p. 217—258. Wyss, Max, and Koyanagi, Robert, in press, Isoseismal maps, macroseismic epicenters and estimated magnitudes of historical earthquakes in the Hawaiian Islands: US Geological Survey Bulletin. ’ Wyss, Max, and Brune, J.N., 1968, Seismic moment, stress, and source dimensions for earthquakes in the California-Nevada region: Journal of Geophysical Research, v. 73, no., 14, p. 4681—1694. Yelin, Tom, 1991, University of Washington. personal communication. Yelin, TS, and Patton, H.J., 1991, Seismotectonics of the Portland. Oregon, region: Seismological Society of America Bulletin, v. 81, no. 1, p. 109—130. SEISMICITY OF THE UNITED STATES, 1568—1989 (REVISED) TABLE 3.——Deaths from earthquakes in the United States Date Eanhquake locality No. of deaths December 16. 1811—February 7. 1812 ....................... Northeast Arkansas—New Madrid. Missouri .................................................. Several December 8. 1812 ...................................................... San Juan Capistrano. California 40 December 21. 1812 .................................................... Santa Barbara, California 1 January 9, 1857 .......................................................... Fort Tejon. California 1 April 3, 1868.. Hawaii island. Hawaii (landslides—31,tsunami—~46) ................................... 77 October 21. 1868. Hayward. California 80 March 26. 1872 ............................................... Owens Valley. California 27 May 10, 1877 Hawaii Island. Hawaii 5 September 1. 1886 .......................................... Charleston. South Carolina 60 April 19, 1892 ............................................................ Vacaville. California ...1 December 25. 1899 ......................................... San Jacinto. California... .6 April 18, 1906 San Francisco. California (earthquake and fire) ............................... about 3,000 June 23. 1915 imperial Valley. California 6 April 21. 1918 San Jacinto. California ............ 1 June 29, 1925 Santa Barbara. California ‘ 13 June 29, 1926 Santa Barbara. California 1 June 6. 1932 Fureka, California 1 March 11. 1933 1 ong Beach. California 115 October 19. 1935 ...................................................... Helena. Montana 2 October 31. 1935 ............................................. Helena. Montana 2 May 19. 1940 Imperial Valley. California ........... 9 April 1, 1946 Aleutian Islands. Alaska (tsunami—159 Hawaii. 5 Alaska. 1 California) ............................................ 165 April 13. 1949 ............................................................ Puget Sound. Washington. 8 July 21. 1952 Kern County. California ..12 August 22. 1952 ......................................................... Kern County. California 2 i December 21. 1954 .................................................... Eureka. California 1 October 24. 1955 ........................................................ Concord, California 1 March 22. 1957 Daly City. California ....1 July 10. 1958 Southeastern Alaska 5 August 18. 1959 ......................................................... Hebgen Lake. Montana 28 May 21. 1960 Chile, South America (tsunami in Hawaii) ...................................................... 61 March 28. 1964 .......................................................... Prince William Sound. Alaska (tsunami—98 Alaska. 11 California. 1 Oregon: earthquake—15 Alaskai 125 April 29. 1965 Seattle. Washington 7 October 2, 1969 Rama Rosa. California February 9, 1971 ........................................................ San Fernando. California 65 November 29. 1975 .................................................... Hawaii Island. Hawaii ” October 28, 1983 ........................................................ Borah Peak, Idaho 2 October 1. 1987 1 os Angeles—Whittier, California 8 October 4, 1987 1 m Angeles-Whittier. California 1 August 8. 1989 Santa Cruz County. California 1 October 18. 1989 Qanta Cruz County. California 63 fiU.S. GOVERNMENT PRINTING OFFICE: 1993-774-049/66043 THE ROLE OF SALT IN THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current-year issues of the monthly catalog “New Publications of the U.S. Geological Survey." 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Maps Only Maps may be purchased over the counter at the following U.S. Geological Survey offices: - FAIRBANKS, Alaska—New Federal Bldg, 101 Twelfth Ave. 0 ROLLA, Missouri—1400 Independence Rd. - STENNIS SPACE CENTER, Mississippi—Bldg. 3101 The Role of Salt in the Structural Development of Central Utah— By IRVING]. WITKIND U.S. GEO Multiple episod determined the causative salt a of the Arapien t unusual stratig LOGICAL SURVEY PROFESSIONAL PAPER 1528 es of diapirism, probably salt—generated, have structural pattern of central Utah. The nd other evaporites are integral components Ehale of Middle jurassic age, one of the most raphic units in central Utah UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994 U. S. DEPOSITORY FFR 1 01995 US. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the US. Government. Library of Congress Cataloging-in-Publication Data Witkind, Irving Jerome, 1917— The role of salt in the structural development of central Utah / by Irving J. Witkind. p. cm.—(U.S. Geological Survey professional paper ; 1528) Includes bibliographical references. Supt. of Docs. no.: I 19.16: 1528 1. Diapirs—Utah. 2. Salt domes—Utah. 3. Geology, Structural—Utah. 4. Geology, Stratigraphic—Jurassic. 5. Arapien Shale (Utah). I. Title. II. Series. QE75.P9 no. 1528 [QE606.5.U6] 557.3 s—chO 92—15520 [551.8’7] CIP For sale by USGS Map Distribution Box 25286, Building 810 Denver Federal Center Denver, CO 80225 Abstract ........................ Introduction .......... Previous work... Current work ........................... Physiographic and Middle Rocky Sanpete—S Areal exten geologic setting .................... Mountains province ............................... Southern Wasatch Range ....... Colorado Platelaus province ...... Wasatch P ateau ................. avier Valley area .................. Basin and Range province .......................... Great Basin section ...... Disturbed zone .................... Definitions .................................. Stratigraphy .................. General stratigrapl The Arapien Shale. Nomenclature. 'IVvist Gulch Fo Arapien Shale Lithology .. Contact relations Lower ontact ................................. Upper ontact ................................. t ........................................... .................. 11 CONTENTS '0 0% m monocoooooooooMH .................. 19 .................. 20 .................. 20 Arapien embayment and the Arapien basin .. 23 Contained salt ......................................................... 23 Litholo {y ........................................................... 23 Thickness of salt ............................................... 24 Thickness of Arapien Shale 25 Age ....................................... 25 Diapiric structures .......................................... 27 Intrusive aspects of the Arapien Shale ............................... 27 Minor structures ................................................................... 29 Thistle area ...................................... 29 Dome near ancestral Willow Creek.... 29 Red Knolls area ................................. 30 Cuesta north of Redmond ............................................. 31 Hogbacks in eastern Sevier Valley ............................... 33 Small hill near Ninemile Reservoir. 37 Major structures (diapiric folds) ............................... 37 Sanpete—Sevier Valley diapiric fold .............. 38 Red Rocks—Eiixmile Canyon area ............................ 41 Red Rocks area .............................................. 41 Sixmile Creek canyon area.. 48 Wales Gap .. ............................................................. 50 Ancestral W llow Creek area .................................. 51 Geologic setting ............. 51 Discussion ......... 51 Gunnison Reservoir area .. .. 55 Redmond diapiric fold .................................................... 57 Diapiric structures—Continued Major structures—Continued Sevier Bridge Reservoir diapiric fold .......................... Geologic setting ....................................................... Complex structural relations .......................... Anomalous depositional thinning ....... Red Canyon area (Valley Mountains) ....... Discussion ............................................................... First diapiric episode... Second diapiric episode Third diapiric episode Levan diapiric fold ........................................................ Pigeon Creek area .................................................. Gardner Canyon—Red Canyon area . Gardner Canyon area ...................................... Red Canyon area (southern Wasatch Range) Skinner Peaks area ......................................... Pole Creek diapiric fold ................................................ Geologic setting ..................... KOA Campground area.... Middle Fork Pole Creek ..... Discussion ............................................................... Footes Canyon diapiric(?) fold ...................................... Dry Hollow diapiric fold .......... Thistle Creek diapiric(?) fold......... ..... Geologic setting ............................... . Charleston-Nebo thrust plate ......................... Sedimentary sequence of younger rocks ........ Strata north of Spanish Fork Canyon (“Billies Mountain” area) ...................... Strata south and west of Spanish Fork Canyon ................................................... Discussion of alternative interpretations ...... Faulted terrain .................................. Diapiric deformation ................................ Hjorth Canyon diapiric fold ......................................... Geologic setting ............... Discussion ...................... Little Clear Creek diapiric fold... Geologic setting ....................................................... Discussion ............................................................... F airview diapiric(?) fold.. Geologic setting ......... Discussion .................... West Hills diapiric(?) fold ............................................. Geologic setting ....................................................... Discussion .............................. Valley Mountains diapiric(?) fold ................................. Geologic setting ....................................................... Discussion ..................... Gravity data ............ III Page 57 61 61 63 63 66 66 67 67 69 69 70 70 75 75 77 77 77 77 81 81 83 83 83 83 84 84 86 92 92 92 93 93 95 96 96 96 98 98 98 100 100 101 101 101 102 IV CONTENTS Page Page Diapiric deformation of the east flank of the Charleston-Nebo Diapiric processes—Continued thrust plate .................................................................. 104 Growth and collapse of diapiric folds—Continued Implications of the tilted strata .................................... 104 Collapse 0f diaPiric fOIdS " """"""""""""""""""""" 119 Drag along normal fault or faults ............ .. 105 D. ' ' Palred, facmg-monocllnes ................................ 121 1ap1r1c stages and episodes ........ 124 Movement along the Wasatch fault zone -------------- 105 Geologic pattern .............................................................. 125 Uneven compaction of unconsolidated North Horn Cyclical aspects ............................................................... 129 Formation and younger sediments ..................... 105 Localization and causative forces . Uplift as a result of salt diapirism ........................ 105 Economic implications ........................................................... 132 Discussion ....................................................................... 105 Oil and gas ---------------------------------------------------------------- 132 Depositional thinning ............................................................ 107 some beds ------------ - 132 Sanpete—Sevier Valley diapiric fold .............................. 109 fiancos Shale """"""""" i 132 , _ . . , _ annmg Canyon Shale.. .132 Sev1er Bridge Reservoir diapiric fold ............................ 109 Arapien Shale .............................. 133 Pole Creek diapiric fold ................................................... 111 Reservoir beds ..................................... 133 Thistle Creek diapiric fold .............................................. 111 Potential traps ......................................... 133 Discussion ........................................................................ 111 Salt-bearing and younger strata ..................... 133 Diapiric processes ................................................................... 117 Pre-salt strata -------------------- ~ ~~~~~ . -------------------------- 1 34 Growth and collapse of diapiric folds ............................. 117 , Overthrust belt and salt diaplrs. “““ 134 . , , Mlneral depos1ts ............................................................. 135 Growth Of dlapmc fOIdS """"""""""""""""""""""" 117 Summary ................................................................................. 135 Slow upwelling ................................................... 119 References cited ..... 138 Rapid, upward, forceful surges ......................... 119 Index ..................................................................... 142 ILLUSTRATIONS Page FIGURE 1. Map showing physiographic provinces in central Utah .............................................................................................................. 3 2. Index map of central Utah .............................................................................. 4 3. Index map showing sites of geologic maps ................................................................................................................ 7 4. Diagrammatic cross sections showing possible relations between thrust plate and Cretaceous and Tertiary cover ............ 10 5. Cross section of diapiric fold ......................................................................................................................................................... 13 6. Photographs showing aspects of the Twist Gulch Formation and the Arapien Shale ............................................................. 17 7. Photograph of gypsum bed in the Arapien Shale, being mined near Nephi ...................... 19 8. Map showing distribution of Arapien Shale exposures ............................................................................................ 22 9. Map showing location of major test wells in central Utah, and their spatial relation to recognized diapiric folds .............. 26 10. Photographs of deformed beds of the Arapien Shale ........................................................................................................ 28 11. Photographs showing intrusive aspects of the Arapien Shale in the Thistle area ...................................................... 3O 12. Geologic map and cross section of an intrusive mass of Arapien Shale in the ancestral Willow Creek area... ..... 31 13. Geologic map of the Red Knolls area ........................................................................................................................................... 32 14. Photographs of features formed as a result of intrusion and uplift by the Arapien Shale ..................................................... 33 15. Geologic map and cross section of an isolated hill near Ninemile Reservoir .......................... 34 16. Map showing distribution pattern of major diapiric folds ............................................... 36 17. Photographs showing deformation along east flank of Gunnison Plateau .. ..... 39 18. Photographs and annotated sketch of Red Rocks area ............................................................................................................... 4O 19. Geologic map and cross section of Red Rocks area. .................................................................................................................... 42 20. Diagrammatic sketches illustrating how Red Rocks area may have evolved ........................................................................... 44 21. Geologic map and cross section of Sixmile Creek canyon area, and annotated sketch of north valley wall, Sixmile Creek canyon ........................................................................................................................................................... 46 22. Diagrammatic sketches illustrating how Sixmile Creek canyon area may have evolved ........................................................ 49 23. Photographs of overturned strata as exposed along east flank of Gunnison Plateau .............................................................. 50 24. Geologic map and cross section near Wales Gap ............................................................ 52 25. Diagrammatic sketches illustrating how Wales Gap area may have evolved ............................................ 54 26. Photographs of cuestas in the ancestral Willow Creek area ...................................................................................................... 56 27. Geologic map of ancestral Willow Creek area, and diagrammatic sketches illustrating how area may have evolved 58 28. Photograph of vertical, semiconsolidated gravels exposed near Gunnison Reservoir ........................................ .. 61 29. Photographs of complex geologic relations along northeast flank of Valley Mountains, near Yuba Dam .............................. 62 30. Geologic map of northeast flank of Valley Mountains, and diagrammatic sketches illustrating how area may have evolved .................................................................................................................................................................................... 64 FIGURE 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. TABLE 1. Photograph an Diagrammat c Geologic map Photographs Geologic map Photograph of Photograph of Geologic map Photographs Photographs Photograph sh exposed Diagrammatic and cross section of Pigeon Creek area .......................................................................... showing overturned fold as exposed in Pigeon Creek area ................................................ and cross section of Gardner Canyon—Red Canyon—Birch Creek area, Wasatch Range ................................ and cross section of Middle Fork Pole Creek (Pole Creek—Hop Creek area) ......................... showing geologic relations in and near Middle Fork Pole Creek ............................................. of complex geologic relations along Hop Creek Ridge and in Hop Creek .. Geologic map and cross section of Dry Hollow area ................................................................................................................. CONTENTS d annotated sketch of Red Canyon area, Valley Mountains ............................................................................ sketches illustrating how Red Canyon area, Valley Mountains, may have evolved . overturned fold as exposed in Gardner Canyon ........ ’I‘win Creek Limestone, Red Canyon, Wasatch Range ................................. owing angular unconformity between vertical Indianola beds and near-horizontal North Horn strata as near head of Dry Hollow ........................................................................................................................................ sketches illustrating development of Dry Hollow diapiric fold ....................................................................... Geologic map and cross sections of Thistle area ....................................................................................................................... Photographs Cretaceo .1 Photographs Sketches of tw Geologic map Photographs Stereographic and cross section, Hjorth Canyon area ........................................... Geologic map and cross sections, Little Clear Creek area ................... f landslide and earthflow phenomena along Wasatch front ............................................................................. )f Thistle area showing relations between the Charleston-Nebo thrust plate and an overlying mantle of s and Tertiary rocks ............................................................................................................................................. Showing Arapien sill intruded into the Twin Creek Limestone, “Billies Mountain” ........................................ 0 alternative interpretations of geologic relations in Thistle area .................................................................. pair of vertical aerial photographs showing landslide block on which Mormon temple at Manti is built... Bouguer grav ty map of central Utah on which axes of major diapiric folds are superimposed ........................................... Photographic overviews of localities adjacent to Charleston-Nebo thrust plate ........................... of Salt Creek area ....................................................................................... Geologic map of Black Canyon area ................................................................................. and cross section of Taylor Fork area and cross section of Red Lake area ..................................................................................................................... Geologic map End cross section of Payson Canyon and Bennie Creek area . Geologic map Geologic map Geologic map Geologic map Diagrammatic Diagrammatic Diagrammatic Plateau .. Diagrammatic nd cross section of Dry Mountain area .......................................................................... cross sections illustrating two alternative interpretations of how diapiric folds may fail .. .. sketches of paired, facing monoclines in Sanpete—Sevier Valley area ............................................................ cross sections showing suggested geologic relations along both east and west flanks of Gunnison cross sections illustrating pattern of repeated growth and collapse of diapiric folds during three major diapiric episodes ................................................................................................................................................................... Diagrammatic Sketch map of Geologic map cross section illustrating how extent of erosion can influence interpretation of a geologic pattern ............ Utah showing alignment of several diapiric folds with major fault zones. and cross sections near “Redmond silver mine” ................................................................................................ TABLES Some stratigraphic units exposed in the Sanpete—Sevier Valley area, central Utah ................................................................... 2. Some stratigraphic units exposed in the Charleston-Nebo thrust plate. Mount Nebo area, central Utah ................................ 3. Correlation chart for some Middle Jurassic formations in central Utah ....................................................................................... 90 91 93 94 97 99 100 103 106 108 110 112 114 116 118 120 122 126 128 130 Page 14 15 20 THE ROLE OF SALT IN THE STRUCTURAL DEVELOPMENT Multiple episodes of salt diapirism can explain the complex structural history of cent a1 Utah. Previous workers in that area have ascribed the intense localized deformation between the Colo- rado Plateaus and the Ba in and Range provinces either to multi- ple episodes of orogeny, or to repeated mobilization of plastic mudstones. An alternative interpretation, offered here, is that salt, contained within the Ara ien Shale of Middle Jurassic age, has been moving continuously almost since it was deposited. Some of this movement has been slow upwelling, but at times this slow upwelling appears to have been disrupted by sudden and sporadic upward surges of the salt during which the calcareous mudstones and gypsiferous shaly silt tones of the Arapien have been forced upward. They, in turn, ha e bowed up and folded back the overly- ing younger sedimentary strata to form elongate, narrow, salt- cored anticlines (here ter ed diapiric folds). These upwarps are fan-shaped in cross sectio , and are as much as 100 kilometers (60 miles) long. I view th Arapien Shale, thus, as an intrusive sedimentary unit; and the contacts between it and the overlying consolidated sedimentary cks, described by others in the past as strip-thrusts or unconform’ ies, I consider as chiefly intrusive. The salt has surged up ard repeatedly, and time and again has been removed chiefly by e rusion or dissolution, causing the folds to fail. This cyclical growth and subsequent failure of the diapiric folds has occurred at least three times; each time the reactivated younger folds occupied the same sites and had the same trends as the previous older folds. This pattern, involving the growth and collapse of discrete diapiric folds, is here called a diapiric episode, and each episode is arbitralily divided into three stages: 1. An intrusive stage durmg which the salt surges upward and forces the Arapien mudstones to deform the overlying sedimentary rocks into a diapiric fold. 2. An erosional stage during which the removal of the salt results in failure of the fold. Subsequent erosion removes the collapsed and brecciated remnants oi the fold leaving a widespread surface of low relief. 3. A depositional stage luring which younger sediments are deposited across this newly cut surface. As the sedimentary uniis either wedge out or thin along the flanks of these folds, it is probable that the salt, during this stage, was slowly rising and grad aally forcing up the overlying strata to OF CENTRAL UTAH By IRVING J. WITKIND ABSTRACT form a barrier—in essence, a paleo-high. In those localities where the sedimentary units pass over the crests of the folds, the strata, invariably, are anomalously thin and represent the youngest parts of the formations. Seemingly, the slowly growing barrier was not high enough to block deposition completely, but was able to restrict it. The depositional stage ends with a renewed surge of salt, mark- ing the intrusive stage of the next diapiric episode. This repeated movement of the Arapien suggests that it has dif- ferent “ages.” Its depositional age is Middle Jurassic; it contains Middle Jurassic fossils. It has several emplacement ages—different geologic ages of movement—each reflecting an upward surge of salt. Although tenuous evidence suggests that the first major diapiric episode occurred prior to Late Cretaceous time, possibly during the Late Jurassic, the earliest recognizable diapiric episode began in Late Cretaceous time and probably extended into the early Pale- ocene. A second episode began then and lasted into the late(?) Oli- gocene, or possibly the Miocene. The third major episode began in the late(?) Oligocene (or Miocene) and persisted into the Pliocene or Pleistocene. A minor diapiric episode may have occurred during the late Pliocene or Pleistocene; if so, this implies that the salt diapirs that underlie the area may still be active. I recognize 13 major diapiric folds; of these, many of the smaller folds appear to branch off the larger ones much as distributary streams branch off a major stream. The longest fold appears to be the Sanpete—Sevier Valley diapiric fold, which extends northeast- ward at least 100 kilometers (60 miles) from near Richfield on the south to beyond Fountain Green on the north. Its core, exposed along the east side of Sevier Valley as a continuous belt of Arapien mudstones, is concealed northward beneath the alluvial fill of San- pete Valley. The Redmond fold, which seems to branch off the south end of the Sanpete—Sevier Valley fold, extends northward about 50 kilometers (30 miles) from near Sigurd on the south to near Gunnison on the north. The Levan diapiric fold, possibly the northern extension of the Redmond fold, is about 40 kilometers (25 miles) long, and extends northward along the west flank of the Gunnison Plateau. The Levan fold starts near Little Salt Creek; at Salt Creek, near Nephi, the fold appears to split into three branches. The western branch, for which I retain the name Levan fold, extends northward and passes beneath and deforms the 1 2 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH Charleston-Nebo thrust plate. The eastern branch, known as the Pole Creek diapiric fold (probably about 25 kilometers (15 miles) long), extends northeastward and has determined the structural pattern of Cedar Hills; this branch is probably continuous with the Dry Hollow diapiric fold, of which only about 6 kilometers (4 miles) is exposed near Thistle. The middle branch, which I call the Footes Canyon fold, is concealed for the most part but possibly is about 45 kilometers (27 miles) long. It may extend along and deform the east flank of the Charleston—Nebo thrust plate. The Sevier Bridge Reservoir fold extends northwestward about 24 kilo- meters (15 miles) from near Fayette to near Yuba Dam. Probably the Sevier Bridge Reservoir fold is an offshoot of the Redmond fold. Other large diapiric folds are partly exposed in the Indianola— Thistle area; Little Clear Creek follows the crest of a fold that I refer to as the Little Clear Creek fold, which is about 20 kilometers (12 miles) long. Another fold, the H jorth Canyon fold, which I esti- mate to be about 10 kilometers (6 miles) long, crops out in Hjorth Canyon, and still a third fold, the Thistle Creek fold (about 20 kil— ometers (13 miles) long), is near the junction of Thistle and Soldier Creeks. The Thistle Creek fold may be the northern extension of the Footes Canyon fold. Tenuous evidence suggests that another diapiric fold (Fairview diapirid?) fold) underlies the eastern fork of Sanpete Valley, extending northeastward from near Ephraim to near Indianola. This fold may be as long as 40 kilometers (25 miles). Other diapiric folds may underlie the Valley Mountains (Valley Mountains diapiric(?) fold, about 30 kilometers (19 miles) long), and the West Hills, the southern extension of Long Ridge (the West Hills diapiric(?) fold; about 18 kilometers (11 miles) long). Arapien mudstones have deformed the eroded upper plate of the Charleston-Nebo thrust fault, which forms the southern Wasatch Range. In places, they have intruded and broken the thrust plate; elsewhere they have bowed it up and arched it. This upper plate, known as the Charleston—Nebo thrust plate, is the lower limb of an overturned, almost recumbent anticline; most of the strata, thus, are overturned. Collapsed diapiric structures, almost certainly salt-controlled, are along the southwest flank of the Gunnison Plateau between Mellor and Timber Canyons. A small salt plug probably underlies the westward-trending transverse graben that lies along the east margin of the Gunnison Plateau between Dry and Maple Canyons. The trends of the diapiric folds appear to parallel the major tec- tonic lineaments, implying some form of structural control. Such control is emphasized by the striking linearity of the diapiric folds and their great lengths; two folds are collinear with major fault zones. Moreover, the cyclical nature of the diapirism also hints at some form of structural control—the same sequence of diapiric epi- sodes can be recognized in many widely separated exposed folds. This suggests that the diapirism is regional in extent, and that all diapirs in the area were reactivated, not only repeatedly, but more or less in unison. I propose that the salt, under static load, was triggered into movement by reactivation of old well-established faults. The salt, presumably, was deposited in a Middle Jurassic saline Arapien basin that overlay preexisting, deep-seated, fundamental faults. As the salt was buried ever more deeply beneath younger sediments, it was placed under increasing static load. When these ancient faults reactivated, probably in response to regional compressive forces—the Sevier orogeny—in pre-Paleocene time and extensional forces from late(?) Oligocene time on, they broke through both the salt and the overlying beds. The salt and accompanying mud- stones, under great confining load, sought relief by surging up the newly formed fault planes, using them as conduits. As a result, these parts of the fault planes were obliterated and in their place were formed a series of long, linear, fan-shaped diapiric folds, the trends and extent of which reflect the trends and extent of the buried faults. Subsequent reactivation of these same ancient faults resulted in renewed movement of the salt and mudstones; predict- ably the younger diapiric folds followed the same trends and occu- pied the same sites as the older folds. As a result of the repeated episodes of salt diapirism, there appears to be a contrast in structural style between an upper sequence of salt-bearing and younger rocks and a lower sequence of older pre-salt rocks. The upper sequence is intensely deformed by the repeated episodes of salt movement; the lower sequence, essentially uninfluenced by the salt, may not be as intensely deformed. This division of the sedimentary stack into two structurally dis— tinct sequences, as Well as the type of structural deformation involved, implies that each sequence may contain specific types of potential oil and gas traps. Potential traps in the intensely deformed (salt-bearing and younger) beds would coincide closely with the salt walls and the upthrust masses of the Arapien. Poten— tial traps in the pre-salt strata would include structures of various sizes and shapes that resulted from a variety of orogenic (compres- sive) forces; such structures may well be wholly unrelated to those formed in the salt—bearing and younger beds. Possible source rocks for oil and gas include the Mancos Shale of Late Cretaceous age, the Manning Canyon Shale of Pennsylva- nian and Mississippian age, and the Arapien Shale of Middle Jurassic age. Of these, however, the Mancos Shale probably extends no farther west than a north-trending line through Wales, the Manning Canyon Shale is probably supermature, and the Arapien Shale is submature. Suitable reservoir rocks include the Ferron Sandstone Member of the Mancos Shale, and various sandstone beds in the Emery Sandstone Member of the Mancos Shale of Late Cretaceous age. Degree of fracturing may be more important than inherent pri— mary porosity in determining which units are good reservoir rocks. Mineral deposits, mainly zinc, were probably derived from saline solutions that appear to have been localized along the con- tacts between the intrusive Arapien Shale and the country rocks. INTRODUCTION A broad, ill-defined zone, commonly referred to as a transition zone, trends southward through central Utah, separating the Colorado Plateaus province from the Basin and Range province (fig. 1). Within this zone, the stratigraphic units, for the most part, are but gently to moderately folded; locally, however, they are tilted into vertical or overturned attitudes, and form belts of unusual structural complexity. Com- monly these structurally complex belts are linear and narrow; some extend for many kilometers. Striking angular unconformities abound within these complex belts, and in places, several such unconformities are exposed in a single outcrop. Surprisingly, these uncon- formities do not persist for long distances perpendicu- lar to the structurally complex belts. Strata that are separated by an angular unconformity, when traced away from these belts, rapidly approach parallelism and commonly become conformable in distances as short as three-fourths of a kilometer (#2 mi). These singularly complex areas tend to coincide with INTRODUCTION 3 elongate, northward—trending upwarps that dominate the area. Where exposed within these structurally complex areas, an entire sequence of stratigraphic units thins anomalously toward the crest of one of these upwarps, and locally some units in the sequence pinch out against the flanks of the upwarp. This unusual structural and stratigraphic complex- ity has attracted geologists since the days of Gilbert and Dutton, and its fascination stems in large part from the fact that the field evidence lends itself to conflicting interpretations. Many workers, both past and present, attribute this localized deformation either to multiple episodes of orogeny (Spieker, 1946, 1949; Standlee, 1982; Lawton, 1985; Villien and Klig- field, 1986), or to mobilization of the plastic mud- stone beds of the Middle Jurassic Arapien Shale (Gilliland, 1963). I believe, however, that much of the 113°00' 112°00’ complexity stems from multiple episodes of salt diapirism—in essence, the repeated growth and col- lapse of salt-cored anticlines (here called diapiric folds). These folds, of prime importance, have deter- mined both the local and regional structural frame- work of this sector of central Utah. Major geologic misconceptions are inevitable unless one grasps their significance. Nearly a half-century ago, Stokes (1952, p. 961), referring to salt-generated structures of the Sanpete—Sevier Valley area, wrote: “Caution is sug- gested in interpreting strong local structures of the sort found in these areas [central Utah] as evidence for orogenic activity.” I concur in the strongest possi- ble way. The causative rock salt (halite) is contained within the Arapien Shale of Middle Jurassic depositional age, and I propose that upward, near-vertical, local IIU°00’ 40°30 l BASIN AND RANGE PROVINCE III°DU’ I o. MIDDLE ROCKY MOUNTAINS 09/ PROVINCE 4U °00’ — East Tintic Mountainsr Gilson Mountains 1:) Hills Desert 39°3ll’ — Canyon Range Sevier Approximate west/ margin Oftransition zone 39°UU’ — Uinta Basin PLATEAUS H V'alley Mountains BASIN AND RANGE PROVINCE K. C (bib Q —-Area of figure 2 Approximate east margin of transition zone PROVINCE 38 °30’ 30 40 50 IOU KILUMETEPQ | 50 MILES FIGURE 1.—Physiographic provinces in central Utah. Parts of three major physiographic provinces meet in central Utah—the Colorado Plateaus on the east, the Basin and Range on the west, and the Middle Rocky Mountains, represented by the southward-pointing wedge of the southern Wasatch Range, on the north. SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH » km. Eém / p 5:36 83> , :9»ch “gm -’ 1 P1313 , I %_,__ / ,bmwfizm e 00 20,929 \w\\ _______ \S/x \ hm OZ) ELHdNVS W, {QFWW Mam @ EEQmm ufi 580 Eflfiom . \x 1 . , _ _ ‘ WW, dowéma _;:> ..,, , \ mzzfiznos. 2026 ///.\ a“ K, ()x/ ‘ U £32398 8E . am 53:: o O, ‘9“an m 6"} \‘L‘ -\ ___—_ OZ) gVflI’ 52v 0:) ELLHdNVS ,( a _ 8,anme , opfizs _ T a, , ,i/ 3;» _ , / , :2 .0 / If, , __ .,,,. _.T 39 oo :5: M; , ,, _, _,\ ._110w. 52%;, of V x I _ . r 4.x \ @825 J W) < 4 \_I\ l , i r ,, X _ _ I ,,.V (\mfiEm _ , _, /2 ,, {33:52 , 0. . ,, / .33: 2:: ‘2 2 may a. TIL \\\\ m J,,,, :55sz flow rm _ EON: \gcwmwoe fl INTRODUCTION 65 5:33 .59 $93 migozom 8m 5 00¢; 19¢qu .5355 A58 hvmmC zmism oflowoww «Em ammoo .m.D 53:0 Hwoflsmcemé Each—com 8er; £05054 ~5th Sod wmmm .92: N32: m1: 3 coho: 0.5 mficmawowmufiofim 5:503 :25 =< ATM: EEEEH £55 3x3 9: encamEfifi cocoflamfi mwfim 882 Saab: was .832 < .ASD 35:8 mo AME xwwnHIN 55on N H bi: bi: 3.22 2: on D _|~|_|_I|* mEEzS; SN 9: : Kama mm i 5313i; r _ _/‘, , r :33 $25 onmfimoHWw_w,L/ r i F. a $52 on cm 9 _ _ $3523: am bees: I 80% O O 0:) EILEIdNV§ 3371an .m— 6 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH FIGURE 2—Continued.—Locality file for index map of central Utah. FIGURE 2—Continued.—L0cality file for index map of central Utah. Name Location Name Location Ancestral Willow Creek G—3 Little Salt Creek D—3 Arapien Valley G—3 Loafer Mountain A—4 Aurora H-2 Long Ridge 3—2 Axhandle Canyon D—3 . Manti E—4 Birdsey e A_4 Maple Canyon (Northeast flank-Gunnison Plateau) C—4 Burrv1lle J_3 Maple Canyon (Southeast flank—Gunnison Plateau) E—3 Canyon Mountains Mayfield F_3 Castle Dale Mellor Canyon E—3 Castle Gate Middle Fork Pole Creek B—4 Castle Valley Milburn B—5 Cedar Hills Mona B—3 Centerfield Monroe J—l Chicken Creek Reservoir Moroni D—4 Clawson Mount Nebo B—3 Cleveland Mount Pleasant D-5 Colton Musinia Peak G—4 Deep Creek National C—7 Dividend Nebo Creek 3-4 Dry Canyon Nephi 13-3 Dry Hollow Oak Creek C—5 East Tintic Mountains Orangeville F—7 Elsinore Ephraim Painted Rock Canyon E—2 Eureka Pavant Range H—l Pigeon Creek C—3 Fairview Pole Creek B—4 Fayette Price C—8 Ferron Price River B—8 Footes Canyon R d C (V 11 M t . ) E 2 . e anyon a ey oun ains — F:::dt:rl: Green Red Canyon (Wasatch Range) B—3 Red Rocks F—3 Gardner Canyon Redmond G_3 Gilson Mountains Richfield 1—1 G1 e nw 00 d Rock Canyon E-3 Goshen Round Valley F—2 Gunnison . Gunnison Plateau (San Pitch Mountains) Salina G_3 Gunnison Reservoir Salina Canyon (Salina Creek Canyon) H—3 Salt Creek B—3 Helper Sanpete Valley E—4 Hiawatha San Pitch Mountains (Gunnison Plateau) D—3 Hjorth Canyon San Pitch River E-4 Huntington Santaquin A—3 Indianola SCIPIO F_1 Scipio Lake F—2 Joes Valley Scipio Valley 13-1 Joes Valley Reservoir Scofield B_6 Joseph Scofield Reservoir B—6 Juab Valley Sevier Bridge Reservoir (Yuba Lake) E—2 Kenilworth Sevier Plateau J_2 KO A Campground _ Sevier River 1—2 Koosharem Sev1er Valley G—2 Sigurd H—2 Lake Fork Silver City A—l Levan Sixmile Canyon (Sixmile Creek canyon) F—4 Little Clear Creek Soldier Creek , A—5 INTRODUCTION FIGURE 2—Continued.—L0cality file for index map of central Utah. Name Location South Valley (Valley Mountains) G—2 Southern Wasatch Mountains (Wasatch Range) A—3 Spring City D—5 Spring Glen C—8 Sterling F—4 The Washboard D—2 Thistle A—5 Thistle Creek A—4 Timber Canyon E—3 Twelvemile Creek F—3 Valley Mountains G—2 Valley Mountains monocline G—2 Wales D—4 Wales Gap D—4 Wasatch monocline E—5 Wasatch Plateau F—5 Wasatch Range (Southern Wasatch Mountains) A—3 Washboard, The D—2 Wattis D—7 West Hills D—2 White Hills G—3 Willow Creek G—3 Yuba Dam E—2 Yuba Lake (Sevier Bridge Reservoir) E—2 movements of the buried salt are ultimately responsi- ble for the intense deformation. I am much impressed by the striking similarities between the salt-generated features exposed in the Paradox Basin of southwestern Colorado and southeastern Utah and almost identical features exposed in this sector of central Utah (fig. 2). Stokes (1982), similarly impressed, has proposed the name “Arapien basin” for this salt-rich sector of central Utah. In this Professional Paper, I bring together many of the data and views that I have published else- where, either as articles in scientific journals or as descriptive textual material accompanying geologic maps. This report is thus a synthesis—in essence, a comprehensive discussion in one publication of my views on the role of salt in the structural evolution of central Utah. It might ease the burden of searching for and digging out the pertinent literature even for those who have ready access to modern, well-stocked geologic libraries. Locations mentioned in the text are keyed to figure 2, the index map of central Utah, by an arbitrary grid placed on the map. Figure 3 shows those areas for which geologic maps have been prepared. llzclfl’ 112000: 45’ 30' ”1015’ 40 °05 ‘ | Utah Lake PaVSOH o oSalem o / — i 4U 00 Santaquin Thistl: oEureka o 57g] oshen 59 56 41 Olndianola El 38 We Fountain Green 0 45’— . . . Falrvxew Levano 3‘33 OMt. Pleasant . Moroni oSpring City 39°00’- 38 °45’ [J 10 20 30 KILUMETEHS 20 MILES FIGURE 3.—Index map of central Utah showing locations of all geologic maps discussed in this report, listed by illustration number. Figure 12, Intrusive mass of Arapien Shale; 13, Red Knolls area; 15, Hill near Ninemile Reservoir; 19, Red Rocks area; 21, Sixmile Creek canyon area; 27, Ancestral Willow Creek area; 30, Northeast flank of Valley Mountains; 33, Pigeon Creek area; 35, Gardner Canyon—Red Canyon area, Wasatch Range; 38, Middle Fork Pole Creek; 41, Dry Hollow area; 44, Thistle area; 48, Hjorth Canyon area; 49, Little Clear Creek area; 54, Salt Creek area; 55, Black Canyon ar- ea; 56, Taylor Fork area; 57, Red Lake area; 58, Payson Can- yon and Bennie Creek area; 59, Dry Mountain area. Base from Grand Junction (T—3) Sectional Aeronautical Chart, US. Coast and Geodetic Survey (1954, rev.). 8 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH PREVIOUS WORK Stokes, in two perceptive abstracts (1952, 1956), first advanced the possibility that the growth and collapse of salt structures might be significant in the structural development of central Utah. Regrettably, he never fully developed his views in the published literature. Because the evidence, on the whole, is inconclusive, Stokes’ views initially failed to gain much acceptance. As the search for oil in central Utah led to more and more exploratory drilling, the extent of the Arapien salt became evident, and the importance of salt diapirism in the structural devel- opment of central Utah was again emphasized by Christiansen (1963), Eardley (1969), Moulton (1975), and Baer (1976). Baer, in particular, stressed the importance of periodic diapirism in the area, noting that diapirism seemingly had persisted from the Cre- taceous through the Pleistocene, and he attributed much of the structural deformation in central Utah to this diapirism. The diapiric concept has gradually gained adherents, and additional papers by workers in central Utah have added to our knowledge. Run- yon (1977a; 1977b) described collapsed diapirs near Indianola. Hawks (1980) described several diapiric localities in the Cedar Hills, and Taylor (1980) has attributed the deformation in the Sterling area to diapirism. Recently Picard (1980) discussed the stratigraphy and petrography of the Arapien Shale, and speculated about the origin of this salt- and evaporite—rich unit. Hansen (1976) suggested that the beds of salt in central Utah are but part of a much larger Jurassic evaporite belt that extends from southeast Arizona to southeast Idaho. CURRENT WORK I began work in central Utah in 1977 as part of the US. Geological Survey’s Coal Exploratory Program. By 1979 I had become convinced that salt had played, and continues to play, a dominant role in the structural evolution of central Utah. My Views have been offered in a series of maps and papers published in various guidebooks and journals (Witkind, 1981, 1982, 1983, 1986, 1987, 1988, 1992; Sprinkel, Wit- kind, and Baer, 1982; Witkind and Page, 1984; Wit- kind, Weiss, and Brown, 1987, and Witkind and Marvin, 1989). Those who oppose the salt-diapiric concept question whether the vast amounts of salt called for by that concept ever did underlie central Utah (Standlee, 1982, p. 376—377). The existence of concealed salt diapirs in central Utah is inferred to some extent from test-well data, but chiefly from the shapes of the minor and major landforms that extend across this sector of Utah. Although the area has been crisscrossed repeatedly by seismic surveys, all the resultant reflection pro— files are proprietary. Chevron USA, Inc., has been kind enough to permit me to examine some of their seismic profiles that cross the Wasatch Plateau and the Sanpete Valley area. The general structural pat- tern reflected by various of the reflection profiles is perhaps best described as upturned Cretaceous beds overlain by downturned Tertiary strata—a pattern displayed in many surface exposures (p. 121). PHYSIOGRAPHIC AND GEOLOGIC SETTING This sector of central Utah includes parts of three major physiographic provinces: the Middle Rocky Mountains, the Colorado Plateaus, and the Basin and Range (fig. 1). A broad north-trending lowland formed by the collinear alignment of three major valleys—— Utah, Juab, and Sevier Valleys—effectively divides the area into two unequal sectors. Parts of both the Middle Rocky Mountains and Colorado Plateaus prov- inces are east of the lowland; the Basin and Range province is wholly west of the lowland. MIDDLE ROCKY MOUNTAINS PROVINCE SOUTHERN WASAT( 1H RANGE The north-trending Wasatch Range, one of the great mountain masses of Utah, extends for about 240 km (150 mi) from near the Idaho border into cen- tral Utah. The south half of the range is formed by the upper plate of a thrust fault that I refer to as the Charleston-Nebo thrust fault. Other geologists, nota- bly Bruce Bryant (US. Geological Survey, written commun, 1989), have objected to this coupling of what they perceive to be two separate thrust faults— the Charleston and the Nebo thrust faults. Bryant believes that my Charleston-Nebo upper plate is divisible into two parts—a lower segment that is the upper plate of the Charleston thrust fault, and an upper segment that is the upper plate of the Nebo thrust fault. In Bryant’s view, then, the Nebo thrust fault is an upper split off the Charleston thrust fault, and the Nebo fault dies out in the area northeast of Nephi (fig. 2, B—3) and southwest of Thistle (A—5). I disagree with Bryant’s interpretation. The strati- graphic units that I have mapped as part of the upper plate of the Charleston—Nebo thrust fault can be traced northeastward to Thistle where they join similar units that are part of the upper plate of the Charleston thrust fault. Neither the Nebo anI‘ the INTRODUCTION 9 Charleston thrust fault is exposed in the sector between Nephi and Thistle. Consequently, I am uncertain not only as to how many thrust faults underlie the area, but also as to where the fault(s) end (fig. 4). I believe that the Nebo thrust fault trends northeastward and eventually merges with the Charleston thrust fault; hence my use of the terms “Charleston-Nebo thrust fault” and “upper plate of the Charleston-Nebo thrust fault.” This upper plate of the Charleston-Nebo thrust fault, which reaches from near Salt Lake City south- ward to Nephi (B—3) (fig. 2, inset map), consists of a mass of basin-type rocks, at least 9,150 m (30,000 ft) thick (Crittenden, 1961) that was transported south- eastward and eastward along the Charleston-Nebo thrust fault. How far the plate moved is unknown; various lines of evidence suggest a displacement of about 65 km (40 mi) (Crittenden, 1961, p. D—129). Very generally, this upper plate can be divided into two segments: A northern part, east of Provo, that extends as far south as Spanish Fork Canyon; and a southern part, a wedge-shaped, imposing mountain range known locally as the southern Wasatch Moun- tains (or the southern Wasatch Range), that extends southward from Spanish Fork Canyon to Nephi (B—3). The extent of the plate south and west of N ephi is less certain, owing to basin and range structures. Part of the plate may be preserved west of Juab Valley (C—2), near the south end of Dog Valley (C—2), along the northwest flank of the West Hills (C—2). An erosional outlier near Levan (C—3) may be still another part of the plate (Witkind, 1983, p. 49). Morris (1983, p. 77) has suggested, however, that near Nephi the caus— ative, underlying Charleston-Nebo thrust fault may merge with the Leamington transcurrent fault. The southern Wasatch Mountains now appear as the huge, intensely dissected east limb of an over- turned, almost recumbent anticline. At the north end of the mountains, near Santaquin (A—3), the beds are right side up and dip moderately southeastward. Far- ther south the beds steepen, and near Mona (B—3), they are vertical. Still farther south, at the south end of the mountains, near Nephi, the beds are over- turned and dip moderately to the northwest. The Wasatch fault zone truncates the west edge of the mountains, which thus appears as a straight, com- manding escarpment overlooking Juab Valley. The east margin of the mountains—which I View as an erosional escarpment cut across the Charleston-Nebo thrust plate—is much less imposing, chiefly because it has been extensively eroded and then partly buried beneath younger Mesozoic and Tertiary rocks (Wit- kind, 1987). This erosional escarpment, which extends northeastward from Nephi toward Thistle (A—5), may be the distal margin of the thrust plate (fig. 4B), or the distal margin may be concealed somewhere to the east beneath younger Mesozoic and Tertiary strata (fig. 4C). Near Thistle, the attitude of the beds that form the thrust plate in the subsurface is conjectural; they may be overturned. COLORADO PLATEAUS PROVINCE The terrain south and east of the southern Wasatch Mountains, and east of the lowland formed by the collinear alignment of Utah, Juab, and Sevier Valleys, is within the Colorado Plateaus province. I arbitrarily divide the area into two parts: the huge mass of the Wasatch Plateau, and the remainder to which I apply the well-established name Sanpete— Sevier Valley area. WASATCH I’I .ATEAU The Wasatch Plateau, the northernmost of the High Plateaus of Utah, is a flat-topped mass about 130 km (80 mi) long that extends from Salina Creek Canyon (fig. 2, H—3) on the south to the valleys of Soldier Creek (A—6) and Price River (B—8) on the north. The plateau trends about N. 20° E., maintain- ing a nearly constant width of about 40 km (25 mi), and an altitude of about 3,050 m (10,000 ft). It sepa- rates Sanpete Valley (E—4) on the west from Castle Valley (E—7) on the east. The plateau is underlain by flat-lying Cretaceous and Tertiary beds, most of which are well exposed in the dissected cliffs that delineate its eastern flank. These strata flex down sharply along much of the western flank of the plateau to form the Wasatch monocline (E—5). The monocline, about 100 km (62 mi) long, extends northward from Salina Creek Canyon (H—3) to its end, north of Milburn (B—5) and east of Indianola (B—5), near the north end of the east fork of Sanpete Valley. Westward-flowing consequent streams on the monocline have locally cut through the tilted beds, exposing them along the walls of deep, serpen- tine canyons that extend far back toward the crest of the plateau. Much of the plateau and the monocline are broken by high-angle normal faults that trend between due north and about N. 20° E. and that locally are paired to form grabens. SANPETE—SEVIER VALLEY AREA The term “Sanpete—Sevier Valley area” refers to an ill-defined area drained by both the south- flowing San Pitch River and the lower reaches of the north-flowing Sevier River. Over the years the 10 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH WEST EAST Tertiary and Erosional s Eretaceous escarpment e Imentary and . A. ~_»__ ALLOCHTHON (chiefly Paleozoic strata) / 5—4;,5‘ CHARLESTON-NEED {: f. Distal margin of allochthon CHARLESTON—NEBO THRUST FAULT ALLOCHTHON strata) Autochthon A WEST EAST . Tertiary and Erosuonal Cretaceous CHARLESTON-NEBO (chiefly Paleozoic / escarpment sedimentary and volcanic rocks CHARLESTON-NEBO THRUST FAULT Autochthon WEST CHARLESTON-NEBO ALLOCHTHON (chiefly Paleozoic strata) Erosional escarpment Distal margin of allochthon concealed beneath sedimentary and volcanic ’—)- cover (beyond il|ustrati°:/ /) EAST Tertiary and Cretaceous sedimentary and volcanic rocks CHARLESTON-NEBO Aut°chth°n THRUST FAULT FIGURE 4.—Diagrammatic cross sections illustrating possible rela- tions between an eastward-facing erosional escarpment formed on the Charleston-Nebo thrust plate and a partial cover of Cre- taceous and Tertiary rocks. Escarpment was formed as the plate was thrust eastward. A, After eroded plate ground to a halt, sedimentary units of Cretaceous and Tertiary age, as well as some Tertiary volcanic units, were deposited against it, and in time may even have buried the entire plate. B, Erosional escarp- ment is at the distal margin of eroded thrust plate. C, Erosional escarpment is along east flank of eroded thrust plate but not at distal margin, which is farther to the east concealed beneath the Cretaceous and Tertiary cover. B and C represent two possible alternatives to explain present geologic relations. Both alterna- tives are viable; lack of data precludes a definitive statement as to position of the thrust plate’s distal margin. name San Pitch—derived from the name Sam Pete, a local Indian—has been garbled to Sanpete (MP. Weiss, Northern Illinois University, oral commun., 1989), and this latter name is applied to the valley occupied by the San Pitch River. The Sanpete— Sevier Valley area has figured prominently in the geologic literature describing central Utah, and although certain localities in central Utah discussed in this report extend beyond the generally accepted limits of the Sanpete—Sevier Valley area, the name is so well known that I have used the name for the larger area. In general, the Sanpete—Sevier Valley area appears as a series of north-trending plateaus and low hills, considerably lower than the adjacent Wasatch Range. Among the major landmasses in the Sanpete—Sevier Valley area are the Gunnison Plateau (D—3) (also known as the San Pitch Mountains),1 the Cedar Hills (B—4), and the Valley Mountains (G—2). Jurassic, Cretaceous, and Tertiary sedimentary strata underlie the Sanpete—Sevier Valley area. Locally, these units are overlain by layered volcanic rocks and volcaniclastic detritus of Tertiary age. Commonly, both the sedimentary strata and the vol- canic units are gently warped, to form broad folds that are broken, in places, by small high-angle nor- mal faults. Here and there, however, these strata are complexly deformed into narrow elongate belts that trend northward. 1The range of hills known to geologists as the “Gunnison Plateau” is known to governmental agencies as the “San Pitch Mountains.” Indeed, the latter name is used on published topographic maps of the US. Geological Survey. Nevertheless, the name Gunnison Plateau is so deeply entrenched in the geo- logic literature, chiefly as a result of the reports of the late Prof. EM. Spieker and his many Ohio State University graduate students, that the name is retained and used throughout this report to avoid confusion. INTRODUCTION 1 1 BASIN AND RANGE PROVINCE GREAT BASIN SECTION The Great Basin section is an arid lowland that ends abruptly eastward against the north-trending lowland formed by the collinear alignment of Utah, Juab, and Sevier Valleys. The abrupt change is emphasized by the impressive topographic high formed by the combined masses of the southern Wasatch Range (A—3) and the Gunnison Plateau (D—3) along the east side of the lowland. This abrupt topo- graphic change is directly attributable to movement along the Wasatch fault zone, a major high-angle nor- mal fault zone that trends northward across this part of central Utah, and along which the crustal block west of the fault zone has been downthrown relative to the block east of the fault zone. The Great Basin sector consists of a series of thrust slices, composed chiefly of Precambrian and Paleozoic rocks. These thrust slices were deeply eroded during transport and after being emplaced, then buried beneath younger rocks, and broken by block faulting. Much of our knowledge of the Great Basin sector within this part of central Utah comes from two major mountain ranges that dominate the area: the Canyon Mountains (E—l), on the north, which have been described by Campbell (1979), Christiansen (1952), and Stolle (1978); and the Pavant Range (H—l) on the south, which has been described in part by Crosby (1959), and Lauten- schlager (1952). As this discussion of diapirism in central Utah is confined chiefly to areas east of these ranges, no summary description is given here of the units that form them. DISTURBED ZONE Previous workers have suggested that the Sanpete— Sevier Valley area is best visualized as a transition zone between the Basin and Range province on the west and the Colorado Plateaus province on the east (Spieker, 1949). I suggest instead that although a zone does separate the two provinces, that zone is not a true transition zone in which features of one prov- ince gradually give way laterally to features of the adjacent province. Rather, I see the area between the two provinces as a disturbed zone marked by unusual, almost unique structural features that, for the most part, are foreign to both provinces. So, for example, the zone is unusual in that, in places, it is marked by both localized depositional thinning and complex structural deformation. Elongate, northward- trending upwarps—huge upthrown masses of sedi— mentary rock—dominate the zone, yet comparable downwarps of the sedimentary units are nowhere to be found. In places, the beds are overturned, stand on end, or are downdropped to form long, linear grabens. Angular unconformities, otherwise sparse throughout this part of central Utah, are common and wide- spread. Locally, single outcrops contain several angu- lar unconformities (figs. 19 and 32). The sedimentary beds thin drastically and anomalously, and locally pinch out near the crestal parts of these upwarps, but assume their regional thicknesses just short distances away. Those sedimentary units that do extend across the crestal parts of the upwarps are the uppermost, youngest parts of the formations. The contrast between the attitudes of the beds exposed in this zone and those flanking it is striking, and made even more so by the fact that this intense structural complexity is localized. In places, the overturned beds, traced lat- erally, resume their near-horizontal attitudes in dis- tances as short as a kilometer (half a mile). Units that are in angular discordance can be traced later- ally and within several kilometers become conform- able. The rocks in the zone have been much disturbed, hence my preference for the term Dis- turbed Zone, rather than the more commonly accepted Transition Zone. In my opinion, the trend and position of this dis- turbed zone reflect a fundamental flaw in the under- lying basement rocks. This view is supported by the fact that three major structural elements have influ- enced this part of central Utah during time periods that span most of geologic time: 1. During the Paleozoic, the hingeline between the Cordilleran geosyncline on the west and the cra— ton on the east trended northward through this area. 2. During the Jurassic, essentially the same geo- graphic area was occupied by a major, structurally determined saline basin, termed the Arapien basin by Stokes (1982). 3. During the Tertiary and Quaternary, the struc- tural seam between the Basin and Range and the Colorado Plateaus provinces extended northward through the area. The disturbed zone overlies much of Stokes’ Arapien basin. The greatest thickness of salt appears to have been deposited in this saline basin (D.A. Sprinkel, Placid Oil Co., oral commun., 1983), imply- ing strongly that the anomalous sedimentary thinning and the complex structures so characteristic of the disturbed zone stem, in one way or another, from 12 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH movement of these thick salt deposits. As Halbouty noted (1967, p. 5): “The major salt basins of the world * * >“are not simple, arbitrarily positioned evaporite pans* * *but rather* * *reflect major negative elements which are probably related to re—activation of basement structures.” DEFINITIONS I use four terms throughout this Professional Paper, and it seems wise to explain my usage of them and how they differ from similar or comparable terms used in and near the Gulf Coast. Salt diapir. As used along the Gulf Coast, “salt diapir” commonly refers to a body of almost pure rock salt, generally round or crudely elliptical and with nearly vertical sides, whose shape has deter- mined the configuration of a salt—cored dome. By con- trast, in this part of central Utah, I believe that the salt diapirs are elongate, narrow, somewhat sinuous bodies of salt and intercalated mudstone that extend for tens of kilometers. They appear to be comparable to the linear “salt cores” of the Paradox Basin, Colo- rado and Utah (Shoemaker and others, 1958, p. 39), or the “salt walls,” described by Trusheim (1960, fig. 4), that formed in the Zechstein salt of northern Germany. Rather than almost pure rock salt, the salt diapirs in central Utah consist of thick beds and stringers of salt and anhydrite interlayered with cal- careous mudstone and shaly siltstone. I visualize these salt diapirs, like those along the Gulf Coast, as piercement structures which, in their upward rise, intruded, arched, and deformed the overlying sedi- mentary rocks (fig. 5). The salt diapirs in central Utah probably stem from one or more source beds of salt. Diapiric sheath. I believe that each salt diapir in central Utah is sheathed by calcareous mudstone and shaly siltstone beds that deformed plastically with the rising salt. These rocks are part of the Arapien Shale; pushed up by the driving salt they have intruded and deformed the overlying sedimentary rocks. I interpret them as intrusive sedimentary beds. In most places, I suspect that these calcareous mudstone beds are in intrusive contact with those consolidated and semiconsolidated rocks that overlie them. Although a similar sheath, but of shale, was called a “diapiric shale” by Atwater and Forman (1959), I believe the term “sheath” better describes the relations between the enveloping mudstone beds and the salt diapir. Diapiric fold. The younger sedimentary rocks deformed by the diapiric sheaths are generally flexed up to form elongate, faintly sinuous, narrow upwarps, whose trend and extent reflect the underly- ing causative salt diapir. These upwarps, most of which probably were originally fan—shaped in cross section, can be traced for long distances through cen— tral Utah. Other workers (Spieker, 1949; Gilliland, 1963; Willis, 1986) have referred to these linear upwarps as “anticlines,” but I prefer the term “dia— piric folds,” to emphasize the critical concept that only the salt-bearing and younger beds have been intensely deformed by the rising salt. The pre-salt units may be greatly deformed, but that deformation probably stems from orogenic forces, and not from the rising salt (p. 16). In this sense, then, I view the stack of sedimentary units in central Utah as consist— ing of two parts: the salt-bearing and oirerlying younger rocks, and an older pre-salt sequence. The complex structures I describe stem from repeated movement of the salt—bearing and younger rocks. Another acceptable term to describe these upwarps is “salt-cored anticline”; I arbitrarily chose “diapiric fold” because it clearly conveys the diapiric concept and also contains fewer letters. Salt is the motive force ultimately responsible for development of the diapiric folds. Subsequent with— drawal of the salt, by dissolution or extrusion, resulted in failure of the folds. Prior to erosion, these diapiric folds must have resembled the "salt anticlines" (salt-cored anticlines) 0f the Paradox Basin. Diapiric core. The core of a diapiric fold consists of both the innermost salt diapir and its surrounding diapiric sheath. In most localities in central Utah, it is mainly the diapiric sheath of Arapien Shale mud— stone beds that is exposed. STRATIGRAPHY GENERAL STRATIGRAPHY The sedimentary rocks that crop out in this part of central Utah consist of two sequences: one sequence comprises the autochthonous plate that underlies much of the Sanpete—Sevier Valley area (table 1); the second forms much of the Charleston—Nebo thrust plate, which extends northeastward from the Mount Nebo area to Thistle and beyond (table 2). No attempt is made to describe either of these sequences in detail. The rocks of the Sanpete—Sevier Valley area have been described repeatedly and thoroughly by Spieker and his many graduate students (Spieker, 1946, 1949; Gilliland, 1948, 1951; Hardy, 1952; Schoff, 1951; Hardy and Zeller, 1953; and McGookey, 1960, among others). Those underlying the area are from Cambrian to Holocene in age; most of the indurated units that STRATIGRAPHY 1 3 \ // \\ / \\ l/ \ i‘ l,’ Diapiric fold \\ fll | l l l \\ . .. / ’I ‘ \ \\\\\\ Dlaplnc core // I \\ \ \ \ / // / \ \ \ \ I / / \\ \ \ \\ // // / / / lx/ / \ \ / / \ / —— fl _/ / \ \ _ i: I ’ \\ \ __ fl / \:—\_;—1 _‘ \ ‘ Deformed ’ / \ \ flmed ’— ’/ K _ c unt ocks o W r/ / / Diapiric sheath Diapiric sheath \ country rocks ~— — ”/ / of crumpled of crumpled ‘ \ \ / / mudstone mudstone \ \ \ \ \ \ ~ \ \ \ \ \ E .5 ‘l 2 KILOMETEHS l I ll? 1 MILE FIGURE 5,—Possible geologic relations between a salt diapir, the diapiric sheath of mudstones of the Arapien Shale, and the upturned country rock that together form the diapiric fold. The salt diapir and its diapiric sheath compose the diapiric core of the fold. Arrows denote general direction of movement of plastic and mobile salt and mudstone. In places, vertical forces, stemming from the intrusive salt diapir, are translated laterally into horizontal compressive forces. Scale is approximate. figure prominently in my report are of Mesozoic and As noted previously, I attribute much of the struc- Cenozoic age. The rocks of the thrust plate have been tural deformation in central Utah to multiple episodes described by Eardley(1933a, 1933b), Muessig (1951), of salt diapirism. The rock salt (halite) and other Johnson (1959), Hintze (1962), Bissell (1962), Rigby evaporites that I believe are ultimately responsible for and Clark (1962), Black (1965), and most recently by this structural complexity in central Utah are con- LeVot(1984), Banks(1986, 1988), and Biek(1988a, b). tained within the Arapien Shale—one of the most Exposed units range in age from Pennsylvanian to unusual stratigraphic units in central Utah. Conse- Jurassic. Tables 1 and 2 summarize the salient details quently, in the following pages, I discuss that unit in of the stratigraphic section. considerable detail. 14 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH TABLE 1.—Some stratigraphic units exposed in the Sanpete—Sevier Valley area, central Utah (Query, age, boundary, or thickness uncertain] APPROXIMATE SYSTEM SERIES UNIT TH'CKNESS LITHOLOGY METERS FEET Quaternary Pleistocenel?) Conglomeratic sandstone and sandstone, locally conglomeratic; 7 Axtell Formation light gray to gray; thin bedded to massive; semiconsolidated; ‘ _ 15—23 50—75 . , (7) of Sp|eker (1949) forms broad gravel—capped benches that flank modern major Pliocene ‘ stream valleys. Tuff, light—gray to dark—gray to black, thick- bedded to massive, Miocene Osiris Tuff 152 500 fine-grained, porphyritic; disintegrates into angular blocks and fragments that form extensive debris fields. 7 l ' h . ' h ' . . o— 0- mattress“: :1“..'“‘i’tidszzd::"S:‘;::..::;‘:..::: of Spieker (1949) 213 700 ' y 9 9 y' ' ' weathers to moderate slopes. Oligocene . Mudstone, siltstone, and sandstone, light-gray to tan, Bald Knoll Formation 7 1,00 ? . _ ; . . . _ , . . of Gilliland (1951“ 305 0 thin bedded few thin intercalated light gray aphanic limestone 7 beds. Sandstone, shaly siltstone, and some conglomerate; light gray Crazy Hollow Formation 0— 0— to reddish brown; thin to medium bedded, locally crossbedded. of Spieker (1949) 305 1,000 Light-gray salt—and-pepper sandstone containing distinctive black, well-rounded chert pebbles at base. Tertiary Consists of a limestone unit underlain by a shale unit. Limestone unit. —Yellowish gray to yellow brown to light brown; thin to thick bedded; even bedded. Contains thin sandstone and tuff beds. Green River Formation 365 1,200 Limestone beds are dense and commonly oolitic. Forms resistant Eocene ledges and low cliffs. Shale unit.—Light green to grayish green; fissile; thin bedded; a few interleaved limestone beds. Forms gentle slopes. Claystone and mudstone, variegated in shades of red and gray; 137 450 few thin interbeds of light—brown to reddish—brown siltstone, Colton Formation 487— 1 600 fine—grained sandstone, and conglomerate; sparse thin beds of ’ light-gray aphanic limestone; irregularly bedded. Locally, basal units are coarsely conglomeratic. Limestone and dolomitic limestone, light-gray to yellowish—gray . 16- 50- to light-brown; locally pale red; thin to thick bedded, locally Fl t ff L t . . . ags a imes one 548 1,800 massive; even bedded, aphanic. Contains subordinate inter- bedded dark—gray, gray, and greenish—gray shale. Paleocene Mudstone, sandstone, conglomeratic sandstone, and sparse North Horn Formation 45- 150- limestone; units alternate irregularly. Light'yellow, buff, and light 915 3,000 brown, locally reddish brown; thin to thick bedded. Unstable, marked by many mass—wasting deposits. Conglomerate, conglomeratic sandstone, sandstone, and sparse . . . 6— 20- . . . . Price River Formation shaly Siltstone; light gray to grey; thin to thick bedded, locally 609 2,000 . crossbedded. Forms steep slopes and low cliffs. West of East of Sanpete Valley: Sanpete Valley: Sandstone, conglomeratic sandstone, carbonaceous shale, and , Sixmile Canyon some coal; brown to brownish gray, locally light tan to light gray; "ldla'm'a Group, un- Formation 830 2'725 thin to medium bedded; conglomeratic in basal part. Cretaceous Upliler dIVIded (915—2,130 m Cretaceous (3900—7900 ftlll Con» F k V II Sandstone and interbedded shale; sandstone is light brown to glgdmfirtfte' rill? tko Egrmataioeny 685 2,250 yellow brown, thin to medium bedded, fine to medium grained; re is rown ic — . . . ' . , , f . bedded to masswe, shale is gray even bedded and issue wen-cemented; con‘ Sh i d k t bl k th' d b dd d t ' th' - e, a — a ac, in—an eene e;conains in srsts of well—rounded Allen Valley 182- 600— a r _9’ V 0 _ _V pebbles, cobbles, and Shale 245 800 beds of Siltstone, of very fine-grained sandstone, and gray boulders of quartizite, limestone” (Spieker, 1946, p. 128). quartz, chert, and limestone; few inter- S t Sandstone and conglomeratic sandstone, brown to leaved reddish-brown F022;; 410 1,350 brownish—gray; thin— to medium bedded: sandstones are fine to sandstone beds. medium grained; basal part of formation is conglomeratic. STRATIGRAPHY 1 5 TABLE 1,—Some stratigraphic units exposed in the Sanpete—Seuier Valley area, central Utah—Continued APPROXIMATE SYSTEM SERIES UNIT TH'CKNESS LITHOLOGY METERS FEET Shaly siltstone and mudstone; reddish brown to light gray, but locally variegated in shades of pink and violet; contains white Lower . . 90- 300— . . Cretaceous Cretaceous Cedar MountaIn FormatIon 610 2 000 lImestone bed. Contains abundant IIght-gray, small, rounded ' limestone nodules. Unstable, marked by many earthflows and landslides. Shaly siltstone and sandstone, reddish—brown, thin— and even Twist Gulch Formation 915 3,000 bedded; contains many very thin interbeds of light-gray, fine-grained sandstone and siltstone. Calcareous mudstone, shaly siltstone, shale, sparse limestone, Arapien Shale 13129262; $30886 with much salt and other evaporites. Variegated; commonly Middle ' ' mottled red and gray. Jurassic JuraSSIc Dominantly limestone, light— to dark-gray, thin to massive, even—bedded, dense, argillaceous. In places, intensely folded and Members Of the 100- 320- fractured. Includes the following seven members in descending Twin Creek Limestone 137 450 order: Giraffe Creek, Leeds Creek, Watton Canyon, Boundary Ridge, Rich, Sliderock, and Gypsum Spring. All members except the Giraffe Creek are exposed in central Utah. Lower Navajo Sandstone 1 50— 500- Sandstone, light-brown to buff, locally reddish orange, medium- Jurassic (Nugget Sandstone) 305 1,000 to thick—bedded, massive, fine— to medium—grained, quartzose. 1Recent work by Willis (1986) has suggested that the Bald Knoll strata exposed in the type section are not correlative with other rocks mapped as Bald Knoll elsewhere in central Sevier Valley. Pending resolution of this problem, Willis (1986, p. 6) used the term ”The formation of Aurora” for the units here designated as the Bald Knoll Formation of Gilliland (1951). TABLE 2.—S0me stratigraphic units exposed in the Charleston-Nebo thrust plate, Mount Nebo area, central Utah [Query, boundary or thickness uncertain] APPROXIMATE 1 SYSTEM SERIES UNIT TH'CKNESS LITHOLOGY METERS FEET ' h'fll' ,h'— I' ;'| ‘ MIddle Twin Creek Limestone ? ? C la y Ight gray t In bedded Imestone Inc udes Interbedded JuraSSIc reddIsh-brown shaly sIltstone members. Jurassic ‘ . _ _ Lower Navajo Sandstone 180 600? Orange-brown to reddIsh—brown to IIght—brown, thIck—bedded, fIne— to Jurassrc medIum—gralned quartzose sandstone. ? Upper to _ Reddish—brown shaly siltstone and crossbedded sandstone with some Lowe-r Ankareh FormatIon 122 400 intercalated thin conglomerate beds. TriaSSIC . . _ 300_ . . . . . _ . _ TrIaSSIc Thaynes Limestone 90 Chiefly IIght gray limestone WIth some reddIsh brown to IIght gray Shaly Lower 305 1.000 SIItstone and sandstone beds. Triassic dd‘ h— . . _ . _ . Woodside Sandstone 120 400 Re Is brown Shaly sIltstone and crossbedded, fine to medlum graIned sandstone. , . Chiefly light gray to pale-red, thin— to thick—bedded limestone; includes beds Park City Formation 200 650 of brownish-black cherty limestone. Permian Lower Diamond Creek Sandstone 120 400 ReddIsh—brown to IIght-brown crossbedded sandstone; some Intercalated Permian IImestone. Kirkman Limestone 113 320 Light- to medium-gray, thin— to thick-bedded limestone; contains chert. Upper to Gra . . . . . _ , y to brownIsh—gray, thIn- to thick—bedded lImestone and Interbedded PennsylvanIan Lower _ Oqurrrh Group 3'505 11’500 light-brown, fine- to medium-grained sandstone. PennsylvanIan 1Thicknesses from Eardley, 1933a; Johnson, 1959; and Black, 1965. 16 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH The stratigraphic units that form the autochtho- nous plate are divisible into two parts—the salt— bearing (Arapien Shale) and younger strata, which locally are intensely deformed, and the pre-salt units, which, although deformed, owe their deforma— tion to orogenic forces and not to the repeated move- ment of the salt. This division of the sedimentary stack is important, not only in visualizing more clearly the structural relations, but also for economic reasons: suitable traps for the accumulation of oil and gas may be formed either along the flanks of the salt diapirs, or in those folded, older rocks that underlie the masking blanket of diapirically folded rocks. Unless one recognizes this structural disconti- nuity, one might never realize that two different types of structural traps are in the area. THE ARAPIEN SHALE NOMENCLATURE The Arapien was originally defined by Spieker (1946, p. 123—125) who recognized five lithologic rock types. He described them as follows (1946, p. 124): * * *thcre are five different types of lithologic assemblage, in which the order of succession, beginning with the lowermost, is commonly but by no means regularly as follows: (1) Gray lime- stone, generally thin-bedded; (2) light-gray siltstone and shale, very thin—bedded, with occasional thin beds of finely rippled sand- stone; (3) gray shale, argillaceous and gypsiferous, with irregular red blotches, which locally become dominant; (4) compact red salt- bearing shale; (5) thin—bedded red siltstone and shale with many thin layers of greenish white siltstone and occasional zones of gray sandstone, some of which is fairly coarse grained. Of the five units recognized, Spieker believed that the first four could not be traced over long distances. Type 5, by contrast, appeared to Spieker to be suffi- ciently consistent in lithology and appearance to war- rant its being a named member. Spieker, therefore, divided the five types into two members; he named type 5 the “Twist Gulch member,” and grouped and named the underlying four units the “Twelvemile Canyon member.” In the late 1940’s, Clyde T. Hardy, then one of Spieker’s graduate students, began a study of the Twelvemile Canyon Member. Hardy soon became convinced that the Twist Gulch and 'I\Nelvemile Can— yon Members were sufficiently distinct and wide- spread to warrant separate formational status. Spieker agreed, and consequently Hardy (1952, p. 14) noted: “The Arapien shale was defined by EM. Spieker in 1946, as a formation with two distinct members (Spieker, 1946, pp. 123—125). The term is now restricted to the strata formerly included in the Twelvemile Canyon member, and the Twist Gulch member is redesignated as a formation because of its great areal extent in central Utah (Hardy and Spieker, in preparation)” The Hardy—Spieker paper was never published, but most subsequent authors seemingly assumed that the paper was in print, or simply accepted the reason- ableness of Hardy’s proposal, and used the term “Arapien shale” in a formational sense much as pro- posed by Hardy, and as an exact replacement for the name “Twelvemile Canyon Member.” Regrettably, Hardy’s proposal infringed on the existing code of stratigraphic nomenclature, which forbade using the original name of a unit (“Arapien shale”) for one of its divisions (“’1\1ve1vemile Canyon Member”). The result was dual usage of the name “Arapien shale.” US. Geological Survey geologists used the name in its original sense, as a formation with an upper Twist Gulch Member and a lower Twelvemile Canyon Mem- ber. Industry and academic geologists used the name in its formational sense and as a direct replacement for the term “Twelvemile Canyon member.” This dual usage caused much confusion. To resolve the problem, Hardy and I proposed (Witkind and Hardy, 1984) that the Twist Gulch Member be raised to formational rank, that the units now grouped as the Twelvemile Canyon Member be known as the Arapien Shale, and that the name 'IVvelvemile Canyon Member be aban- doned. Although this action also violates Article 19g of the North American Stratigraphic Code (North American Commission on Stratigraphic Nomencla- ture, 1983), we believed that widespread and common usage argued persuasively for such a change. In this Professional Paper I follow this terminology and treat the Twist Gulch and the Arapien Shale as separate formations. FIGURE 6 (facing page).—Aspects of the Twist Gulch Formation, and the Arapien Shale. A, Exposure of the Twist Gulch For— mation at north end of a low hogback near an ancestral course of Willow Creek. Twist Gulch strata, downthrown along a near—vertical, normal fault, dip westward and abut vertical beds of the Flagstaff Limestone. Structural relations in this locality are discussed in the section, “Ancestral Willow Creek area.” B, Arapien Shale exposure in the White Hills, Willow Creek area. Masses of pale-red mudstone scattered irregularly through light-gray mudstone give unit a distinc— > tive mottled appearance. As mudstone beds are readily dis— sected, badland topography commonly characterizes Arapien exposures. C, View looking eastward across Sanpete Valley at a low, gray, unnamed, north—trending ridge (west of Ninemile Reservoir), composed of Arapien strata, chiefly overturned beds of limy mudstone, siltstone, and sandstone. Overturned beds of the Indianola Group (foreground) are part of the expo- sure that makes up the Red Rocks area. D, Exposure about 5 km (3 mi) east of Nephi, along north valley wall of Salt Creek, of light-gray, thin, vertical platy beds characteristic of some facies of the Arapien Shale. 17 STRATIGRAPHY .Uwc_:tm>o 92:0 20:96:. \ coszSu £35322 ammo >w_.m> Smacmm , _ Ewcito>8 imam $694 . . 4mm><§10i .m: _ 3mm v=EwEZ :3me 52335 :o>cmu,,.xmw.o o._Ex_w :33 3E3: 2951.51 383E... $33.2“. 9: 3 83 .83.; hm. D (g 2 28 17 :3 Reservoir 15' 18 a <3“ § co 2 4TH AN DARD 39 ”00 Fillmore ‘4’ $3 v Kanosh $7 {9’ Richfield 45' Q / 4n KILUMETEHS / n m 20 an I l I'I '.' l | | l U 10 ZUMILES 38°30’ FIGURE 9 (above and facing page).—Major test wells in central Utah, and their spatial relation to recognized diapiric folds. All wells are approximately located. Index A, location of figure 9; index B, general structural setting. DIAPIRIC STRUCTURES EXPLANATION Diapiric fold—Dashed where inferred Sanpete—Sevier Valley Redmond Levan Sevier Bridge Reservoir West Hills Valley Mountains Fairview Little Clear Creek Hjorth Canyon Dry Hollow Thistle Creek Pole Creek Footes Canyon -¢—B Well names and locations (Listed alphabetically) 37.11.51. .L A IO'HI'HUON i ~ TFJiTlARY Eocene Colton Formation l 1 1 l ,1 ‘ Middle Arapien j Jurassic JURASSIC Shale Contact -—- Intrusive contact—Oblongs on intrusive unit —7— F ault—Dashed where inferred; bar and ball on downthrown block 25 —‘— Strike and dip of inclined beds X33 Abandoned salt mine X U Uranium prospect 1 northwestward at high angles. Semiconsolidated sands and gravels, here mapped as pediment mantle (QTpm) but proba- bly part of the Axtell Formation, overlie these steeply tilted Green River strata. These surficial deposits also dip north- westward at angles greater than their normal angle of repose. Fig. 14A gives a photographic overview of the intrusive dome. Base modified from US. Geological Survey 1224,000 Redmond (Utah), 1966. Topographic contour interval 100 ft. above the ground surface and abuts the south end of the ridge (fig. 143). I interpret the cuesta as a remnant of the east flank of the Redmond diapiric fold. Presumably, the Green River(?) beds were bowed up by upward movement of the Arapien Shale, which in this area is part of the diapiric core of the fold. The Arapien mudstones in the small mound probably did not break through to the surface during this intrusive stage; if they had, they would have been removed long ago. More likely, in View of their soft and easily eroded nature, they broke through at some time—late Pleistocene or early Holocene—after the erosion surface that encircles the ridge was formed. 32 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°52’3U’ ",s‘ ‘A'l' 39"00’ 1 2 KILUMETEHS | l 1 MILE EXPLANATION 1 } Holocene l l l l Alluvium Slope wash , } Pleistocene | Older alluvial- L . Pliocene(?) fan deposits ’ ? Coalesced alluvial- fan deposits I Middle Jurassic Arapien Shale Contact—Approximately located or inferred QUATERNARY W > i l | | | | > TERTIARY | | JURASSIC DIAPIRIC STRUCTURES 33 FIGURE 13 (facing page).—Geology of the Red Knolls area near Redmond, Utah. Base modified from US. Geological Survey 1224,000 Redmond Canyon and Redmond (1966). Contour in- terval 40 ft. Each of the Red Knolls is composed of red mud- stones of the Arapien Shale (O(Ja)), and all are part of a northeast—trending ridge formed of the same material. The older alluvial-fan deposits (00f) are rich in basaltic fragments not found in the Valley Mountains west of Redmond. Presence of these older fan deposits (00f) on both sides of the north- east-trending Arapien ridge suggests that they were once a continuous deposit that has since been separated by the up- thrust mass of the Arapien Shale. NORTH SOUTH Eastward-tilted beds of the Green River Formation Sand and Red mudstones of the Wasatch Plateau gravel deposit Arapien Shale Green River Formation , Arapie Sh FIGURE 14.—Small-scale features throughout the Sanpete—Sevier Valley area that suggest intrusive movement by the Arapien Shale. A, Small intrusive dome near an ancestral course of Wil- low Creek. The red mudstones of the Arapien Shale have bowed up the overlying Green River strata to form an elongate, north- east-trending dome. See figure 12 for geologic map of area. B, Small mound composed of mudstones of the Arapien Shale that abut, deform, and probably intrude units of the Green River(?) Formation. Because the mudstones are soft and easily eroded, their presence in the mound suggests that they probably broke through to the surface only in late Pleistocene or even Holocene HOGBACKS IN EASTERN SEVIER VALLEY The moderately to steeply inclined beds that form the hogbacks in the eastern Sevier Valley (between Mayfield (F—3) and Salina (G—3)) also strongly imply upward movement of the Arapien Shale. The hog- backs; consist of Green River beds unconformably overlying the Arapien Shale; the Green River beds, in turn, are conformably overlain by beds of the NORTH SOUTH Steeply dipping beds of the Green River Form ' Wasatch Plateau anon Steeply dipping beds of Crazy Hollow Formation concea|ed beneath slope wash 1 NORTH Eastward»dipping beds of Grelen River Formation SOUTH Wasatch Plateau ».Scm Pitch River ‘ Sanpete Valley [U S. "MGHWA v 39 time. C, One of several large northeast-trending hogbacks north of Salina in which Green River beds, dipping steeply to the west and that form the back slope of the hogback, overlie Arapien mudstones (not shown). View is eastward. These rela— tions have been interpreted by Billings (1933) to be the result of strip-thrusting. I suggest instead that they stem from the intrusive action of the Arapien mudstones that were forced upward by upwelling salt. D, View looking southeastward across Sanpete Valley at the face of a small knoll south of Nine- mile Reservoir that displays upward tilting of the Green River Formation by the underlying Arapien Shale. See figure 15 for geologic map of area. 34 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH GUNMSON PLATEAU I aAreaof figure15 / , 2 9'30"” 7 Ninéfifile Reservoir , 39°07 ’30” Sanpete Valley T(Ja) Arapien Valley T h | SW 9 (s a e u *1 . ”Xmas DIAPIRIC STRUCTURES 35 EXPLANATION " Contact—Approximately located or inferred; ;- H l -' ‘ . 076' 03w Pl:i:tC:::ne } QUATERNARY dashed in cross section where Alluwal fan Alluvium 7" 7- Slope' wash 1 speculative ' | Older alluvtum | --———- Intrusive contact—Approximately located or 1 interred; oblongs on intrusive unit —L-— F ault—Dashed where approximately located; dotted where concealed; bar and ball on Green R1 mation downthrown block; barb shows downthrown block in cross section Eocene —L Strike and dip of inclined beds . 80 Colton Formation L TERTIARY —b— Strike and dip of overturned beds Flagstaff Limestone Paleocene fl North Horn Formation - > Up” Cretaceous > CRETACEOUS Price River Formation Lower lndianola Group and i Cretaceous i Cedar Mountain Formation l . l $ M‘d‘“? k JURASSIC Jurasstc Arapien Shale J FIGURE 15 (above and facing page).——Geology of an isolated, unnamed hill directly south of Ninemile Reservoir. Strata of the Green River Formation (Tg) dip west as part of the Wasatch monocline. West of Arapien Valley the Green River directly overlies the Arapien Shale and dips east, reflecting Crazy Hollow Formation of Eocene age. The Green River and younger beds dip westward at moderate to steep angles, and in a few places are near-vertical (fig. 140). Commonly, the contact between the Green River and Arapien beds is even and regular, but locally it is ragged and irregular. In one or two places the Green River strata are broken to form an imbricate sheet, and here and there these strata dip into the contact at angles of 30° to 60° (Billings, 1933, p. 153-154). Billings interpreted these rela- tions to be the result of thrusting during which younger beds (the Green River and overlying strata) were shoved eastward along a preexisting unconfor- mity onto older Jurassic shales (Arapien Shale). The term “strip-thrust” was coined by Billings to describe these thrust relations. It is difficult to visualize, however, how the steep to vertical dip of these beds could have been formed solely by strip-thrusting. A more reasonable upward movement of the Arapien mudstones, which have been forced upward by the upwelling of the Sanpete—Sevier Valley salt‘ diapir under Sanpete Valley. Base modified from US. Geological Survey 124,000 Sterling (1966). Contour interval 200 ft. explanation, it seems to me, involves the bowing up and folding back of the Green River and younger strata by the upward movement of the Arapien Shale. Some support for this intrusive concept is given by the age relations. If the Green River Forma- tion overlies the Arapien mudstones as a result of strip-thrusting, this thrusting must have begun at some time following deposition of the Crazy Hollow Formation of Eocene age, presumably during either the late Eocene, Oligocene, or later. This, however, raises vexatious problems. The thrusting that marks the Sevier orogeny began in either Late Jurassic (Armstrong, 1968) or Early Cretaceous (Heller and others, 1986) time, continued as episodic pulses throughout much of Cretaceous time, and seems to have ended during the Late Cretaceous or early Pale- ocene (Armstrong, 1968, p. 449). This lengthy episode of thrusting was followed by one of extensional tec- tonism that began during either the late Oligocene or 36 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 15’ 111°UO' 112°15' 112°00' l Gunnison L1 Raw» 1%???” 15'— |Area of L ”U 39" I ' UTAH 4: 370L__L__L_'I {DAV/M1? 38°L_ 45' 2f] 30 40 KILUMETEHS | [l | l . I J | I Y I V I l I l] 20 MILES DIAPIRIC STRUCTURES 37 Miocene and that has persisted to the present. If strip thrusts were indeed formed during the Oli- gocene, or later, as Billings suggested for this sector of the Sevier Valley, this Tertiary thrusting would have begun long after thrusting ended elsewhere, and even as block faulting was beginning in this area in response to the widespread episode of crustal extension. The pattern of crustal deformation, so widespread throughout the Western Interior of the United States, argues against thrusting in this area after Paleocene time. In my View, the most plausible explanation for the structural deformation of these hogbacks involves the upward tilting of the Green River beds by the upward, rising movement of the Arapien Shale. SMALL HILL NEAR NINEMILE RESERVOIR A small hill directly south of Ninemile Reservoir (F—3) displays upward tilting of Green River beds by the Arapien Shale. Directly east of the hill, Green River limestone beds, dipping west as part of the Wasatch monocline, pass below the east edge of Arapien Valley (fig. 15). These Green River limestone beds reappear along the west side of the valley, but dip east, and thus form a small north-trending syncline whose axis has determined the trend of Arapien Valley. These limestone beds, part of the upper unit of the Green River Formation, directly overlie the Arapien Shale. The fact that units com— monly found below these limestone beds, such as the shale unit that makes up the lower part of the Green River\Formation, fail to crop out implies that these FIGURE 16 (facing page).—Major diapiric folds in central Utah. Thick dark lines represent approximate position of fold crests; dashed lines represent inferred position. Query reflects uncertainty as to whether mapped structure is a diapiric fold. Encircled numbers identify folds. Page numbers refer to description of fold in text. 1 Sanpete—Sevier Valley diapiric fold (p. 38). 2 Redmond diapiric fold (p. 57). 3 Levan diapiric fold (p. 69). 4 Sevier Bridge Reservoir diapiric fold (p. 57). 5 West Hills diapiric(?) fold (p. 100). 6 Valley Mountains diapiric(?) fold (p. 101). 7 Fairview diapiric(?) fold (p. 98). 8 Little Clear Creek diapiric fold (p. 96). 9 Hjorth Canyon diapiric fold (p. 93). 10 Dry Hollow diapiric fold (p. 83). 11 Thistle Creek diapiric(?) fold (p. 83). 12 Pole Creek diapiric fold (p. 77). 13 Footes Canyon diapiric(?) fold (p. 81). older units pinched out against a rising paleo-high— the core of the Sanpete—Sevier Valley diapiric fold (cross section, fig. 15). The abrupt reversal of the Green River beds to an eastward dip must reflect the upward push of Arapien beds. The relations between the intrusive Arapien and the upward tilted Green River beds are well exposed along the west flank of the knoll (fig. 14D). MAJOR STRUCTURES (DIAPIRIC FOLDS) I recognize 13 diapiric folds in and adjacent to the Sanpete—Sevier Valley area (fig. 16), and believe that other comparable folds are still to be found. The folds appear as elongate, narrow, linear to faintly sinuous upwarps whose trend and extent reflect the underly- ing salt diapirs. The folds are much like the “salt anticlines” (salt—cored anticlines) of the Paradox Basin in southwestern Colorado and northeastern Utah (Cater, 1955, p. 125), and the “elongate salt structures” of northern Germany (Trusheim, 1960, fig. 3). Although the folds in central Utah have been deeply eroded, one is impressed by the similarities between the central Utah folds and those exposed in the‘ Paradox Basin. These central Utah diapiric folds extend for tens of kilometers. In places, the position and trend of individual folds are expressed by out- crops of the calcareous mudstones of the Arapien Shale, which I interpret as the “diapiric core” of the fold (fig. 5). Elsewhere, the Arapien Shale is con- cealed beneath surficial deposits, and the fold is expressed by elongate, linear belts of steeply dipping to vertical and overturned sedimentary beds (the deformed country rocks of fig. 5). I interpret these complexly deformed sedimentary beds to be the eroded flanks of the fold. I believe that the strike of these vertical or overturned beds precisely reflects the trend of the diapiric fold and its underlying caus- ative salt diapir. The contorted beds of Arapien Shale that underlie the White Hills (G—3), along the east side of Sevier Valley, are an excellent example of the exposed core of a north-trending diapiric fold; the vertical to over- turned beds that delineate much of the east flank of the Gunnison Plateau are an outstanding example of the eroded west flank of the same north-trending fold—the Sanpete—Sevier Valley diapiric fold. These vertical to overturned beds of the deformed country rock (fig. 5) are typically confined to a nar- row zone. In place after place, these beds, traced perpendicular to strike, abruptly lessen in dip away 38 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH from the diapiric core and conform to the regional dip in distances as short as several kilometers. If these steeply tilted beds were concealed beneath surficial deposits, it would be almost impossible from surface exposures to recognize the presence of one of these folds (fig. 64). The 13 diapiric folds trend generally northward through the Sanpete—Sevier Valley area (fig. 16), more or less parallel to the many grabens and high— angle normal faults that break the crest of the Wasatch Plateau. Most of the folds trend northeast; a few—mainly those that flank the Gunnison Plateau— trend north; a single fold, the Sevier Bridge Reservoir fold, trends northwest. Their spatial distribution sug- gests that most are interrelated, each branching off another much as distributary streams branch off a master stream. The Sanpete—Sevier Valley fold (fig. 16, 1) appears to be the master fold. Branching off its south end is the Redmond fold (2), which extends at least from Redmond (possibly Sigurd) to near Gunnison and may continue northward to join the Levan fold (3). Near Fayette, the Sevier Bridge Reservoir fold (4) may branch off the Redmond fold. The West Hills fold (5), trending north, has been drilled and much salt found in its core. The Valley Mountains fold (6) also may once have had a salt core; recent drilling failed to penetrate any salt. A north—trending graben in the Valley Mountains, Japanese Valley, suggests that the salt core of the fold may have been dissolved and removed, with subsequent collapse of the overly- ing strata to form the graben. The Fairview diapiric(?) fold (7) may branch off the master Sanpete—Sevier Valley fold near Ephraim and extend northeastward to near Indianola. The Little Clear Creek fold (8) trends northeastward; its crest has determined the position of Little Clear Creek. The northeast end of the Little Clear Creek fold passes directly into the Dairy Fork graben, implying dissolu- tion of the salt core with subsequent collapse of the overlying beds to form a graben. The Hjorth Canyon fold (9) appears as an elongate northeast—trending dome. The Dry Hollow fold (10) is collinear with and may be the north end of the northeast-trending Pole Creek fold (12). The Thistle Creek fold (11) and the Footes Canyon fold (13) seemingly have deformed part of the Charleston-Nebo thrust plate. SAN PETE—SEVIER VALLEY DIAPIRIC FOLD The Sanpete—Sevier Valley diapiric fold (the Sanpete—Sevier Valley anticline of Gilliland (1963)) appears to be the longest of the 13 folds so far recog— nized (fig. 16, 1). On the basis of diverse geologic evi- dence (such as exposures of the Arapien Shale, steeply tilted to overturned sedimentary beds, test- well data, and collapse phenomena), I believe that the fold extends northward from near Richfield (I—1) to at least Moroni (D—4). Gravity data (fig. 52) imply that the fold extends northward beyond Moroni, pos- sibly reaching Fountain Green (0—4). If so, the fold has a minimum length of at least 95 km (60 mi), and may be as much as 125 km (75 mi) long. In general, the fold trends about N. 30° E., although its course is faintly sinuous. The exposed diapiric core of the fold, expressed as an unbroken belt of Arapien mudstone, extends from near Richfield on the south to near Manti (E—4) (fig. 8). Northward, beyond Manti, the core is completely concealed beneath the surficial deposits that floor Sanpete Valley. Between Richfield and Salina (G—3), the core clings to the east side of Sevier Valley, where volcanic flows mantle both flanks. Those volcanic rocks along the east flank of the core dip eastward; those along the west flank dip westward. Locally, these volcanic rocks are overturned (Gilliland, 1963, p. 121). Farther north, between Salina and Mayfield (F—3), the core of the fold still hugs the east side of Sevier Valley, but here the core’s west flank is over- lain by Green River strata that dip moderately to steeply westward. The core’s east flank, presumably eroded, is concealed beneath the surficial deposits that floor Arapien Valley (G—3). Near Sterling (F—4), the core fills the narrow mouth of Sanpete Valley; both flanks of the fold are exposed as near-vertical to overturned beds of Cretaceous rocks (figs. 19 and 21). The vertical to overturned Indianola beds along the east flank of the Gunnison Plateau (D—3) represent the partly eroded west flank of the fold (fig. 17). These strata are unconformably overlain either by the Price River Formation, or, where Price River strata pinch out presumably against the flanks of the fold, by the North Horn Formation. Invariably, these younger Price River and North Horn strata dip away from the crestal part of the fold at moderate angles (20° to 30°). In the Sterling area, where both flanks of the fold are exposed, Indianola beds east of the core are overlain by North Horn strata that dip east 20° to 30°. West of the core, North Horn strata dip west at comparable angles. I believe that the Sanpete—Sevier Valley diapiric fold abuts the east side of the Gunnison Plateau as far north as Freedom (D—4); beyond Freedom the crestal part of the fold trends northward toward Fountain Green (C—4), even as the front of the Gunnison Plateau bends t0 the northwest. In this sector, thus, the crest of the fold may be about 2.5 km (1.5 mi) east of the steep slopes and cliffs that mark this part of the plateau front. I suspect that the fold curves near DIAPIRIC STRUCTURES WEST EAST ' Westward—dipping beds of Flagstaff Limestone WestwardAdipping beds of North Horn Formation Vertical and overturned beds of Price River Formation Overturned beds of lndianola Group RTH SOUTH Westward-dipping beds ’ . N0 of Flagstaff Limestone ' JCbntact A... / Westwardidipping beds of North Horn Formation Vertical beds of Price River Formation / Overturned beds of Indianola Group FIGURE 17.—Aerial views along east flank of Gunnison Plateau. Vertical to overturned beds of the Indianola Group and Price River Formation form a striking reef along part of the plateau’s east front. In most places, gently to moderately inclined Price River strata un- conformably overlie vertical and overturned beds of the Indianola Group. A, In the View shown here (looking northward), the Price River beds, along with the underlying Indianola strata, have been tilted upward to vertical and overturned attitudes. These vertical and overturned beds flatten westward and underlie the westward-dipping, reddish-brown mud- stones and brown sandstone beds of the North Horn Formation, which form the steep escarpment. The North Horn Formation, in turn, is overlain conformably by westward- dipping beds of the Flagstaff Limestone. B, Vlew looking westward, showing reef formed by vertical and overturned beds of the Price River and Indianola Group (center of photo— graph), and still farther west, the westward-dipping North Horn strata conformably over- lain by the Flagstaff Limestone (on horizon). See cross section A—A’, figure 24, for details. Photographs by DA. Sprinkel, Placid Oil Company. 39 {@555me ED wnwm 955 20565 / x /k\ ._.m> SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 40 E33260 >:E.2couc= 539.3 5am , 535 35235595 Emcd J\ 35.0 3956:. mc=oc>m , hw> DIAPIRIC STRUCTURES 41 Fountain Green and trends northwestward, conform- ing to the trend of the west fork of Sanpete Valley. In my View, the 620 m (2,038 ft) of salt and inter- layered subordinate mudstone penetrated by the Price “N” well (fig. 9), which was about 2.8 km (1.7 mi) east of the Gunnison Plateau front, reflects the east flank of the causative salt diapir. Had the well been drilled farther to the west, in essence, closer to the plateau front, I believe that thicker deposits of salt would have been found. The Hanson Oil Com— pany’s Moroni wells, drilled about 5 km (3 mi) east of the Price “N” well, penetrated great thicknesses of Arapien mudstone, but found no salt. Seemingly, the Moroni wells are substantially east of and beyond the flanks of the salt diapir. Unusual geologic and structural relations at four discrete localities along the flanks of the fold demon- strate how this fold repeatedly grew and collapsed. These localities are: (1) the Red Rocks (F—3)—Sixmile Canyon area (F—3), (2) Wales Gap (D—4), (3) the ancestral Willow Creek area (also known as the Wil- low Creek gap), and (4) the Gunnison Reservoir (F—3) area. For each area, I discuss the salient features and propose a sequence of diapiric events to explain the present configuration of the strata. RED ROCKS—SIXMII.E (IANYON AREA The Red Rocks (Christianburg) and Sixmile Can- yon areas represent the west and east flanks, respec- tively, of the Sanpete—Sevier Valley fold. In these two areas the exposed rocks demonstrate not only deposi- tional thinning but also how diapiric folds grew and collapsed. FIGURE 18 (facing page).—Red Rocks area, north of US Highway 89, between Gunnison (F—3) and Sterling (F-4). A, Distant view, looking north at the Red Rocks area. As the open syncline (along skyline), in conglomerate beds of the Indianola Group, is traced southward (toward camera), the syncline closes to be— come an isoclinal fold whose axial plane dips steeply eastward. The eastward-dipping conglomerate ledges (slightly to right of center) are part of the west flank of that fold. These conglomer— ate beds are overlain with striking angular unconformity by both Price River and North Horn strata. B, Close—up view of Red Rocks exposure showing unconformable relations between eastward-dipping beds of the Indianola Group (right side of pho- to), and westward—dipping beds of the Price River and North Horn Formations. C, Detailed View of angular unconformity be- tween Indianola Group and the overlying North Horn strata. Geologist stands on eastward—dipping Indianola strata; dog stands on westward-dipping North Horn. D, Sketch illustrating details of photograph shown in B. RED Rooks ARM The southeast end of the Gunnison Plateau, north of US. Highway 89 between Gunnison (F—3) and Sterling (F—4), is known locally as the “Red Rocks area” because of the well-exposed reddish conglomer— ate beds that here make up the undivided Indianola Group (fig. 18A, and fig. 19). Spieker (1949, p. 76) referred to the site as the Christianburg area; I have not used that name because Christianburg is not on modern highway maps. The critical exposures occupy parts of secs. 12 and 13, T. 19 S., R. 1 E., and sec. 7, T. 19 S., R. 2 E. Among the oldest units exposed in the Red Rocks area are the steeply inclined and overturned, coarse conglomerate beds of the Indianola Group (fig. 18A, B). These beds dip eastward, and are flexed to form an isoclinal syncline whose axial plane dips steeply t0 the east. An angular unconformity that dips about 25° W. (fig. 18A—D) truncates the conglomerates, and an unusually thin section of the Price River Forma- tion (0.5 to 1.5 m (2 to 5 ft) thick) overlies the uncon- formity. The Price River is, in turn, conformably overlain by about 40 m (135 ft) of North Horn strata. The ‘ Price River and North Horn sequence dips northwestward at about 30°. The North Horn strata are overlain by beds of the Flagstaff Limestone, which also dip northwest at about 30°. These lime- stone beds belong to a zone in the Flagstaff Lime- stone that is “some distance above the North Horn” (Spieker, 1949, p. 76). Thus, the structural relations between the North Horn and Flagstaff are uncertain. Spieker (1949, p. 76), referring to these relations, commented: “The question is whether or not there is an angular relation at the contact between the Flag- staff and North Horn formations, and it is not set- tled. The contact is concealed“ * *.” I suspect that an unconformity separates the North Horn beds from the Flagstaff, and that this unconformity, too, is tilted northwestward. In gross aspect, then, the exposed sequence is bro- ken by an angular unconformity between the Indi- anola beds and the Price River and North Horn sequence, and a disconformity(?) between North Horn and Flagstaff strata. All units exposed in the Red Rocks area, from the Price River to the Flagstaff, are anomalously thin compared with their thicknesses some 13 km (8 mi) to the east along the flanks and crest of the Wasatch Plateau. Figure 20, which schematically depicts the west limb of the Sanpete—Sevier Valley fold, illustrates the sequence of events that I believe led to the present 42 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°43’ .. 1/, ,, e / 699/ a . / NI?‘1(3MI{€¥’,T L7" * Reservairf 1’ /' 1 09, " R1 E R 2E ‘ I I 4» 0 5 1 2 KlLUMETERS [l—‘—‘1 ”‘1 1| 1 l | I g 1/2 1 MILE NORTHWEST g SOUTHEAST A a +3 1;“ A I g > Area discussed Red Rocks 1L: 3 FEET 53 g in figure 20 area C § 8 T FEET 6000 2% § <3 E E g 6000 05 Cal U’ FIGURE 19 (above and facing page).—Geology of Red Rocks area (F—3). Strata represent part of the west flank of the Sanpete—Sevier Valley diapiric fold. Base modified from US. Geological Survey 1224,000 Sterling and Gunnison (1966). Contour interval 200 ft. geologic relations; the following discussion is keyed to consolidation of the Indianola, probably during Late that figure. Cretaceous (Campanian?) time. The Indianola beds The isoclinal fold in the Indianola conglomerates were bowed up and then steeply tilted or overturned (fig. 20, I) suggests that major movement of the as the diapiric fold developed. Probably, Indianola Sanpete—Sevier Valley diapir first occurred after strata on both sides of the fold were overturned DIAPIRIC STRUCTURES EXPIANATION . C Q ‘4 , Aguvlalwlan Alluvrum Slgpe “(Th Landslide Older alluvial Older alluvial- eposl s 91305' 5 deposits deposits fan deposits 2? \j Green River Formation Colton Formation Flagstaff Limestone North Horn Formation TlJai Price River Formation lndranola Group < Cedar Mountain Formation Twist Gulch Formation 7 . Arapien Shale : Arapien Shale Contact—Approximately located or inferred —-—-— Intrusive contact—Approximately located or inferred; oblongs on intrusive unit -—T— F ault—Dashed where approximately located; dotted where concealed; bar and ball 20 on downthrown block —I— Strike and dip of inclined beds 80 —d— Strike and dip of overturned beds —U— Overturned syncline—Approximately located; showing direction of dip of limbs 111°4B’ 45’ 44’ 111°43’ | | 0 13? a Modified somewhat from _ original mapping by MP. Weiss, Northern Illinois University 39° _ Mapped by 10' Irving J. Witkind l l l SOURCES OF GEOLOGlC DATA 43 L Holocene l QUATERNARY ‘ Eocene > TERTIARY Paleocene Upper Cretaceous > CRETACEOUS Lower Cretaceous Middle Jurassic JURASSlC 44 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH I 1 WEST \ \ \ \J g I EAST WEST EAST WEST jAST EXPLANATION WEST EAST Tch Crazy Hollow Formation T9 Green River Formation Eocene To $ TERTIARY Colton Formation Tf Flagstaff Limestone Paleocene TKn < North Horn Formation Upper Cretaceous Price River Formation > CRETACEOUS Lower lndianola Group and Cretaceous Cedar Mountain Formation J Contact DIAPIRIC STRUCTURES FIGURE 20 (facing page).—Diagrammatic cross sections suggesting how the Red Rocks area evolved. All sketches depict part of the west flank of the Sanpete—Sevier Valley diapiric fold. Ground surface in I—V speculative, not shown. I. At some time during the Late Cretaceous (Campanian?), beds of the Indianola Group and the underlying Cedar Mountain For- mation (Kic) were folded and locally overturned as a result of upward movement of the Sanpete—Sevier Valley salt diapir. A small isoclinal syncline, whose axial plane dips steeply east- ward, was formed in the Red Rocks area. 11. As rate of upward movement decreased, erosion cut a surface of low relief across the diapiric fold. Price River strata (Kpr), deposited on this surface, thin eastward (toward the diapir) and locally pinch out, reflecting the diapir's slow persistent upward movement. North Horn strata (TKn), deposited conformably on the Price River (Kpr), also thin eastward; both North Horn and Price River were warped upward in response to the slowly rising diapir. III. A renewed upward surge of the salt diapir warped up and deformed the Price River (Kpr) and North Horn (TKn) sequence, and Flagstaff Limestone (Tf) deposited above. Underlying Indianola and older strata (Kic) were tilted to more recumbent positions. IV. Again a surface of low relief was cut across the fold; this time, however, the surface beveled both the Price River (Kpr) and North Horn (TKn) sequence and some of the underlying Indianola and Cedar Mountain strata (Kic). Flagstaff sediments (Tf), deposited on this surface, thin eastward and were warped up in response to the slow, persistent upward movement of the diapir. Younger sediments (Colton (Tc), Green River (T9), and probably Crazy Hollow (Tch)) also thin eastward and also were warped by movement of the diapir. V. As in the Sixmile Creek canyon area to the east, two alterna- tives can explain what occurred next. The first suggests that the newly deposited Tertiary strata (Flagstaff to Crazy Hollow stra- ta) were warped up to form a diapiric fold by a renewed upward surge of the diapir. A second alternative is that the newly depos- ited strata subsided, presumably as a result of removal of salt, to form the eastward-facing East Gunnison monocline that has since been destroyed by erosion. For the Red Rocks area, as for the Sixmile Creek canyon area to the east (fig. 22), the first alternative would seem to be cor- rect, based on the vertical attitudes of the Flagstaff and younger strata in the ancestral Willow Creek area, just some 11 km (7 mi) south of the Red Rocks area. After this new fold was destroyed and much of the underlying salt was removed, the upwarped strata subsided to form the eastward-facing East Gunnison monocline. VI. Erosion has since destroyed the monocline, removed much of the younger sedimentary cover, and exposed part of the intense- ly folded underlying Indianola and older strata (Kic). Compare this illustration with the photographs and sketch of figure 18 and with that part of the cross section indicated in figure 19. during this intrusive stage: those in the Red Rocks area were overturned to the west (and so dipping east), those in the Sixmile Canyon area were over- turned to the east (and so dipping west). I suspect that the fold failed shortly after it was formed and the remnants then quickly eroded. 45 Erosion beveled the tilted beds to a broad surface of low relief. As Price River strata unconformably overlie this erosional surface, the surface must have been formed during the Late Cretaceous, presum- ably during middle Campanian time, assuming that Price River beds are correctly dated as late Campa- nian (Fouch and others, 1982, chart, p. 270—271). Even as Price River sediments were spread across this erosion surface, the slow, imperceptible upwelling of the diapir gradually arched the surface, effectively restricting deposition of these sediments. In places, Price River sediments pinched out against this rising barrier (fig. 20, II). In time, North Horn sediments were deposited, conformably overlying Price River units. As North Horn strata also thin in this general area, I assume that the slow, continuous upwelling of the salt persisted into North Horn time. In central Utah the North Horn ranges in age from Late Creta- ceous (Maastrichtian) to Paleocene, possibly early Eocene (Fouch and others, 1982, chart, p. 270—271), so deposition must have continued uninterrupted during this interval. Reactivation of the salt diapir during the Paleocene resulted in a new daughter fold that appears to have occupied the same site and had the same trend as the earlier parent fold. The recently deposited Price River and North Horn sequence was bowed up to form a fan-shaped diapiric fold (fig. 20, III), even as the older, underlying Indianola strata were tilted to still steeper angles. Again the fold failed, presumably as a result of renewed removal of salt from the underlying causative salt diapir. The fold partially collapsed; its remnants were then once again quickly eroded to form a surface of low relief—one, however, that truncated both the upturned Price River and North Horn sequence as well the near-vertical Indi- anola strata. Even as sediments of the Flagstaff Limestone began to be deposited upon this newly formed erosion surface, the persistent slow upwelling of the salt forced up the crestal part of the fold, and the lower and medial parts of the Flagstaff Lime- stone wedged out against this rising barrier. The younger (upper) parts of the Flagstaff extended across the crest of the fold, but they, too, were greatly attenuated by the rising fold. In time, still younger sediments (now represented by the Colton and Green River Formations) were deposited. The anomalous thinness of these units near the crestal part of the diapir suggests that the salt continued its persistent upward movement even as these units were being formed (fig. 20, IV). 46 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°41’ 4[]' €3an oar Reservoir 39 °14 ' _, Palisade " Lake 39’ ‘ 111°38' ~l 3> Gunnison Reservoir O 3 FIGURE 21 (above and facing page).—Geology of Sixmile Creek can- yon area. Map and cross section show geology of part of area. Base modified from US. Geological Survey 1:24,000 Sterling (1966). Contour interval 200 ft. Area includes sectors north of Sterling, including part of Sanpete Valley, Palisade State Park, and the mouth of Sixmile Creek canyon. Strata represent part of east flank of Sanpete—Sevier Valley diapiric fold. When all or part of the Sanpete—Sevier Valley salt diapir was removed, the late Oligocene(?) version of the fold collapsed. Arapien mud- stones, which I believe underlie the entire area, subsided into the newly formed void; this effectively removed th support for the overlying sedimentary strata which then collaised, in part along high-angle faults and in part by gradual subsidence. Most of the crustal blocks were downthrown (western part of cross 'section) toward core of fold. Westward tilt of the Flagstaff 2 KILUMETERS | 11 Sixmile Creek 3> Limestone (Tf) defines the Wasatch monocline, which formed in response to this subsidence of the mudstones. Fault “F” marks west margin of Wasatch monocline. Sketch shows north valley wall at mouth of Sixmile Creek canyon. Two angular unconformities are exposed: The older is between the Sixmile Canyon Formation of the Indianola Group and the overlying Price River and North Horn Formations. The younger is between the Flagstaff Limestone and underlying strata. Near center and right edge of sketch, the Flagstaff Lime- stone truncates both North Horn and Price River strata. Left side of sketch shows Flagstaff strata cutting across steeply dip- ping beds of the Sixmile Canyon Formation of the Indianola Group. Compare this sketch with figure 31, which displays rela- tions near the mouth of Red Canyon in the Valley Mountains, some 20 km (12 mi) west. DIAPIRIC STRUCTURES WEST Flagstaff Limestone \ Sixmile Canyon Formation\of lndlanola Group EAST \North Horn‘ \ Form‘ation \ \ \ 9' Formation\ \ \ \ 47 \ \ \ \ \ \ \ \ \ \ EXPLANATION wt, 91 ‘ j. . l Holocene Alluvium - ' ,j‘ . C; Q ‘ I A e s f } Pleistocene ‘ « C ’ ‘ l Older alluvium Mass-wasting Landslide S ope wash Terrace f Pliocene? deposits deposits deposits Crazy Hollow Formation \“x \Q\ \ ‘ ‘\ Green River Formation Colton Formation Flagstaff Limestone North Horn Formation Price River Formation Ki u lndianola Group Coalesced alluvial fans Eocene Paleocene Upper Cretaceous Middle Arapien Shale Contact—Approximately located or inferred -—-— intrusive contact—Oblongs on intrusive unit —l—— Fault—Dotted where concealed; bar and ball 70 _J_ + The salt diapir may have reactivated a third time to form still another daughter fold that again occupied the same site and had the same trend as the previous on downthrown block; barb shows downthrown block in cross section; clashed in cross section where reconstructed above eroded surface Strike and dip of inclined beds Strike and dip of vertical beds Jurassic two folds (fig. 20, V). This reactivation is suggested by the westward dip of the Flagstaff strata exposed in the Red Rocks area (fig. 20, VI). Subsequently, the 48 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH diapiric fold failed again, as salt was removed from the underlying diapir, and the overlying beds subsided into the resultant void. The end result was the devel- opment of the Wasatch monocline along the west flank of the Wasatch Plateau, even as another opposing monocline probably developed along the east flank of the Gunnison Plateau. This second monocline along the east flank of the Gunnison Plateau has been destroyed by erosion, and its remnants are now con- cealed beneath the alluvial floor of Sanpete Valley. SIXMIH‘, CREEK CANYON AREA The Sixmile Creek canyon (F—4) area, east of Ster- ling, is some 10 km (6 mi) northeast of the Red Rocks area; the critical exposures underlie parts of secs. 25, 26, 35, and 36 of T. 18 S., R. 2 E. The exposures here closely resemble those of the Red Rocks area. The Indianola Group, exposed at and near the mouth of Sixmile Creek canyon, consists of vertical to steeply tilted beds that dip eastward (fig. 21). Near the east edge of its exposure, the uppermost unit of the Indianola Group—the Sixmile Canyon Formation—dips southeastward 30° to 60°, and is truncated by an angular unconformity that also dips eastward but at about 10°. This uncon- formity is overlain by a thin sequence of Price River strata, which, in turn, is conformably overlain by a thin North Horn sequence. The Price River and North Horn sequence dips about 30° E., and totals about 20 m (65 ft). This sequence is cut out near the west— ern part of the exposure by Flagstaff Limestone, some 10 to 15 m (35 to 50 ft) thick, which dips westward at about 35°. Thus, the upturned edges of both the Price River and North Horn are unconformably overlain by Flagstaff Limestone. West of the pinchout of the Price River and North Horn sequence, the downwarped Flagstaff Limestone unconformably overlies the steeply tilted to vertical beds of the Sixmile Canyon Formation. In summary, the stratigraphic sequence at the mouth of Sixmile Creek canyon is broken by two dis- tinct unconformities: the first truncates the Indianola beds and is overlain by the Price River and North Horn sequence. The second not only truncates the upturned Price River and North Horn beds but also extends across the steeply inclined Indianola beds; west-dipping Flagstaff beds overlie this unconformity. Figure 22 depicts, in a series of diagrammatic sketches, how I visualize the relations in Sixmile Creek canyon to have formed. Subsidence of the sedi- mentary units, as shown in the last sketch, resulted in the development of the Wasatch monocline. FIGURE 22 (facing page).—Diagrammatic cross sections suggesting how Sixmile Creek canyon area evolved, with resultant forma- tion of the Wasatch monocline. All sections represent part of east limb of Sanpete-Sevier Valley diapiric fold. In views I—VII, ground surface speculative, not shown. 1. Geologic relations at the mouth of Sixmile Creek canyon. See figure 21 for geologic map of the area and sketch of north val- ley wall at the mouth of Sixmile Creek canyon. The geologic pattern is almost a mirror image of that exposed in the Red Rocks area to the west (assumed to be west limb of Sanpete— Sevier Valley diapiric fold); in essence, steeply dipping beds of the Sixmile Canyon Formation of the Indianola Group (Kis) are unconformably overlain by a Price River (Kpr) and North Horn (TKn) sequence, which in turn is unconformably overlain by the Flagstaff Limestone (Tf). 11. During the first diapiric episode, an upward surge of the Sanpete—Sevier Valley salt diapir warped rocks of the Sixmile Canyon Formation (Kis) into a diapiric fold, mushroom-shaped in cross section. III. The rate of uplift decreased and the fold was eroded to a surface of low relief. A Price River (Kpr) and North Horn (TKn) sequence was deposited on this surface. IV. The beginning of the second diapiric episode was marked by a second upward surge of the salt diapir, which raised and deformed all strata. The newly deposited Price River and North Horn sequence was warped to form a diapiric fold, and the previously tilted beds of the Sixmile Canyon Formation were rotated to still steeper angles. V. This second diapiric fold also was eroded to a near-horizon- tal surface. Flagstaff (Tf) was deposited across this surface, and in time still younger units (at least the Colton (Tc), and Green River (Tg) Formations) accumulated. VI. Two alternative interpretations for what occurred next are possible: In the first, a renewed upward surge of the salt warped these newly deposited Tertiary units into a new diapiric fold. The second alternative suggests that as part of the salt diapir was removed, the overlying sedimentary units subsided into the resultant void to form a westward-facing monocline. I sketch the first alternative here, chiefly because the westward tilt of the Flagstaff and younger strata in the Red Rocks area to the west imply that a new fold was formed shortly after deposi- tion of these younger Tertiary strata. VII. Subsequent removal of salt from the Sanpete—Sevier Valley diapir resulted in failure of the fold. The mudstones of the Arapien sank into the newly created void, and the upturned country'rocks, lacking the support of the mudstones, subsided to form the westward-facing Wasatch monocline. VIII. Erosion and removal of younger units (Green River (T9), and Colton (Tc)) expose the westward-dipping Flagstaff Lime- stone (Tf) overlying eastward-dipping strata (Kis, Kpr, TKn). The Red Rocks and Sixmile Creek canyon expo- sures are unusual in two respects: (1) Most of the units are much thinner in these areas than in the Wasatch Plateau to the east, and (2) strata that are conformable only a kilometer or two away are sepa- rated here by striking angular unconformities. In the Sixmile Creek canyon area, for example, where expo- sures are good and easily traceable, the Price River and North Horn strata thicken gradually eastward, and attain thicknesses of hundreds of meters just a DIAPIRIC STRUCTURES 49 WEST EAST EXPLANATION T9 Green River Formation Eocene I O Colton Formation > TERTIARY I _. Flagstaff Limestone Paleocene TKn < North Horn Formation Kpr Upper Cretaceous v Price River Formation Sixmlle Canyon Formation _ - (of Indianola Group) . Arapien Middle } WEST 1 EAST Shale Jurassic JURASSIC CRETACEOUS Tg ‘ WEST I11 :9 m —I \ WEST EAST WEST \\ \ \ EAST WEST EAST 50 few kilometers to the east. The North Horn and Flag- staff beds, unconformable at the canyon mouth, are conformable about 2 km (1.2 mi) to the east. I interpret the exposures in the Red Rocks area to be remnants of the west limb of the Sanpete—Sevier Valley diapiric fold, and the similar exposures in Sixmile Creek canyon to be remnants of the opposite (east) limb of the same fold. WALES GAP Wales Gap (D—4), at the mouth of Wales Canyon, is along the east flank of the Gunnison Plateau, some 37 km (23 mi) north of the Red Rocks area. Essen- tially the same stratigraphic units are exposed at Wales Gap as at Red Rocks, but the Wales Gap rocks have been more intensely deformed. At Wales Gap, overturned conglomerate beds of both the Indianola Group and the Price River Forma- tion form a steep, narrow ridge (figs. 23A, 24). The structural relations between the two units are some- what masked by their similar lithologies and by the low angular discordance between them (Spieker, 1946, pl. 24B). The overturned Indianola conglomerate beds form the eastern part of the ridge and dip eastward at about 50° (fig. 23B). They abut, and stratigraphically underlie, overturned conglomerate beds of the Price River Formation that form the western part of the ridge. These Price River beds also dip eastward, but at about 800 (fig. 25). Just west of the ridge the gray and red mudstone and brown sandstone beds of the North Horn Formation are right-side-up and dip gently westward. East of the ridge, overturned pale- red and orange mudstone, siltstone, and sandstone beds of the Cedar Mountain Formation, which dip about 600 E., stratigraphically underlie the Indianola beds. The Cedar Mountain strata, in turn, are strati- graphically underlain by overturned light-brown and gray thin sandstone beds of the Twist Gulch Forma- tion, which also dip about 60° E. All units for which an upper and lower contact can be found are anoma- lously thin compared with their thicknesses else- where in the area. I attribute the anomalous thinness of the sedimen- tary units to the gradual upwelling of the Sanpete— Sevier Valley diapir, and the deformation to repeated upward surges of the diapir. In figure 25 I suggest a sequence of events to explain these structural relations. At some time after Indianola strata were deposited, the Sanpete—Sevier Valley diapir surged upward and forced the Arapien mudstones to bow up and fold back the Twist Gulch, Cedar Mountain, and Indianola beds, forming a fan- SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH WE ST EAST Flagstaff Limestone (Tf) North Horn Formation (TKn) Price River Formation (Kpr) indianoia Group (K.§)..V ‘ (covered by debris) Iv . FIGURE 23.—East front of Gunnison Plateau near Wales. A, Aerial view, looking north along east flank of the Gunnison Plateau. Wales Gap (D—4) is just beyond skyline. Overturned to vertical conglomerate beds of the Price River Formation (Kpr) and the Indianola Group (Ki) form the narrow, elongate, north-trending ridge. These upturned conglomerate beds abruptly flatten westward (left) in the subsurface, and in a distance as short as several kilometers assume the gentle westward dip suggested by the overlying North Horn (TKn) and Flagstaff (Tf) strata that form the steep, imposing front of the Gunnison Plateau (left side of photo). Photograph by DA. Sprinkel, Placid Oil Company. B, View northward of the Indianola and Price River relations as exposed in a road cut (Wales Gap) through the north-trending ridge shown in A. Price River strata (left side of photograph) are vertical to overturned; Indianola beds (right side) are overturned and dip about 50° E. shaped fold (only the west flank of this fold is shown in fig. 25, sketch 1). Although no evidence is available to indicate how the fold failed, most likely, removal of the salt caused collapse of the crestal part of the fold. Erosion then beveled the area to a surface of low relief. Price River sediments were deposited on this DIAPIRIC STRUCTURES 51 surface, and in time, these were covered by North Horn sediments (fig. 25, II). The sequence, thus, is identical to that postulated for the Red Rocks— Sixmile Creek canyon area. At some time during or after North Horn time the salt diapir welled upward once more, and again forced the Arapien mudstones to bow up and fold back the overlying strata. The Price River and North Horn sequence was probably warped into a fan- shaped fold, and the underlying Indianola beds were rotated into overturned attitudes (fig. 25, III). Subse- quently, this newly formed fold failed, presumably when the supporting salt was removed. On the basis of exposures elsewhere in the area (as in the Red Rocks area), I assume that the area was again reduced to a surface of low relief. Flagstaff sediments were deposited on this surface, and these, eventually, were covered by a sequence of still younger Tertiary beds. Subsequently, when salt was removed from the causative salt diapir, the overlying Tertiary beds were let down to form an eastward-facing mono- cline—the East Gunnison monocline—comparable to and paired with the westward-facing Wasatch mono- cline. Erosion has since removed all traces of the East Gunnison monocline, leaving only the structur- ally complex west flank as evidence of the diapiric activity (fig. 25, sketch IV). ANCESTRAI. WILLOW CREEK AREA GEOLOGIC SETTING The ancestral Willow Creek (G—3) area, also known as the Willow Creek gap, is some 8 km (5 mi) northeast of Salina (G—3) astride an ancestral course of Willow Creek. 'IVvo low cuestas that trend about N. 30° E. dominate the area (fig. 26). The cuestas are collinear and the resulting ridge extends for some 4.5 km (2.7 mi) through parts or all of sections 26, 27, 34, and 35 of T. 20 S., R. 1 E. The aligned cuestas parallel the crest of the White Hills, com- posed of deformed mudstone beds of the Arapien Shale, which is about 1.6 km (1 mi) to_the northeast. Sedimentary rocks exposed in and near the cuestas range from the Arapien Shale (Middle Jurassic) to the Crazy Hollow Formation (Eocene). All units exposed in the cuestas are anomalously thin com- pared to their thicknesses in and near the Wasatch Plateau some 8 km (5 mi) to the east. So, for exam- ple, the Flagstaff Limestone is about 30 m (100 ft) thick here, but more than 365 m (1,200 ft) thick where it caps the plateau. In detail, the cuestas consist of steeply dipping to vertical beds of the Colton Formation and the under- lying Flagstaff Limestone (fig. 26). Some uncertainty and differences of opinion exist as to just what units should be included in the Flagstaff. Spieker (1949, p. 56) considered the Flagstaff in the Willow Creek area to be a composite unit consisting of a light-gray, fine-grained limestone bed plus some conglomerate beds that crop out on both sides of the near-vertical to vertical limestone. The conglomerate beds dip steeply and appear to conform to the attitude of the limestone bed. G.E. Moore, Jr., and K.E. Stanley (Ohio State University, written commun., 1979) con- sidered only the limestone bed to be Flagstaff. They interpreted those conglomerate beds west of the lime- stone bed to be basal units of the Colton Formation, and those east of the limestone bed to be uppermost North Horn strata—in essence, a normal strati- graphic sequence. I offer a third interpretation. I con- cur with Moore and Stanley that the limestone bed is Flagstaff and that the conglomerate beds west of the limestone bed are basal Colton. I believe, however, that the conglomerate beds east of the limestone bed are part of a block of the Colton Formation that was downthrown along a high-angle normal fault that delineates the east side of the steeply inclined bed of Flagstaff Limestone. The fault, which follows the crests of the two cuestas, is marked in many places by vertical slickensides. Small steps, or heels, along the slickensides suggest that the crustal block east of the fault has been downthrown. The fault is best exposed along the north end of the northern cuesta, where beds of the ’l\zvist Gulch Formation, east of the fault, dip westward at 35° to 65° and abut vertical beds of the Flagstaff Limestone west of the fault (fig. 6A). DISCUSSION Figure 27 is a geologic map of the ancestral Willow Creek area. I include a series of diagrammatic sketches and cross sections that illustrate how I believe the ancestral Willow Creek area evolved. In my interpretation the welt of contorted Arapien Shale mudstones that makes up the White Hills is part of the exposed core of the Sanpete—Sevier Valley diapiric fold, and the two northeast-trending, aligned cuestas are the broken and dissected remnants of the fold’s west flank. The east flank of the fold is not exposed; apparently it was obliterated by collapse and erosion, and now is concealed beneath surficial deposits. Its former position is followed approxi- mately by the Cedar Mountain road (fig. 27). I propose that the Sanpete—Sevier Valley salt diapir surged upward at some time after deposition of the Crazy Hollow Formation (Eocene), presumably during 52 30°30’ 30°29 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°41' 40' 39' 111°30’ D——o FIGURE 24 (above and facing page).—Geology of an area near Wales, Utah. A small area along the east flank of the Gunnison Plateau, centered on Wales Gap, displays well the unusual structural and stratigraphic relations that characterize the plateau’s east flank. Geology by M.P. Weiss, modified by I.J. Wit- kind. Base modified from US. Geological Survey 1124,000 Wales (1965). Contour interval 200 ft. Vertical and overturned beds of the Price River Formation and Indianola Group form an elongate, narrow, north-trending ridge. These clastic units are stratigraphically underlain by overturned beds of both the Cedar Mountain and Twist Gulch Formations. AI West flank of the Sanpetr FEET Sevier Valley diapiric fold 4 7000 GUNNISON FAULT 6000 5000 I interpret the vertical and overturned Price River and older strata to be part of the west flank of the Sanpete—Sevier Valley diapiric fold; surficial deposits that floor Sanpete Valley conceal the bulk of the fold. The attitude of these upturned Price River and older beds resulted from repeated upward movements of the Arapien Shale. See figure 25 for a diagrammatic explana- tion. The Gunnison fault, a much younger feature, likely formed when the salt in the core of the Sanpete—Sevier Valley fold dis- solved, resulting in collapse of the crestal part of the fold and subsidence of the overlying strata. DIAPIRIC STRUCTURES 53 EXPLANATION i '1 OE ' ,. Q W? Holocene " ‘ " ’ ’ 1 QUATERNARY Alluvium '- 7' . ~ Landslide | Coalesced deposits 1 l 2 alluvial fans mantle Eocene > TERTIARY Paleocene < TUE) Upper Cretaceous lndianola Group Cedar Mountain Formation Twist Gulch Formation 7 Arapien Shale Contact—Approximately located or inferred —I— Fault—Dashed where approximately located; dotted where concealed; bar and ball on downthrown block; barb shows downthrown block in cross section post-Eocene time. During this upward surge the salt forced the mudstone beds of the Arapien Shale to bow up the overlying sedimentary strata and thus form a fan-shaped diapiric fold. Only the west limb of this fold is shown in stage I of cross sections A—A’, B—B’, and C—C’, figure 27. Upon removal of the salt, the crest of the fold collapsed unevenly between high- angle faults that developed along the flanks of the fold (stage II of cross sections A—A’, B—B’, and C—C’, fig. 27). The western fault developed adjacent to and east of the vertical bed of Flagstaff Limestone. Depending upon the amount of stratigraphic throw, different units, east of the fault, were downthrown and juxtaposed against the Flagstaff Limestone. As shown in cross section A—A’, Twist Gulch beds, part of the downthrown crest, were dropped against vertical Flagstaff beds. In cross section B—B’, steeply dipping to near-vertical beds of the Colton were downthrown against the Flagstaff. The geologic relations shown in interpretation B—B’ form the basis for my suggestion > CRETACEOUS Cretaceous and Jurassic rocks, Lower Cretaceous undivided Middle Jurassic JURASSIC J 25 —‘— Strike and dip of inclined beds 65 —b— Strike and dip of overturned beds —l— Strike and dip of vertical beds U Angular unconformity that the correct stratigraphic sequence at Willow Creek gap involves near-vertical to vertical Flagstaff beds flanked by near-vertical Colton strata. Colton strata west of the Flagstaff Limestone conformably overlie the Flagstaff; Colton strata east of the Flag- staff are in fault contact with that unit (stage III of cross section B—B’). Other unusual geologic relations in the same area can also be explained by invoking different amounts of downthrow along the same vertical fault. So, for example, about 365 in (1,200 ft) east of the cuesta south of the Willow Creek road, beds of the Flagstaff Limestone crop out along a small knoll (fig. 27). These limestone beds are overturned and dip about 85° E. Stratigraphically, they underlie overturned beds of the Colton Formation that also dip eastward. As shown in cross section C—C’, figure 27, these unusual stratigraphic relations are readily explained by again invoking downthrow of the west limb of the diapiric fold. 54 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH EAST Graveled road connecting Wales, east of Gunnison Plateau, with Levan, west of the plateau WEST EAST WEST Fold eroded to this plane EAST WEST EXPLANATION } H°l°.°e“e and } QUATERNARY Plerstocene Colluvium TK n Paleocene TERTIARY North Horn Formation Pnce River ”PM CRETACEOUS . Cretaceous Formation lndianola Group, undivided DIAPIRIC STRUCTURES At the north end of the cuesta north of the Willow Creek Road, where 'IVvist Gulch beds abut vertical Flagstaff beds, the amount of downthrow along the fault is somewhat less than the amount of throw involved in the juxtaposition of Colton beds against the Flagstaff. As all units, however, are anomalously thin in this locality, the differences in amount of throw between the two areas are not excessive. Here, as in the Red Rocks—Sixmile Canyon area, the crustal blocks adjacent to a fault are downthrown valleyward (eastward in the ancestral Willow Creek area) toward the core of the collapsed fold. I stress that these geologic relations in the ances- tral Willow Creek area represent but one episode in the many that mark the repeated growth and col- lapse of the Sanpete—Sevier Valley salt diapir. Because Tertiary units—Flagstaff, Colton, Green River, and Crazy Hollow—are steeply tilted, the deformation must have occurred at some time after Crazy Hollow strata (Eocene) were deposited—long after Sevier thrusting had come to an end. It would FIGURE 25 (facing page).—Wales Gap (D—4), along east flank of the Gunnison Plateau. Diagrammatic field sketch, looking south, shows exposures along south wall of Wales Gap. Both the Indi- anola Group (Ki) and the Price River Formation (Kpr) are over- turned and dip eastward (left) but at different angles. Both units consist of coarse conglomerate beds that are very much alike. Sketches I to IV suggest how these relations may have formed as a result of repeated episodes of salt diapirism. Area is part of west flank of the Sanpete—Sevier Valley diapiric fold; Sanpete—Sevier Valley salt diapir (not shown) is concealed to the east (left) beneath alluvial floor of Sanpete Valley. I. Conglomerate beds of the Indianola Group (Ki) were deformed into a fan-shaped fold as a result of an upward surge of the Sanpete—Sevier Valley salt diapir. 11. Subsequently, the fold collapsed, and was eventually eroded to a broad surface of low relief. On this newly formed surface, sediments of the Price River Formation (Kpr) were deposited, and in time these were mantled by sediments of the North Horn Formation (TKn). Although not shown in these diagrammatic sketches, both the Price River (Kpr) and North Horn (TKn) For- mations thin in this area, presumably as a result of a slow but persistent upwelling of the Sanpete—Sevier Valley salt diapir. III. Another rapid upward surge of the Sanpete—Sevier Valley salt diapir deformed the area once again. The newly deposited Price River (Kpr) and North Horn (TKn) Formations were de- formed into a fan-shaped fold whose general trend and position coincide closely with that of the previously formed diapiric fold. The tilted Indianola strata (Ki) were overturned. IV. Collapse of the most recently formed fold and subsequent erosion have almost obliterated all evidence of the two diapiric folds. Remnants of the deformed rocks are exposed only along the east flank of the Gunnison Pleateau. (Compare with field sketch.) About 0.8 km (0.5 mi) to the west (right), both the Indi- anola (Ki) and Price River (Kpr) strata flex sharply in the sub- surface and conformably underlie the North Horn (TKn) . 55 seem, therefore, that of the three major diapiric epi- sodes recognized in the Red Rocks—Sixmile Canyon area, only the third episode, (late(?) Oligocene— Pliocene(?)), is represented in the ancestral Willow Creek area. All evidence of the first and second dia- piric episodes is still concealed. GUNNISON RESERVOIR AREA The previous areas discussed demonstrate that consolidated sedimentary strata were repeatedly deformed during the Cretaceous and Tertiary, presumably as a result of the recurrent growth and collapse of the Sanpete—Sevier Valley salt diapir. In my opinion, the results of these diapiric episodes can be recognized throughout much of central Utah, and I believe that they determined the structural pattern of central Utah. Deformation was extensive and, although localized in specific belts, extends along strike for tens of kilometers. By contrast, in several small areas evidence suggests that diapirism may have persisted into the late Tertiary or Quaternary. In one such area, along the east shore of the Gunni- son Reservoir (F—3), semiconsolidated sediments have been warped into a deformational pattern that is strikingly like those discussed previously. Beds of semiconsolidated gravels, tilted on end, crop out along the east side of Gunnison Reservoir, chiefly in the SE 1/4 sec. 21, T. 18 S., R. 2 E. (fig. 28). Near-horizontal beds of younger gravels overlie these vertical gravels, and the angular unconformity between the two gravels is as spectacular as any of the angular unconformities exposed in the Sanpete— Sevier Valley area. The discordant relations between the two gravels does not extend for more than 1 km (1/2 mi) and has been found only near the reservoir. The age of the vertical gravels is unknown, but their lack of consolidation and their thin caliche rinds imply that they were probably formed during the late Tertiary (Miocene or Pliocene) or Pleistocene. I tenta- tively correlate these vertical gravels with the Axtell Formation (Spieker, 1949, p. 38), which Spieker (1949) believed may be of “late Tertiary” age. Elsewhere in this general area several small deposits of sand and gravel, correlated with the Axtell Formation, have been warped into synclines with dips as high as 45° (Gilliland, 1963, p. 121 and plate 3, fig. 2; Hardy, 1952, p. 60). One of these localities is near a small dome in the ancestral Willow Creek area (p. 29) where a pediment mantle of sand and gravel dips northwestward at about 20° (fig. 14A). 56 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH WEST Westward-dipping of Green River Format- EAST Detachment slide block composed chiefly of beds of Green River Formation High-angle normal fault 'Near vertical beds of ”M Colton Formation 3 How the lowermost gravels exposed near Gunnison Reservoir were tilted to a vertical position is not clear. Although it is possible that they are part of a slump block that was tilted to steeper and steeper angles during successive valleyward rotational slumps, their vertical attitude suggests that this ori- gin is unlikely. A more reasonable explanation, it seems to me, is that they were bowed up and folded back to form a diapiric fold by the upward movement WEST Near~vertica| beds of Flagstaff Limestone Near-vertical beds of Colton Formation of part—a cell—of the much larger Sanpete—Sevier Valley salt diapir, the crest of which underlies the reservoir, directly west of the vertical gravels. If so, these vertical gravels represent the east flank of a reactivated segment of the north-trending Sanpete— Sevier Valley diapiric fold. Prof. M.P. Weiss, of Northern Illinois University, has suggested (oral commun, 1987) that the gravels may have been tilted to their vertical position as a DIAPIRIC STRUCTURES 57 FIGURE 26 (facing page).—Views of ancestral Willow Creek area. These exposures are part of west flank of the Sanpete—Sevier Valley diapiric fold. Structural relations reflect collapse of the crest of the fold between two high-angle normal faults (a graben), of which only the western fault is shown here. (U, relatively upthrown block; D, relatively downthrown block.) See geologic map and cross sections, figure 27, for additional details. A, View, looking northward, of the cuesta north of Willow Creek road. West (left) of the near-vertical Flagstaff Limestone, stratigraphic sequence is normal, extending through the Colton Formation into the Green River Formation. A high-angle fault, however, flanks east (right) edge of the Flagstaff Limestone, and Colton strata are downthrown against the Flagstaff Limestone. (See geologic map, fig. 27.) B, View, looking southward, of the cuesta south of the Willow Creek road. Colton strata west (right) of the high-angle fault are part of the normal stratigraphic sequence; those Colton strata east (left) of fault are downthrown, along a high-angle normal fault, against vertical beds of Flagstaff Lime- stone. (Compare with cross section C—C' (111), fig. 27. Note that view shown here is reversed with respect to that cross section.) As these vertical and near-vertical strata are traced southward, they pass below a westward-inclined slide block composed of Green River strata. result of upward movement by an unrecognized dia- pir that underlies that sector of Sanpete Valley north of Sterling and directly east of the upturned, vertical gravels. In Weiss’ interpretation, the tops of the upturned gravels would be to the west. In my inter- pretation, the tops would be to the east. I do not know how the diapiric fold was destroyed. Presumably it collapsed, much as postulated for those diapiric folds previously discussed, and the fold remnants were then eroded during the late Pliocene or early Pleistocene to form an even surface of local extent. Younger sands and gravels, carried either by Pleis- tocene(?) streams or by Holocene descendants of those streams, were spread across this newly formed surface. Subsequent erosion by the San Pitch River exposed this remnant. Seemingly, the driving salt has moved throughout much of the late Mesozoic and Cenozoic, and proba- bly is continuing to well upward slowly today. Pedi- ment gravels that overlie Arapien Shale exposures, near the junction of Twelvemile Creek with the San Pitch River (the northeast corner of sec. 24, T. 19 S., R. 1 E.), dip about 25° NW. (M.P. Weiss, Northern Illinois University, written commun., 1989). These gravel exposures, as well as the vertical gravels exposed near Gunnison Reservoir, imply that the underlying salt diapirs are still active; if so, they pose a potential threat to man-made structures (Wit- kind, 1981). REDMOND DIAPIRIC FOLD The surface evidence for the Redmond diapiric fold (fig. 16, 2), originally named the Redmond Hills anticline by Gilliland (1963, p. 121), consists of a string of Arapien Shale outcrops that begins at Redmond (G—3) and extends as far north as Gunni- son (F—3) (fig. 8). A gravity low coincides with the string of Arapien outcrops, and in my view this low reflects the crest of the diapiric fold (fig. 52). Gravity data (fig. 52) imply that the Redmond fold branches off the Sanpete—Sevier Valley fold near Salina (G—3), and then extends northward to some indefinite point beyond Gunnison, possibly joining the Levan fold (fig. 16, 3). On the assumption that the Redmond fold does extend, at least, from near Salina to Gunnison, the fold has a minimum length of about 49 km (30 mi), and trends almost due north. I interpret a small east—dipping (valleyward) exposure of Green River(?) beds (p. 31) (in the 81/2 sec. 12, T. 20 S., R. 1 W.), about 8 km (5 mi) north of Redmond, to be a rem- nant of the east flank of the fold (fig. 143). SEVIER BRIDGE RESERVOIR DIAPIRIC FOLD Generally, Arapien Shale outcrops flanked by upturned, commonly vertical to overturned beds of consolidated sedimentary rock identify many diapiric folds. In places, however, the Arapien beds, being soft and easily eroded, are concealed beneath surficial deposits and only the upturned beds reflect the pres- ence of the fold. Thus, for example, at the south end of the Sanpete—Sevier Valley fold (fig. 16, 1), west of Mayfield (F—3), the Arapien Shale forms the White Hills (G~3). I interpret these Arapien outcrops to be the core of the Sanpete—Sevier Valley fold, and the adjacent upturned beds (along the west flank of these exposures) to be part of the west limb of the fold. As these Arapien exposures are traced northward they pass below the alluvial fill of Sanpete Valley, and only upturned vertical to overturned Indianola beds, as, for example, at Wales Gap (D—4), indicate the position and trend of the fold. By contrast, in the Sevier Bridge Reservoir (E—2) area, Arapien beds are not exposed, and only a nar- row band of steeply tilted to overturned conglomerate beds of the Indianola Group exposed along the north- east flank of the Valley Mountains suggests the pres- ence of a diapiric fold (fig. 16, 4; fig. 29A). Additional evidence, including both the complex structural rela- tions and the anomalous depositional thinning best displayed at Red Canyon (E—2) along the northeast SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°4B’ 47' 45' 111°45’ ..-..| 39°11? ,4. ' T208 ._ T213 39°01H~W~ 1 .5 l 2 KILOMETEHS l J l 1/2 1 MILE FIGURE 27 (above and following pages).—Geology of ancestral Willow Creek area, plus cross sections, across part of west limb of the late(?) Oligocene version of the Sanpete—Sevier Valley diapiric fold. Base modified from US. Geological Survey 1:24,000 Redmond (1966). Contour interval 100 ft. In the three schematic cross section panels labeled 1, reactivation of the Sanpete—Sevier Valley salt diapir (not shown) forced up the mudstones of the Arapien Shale (T(Ja)), which in turn bowed up (arrows) the overlying sedimentary strata to form a diapiric fold, roughly mushroom shaped in cross section. In places, the beds were folded back and overturned; cross-sectional shape of the fold differs from place to place along the folds length. The three schematic cross-section panels labeled II represent failure of fold along a high-angle normal fault. The three cross-section panels labeled 111 show present-day configuration. Cross section A—A’: I. The beds were bowed up and folded back to form a fan-shaped fold. Only the west flank of that fold is shown. II. Upon partial removal of the salt core (not shown) the fold collapsed between two high-angle faults. Only the west fault is shown. Crest of fold was dropped down against the vertical to over- turned beds of the relatively upthrown limb. III. After erosion, only remnants (th) of the downthrown limb are preserved, juxtaposed by a fault against vertical beds of the Flagstaff Limestone (Tf). DIAPIRIC STRUCTURES 59 EXPLANATION \ 1 Holocene “3 l Slope wash L Pleistocene ( QUATERNARY ? , Coalesced alluvial j Pliocene? : Pediment mantle fan deposits 4 Unconformity , , , } Miocene? Tu Crazy Hollow Formation Green River Formation (Detachment blocks) Tertiary units, undivided Crazy Hollow Formation Green River Formation Colton Formation > TERTIARY Eocene Flagstaff Limestone Paleocene Upper Cretaceous i CRETACEOUS I North Horn Formation | Paleocene, Cretaceous and Middle Jurassic g JURASSIC Jurassic units, undivided Arapien Shale / 45 Contact—Approximately located or inferred —‘— Strike and dip of inclined beds —-—-— Intrusive contact—Oblongs on intrusive unit —l— Strike and dip of vertical beds 85 -—I—-- Fault—Bar and ball on downthrown block -b— Strike and dip of overturned beds F —L Detachment fault Cross section B-B’: I. The beds were bowed up but not overturned. Only the west flank of the fold is shown. II. Upon partial removal of the salt core (not shown), the fold collapsed between two high-angle faults (only the faults that are part of the west fault zone are shown), and the crest of the fold dropped down against vertical to steeply tilted beds of the relatively upthrown limb. III. After erosion, beds of the Colton Formation (Tc) (of the downthrown limb) are preserved, juxtaposed along one of the west faults, against vertical beds of the Flagstaff Limestone (Tf). In this area, then, the Flagstaff Limestone (Tf) is both overlain and underlain by the Colton Formation (Tc). Cross section C—C’: I. The beds were bowed up and folded back. Only the west flank of the fold is shown. II. Upon partial removal of the salt core (not shown), the fold collapsed along a high-angle fault and the overturned limb of the fold dropped down against vertical to overturned beds of the relatively upthrown limb. III. After erosion, overturned beds of the Colton Formation (Tc) are preserved, juxtaposed by a fault, against steeply dipping to vertical beds of the Flagstaff Limestone (Tf). In this area, the Colton Formation (Tc) (east of the high-angle fault) is both overlain and underlain by the Flagstaff Limestone (Tf). A photograph of this area, fig. 268, shows these units as viewed from the north (so that, in essence, the View is reversed). 60 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH Cuesta north of Willow Creek road—north end (Cross section A—A ') Cuesta north of Willow Creek road—central part (Cross section B-B ’) \ \\\\ ~_~.-\\\\\ \\\ \\\ \\\\\\ ,, :, Tums omitted for : cartographic purposes Proposed fault Proposed fault— max Proposed fault /// 5,,,/,/, ////// -/////////// Units Qmittfld tor \m ,, ricfimgtflfihlé'purposes I Units omitted for cartographic purposes ii Unltsamittad for Faflpamphle rrpurposes T138} ll lll FIGURE 27 (above and facing column)—Continued.—How the ancestral Willow Creek area may have evolved. Cuesta south of Willow Creek road (Cross section C-C’) DIAPIRIC STRUCTURES 61 NW SE l NW SE 11 NW C C , SE 0ch FEET T(Tch) l TUB) Ill WEST EAST FIGURE 28.——Deformed gravels exposed along east shore of Gunni- son Reservoir. Near-vertical gravels of late Tertiary(?) age are truncated and overlain by near-horizontal gravels of Holocene(?) age. It seems likely that the older gravels were bowed up into their present position when salt in the underlying Arapien Shale welled upward. Outcrop is viewed by eminent U.S. Geo- logical Survey geologist C.B. Hunt, who has mapped extensive areas throughout Utah. flank of the mountains, supports the existence of this fold (Witkind and Page, 1984). GEOLOGIC SETTING COMPLEX STRUCTURAL REIATIONS An eastward-facing monocline extends all along the northeast and east flank of the Valley Mountains. Downwarped beds of the Flagstaff Limestone express the general configuration of the monocline. Locally, 62 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH WEST .EASTk Overturned beds of Indianola Group WéStward-dipping beds of Price River and North Horn Formations EAST . ‘23 Green River(?) ‘ Formation : l. -: FIGURE 29.—Exposures along northeast flank of the Valley Mountains near Yuba Dam. A, Eastward-dipping, overturned beds of the Indianola Group. Locally these beds are vertical or right-side—up and dip steeply to the south and southwest. Price River strata, exposed on distant hillside behind geologist, dip moderately westward and unconformably overlie the overturned Indianola. B, Beds of the Green River(?) Formation are downthrown along a high-angle normal fault and juxtaposed against overturned to steeply dipping beds of the Indianola Group. U, relatively upthrown block; D, relatively downthrown block. these downwarped beds are overlain conformably by younger strata, chiefly units of the Colton, Green River, and Crazy Hollow Formations. Near Yuba Dam, the monocline has been breached for a length of almost 8 km (5 mi), with the breached area extending from the N1/2 sec. 8, T. 17 S., R. 1 W. on the north, to C sec. 29, T. 17 S., R. 1 W. on the south. The strata exposed in the breached area, rather than conforming in attitude to the downwarped beds that form the monocline, are tilted at unusual and vary- ing angles. So, for example, the basal beds exposed, part of the Indianola Group, are vertical or over- turned, and strike between N. 10° W. and N. 20° W (fig. 29A). Unconformably overlying these Indianola beds is a sequence of Price River and North Horn strata that dips gently to moderately westward (toward the mountains) (fig. 29A). In this area, thus, two striking angular unconformities break the strati- graphic sequence: an older unconformity between the vertical Indianola and the inclined Price River and North Horn sequence, and a younger unconformity between the upturned Price River and North Horn sequence and the downwarped Flagstaff Limestone that forms the monoclinal slope. Much the same stratigraphic relations can be seen in the Sixmile Canyon (F—4) area (along the east side of Sanpete Valley) exposed in a breached sector of the Wasatch monocline. Along the northeast flank of the Valley Mountains, near Yuba Dam, beds of the North Horn, Flagstaff, Colton, and Green River are downthrown along a high-angle normal fault, against the overturned Indianola strata (figs. 293, 30). These downthrown units are much disrupted, and most dip at various angles both into and away from the fault. In a few places, where exposures are good, Green River(?) DIAPIRIC STRUCTURES 63 beds dip northeastward away from the fault at about 35°. Locally, these Green River(?) beds are overlain by light-gray and pale-red mudstones and shaly silt- stones that I correlate with the Colton Formation, and that Prof. J.L. Baer of Brigham Young Univer- sity has stated are indurated surficial deposits of Pliocene or Pleistocene age (oral commun., 1980). If these varicolored mudstones and siltstones are part of the Colton Formation, the Green River beds must be overturned (first alternative, fig. 30). If the mud- stones and siltstones are surficial deposits, as suggested by Prof. Baer, the Green River beds are probably right-side-up (second alternative, fig. 30). Conclusive evidence to resolve this problem was not found. These varicolored beds have also been consid- ered to be part of the Arapien Shale (D.A. Sprinkel, Placid Oil Company, oral commun., 1983). I interpret these exposures to mean that at some time after deposition of the Crazy Hollow Formation (of Eocene age) the Sevier Bridge Reservoir salt diapir reactivated and bowed up the overlying strata to form a diapiric fold. Subsequently, dissolution of salt caused the crestal part of the fold to fail along high-angle normal faults that developed along the flanks of the fold. As a result, the crest of the fold, consisting of the North Horn to Green River sequence, was downthrown and juxtaposed against the Indianola conglomerate beds that form part of the northwest limb of the fold. This interpretation satisfies both alternatives offered in figure 30; the amount of downthrow determines which part of the folded limb of the fold abuts the Indianola. ANOMAmus DEPOSITIONAI. THINNING Sedimentary units exposed in and near this breached sector of the Valley Mountains monocline are anomalously thin. So, for example, near the north end of the breached area, in the center of sec. 8, T. 17 S., R. 1 W., the North Horn Formation is about 38 m (125 ft) thick, the Flagstaff but 11 m (37 ft), the Col- ton only 61 m (200 ft), and the Green River Forma- tion but 35 m (115 ft) thick. I interpret this sector as being adjacent to the crest of the fold. As one moves away from the crestal part of the fold, the units increase in thickness rapidly. Thus, some 600 m (2,000 ft) away, still in the southwest quarter of sec- tion 8, the North Horn is in excess of 100 meters thick (its actual thickness is uncertain because its base is concealed beneath debris), the Flagstaff has increased in thickness to 49 m (162 ft), the Colton is about 83 m (270 ft) thick, and the Green River is about 95 m (310 ft) thick. Although exposures are poor and stratigraphic control is uncertain, I believe that the lower—the older—parts of the units pinch out, and only the upper—and younger—parts of the units are preserved. This depositional thinning, of not one but a sequence of units, must reflect the imperceptible, continuous upward movement of an active diapir. The anomalous thinness of the sedimentary units suggests that this part of the southwest flank of the fold is close to the crest of the concealed fold. The fact that many sedimentary formations thin implies that a dynamic, ancestral topographic high was slowly rising as the sediments that form these forma- tions were being deposited. Were the high not active, but rather a static buried hill, only one or two of the lowermost formations would thin or pinch out against the flanks of the hill. Once the hill was bur- ied, younger formations would pass over the buried hill with their thicknesses unchanged. Possibly, most of the sediments that now form the basal and middle parts of any one formation were deposited against the flanks of this rising dynamic high; only those sediments that now make up the upper part of that specific formation were able to surmount the rising high. This suggests several alternative interpretations: (1) the diapir rose at dif- ferent rates during its growth, (2) sedimentation rates differed from time to time, or (3) some combina- tion of the first two alternatives. I favor the third interpretation, in which changes in rate of both dia- piric growth and sedimentation are responsible for this thinning of sedimentary units near the crestal part of the fold. Thus, I attribute both the structural complexity and the depositional thinning to the recurrent reacti- vation of a major diapiric fold, one that lay directly east of the monocline. I refer to this fold as the Sevier Bridge Reservoir diapiric fold. Presumably, recurrent upward surges of the salt—part of the core of the dia- piric fold—repeatedly deformed the Indianola and overlying beds; subsequent removal of the salt from the concealed diapir resulted in differential subsid- ence of the overlying younger consolidated sedimen- tary units to form the monocline (Witkind and Page, 1984, p. 147—156). In this interpretation, the bulk of the fold underlies the pediment mantle that fringes the mountains and that extends northeastward toward the southwest shore of the reservoir (fig. 30). RED CANYON AREA (VALLEY MOUNTAINS) Red Canyon (E—2), near the south end of the breached area, trends about N. 70° E. as a deep, narrow gorge. The mouth of the canyon, in C see. 29, T. 17 S., R. 1 W, exposes older rocks whose attitudes SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°59’ : 0039 / T173 1 KILDMETEH 0 1/2 MILE FIGURE 30 (above and facing page).—Geology of north- east flank of Valley Mountains, and diagrammatic sketches suggesting how the southwest flank of the Sevier Bridge Reservoir diapiric fold may have grown and then collapsed during the third diapiric episode (late(?) Oligocene—Pliocene). Base modified from US. Geological Survey 1224,000 Hells Kitchen Canyon SW (1965). Contour interval 200 ft. Two alternative explanations are offered reflecting my uncertainty as to whether downthrown beds east of the northwest-trending fault are overturned or right-side—up. I favor the first alternative (that shown on the geologic map)—that a small patch of light-gray and pale-red mudstones above the Green River For- mation is part of the Colton Formation. This implies that the beds east of the fault are overturned. First alternative—beds are overturned: 1. Late(?) Oligocene intrusive stage. Renewed move- ment of the northwest-trending Sevier Bridge Reser- voir salt diapir forced the mudstones of the Arapien Shale (not shown) to raise and fold back the overlying sedimentary strata and so form a fan-shaped fold. Sec- tion is drawn across part of the southwest limb of the fold. EXPLANATION Quaternary 2 QUATERNARY Pliocene(?) Pediment mantle Crazy Hollow Formation V E . Green River Formation Eocene > TERTIARY Colton Formation Flagstaff Limestone Paleocene North Horn Formation . U C t > CRETACE Price River Formation pper re aceous OUS cup 4 Contact—Approximately located or inferred —L-—- F auIt—Bar and ball on downthrown block; barb shows downthrown block in cross section; dashed in cross section where reconstructed 20 above eroded surface -—L Strike and dip of inclined beds —i— Strike and dip of vertical beds 45 —d— Strike and dip of overturned beds 11. Late(?) Oligocene—Pliocene(?) erosional stage. Upon removal of the salt core (not shown) the fold collapsed and the overturned limb of the fold was downthrown along a high-angle fault. 111. Cross section A—A’ . Erosion has removed much of the collapsed fold leaving the overturned, down-thrown beds of the Green River Formation (east of the fault) juxtaposed against the vertical to overturned beds of the Indianola Group (west of the fault). Second alternative—beds are not overturned: 1. Late(?) Oligocene intrusive stage. It is assumed, in this interpretation, that the crest of the fan-shaped fold, formed by the intrusive action of the Arapien Shale (not shown) is flattened and flexed into an un- dulatory pattern. Section is drawn across part of the southwest limb of the fold. II. Late(?) Oligocene—Pliocene(?) erosional stage. As the fold collapsed, due to removal of salt, the crest of the fold was downthrown along a high-angle fault. Amount of stratigraphic throw postulated is greater than that shown in first alternative. III. Cross section A—A’. Erosion has removed much of the collapsed fold, leaving the right-side-up, downthrown beds of the Green River Formation (east of the fault) jux- taposed against the vertical to overturned beds of the In- dianola Group (west of the fault). DIAPIRIC STRUCTURES First alternative—beds are overturned Second alternative—beds are not overturned «93.35% m' p * . “V. ' «A»; 66 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH FIGURE 31 (above and facing page).—Exposures near the mouth of Red Canyon, Valley Mountains. A, View southward of exposures near mouth of Red Canyon. I interpret these exposures to be part of the west flank of the Sevier Bridge Reservoir diapiric fold formed above a salt diapir concealed to east (left) beneath Sevier Valley. B, Sketch of View A. Indianola strata dip steeply westward (right). These are unconform- ably overlain by a Price River and North Horn se- quence that also dips westward but at much lower dips. The North Horn, in turn, is unconformably overlain by Flagstaff Limestone that dips gently eastward (left) to form part of the Valley Mountains monocline. Long-dashed lines represent approximate attitude of bedding planes. Just to south, beyond area shown in this photograph, the deformed older mimic those found elsewhere within the breached sector of the monocline. So, the Indianola beds are near vertical, and these are overlain with profound angular unconformity by Price River beds that dip westward (toward the mountains) at about 15°. North Horn strata overlie the Price River beds con- formably, and this westward-dipping Price River and North Horn sequence is truncated by the down- warped eastward-dipping Flagstaff Limestone to form a second, younger angular unconformity (fig. 31). Here, too, all strata are remarkably thin at the mouth of Red Canyon, near the crest of the postu- lated Sevier Bridge Reservoir diapiric fold, but they thicken rapidly to the west. The North Horn Forma- tion, for example, is about 15 m (50 ft) thick near the rocks (Indianola, Price River, and North Horn) are concealed beneath an unbroken mantle of east- ward-dipping beds of the Flagstaff Limestone that define the Valley Mountains monocline. Compare this photograph with the sketch in fig- ure 21, of an area near the mouth of Sixmile Creek canyon along the west flank of the Wasatch Pla- teau, some 20 km (12 mi) to the east. In both pho- tograph and sketch, steeply upturned beds of the Indianola Group are unconformably overlain by a Price River and North Horn sequence, which dips toward the mountains. This sequence, in turn, is unconformably overlain by downwarped beds of the Flagstaff Limestone, which dip valleyward—toward the causative salt diapirs. In both localities, the downwarped Flagstaff defines major monoclines. canyon mouth, but more than 180 m (600 ft) thick 1.15 km (1 mi) to the west near the head of Red Canyon. As shown in figure 32, I interpret the relations in Red Canyon to reflect three episodes of salt diapirism. DISCUSSION FIRST DIAPIRIC EPISODE During the first diapiric episode, Indianola Group and older rocks (KJu), were bowed up and warped into a diapiric fold by the upward surge of a salt diapir contained within the Arapien Shale (K(Ja); sketch II of fig. 32). With removal of salt from the core of the fold, the fold collapsed (the collapsed axial part of the fold DIAPIRIC STRUCTURES 67 EAST West flank of Gunnison Plateau dipping steeply tiwest \ B \ \ \ \ fLandslide debris lv/ \\ \ \\\ North Horn Formation (TKn) \\ \ \\ \\ \ \\ Price River Formation \ _ \ \ \ \\ (Kprl \\\\ \ \\ \\ \ \\\ Beds of lndianola Group (Ki) \\ \\\\ / / // dF The upper plate was further deformed, in the Gardner appears as a northeast-trending syncline (fig. 35)_ In Creek—Birch Creek area, when an intrusive mass of the Arapi- en Shale forced up a small wedge of the Navajo Sandstone (Jn) detall’ those hmeStone beds along the SOUth edge dlp and the overlying Twin Creek Limestone (Jtc) and juxtaposed northward at abOUt 400’ but In one place Where they these units against overturned beds of the Permian and Penn- directly abut the Arapien mudstones, they are over— sylvanian Oquirrh Group (PIPo). As the Navajo and Thin Creek turned and form a tight anticline (fig. 36) that is are fight-side-up, they probably represent part of the lower much like the overturned fold formed along the east plate of the Charlesmn'NebO ttht- . . . . . . I am uncertain when this uplift of the Navajo—Twin Creek margln 0f the north trendlng antlehne 1n Plgeon wedge occurred, but possibly both intrusive events—the defor- Creek (0—3)- AS these north-dipping beds are tracéd mation of the thrust plate and the uplift of the wedge— northward, they lessen 1n dlp and then reverse dlp occurred at the same time, during the second diapiric episode. SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 72 fi‘ $555.32 N m.__s_ D——D 3 $25, egcoayfi V . an; Fain 3 , , ., .samm Km? mm ~31: ‘39—: 73 DIAPIRIC STRUCTURES v.3 “yr—Ema 5.30.— No 8a.: ENE No :ofimon ennui: I IIMIII mum:— vwFStgo No Ev «Em ”Nu—Em ID.» 2.. 32. 12:: No Ev EB ”UN—Em ll 2.2. 3.52.. 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A E mace—01% a I NEED A _ ZOEn—Xm— .| Sam .1 83 . . » 4354. ”V4.2. aw At..»« 7» 6 ;«¢.;«:»:»«4 4 a>>$:,.:f., : 3.. .l 8?. | 8% 0H V :5» a I as (\ qustw>o Em mums __< 1 Sam :32 $25 onwzlcoummtmco EE No 32a 8am: No tan. < (\ _g 313313 AQUPJDQ \ __—__— —;__ JN 9.39:5 otfimfi UBEQD J uocStm>o 9m mums =< :33 «2:5 3021:93sz0 No ENE Nana: No tun. 74 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH and are inclined southward at about 25° where they abut the Arapien mudstones. The northern ’IVvin Creek exposure, also about 0.8 km (0.5 mi) wide, is separated from the southern exposure by about 300 m (1,000 ft) of Arapien mud- stone. This northern exposure is subparallel to and about 1 km (0.7 mi) east of the mountain front (fig. 35). Both the east and west edges of this Twin Creek exposure are in near-vertical fault contact with overturned, northwest-dipping beds of the Oquirrh Group of Permian and Pennsylvanian age. At the north end of this narrow Twin Creek exposure, Birch Creek has cut a deep, narrow canyon and exposed the underlying Navajo Sandstone. This band of Navajo and Twin Creek strata extends for more than 1 km (0.75 mi) north of Birch Creek before it disappears, near Ingram Canyon, beneath Paleozoic FIGURE 36,—Overturned beds of the Twin Creek Limestone as exposed in Gardner Canyon. The Arapien Shale crops out just to the right of beds exposed in this photograph. I believe this fold, much like the overturned fold in Pigeon Creek (fig. 34), is the result of intrusion and upwarp by the Arapien Shale. strata that form part of the Charleston-Nebo thrust plate. The Arapien mudstones exposed in Gardner Can- yon appear to be a northward outcrop of similar Arapien units exposed to the south near Red Canyon, and I interpret both Arapien exposures to be part of the diapiric core of the Levan fold. Although these geologic relations between the Arapien, Twin Creek, and the Oquirrh may represent a window in a folded thrust sheet, much as inter- preted by Black (1965, cross section C—C’), I believe that the steep to near-vertical contacts between the Arapien Shale and the Oquirrh Group, and between the Twin Creek Limestone and the Oquirrh, are more reasonably explained by vertical uplift. Although it is possible that this vertical compression was induced during southeastward-directed emplacement of the Charleston-Nebo thrust plate (Black, 1965, p. 80), the lack of uniformity in the axial trends of the folds formed in the contorted Arapien strata suggests that the compression, more likely, stems from the later, upward vertical movement of the Arapien Shale as it was forced upward by its salt component. Conse- quently, as suggested by cross section A—A’, figure 35, I interpret the Arapien strata to be a plug of the Levan diapiric core that lifted, tilted, and juxtaposed this band of Navajo Sandstone—Twin Creek Lime- stone against overturned Oquirrh strata, part of the main body of the Charleston-Nebo thrust plate. Dur- ing the upward movement, the Arapien broke the Navajo—Twin Creek mass into two parts, and folded the southern part into a syncline. As the Navajo Sandstone and the overlying Twin Creek Limestone are right-side-up and in a normal stratigraphic sequence, rather than being overturned as one might expect if they were a part of the over- turned beds that form the upper plate, this upthrust mass is probably part of the lower plate of the Charleston-Nebo thrust fault. Exposures to the east, near Rees Flat (fig. 35), sup- port the concept that the Arapien Shale has intruded and deformed part of the thrust sheet. As the contact between the overturned beds of the thrust plate and the Arapien mudstones is traced eastward up Red Canyon, the contact eventually disappears beneath a pediment mantle of sand and gravel that floors Rees Flat. The east edge of Rees Flat is bounded, on the north, by overturned rocks of the thrust plate, and on the south, by a small hill formed by upturned con— glomerate and sandstone beds that have been warped to form an irregular-shaped basin. The Arapien Shale underlies these conglomerate beds along the east and south edges of the basin; because of the pediment mantle (fig. 35), I have not identified DIAPIRIC STRUCTURES 75 the unit underlying the conglomerates along the west and north edges of the basin. The basin, although of somewhat irregular shape, is about 1.2 km (3/4 mi) in diameter. The conglomerate beds nearest the thrust plate are vertical or overturned; those along the east flank of the basin dip westward, even as those along the south flank dip northward. In the past, Johnson (1959) assigned the reddish-brown conglomerate and sandstone beds that form the basin to the Price River Formation; subsequently, Black (1965) assigned them to the Indianola Group; and still later I (1983) also assigned them to the Indianola Group. Biek ( 1988b), however, has decided that the beds in question are part of the Cedar Mountain Formation. Whether the beds are Indianola or Cedar Mountain stems from uncertainty as to just what units should be included in the Cedar Mountain Formation. Wit- kind, Standlee, and Maley (1986, p. 4), studying exposures in the Red Rocks area, along the southeast flank of the Gunnison Plateau, included two units in the Cedar Mountain Formation: “* * *an upper unit that consists primarily of beds of reddish—brown coarse conglomerate, and a lower unit that consists of variegated mudstone* * *.” As the upper conglom- eratic unit is much like the conglomerate beds that make up the bulk of the Indianola Group, the two units are difficult to separate. Co-authors Witkind and Maley (in Witkind, Standlee, and Maley, 1986, p. 5), influenced by the fact that the change from mudstone to conglomerate is an easily recognizable contact, proposed that the “* * *upper unit be provi- sionally assigned to the undivided Indianola Group.” For mapping purposes, therefore, I have considered the upper conglomeratic unit to be part of the Indi- anola. Biek (1988b), however, included both the con- glomerate and mudstone units in his Cedar Mountain Formation. In figure 35 I show the beds as Indianola but add a query to reflect my uncertainty as to the correct assignment of these conglomerate beds. I suspect that the basin is encircled and underlain by the Arapien Shale with much of the Arapien concealed beneath the surficial deposits that form the floor of Rees Flat (Witkind and Weiss, 1991). It is pos- sible that some of the deformation of the north end of the basin is attributable to the southeastward- directed movement of the Charleston-Nebo thrust plate, with some deformation due to the upward thrust of the Arapien. The vertical to overturned beds that mark the north edge of the basin imply that a strip of Arapien, confined between the edge of the thrust plate and the once near-horizontal Indianola(?) beds, pushed up and bowed back the Indianola(?) beds. The westward dip of the beds that form the east edge of the basin probably reflect the west flank of the Footes Canyon diapiric fold, one of the three folds formed when the Levan fold trifurcated. If this deformation of the basin is due, in part, to vertical uplift of the Arapien Shale as well as to eastward movement of the thrust plate (Black, 1965, p. 80), the mudstones of the Arapien not only under- lie the basin but also underlie the toe of the thrust plate. By their upward movement the Arapien mudstones may have bowed up part of the plate even as they deformed the basin (east half of cross section A—A’, fig. 35). RED CANYON AREA (SOUTHERN WASATCH RANGE) Basal thrust plate strata are exposed in and near Red Canyon (B—3) where overturned beds of the Twin Creek Limestone, part of the thrust plate, rest on contorted mudstones of the Arapien Shale. These mudstones and their contained evaporites are severely deformed and give every sign of intense compression. Near the mouth of Red Canyon, the Twin Creek beds that directly overlie the Arapien Shale mudstones are overturned and dip northwest- ward (45°), thus conforming to the attitude of the overlying (stratigraphically older) strata. As these 'IVvin Creek beds are traced northeastward along strike they become vertical, and then right-side—up and dip 80° SE. (fig. 37). It is much as if vertical upward movement of the Arapien Shale has pushed up the overturned beds and bowed them back into their normal right-side-up sequence. SKINNER Prams AREA The extent of the Levan fold south of Little Salt Creek is speculative, being based chiefly on sparse outcrops of the Arapien Shale, and on the develop- ment of the westward-facing West Gunnison mono- cline. Near Skinner Peaks (D—3), about 6 km (31/2 mi) south of Little Salt Creek, the Arapien Shale crops out beneath westward-dipping (20°) volcanic rocks, part of the Goldens Ranch and Moroni Formations (Witkind and Marvin, 1989). I attribute this west- ward dip of the volcanic rocks to the upward move- ment of the underlying Arapien Shale. As these Arapien exposures are directly south of and collinear with those Arapien beds that crop out at Little Salt Creek, it seems reasonable to conclude that all are part of the core of the Levan diapiric fold. Witkind and Marvin (1989), using potassium-argon techniques, have dated these volcanic rocks as having been formed during an interval that extended 76 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH FIGURE 37.——View eastward along south wall of Red Canyon show- ing Twin Creek Limestone dipping steeply to the southeast. Mudstones, which I interpret to be part of the Arapien Shale, are exposed to the right of this view. The rocks exposed along Red Canyon are part of the upper plate of the Charleston-Nebo thrust fault, which in central Utah appears as the lower limb of an overturned anticline. As a result, all strata are overturned and dip moderately to the northwest. In this specific locality, however, near the edge of the thrust plate, the beds of the 'IVvin Creek are right-side-up and dip steeply to the southeast, exactly opposite to the dips of all other units in the area. I interpret these relations to mean that the adjacent Arapien mudstones, part of the Levan diapiric fold, have locally bowed up and flexed back the formerly overturned beds of the 'IVvin Creek Limestone, which once dipped northWest, so they now appear right-side-up dipping to the southeast. from the late Eocene to the middle Oligocene. If the volcanics were indeed tilted as a result of upward movement of the Arapien, as I propose, then that movement must have occurred at some time after the middle Oligocene, long after the compressive events of the Sevier orogeny ended at the close of the Paleocene. Mattox and Weiss (1987, p. 60), studying the southwest flank of the Gunnison Plateau, directly south of Skinner Peaks, have stated that salt diapir- ism has not “played a major role in the structural development of the study area.” To support their con- tention they noted that Indianola beds east of and adjacent to the Chriss—Mellor graben dip gently east- ward (Mattox, 1987) rather than being vertical or overturned as one might expect next to a diapiric upwarp. Seemingly, Mattox and Weiss have failed to grasp Witkind and Page’s (1984) suggested explana- tion of the relations between salt diapirs and the monoclines in the Sanpete—Sevier Valley area. Wit- kind and Page proposed that partial removal of salt from a causative salt diapir resulted in subsidence of the overlying sedimentary beds to form a monocline. The causative diapir, thus, is at the toe—the distal end—of the downwarp. The large north-trending Chriss—Mellor graben of Mattox and Weiss (1987), which breaks the flank of the West Gunnison mono- cline, is at least 3 km (2 mi) east of the crest of the Levan diapir. One would not expect vertical or over- turned beds this distant from the diapir. Mattox and Weiss (1987, p. 58) described a distinc- tive thinning and pinch-out of the North Horn For— mation along the southwest flank of the Gunnison Plateau and attributed it to the gradual uplift of a topographic and structural high west of one of the major faults—the Escarpment fault—in their area (1987, p. 60). I propose an alternative interpretation, that this thinning of the North Horn Formation is much like the depositional thinning that marks the various diapiric folds throughout the area (p. 107). If so, it strongly suggests that salt diapirism has played a significant role in this sector of the Gunnison Plateau. The westward-facing position of the West Gunnison monocline implies that the crest of the Levan diapiric fold is concealed beneath those surficial deposits that fringe the west flank of the Gunnison Plateau. In many respects, the north-trending Chriss- Mellor graben is similar to the many north— and northeast-trending grabens that break the west flank and crest of the Wasatch Plateau. These gra— bens appear to be salt derived; seismic reflection profiles across the Wasatch Plateau suggest strongly that the faults that bound the grabens do not extend below Jurassic strata, in essence, below Arapien and below Carmel beds. The implication is strong that dissolution of bedded salt resulted in t+e development of those grabens. DIAPIRIC STRUCTURES 77 POLE CREEK DIAPIRIC FOLD GEOLOGIC SETTING The Pole Creek diapiric fold (fig. 16, 12) extends northeastward from near the north end of the Gunni- son Plateau (D—3), where the Levan fold trifurcates, to its disappearance beneath young volcanic rocks, some 11 km (7 mi) away, near the head of the Middle Fork Pole Creek (B—4) (fig. 38). KOA C.-\MP(;R()L'NI) AREA About 8 km (5 mi) east of Nephi (B—3), where the scenic Nebo Loop Road joins State Highway 132 (near a KOA Campground (C—3)), amorphous, earthy, reddish-brown Arapien mudstones crop out between extensive exposures of volcaniclastic rocks (southwest corner of area shown in fig. 38). Where these volcani- clastics, part of the Moroni Formation of late Eocene to middle Oligocene age, overlie the northwest flank of the Arapien exposures, they dip about 25° NW; where they overlie the southeast flank they dip southeastward about 30°. About 1.6 km (1 mi) north- east of the aforementioned road junction, Indianola conglomerates, unconformably underlying the volca- niclastic rocks and overlying the Arapien Shale, crop out along the west valley wall of Pole Creek. The conglomerates dip about 60° NW. Directly across the valley, which is floored with alluvium but is most likely underlain by the Arapien Shale, comparable Indianola beds, also unconformably interleaved between the volcaniclastics and the Arapien Shale, are vertical or dip steeply to the southeast. Thus, both Moroni and Indianola units unconformably over- lie and dip away from the Arapien exposures. In places, these Moroni volcaniclastics are overlain unconformably by semiconsolidated sands, gravels, and boulders of the Salt Creek Fanglomerate (Eard- ley, 1933a), which also dip away from the Arapien exposures but not as steeply as the underlying volca- niclastics. I interpret the Arapien beds to be the crest of the diapiric core of the northeast-trending Pole Creek fold, and the upturned beds that flank the Arapien exposures to be segments of the upturned flanks of the fold. From the road junction, the crest of the fold trends about N. 45° E. and can be traced into the Middle Fork Pole Creek (fig. 39A). The fact that units of the Indianola Group, the Moroni Formation, and the Salt Creek Fanglomerate conform in direction of dip but differ greatly in amounts of dip implies several episodes of deforma- tion. Presumably, one episode occurred after the Indi- anola beds (of Late Cretaceous age) were consolidated; a second deformational episode must have occurred after the volcaniclastic sediments (of mid-Tertiary age) were emplaced and partly consolidated, and a third occurred during early(?) Quaternary time, at some time after the Salt Creek Fanglomerate was formed. As shown in cross section A—A’ (center) of figure 38, I propose that the units commonly present between the Arapien and the Indianola—the 'I\Nist Gulch and Cedar Mountain Formations—pinch out against the flanks of the diapiric core. Farther to the northeast, in the Middle Fork Pole Creek, both the Twist Gulch and the Cedar Mountain Formations are exposed between the Arapien and the Indianola but as extremely thin remnants. MIDDLE FORK POLE CREEK The core of the Pole Creek fold and the sedimen- tary rocks that form its southeast flank crop out in the Middle Fork Pole Creek (fig. 39A). Best expo- sures are in C sec. 13, T. 12 S., R. 2 E. The Arapien Shale, part of the core of the fold, forms the north- west bank of Middle Fork; vertical units of the Twist Gulch are exposed in the narrow stream bottom (fig. 393, C), and Cedar Mountain beds form the eastern streatm bank. The Twist Gulch and Cedar Mountain Formations are extremely thin; determining their exact thicknesses is difficult, for much of the area is mantled with colluvium and shrubs. I estimate the Twist Gulch to be about 60 m (200 ft) thick, and the Cedar Mountain to be about 250 m (800 ft) thick. Elsewhere in the Sanpete—Sevier Valley area, the Twist Gulch is about 915 m (3,000 ft), and the Cedar Mountain about 550 m (1,800 ft) thick. These exposures in the Middle Fork Pole Creek are flanked on the southeast by beds of the Indianola Group that are vertical, or dip steeply southeast- ward. To the northwest these Middle Fork exposures are flanked by volcanic beds of the Moroni Formation FIGURE 38 (following pages).—Geology across Pole Creek—Hop Creek area, Cedar Hills. Base modified from U.S. Geological Survey 1:100,000 Nephi (1981). Contour interval 250 m. The broad geologic pattern of the Cedar Hills has been determined by the Pole Creek diapiric fold, whose crest on this map is delineat- ed by a dashed line. The fold trends approximately N. 45° E. through the area, and probably joins the Dry Hollow diapiric fold (fig. 16, 10). Arapien mudstones are exposed beneath volcaniclas- tic sediments at the stream junction shown in the lower left corner of the map, and in Middle Fork Pole Creek. Strata west of the Arapien exposures dip westward, strata east of those expo- sures dip eastward. Crest of the fold is well exposed in Middle Fork Pole Creek. (See fig. 39.) 78 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 4 111% 39°45'- T128 T138 1 2 3 j 5 ? KILUMETEHS ,\ D—— o A METERS 3000 — A I METERS — 3000 ‘ Middle Fork Pole Creek Hop Creek Ridge Mount Baldy Bear Canyon TKn —I 7: 2 _. _. .1 3 _. o | N g a Ki 1 g Hop Creek 1 4000- DIAPIRIC STRUCTURES EXPLANATION Alluvium Alluvial fan deposits _- 7 . Coalesced alluvial- fan deposits Pediment deposits Dike Moroni Formation Colton Formation Flagstaff Formation North Horn Formation Price River Formation lndianola Group Mancos Shale Cedar Mountain Formation Twist Gulch Formation Arapien Shale Arapien Shale Twin Creek Limestone Nugget Sandstone _, NA ”I‘fia‘v ‘3“ . Ankareh Formation Triassic strata, undivided Park City Formation Diamond Creek Sandstone and Kirkman Limestone a PIPow Oquirrh Group Contact—Approximately located or inferred —-—-— Intrusive contact—Approximately located or inferred; oblongs on intrusive unit —-—l— Fault—Dotted where concealed; bar and ball on downthrown block -A—A—A- High-angle reverse fault—Dashed where approximately located; queried where uncertain: sawteeth on upthrown plate; barb shows upthrown plate in cross section a? {:1 ‘ *2 Q ’ | Earthflow deposits ? 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The detailed evidence, involving the deformation of the Charleston-Nebo plate, is summarized elsewhere in this report (p. 104~107). DRY HOLLOW DIAPIRIC FOLD Vertical to overturned beds of the Indianola Group, striking about N. 40° E., crop out southeast of Thistle (A—5) in a deep canyon known as Dry Hollow (A—5) (fig. 41). The canyon, tributary to northwest-flowing Lake Fork (A~5), trends northeastward, its course seemingly determined by the strike of the steeply dipping Indianola beds. These vertical to near-vertical strata are overlain with striking angular unconfor- mity by gently dipping reddish-brown conglomerate, sandstone, and mudstone beds of the North Horn For- mation (fig. 42). North Horn beds that overlie the northwest flank of the fold dip northwestward at about 25°; those that overlie the southeast flank dip southeastward at about 10°. These exposures represent the crest and flanks of the northeast-trending Dry Hollow diapiric fold (fig. 16, 10), of which only part crops out in Dry Hollow. The fold extends to the northeast across both Lake Fork and Soldier Creek (A—5) and passes below inclined North Horn beds exposed along the north valley wall of Soldier Creek. On the basis of these limited exposures the fold trends about N. 40° E. for some 6 km (4 mi), reaching from the head of Dry Hollow to the north wall of Soldier Creek Canyon. The extent of the fold to the southwest is uncertain; it may connect with the Pole Creek fold (fig. 16, 12). North Horn and Flagstaff strata near the upturned Indianola beds are unusually thin compared to their thicknesses elsewhere in the area. As shown in figure 43, I interpret these exposures to represent deformation of part of the Charleston- Nebo thrust plate by a rising mass of the Arapien Shale. The thrust plate—the lower limb of an anti- cline—overrode a mass of the Arapien Shale, proba- bly during the Late Cretaceous (fig. 43, I). Subsequently, Arapien Shale, forced upward by slowly upwelling salt, bowed up the thrust plate to form a paleo-high that restricted deposition of sedi- ments (fig. 43, II). Price River sediments, deposited against the flanks of this rising high, locally pinch out (fig. 43, III). Younger sediments, such as the North Horn and Flagstaff Formations, both pinch out against the flanks of the high and locally bury it. The Arapien probably continued to rise until well into the Tertiary, judging by the fact that volcanic units tentatively dated as late Eocene to middle Oligocene have been deformed along with the underlying sedi- mentary rocks. At some time after the upward move- ment of the rising Arapien ceased, erosion removed the volcanic cover as well as many of the underlying younger Tertiary sedimentary units. In time, erosion effectively breached the crest of the rising high to expose the vertical and overturned Indianola beds of the thrust plate (fig. 43, IV). In several other areas where diapiric folds are exposed, erosion has been extensive enough to break through those sedimentary units that form the crest of the fold and expose the Arapien core. Seemingly, erosion has not been as extensive in the Dry Hollow area, and the upturned Indianola beds have not, as yet, been completely breached to expose the Arapien core (cross section A—A’, fig. 41). THISTLE CREEK DIAPIRIC(P) FOLD The Thistle area (A—5), some 40 km (25 mi) south- east of Provo, is perhaps best known for the disas- trous landslide of April 1983 that effectively blocked the major road and rail connections between Price, east of the Wasatch Plateau, and Provo, west of the plateau. Geologic aspects of the slide, its multiple impacts on the economic life of central Utah, and the potential geologic hazards near the slide have been described and discussed elsewhere (Duncan, Fleming, and Patton, 1986; Kaliser and Fleming, 1986; Wit- kind, 1986; Willis, 1987). GEOLOGIC SE'I'I‘ING In the Thistle area, arched Cretaceous and Tertiary strata overlie the Charleston-Nebo thrust plate and suggest the presence of a diapiric fold (fig. 16, 11; cross section A—A’, fig. 44). Two major elements dominate the geologic frame- work of the Thistle area: the eroded east margin of the major Charleston-Nebo thrust plate, and a sequence of younger Cretaceous and Tertiary sedi- mentary and volcanic rocks that unconformably over- lies and partly buries the thrust plate. CHARLESTON—NEBO THRUST PLATE The basic elements of the Charleston-Nebo thrust plate have been described on pages 8 to 9. In the Thistle area, the easternmost exposed rocks of the thrust plate form a high ridge that trends slightly east of north. It is unclear whether this ridge is at the distal margin of the thrust plate (fig. 4A) or 84 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH whether the distal margin is farther east buried beneath younger strata (fig. 43). If the latter, the plate margin in the Thistle area is an erosional escarpment cut on the thrust plate (fig. 43). Because of uncertainty as to which of these two alternatives is correct, I refer to this eastern part of the thrust plate as an “erosional escarpment,” and delineate it on figure 44 by hachures. Spanish Fork River and its tributaries, west- flowing Soldier Creek (A—5) and north-flowing Thistle Creek (A—4), have cut a deep canyon, shaped some- what like a T on its side, through the ridge. That part of the ridge north of the confluence of Soldier and Thistle Creeks is unnamed; in the past, crews involved in the construction of Thistle dam and the new segment of US. Highway 6 and 89 incorrectly called it “Billies Mountain,” but in fact, Billies Moun- tain is some 3 km (2 mi) to the northeast. Continued incorrect usage, however, has transferred the name Billies Mountain to the north part of the ridge, and in this report I follow that custom but alert the reader to this misusage by placing the name in quotes, thus, “Billies Mountain.” In the Thistle area, the rocks in the thrust plate range in age from Pennsylvanian to Jurassic (table 2). Most of them dip eastward at moderate to high angles; in the ridge, along the eastern part of the thrust plate, Navajo (Jn on the map) and Twin Creek (Jtc) strata dip eastward at about 60°. Farther west, toward the main mass of the thrust plate, succes- sively older strata dip east but at about 40°. SEDIMENTARY SEQUENCE OF YOUNGER ROCKS The deeply eroded plate is partly buried by younger sedimentary rocks of Late Cretaceous to Eocene age. Locally, these rocks are mantled by pyro- clastic volcanic rocks of the Moroni Formation (late Eocene to middle Oligocene). East of the erosional escarpment, the younger sedimentary and volcanic rocks dip eastward at low to moderate angles (10°— 30°). By contrast, the same strata west of the escarp- ment dip westward at moderate angles (fig. 45A). Wherever exposed, these younger sedimentary and volcanic rocks unconformably overlie the eastward- dipping rocks of the thrust plate. These younger sedimentary rocks thin markedly toward the erosional escarpment. This is perhaps best shown in a diagram prepared by Young (1976, fig. 5), which shows a westward thinning of all strata, extending from the North Horn to the Green River Formation. STRATA NORTH OF SPANISH FORK CANYON (“BILLIES MOUNTAIN” AREA) Most of these younger Cretaceous and Tertiary strata are well exposed where they mantle the thrust 2 KILOMETEHS \ 3 2 T: I t o 0 1 MILE SE AI FIGURE 41 (above and facing page).—Geology of Dry Hollow area. Base modified from US. Geological Survey 1:24,000 Thistle (1967). Contour interval 200 ft. In Dry Hollow, which follows the crest of the Dry Hollow diapiric fold, vertical beds of the Indianola Group, possibly part of the Charleston-Nebo thrust plate, pass below and unconformably underlie beds of the North Horn Formation. North Horn strata east of the crest of the fold dip gently eastward; similar strata west of the fold’s crest dip gently westward. Near the west edge of the map area these westward-dipping North Horn strata abruptly reverse dip and dip eastward, reflecting a small intrusive mass of Arapien Shale. DIAPIRIC STRUCTURES 85 EXPLANATION Colluvium and Alluvium .. f [ 09“) H°1°Cene QUATERNARY Landslide and m: 0" Pleistocene 7 mass_wasflng Alluvial- fan deposits earthflow deposits Sand and Pliocene deposits (locally coalesced) gravel deposits 1‘ Valley— l ill Pediment deposits mantle Green River Formation Eocene > TERTIARY and Colton Formation Flagstaff Limestone Paleocene North Florn ormation Upper Cretaceous P CRETACEOUS } Lower Cedar Mountain Formation CretaceousJ Twist Gulch Formation Middle Arapien Shale Jurassic JURASSIC Arapien Shale " Twin Creek Limestone Lower Navajo Sandstone }Jurassic Contact—Approximately located or inferred; dashed and (or) queried in cross section to reflect speculative relations _—-— lntrusive sedimentary contact—Approximately located or inferred; oblongs on intrusive unit ——g F ault—Dashed where approximately located; dotted where concealed; bar and ball on downthrown block plate south and west of Spanish Fork Canyon, but they have largely been eroded from much of the thrust plate north and east of the canyon. Some units do crop out north of the canyon as a series of eastward-dipping strata that lap onto the east mar- gin of the plate. This general pattern of eastward-dipping strata is interrupted, however, north of Soldier Creek directly east of “Billies Mountain.” There, the Flagstaff Lime- stone (Tf) abuts the east flank of “Billies Mountain” at an eastward dip of about 20° (fig. 44). About 150 m (500 ft) east of the ridge, the Flagstaff gradually flattens, and then reverses and dips moderately to steeply westward; locally these strata are almost vertical (fig. 453). Although the Flagstaff Limestone —‘— Strike and dip of inclined beds —l— Strike and dip of vertical beds Zé— Strike and dip of overturned beds U Angular uncontormity is underlain by the North Horn Formation through- out most of central Utah (table 1), in this specific locality the near-vertical beds of the Flagstaff are underlain by the Arapien Shale. These Arapien strata, chiefly calcareous mudstones, are severely contorted and broken. The deformed Arapien strata, and the relations between the Flagstaff and the Arapien, suggest that the Arapien, driven by its contained salt, has raised and tilted back the Flagstaff Limestone. Elsewhere in this general area, other exposures indicate the intrusive nature of the Arapien. Thus, during excavation, the earth-moving equipment time and again exposed wedgelike masses of Arapien Shale that intrude and deform the steeply tilted beds 86 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH Southeastwardvdipping beds of the North Horn Formation Angular nconformity Vertical beds of the] Indianola Group Div H<\\\OW Figure 42.—View southward near head of Dry Hollow showing an- gular unconformity. Vertical light-gray beds of the Indianola Group unconformably underlie reddish-brown North Horn stra- ta that dip gently southeast. of Twin Creek in the thrust plate (fig. 11A). At the east edge of “Billies Mountain” a dike-like mass of the Arapien separates the Twin Creek strata of the thrust plate from the tilted units of the Colton For- mation that lap onto the erosional escarpment of the plate (fig. 11B). Sills of the Arapien, containing both nodules and masses of gypsum and clasts of the Twin Creek Limestone, intrude the 'I\Nin Creek Limestone (fig. 46). East of “Billies Mountain,” where the steeply tilted beds of Flagstaff Limestone are underlain by the intensely contorted Arapien strata (fig. 458), the deformed Arapien beds pass eastward into noncon- torted but nearly vertical Arapien strata. These Arapien beds are right-side—up and lack the crumpled and contorted aspect of the profoundly disturbed Arapien beds. As these steeply dipping Arapien strata are traced eastward, they seem to conformably underlie the 'IVvist Gulch Formation, which in turn underlies the Cedar Mountain Formation. The unbro- ken progression of beds, in normal stratigraphic sequence east from the disturbed mass of Arapien, implies that the thrust plate extends eastward beyond the erosional escarpment. 'I\vo alternatives are possible: (1) the mass of disturbed Arapien punched up through Arapien beds that were part of the plate, or (2) the disturbed Arapien beds, integral elements of the thrust plate, became mobile and then deformed the overlying strata. Of the two interpreta- tions, I prefer the former: I believe that an underly- ing overridden mass of Arapien Shale punched up and deformed the thrust plate (cross section A—A’, fig. 44). Intrusive fingers of the Arapien invaded both the plate and the adjacent younger strata. In this interpretation, the contorted Arapien strata and the less deformed Arapien beds of the thrust plate are fortuitously juxtaposed. Other examples of Arapien deformation are exposed elsewhere in the general area. So, for exam- ple, a small mass of Arapien Shale (labeled T(Ja) in fig. 44) crops out along the east valley wall of Thistle Creek about 0.8 km (W mi) south of the confluence of Soldier and Thistle Creeks. West of that outcrop, North Horn (TKn) beds dipping eastward, off the ero- sional escarpment cut on the thrust plate, flatten and then reverse attitude to assume a steep westward dip directly adjacent to the west flank of the Arapien exposure. East of the Arapien mass, the North Horn beds dip eastward. These opposing dips in North Horn strata that flank the Arapien lead to the infer- ence that consolidated North Horn strata have been arched by an intrusive mass of the Arapien Shale (cross section A— ’, fig. 44). STRATA SOUTH ANI) WEST OF SPANISH FORK CANYON Younger sedimentary and volcanic rocks mantle parts of the thrust plate exposed south and west of Spanish Fork Canyon. Indeed, detritus from these younger rocks, chiefly the North Horn Formation, FIGURE 43 (facing page).—Diagrammatic sketches suggesting how the Dry Hollow diapiric fold developed. All views are oriented in same compass directions. 1. During the Late Cretaceous, the Charleston-Nebo thrust plate—the lower limb of an overturned anticline—overrode units of the Arapien Shale (K(Ja)). In this schematic cross sec- tion only some of the units that make up the thrust plate are shown. 11. After the thrust plate ground to a halt, the overridden Arapien Shale began to well upward slowly, gradually intruding the plate and bowing it upward. In this sketch erosion has beveled the bowed-up thrust plate to produce a surface of low relief. III. Price River sediments (Kpr) began to be deposited on this surface of low relief. Incessant slow upwelling of the Arapien (T(Ja)) continued to bow up the plate, thus restricting deposition of Price River sediments, which locally pinched out against the flanks of the rising high. The Price River units unconformably overlay units of the thrust plate. In time, North Horn sediments (TKn) were deposited on the Price River sediments, and although some units of the North Horn pinched out against the flanks of the rising high, other North Horn units continued across the high and buried it. Ever younger sediments (repre- senting, at the least, the Flagstaff (Tf), and later the Colton and Green River Formations) were deposited across the rising up- warp, and these units too were bowed up by slow upwelling of the Arapien. IV. At some stage, probably after deposition of an Eocene and Oligocene volcanic mantle, erosion removed many of the young- er volcanic and sedimentary units deposited across the crest of the fold, and exposed part of the bowed-up thrust plate, repre- sented here by near-vertical and overturned Indianola (Ki). DIAPIRIC STRUCTURES WEST EAST WEST EAST Tf EXPLANATION Flagstaff Limestone North Horn Formation Price River Formation lndlanola Group Cedar Mountain Formation Twist Gulch Formation s ’ Arapien Shale Arapien Shale Eocene Paleocene TERTIARY Upper Cretaceous CRETACEOUS Lower Cretaceous Middle Jurassic JURASSIC —-—U— Angular unconformity 87 88 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°33’ 32’ 31’ 29' 111°28' 40° 01’ 40° 00’ 50’ l 1 MILE B I FEET 5000 E Thistle Creek (— 8 A E Thistle Creek 5000 4000 3000 DIAPIRIC STRUCTURES 89 EXPLANATION Alluvium Colluvium Earthi'low Deposits of ancestral ' 3?" Lake Bonneville(?) Old landslide deposits Older alluvium Moroni Formation Green River Formation Colton Formation Flagstafl“ Limestone North Horn Formation Cedar Mountain Formation Volcaniclastic sediments Green River and Colton Formations, undivided Alluvial fan Holocene > QUATERNARY Coalesced Pleistocene alluvial fans Pliocene Pediment mantle Middle Oligocene 1 | | Eocene F TERTIARY Paleocene < Upper Cretaceous r CRETACEOUS } Lower Cretaceous < Twist Gulch Formation Arapiei: Shale Middle Jurassic > Arapien Shale , JURASSIC Twin Creek Limestone Lower Jurassic Nugget Sandstone (north of Thistle); Navajo Sandstone (south of Thistle) .1 v V e Louppefrjnd. } TRIASSIC Ankareh Formation W8! 3551C Paleozoic rocks, undivided Contact—Approximately located or inferred; dashed and queried in cross section to reflect speculative relations -—-— intrusive sedimentary contact—Approximately located or inferred; oblongs on intrusive sedimentary unit -—-; Fault—Dashed where approximately located; dotted where concealed; bar and ball on downthrown block } PALEOZOlC w—‘—‘—'— Edge of erosional escarpment—Hachures point in general direction of inclination Strike and dip of inclined beds + Syncline—Approximately located; Uace of axial plane + Crest of diapiric fold—Approximately located; trace of axial plane; dotted where concealed 80 _l__ FIGURE 44 (above and facing page).—Geology of Thistle area. (Caption continued on p. 90.) 90 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH FIGURE 44 (previous pages).—Geology of Thistle area. Base modified from US. Geological Survey 1:24,000 Billies Mtn (1967), Birdseye (1979), Spanish Fork (1949), and Thistle (1967). Contour interval 200 ft. The Charleston-Nebo thrust plate, formed in part by units of the Twin Creek Limestone (Jtc), Nugget Sandstone (Jn) (called the Navajo Sandstone south of Thistle), and the Ankareh Formation ('Ea), is partly concealed beneath a cover of younger sedimentary rocks. These younger rocks include, in ascending order, the North Horn Formation (TKn), the Flagstaff Limestone (Tf), the Colton Formation (Tc), the Green River Formation (T9), and the Moroni Formation (Tm). At one time the thrust plate was completely concealed beneath this younger sedimentary and volcanic mantle. Since then, however, the mantle has been partly breached, exposing parts of the thrust plate, chiefly in and near the valley of Thistle Creek. This younger sedimentary and volcanic cover and the underlying thrust plate appear to have been warped into a northward-trending asymmetric fold. The crest of the fold (shown by a dotted and dashed line) essentially follows the west valley wall of Thistle Creek. West of the crest the younger Tertiary and Cretaceous mantle dips gently westward; east of the crest the beds dip eastward at slightly greater dips. The presence of Arapien exposures (T(Ja)) along the east valley wall of Thistle Creek and along the north valley wall of Soldier Creek suggests that the Arapien both underlies the thrust plate and is responsible for the upwarp of the thrust plate and its overlying mantle of younger sedimentary rocks (cross sections A—A’ and B—B’). Cross section C—C’ is in figure 47. / //’( Angular" .xunconeformi FIGURE 45.—Photographs of Thistle area. See figure 44 for corre- sponding geologic map. A, View northward of the west valley wall of Thistle Creek. The Nugget Sandstone (Jn), part of the Charleston-Nebo thrust plate, dips steeply eastward. The North Horn Formation (TKn), dipping gently westward as part of a mantling younger sequence of rocks, unconformably overlies the Nugget. The North Horn Formation, in turn, is conformably overlain by a Tertiary sequence comprising the Flagstaff (Tf), Colton (Tc), and Green River (Tg) Formations. B, View looking northeastward at beds of the Flagstaff Limestone that dip steeply westward. Exposure is north of Soldier Creek and directly east of “Billies Mountain.” Light-gray Flagstaff Lime- stone, commonly underlain by the North Horn Formation, is underlain, in this specific locality, by reddish-brown contorted and crumpled beds of the Arapien Shale (T(Ja)). I attribute the upwarp of the Flagstaff Limestone and the absence of units com- monly found beneath the Flagstaff to intrusion of the Thistle Creek salt diapir. 91 DIAPIRIC STRUCTURES .5m 23 88:“ 22: Exam :oEmfiw mo mwmfi 33:58 was “.8528 was we 33> adémBO AD imam gamma 2% Egg mama? 23585 xwmxo E39 km .wcgmmfifi xmoao EBB can Em 595m: 8385 no 9:3 88¢:me was: 8:me .waE 5:33 gwdohfi wcuefimom Em mama“. $8885 €th 539 can mummmE EDmEAU .283qu #920 539 9.: wwwsbfi €23 Em 5:992» xx .33 xmmho 25:5. 2553552 mozmma Awash: mm 98 m zmgfiwwm .m.D pom azowmog 26: E mm opbmoaxm 6:33qu xwwgo EBB 23 BE wmwsbfi Em amamiwléw $5on 92 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH forms the bulk of the Thistle landslide. Directly east of the escarpment cut on the thrust plate, these younger sedimentary and volcanic rocks dip east- ward; the same units exposed west of the escarpment dip westward (fig. 45A). Relations between the thrust plate and these overlying sedimentary rocks are well exposed along the west valley wall of Thistle Creek some 6 km (3.5 mi) north of the small community of Birdseye (A—4). One of the best exposures occupies parts of secs. 5, 6, and 7, T. 10 S., R. 4 E. near the junction of Crab and Thistle Creeks (fig. 44). There, the thrust plate is represented by beds of Nugget Sandstone (Jn) (called Navajo Sandstone south of Thistle, Utah (A—5)) and Twin Creek Limestone (Jtc) that dip eastward about 60°. These beds are uncon- formably overlain to the east by the North Horn For- mation (TKn), which also dips eastward, but at about 20°. A small wedge of eastward-dipping Flagstaff Limestone (Tf) (in the NE 1/4 sec. 7, T. 10 S., R. 4 E.) conformably overlies the North Horn. Farther south, near the junction of Aggie and Thistle Creeks, volcanic rocks, part of the Moroni For- mation, unconformably overlie the North Horn strata; the Moroni also dips eastward at this point but at about 30°. West of this exposure (as shown on cross section B—B’, fig. 44), the North Horn (TKn) passes over and conceals the thrust plate, and then dips westward. The North Horn is overlain conformably by the Flagstaff Limestone (Tf), which passes westward beneath ever younger sedimentary beds that also dip westward. This sedimentary sequence is overlain to the west, beyond the area shown in the cross section, by westward-dipping volcanic rocks of the Moroni Formation. It seems clear that the sedimentary rocks were originally overlain by an unbroken blanket of volcanic rocks, now much eroded, that was arched along with the sedimentary rocks. Structurally, then, the sedimentary and volcanic rocks appear to have been warped into a north- trending asymmetric anticline marked by a steep east flank and a gentle west one. After the beds were arched, erosion removed many of them and in the process exhumed part of the buried thrust plate. DISCUSSION OF ALTERNATIVE INTERPRETATIONS FAULTED TERRAIN Although all workers in the area agree that the basic structural pattern involves an eroded thrust plate partly buried beneath younger sedimentary rocks, their explanations for the tilted strata differ. Baker (1976), Harris (1954), and Pinnell (1972) con- cluded that a high—angle, down-to-the-east normal fault, named the Thistle Canyon fault by Harris (1954), separates the younger Cretaceous and Ter- tiary rocks from the thrust plate (fig. 47A). Presum- ably the eastward tilt of the younger rocks, east of and juxtaposed against the erosional escarpment, is the result of drag as the east block dropped along the fault. Downthrow to the east is also suggested by the difference in altitude between Flagstaff (Tf) strata astride the thrust plate west of the escarpment and those Flagstaff strata east of the escarpment. West of the escarpment, the Flagstaff beds are at an altitude of about 6,500 ft; east of the escarpment—about 2.5 km (11/2 mi) away—they are at an altitude of about 5,300 ft, some 1,200 ft lower. To the best of my knowledge, no worker has offered any explanation for the westward tilt of those strata that overlie and are west of the erosional escarpment formed on the thrust plate (fig. 45A). A possible explanation involves westward tilting of a discrete fault block as a result of downthrow along a north- trending normal fault, as yet unrecognized, that may extend along the east flank of Loafer Mountain (A—4) (about 1.6 km (1 mi) west of the area shown in fig. 44). Nor have previous workers offered any explana- tions for the many localized structural complexities that seem related to intrusive masses of the Arapien Shale. These complexities seem to be products of plastic intrusion. DIAPIRIC DEFORMATION I View most of the structural complexity in the Thistle area as a direct result of diapiric deforma- tion that occurred after emplacement of the Charleston-Nebo thrust plate. The localized upwarp of those Flagstaff Limestone beds north of Spanish Fork River (fig. 453), and the arching of the Tertiary strata, both on a small and on a large scale, seem reasonably explained only by assuming that masses of the Arapien Shale deformed the country rocks long after those rocks were emplaced and consolidated. The fact that a sedimentary sequence, extending from the North Horn Formation to the Green River Formation, thins toward the crest of the fold— essentially the erosional escarpment—implies that a dynamic, ancestral paleo-high continued to rise slowly, impeding sedimentary deposition throughout much of the Late Cretaceous and early Tertiary. As the Moroni Formation is involved in the arching, the high must have persisted at least through middle Oligocene time. These structural and stratigraphic relations must mean that even as the younger sediments DIAPIRIC STRUCTURES 93 WEST ‘ EAST U .K : I FEET C Tf ,,-§ % LE ,_ é 'g‘VTHISTLE CANYON 7000 "ff/15 g fié i5 g \‘ FAULT 6500 _ i \ E \ Erosional 6000 \ "3 ‘ escarpment 5500 \-~ "' . Ja (Triassic, Permian, and Pennsylvanian strata, undivided) A “’5 LE _ :: WEST 2 g '5) g E '6 EAST e g“ a; I C :55 U, : 20 C FEET Ik"’::::::::,;:t\ 7000 ~::,,’/’ //// \\\ 6500 ”um / \\ Erosional 6000 ’ \ escarpment 5500 5000 4500 4000 (Triassic, Permian, and Pennsylvanian strata, undivided) 0 1 2 KILOMETERS i . . . . | ' 0 1 MILE FIGURE 47.—Two alternative interpretations of geologic rela- tions in Thistle area. Line of cross section C—C’ is shown in figure 44, geologic map of the Thistle area. Contacts are dashed and (or) queried where relations are speculative. Quaternary units: Old, landslide deposit; Ocl, colluvium; Of, alluvial fan; Qal, alluvium. th, Jurassic Twist Gulch Formation. A, The Thistle Canyon fault, downthrown to the east, separates the younger Cretaceous and Tertiary sedimentary rocks (represented by the Flagstaff Limestone (Tf)) from the Charleston-Nebo thrust plate, represented by beds of the Twin Creek (Jtc), Nugget (Jn), and Ankareh ('fia) Formations. B, A mass of Arapien Shale (T(Ja)) in- truded and raised part of the Charleston-Nebo thrust plate, and in so doing arched the overlying younger Creta- ceous and Tertiary sedimentary and volcanic rocks into a north-trending asymmetric fold. The eastward-dipping Flagstaff (Tf) strata, directly east of the erosional escarp- ment, are part of the fold’s east flank. The westward- dipping North Horn strata (TKn), west of the escarpment, are part of the fold’s west flank. The thinning of all younger sedimentary units (here rep- resented by the North Hom (TKn) and Flagstaff (Tf) For- mations) toward the crest of the fold suggests that a diapiric fold, concealed beneath the thrust plate, has been growing at a slow, almost imperceptible rate impeding sed- imentary deposition. accumulated, a diapiric fold—the Thistle Creek dia- piric fold—began to move upward beneath the thrust plate. Many of the diapiric folds in central Utah are readily recognizable by the juxtaposition of contorted Arapien Shale masses against vertical to overturned beds, commonly of the Indianola Group. In the Thistle area, by contrast, a diapiric fold is indicated by strata arched asymmetrically over the escarpment cut on the Charleston-Nebo thrust plate. The eastward-dipping North Horn (TKn), Flagstaff (Tf), and Moroni (Tm) strata east of the erosional escarpment are in the east flank of the fold; the same strata west of the escarp- ment are in the west-dipping flank. In my view, the opposing (lips of the strata and the difference in alti- tude between Flagstaff strata west and east of the escarpment merely reflect the configuration and asymmetry of the fold draped across the escarpment (fig. 473). I suggest that the erosional escarpment, formed on the thrust plate, was originally buried beneath nearly horizontal North Horn and younger strata. As a diapiric fold developed beneath the thrust plate, it raised the plate, and in so doing arched the overly- ing younger rocks. Erosion has since removed the crestal part of the arched sheet of North Horn and younger rocks and exhumed part of the escarpment. HJORTH CANYON DIAPIRIC FOLD Part of a northeast-trending diapiric fold (fig. 16, 9) is exposed in Hjorth Canyon (A—5) (secs. 15, 16, 21, and 22, T. 11 S., R. 4 E.), some 6 km (31/2 mi) north of Indianola (B—5) (fig. 2). This fold was first recognized and called the “Hjork Creek dome” by Runyon (1977b, p. 76), who noted that the structure “is actually an elongated dome rather than a circular one* * *and is illustrated * * *as a plunging anticline.” GEOLOGIC SETTING Critical exposures, along the north wall of Hjorth Canyon, consist of a narrow band of highly contorted Arapien Shale that trends about N. 40° E., bounded on each flank by beds of the Twist Gulch Formation (fig. 48). Exposures are poor, but I suspect that beds of the Cedar Mountain Formation are stratigraphi- cally above the ’lVVist Gulch beds; in figure 48 I have mapped these Cedar Mountain(?) beds with Twist Gulch strata. The Twist Gulch and Cedar Mountain(?) strata are anomalously thin; the thickness of the Twist Gulch Formation in the Hjorth Canyon area is less than 450 m (1,500 ft). Elsewhere in this general area the Twist Gulch is about 915 m (3,000 ft) thick (Khin, 1956, p. 34). This unusual thinning has been recognized by 94 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°30’ 29’ 28' 111°27’ 39°52’30” ' 52’ 39°51’ [] 5 1 2 KILUMETERS I l ‘ L J I i J 0 | [ 1/2 1 MflE FEET 8000 7000 7000 0000 6000 5000 5000 DIAPIRIC STRUCTURES 95 EXPLANATION ‘ _. , - } Holocene QUATERNARY Alluvium } Middle Oligocene to Moroni Formation lower Eocene TERTIARY , } Paleocene Price River Formation > Upper Cretaceous CRETACEOUS (only on cross section) Indianola Group J Twist Gulch Forma- tion (Units of the Cedar Mountain Formation (Kcm) of Early Cretaceous > Middle Jurassic JURASSIC age may be present) Arapien Arapien Shale Shale 2 Contact—Approximately located or interred; dashed and queried in cross section to indicate speculative relations -—-— Intrusive sedimentary contact—Approximately located or inferred; oblongs on intrusive unit 40 —|— Strike and dip of inclined beds 85 —b— Strike and dip of overturned beds —$—— Crest of diapiric fold—Dotted where concealed FIGURE 48 (above and facing page).—Geology of Hjorth Canyon area showing part of northeast-trending Hjorth Canyon diapiric fold. Base modified from U.S. Geological Survey 1224,000 Indi- anola (1967). Contour interval 200 ft. Beds of the Twist Gulch Formation flank the core—a northeast-trending mass of Arapien Shale—of the diapiric fold. Twist Gulch strata on both flanks of the fold dip steeply southeast; those on the northwest flank are overturned. Overlying North Horn strata reflect the general configuration of the fold, as do the volcanics of the Mo- roni Formation (cross section A—A’). Arapien Shale as unit Ja is listed for completeness but is not shown, as such, on the map. previous workers. Thus, Runyon (1977b, p. 67) attributed this “drastic thinning” to “drag faulting caused by the diapiric upwelling of the underlying Arapien* * *.” Pinnell (1972, p. 97), however, attrib- uted it to “* * *rapid facies changes in* * *environ- ments of deposition or of Laramide thrusting.” Those Twist Gulch beds that form the northwest flank of the fold strike about N. 40° E., are vertical or overturned to the northwest, and so dip about 85° to the southeast. TWISt Gulch beds that form the southeast flank of the fold are right-side-up and dip southeastward between 80° and 85°. The outermost flanks of the fold are formed by units of the Indi- anola Group that dip about 20° NW. along the north— west flank, and about 85° SE. along the southeast flank. All beds that form the fold are unconformably over- lain either by moderately dipping strata of the North Horn Formation or by volcanic units of the Moroni Formation. Here too, as in the Dry Hollow (A—5) fold, these younger beds appear to have been arched dur- ing one or more upward movements of the underly- ing fold. Thus, those North Horn beds that overlie the northwest flank of the fold dip about 10° W.; those North Horn beds that overlie the southeast flank dip 30° to 50° SE. These southeast dips persist southeastward for about 1.6 km (1 mi), after which the North Horn beds pass beneath volcanic units of the Moroni Formation. Although attitudes of the Moroni beds are difficult to determine, I believe that they, too, reflect the configuration of the fold. South- east of the exposures already described, near Little Clear Creek (B——5), Moroni beds dip northwest. This northwest dip of the Moroni strata reflects the north- west flank of the Little Clear Creek diapiric fold, which also trends northeast, and thus is parallel to and about 3 km (2 mi) southeast of the Hjorth Canyon fold (fig. 16). DISCUSSION I attribute the anomalous thinning of the Twist Gulch, Cedar Mountain(?), and most likely the Indi- anola strata, in the Hjorth Canyon area, to the imperceptible upward movement of the salt diapir during much of the time these units were being deposited. The deformed rocks in Hjorth Canyon suggest three distinct diapiric episodes. During the first epi- sode, once near-horizontal Twist Gulch, Cedar Moun- tain, and Indianola strata were bowed up and locally turned over as the Hjorth Canyon salt daipir surged upward to form a mushroom-shaped diapiric fold. This upward surge must have occurred at some time after Indianola strata were deposited and consoli- dated, in essence, during the Late Cretaceous, possi- bly after Santonian but before Campanian time. Subsequently, removal of salt partly destroyed this fold, and erosion then reduced it to a surface of low relief on which Price River sediments were deposited; these were subsequently overlain by North Horn sed- iments. As Price River strata are missing from this specific locality, I assume that they pinched out locally against the flanks of the slowly rising fold. 96 The second diapiric episode, represented by the arched beds of the North Horn, must have occurred at some time during the early Tertiary, for North Horn deposition continued at least into the Pale- ocene. The fact that the arched North Horn dips away from the crest of the fold, represented by the northeast-trending band of Arapien strata (fig. 48), implies that the upward surge of the diapir occurred in the same place and had the same trend as the pre- vious fold. As North Horn strata are unconformably overlain by the volcanic rocks of the Moroni Forma— tion, I assume that whatever younger Tertiary sedi- mentary strata were deposited, following the formation of the North Horn, either pinched out against the flanks of the rising fold or were eroded before volcanics of the Moroni spread across the area. The arched Moroni represents the third diapiric episode. Presumably, a renewed upward surge of the salt diapir bowed up these once near-horizontal flows. Again, the attitudes of the Moroni rocks, dipping away from the crest of the fold, indicate that this renewed surge must have occurred in the same place and with the same trend as the two ancestral folds. This third surge must have come at some time after middle Oligocene time for the Moroni is of late Eocene to middle Oligocene age. LI'I'I‘LE CLEAR CREEK DIAPIRIC FOLD GEOLOGIC SETTING Little Clear Creek (B—5) has cut a deep, narrow canyon into the crest of a major diapiric fold (fig. 16, 8) that trends about N. 45° E. The fold can be traced from the center of sec. 26, T. 11 S., R. 4 E. to the northwest corner of sec. 5, T. 11 S., R. 5 E., where it passes into a large graben known as the Dairy Fork (A—5) graben (fig. 49). Twist Gulch strata form the crest and part of both flanks of the fold. The flanks dip steeply away from the crest for much of the fold’s exposed length. Thus, those 'leist Gulch rocks that are part of the fold’s northwest flank dip about 80° NW.; comparable dips, but to the southeast, mark the fold’s southeast flank. Only a narrow segment of Twist Gulch strata crops out along the fold’s northwest flank; much of that flank is concealed beneath beds of either the North Horn or Moroni Formations that dip northwestward at moderate angles, and that unconformably overlie the steeply dipping Twist Gulch strata. The well- exposed southeast flank of the fold includes units of the 'IVvist Gulch and Cedar Mountain Formations and the Indianola Group. All these strata dip at high angles, commonly to the southeast, but locally some SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH beds are vertical or are overturned and so dip north- westward. These steeply inclined units are uncon- formably overlain by Price River and North Horn strata that dip about 35° SE. Exposures are inadequate to determine whether any of the units involved thin toward the crest of the fold. DISCUSSION I interpret the geologic relations in Little Clear Creek, as in Dry Hollow, and Hjorth Canyon, to indi- cate three distinct episodes of diapiric deformation. During the first episode an upward surge of the causative salt diapir bowed up the 'IVvist Gulch, Cedar Mountain, and Indianola strata to form a mushroom-shaped fold. Collapse of that fold, presum- ably as a result of withdrawal of salt, and subse- quent erosion left a surface of low relief on which the Price River and North Horn were deposited. During the second episode a second upward surge of the causative diapir arched this Price River and North Horn sequence. Inadequate exposures hinder any clear interpretation of What followed. Perhaps the arched Price River and North Horn sequence was eroded to a surface of low relief on which Flagstaff sediments were deposited. In time, these Flagstaff strata were buried beneath younger beds, possibly Colton and Green River strata. Erosion, after Green River time, resulted in a moderately dissected sur- face onto which volcanic flows of the Moroni Forma- tion were extruded. At some time after volcanics of the Moroni were emplaced, the salt diapir surged upward for a third time and warped up the volcanic rocks. The beds deformed by the diapir during this third episode occupy the same site and have the same trend as those older beds deformed during the previous episodes, implying that once again the diapir moved up the same conduit it followed in the previous two episodes. As volcanic rocks of the Moroni Formation (formed between late Eocene and middle Oligocene time) are involved in this last episode of diapirism, the diapiric FIGURE 49 (facing page).—Geology of Little Clear Creek area. Base modified from US. Geological Survey 1:100,000 Nephi (1981). Contour interval 250 m. Little Clear Creek and West Lake Fork follow the crest of the Little Clear Creek diapiric fold. At its north end, the fold passes into the Dairy Fork graben. These relations suggest that part of the causative salt diapir was re- moved, and the overlying beds then subsided into the resultant void or voids to form the graben. Arapien Shale as unit Ja is listed for completeness but is not shown, as such, on the map. DIAPIRIC STRUCTURES 97 4E? 111°25' EXPIANATION E Holocene QUATERNARY Alluvium Landslide Pleistocene Alluvial-fan deposits > Pliocene ' . \ deposits Coalesced alluvial-fan deposfis ‘} ()Hgocene Moroni Formation I ? TERTIARY V sea Green River Formation Flagstaff Limestone Pakaacene J North Horn Formation Upper Price River Formation Cretaceous ? CRETACEOUS lndianola Group Lower Cretaceous . Fonnafion , H 4 E R 5 E U 1 2 3 4 KILOMETEHS o 0 l 2 hAlLES a 4‘ fi Twist Gulch Formation Middle .3’ § 0 E J . > JURASSlC NW E g L) G S urassrc I! 5 Q. § 53% l\' IIIIHIII -*- :1 tn —. :2 - ‘ METERS E §§ 3 2:: Arapien Shale Arapien Shale 2 3000 8 5 C) 3.: g? 2500 o 1’ 2000 Contact—Approximately located or inferred 150“ —-T— Fault—Bar and ball on downthrown block; barb shows downthrown block 1031] in cross section; dashed in cross section where reconstructed above 500 50 eroded surface 0 Strike and dip of inclined beds g E —l— Strike and dip of vertical beds NW 5 g SE 50 B 4‘ a g 5: B , -b— Strike and dip of overturned beds ’5 4: 2 8 a: METERS % L3 3 2% E o Dry hole 3000 E g 3‘: 8i 3 '6 «v 2500 5 T9 9 ‘ 2000 1500 1000 500 98 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH folds presumably developed at some time during or after middle Oligocene time. Near Smiths Reservoir (where Side Canyon joins Lake Fork), the fold passes northeastward into a northeast-trending graben, the Dairy Fork graben of Merrill (1972, p. 79), that is collinear with the fold. Seemingly, the graben represents collapse of the crestal part of the Little Clear Creek fold as a result of salt dissolution (cross section B—B’, fig. 49). Union Oil Company drilled its well, No. G—24, along the crest of the fold in the NE 1/4 sec. 24, T. 11 S., R. 4 E. (fig. 49). The well drilled into the Arapien Shale but did not pass through it. FAIRVIEW DIAPIRIC(?) FOLD The east fork of Sanpete Valley, essentially that sector of Sanpete Valley that extends from Ephraim (E—4) northeastward to and beyond Milburn (B—5), is flanked on the east by the imposing, westward-facing Wasatch monocline. I believe that the Wasatch mono- cline (E—5), much like the Valley Mountains mono- cline (Gr—2), was formed when salt was removed from a major salt diapir that lies at the foot of the mono- cline. Removal of the salt resulted in near-horizontal beds being let down to form the monocline (Witkind and Page, 1984). Much evidence, in the form of upturned Cretaceous and Jurassic beds, and Arapien exposures, suggests that a major diapir, the Sanpete—Sevier Valley diapir, underlies the southern part of Sanpete Valley. Near Ephraim, the diapir appears to bifurcate, with one branch extending northward into the west fork of Sanpete Valley, and the other extending northeast— ward into the east fork of Sanpete Valley. The struc— tural complexity along the east flank of the Gunnison Plateau near Wales Gap (D—4) supports the presence of the west branch of the diapir, for which I have retained the name Sanpete—Sevier Valley diapir. By contrast, mainly the downwarp of strata to form the north end of the Wasatch monocline suggests the presence of the east branch of the diapir, which I call the Fairview diapir(?) (fig. 16, 7). These downwarped strata dip westward at about 20°. At th north end of the Wasatch monocline, near the head of the east fork of Sanpete Valley east of Indianola, the strata are flexed up and dip eastward as part of the east flank of the Little Clear Creek (B—5) diapiric fold. These upwarped strata mark the northernmost extent of the Wasatch monocline. The south half of the Wasatch monocline, thus, may have been formed by the removal of salt from the Sanpete—Sevier Valley diapir, whereas the north half may have been formed by the removal of salt from the Fairview diapir(?). I propose that the Fairview diapiric(?) fold extends in a generally northeastward direction from Ephraim (E—4), through Mount Pleasant (D—5), Fairview (C—5), Oak Creek (C—5), and Milburn (B—5), to end near the head of the east fork of Sanpete Valley. The fold, thus, is about 52 km (32 mi) long, and, in detail, trends about N. 30° E. from Ephraim to Mount Pleasant, and then bends to trend almost due north from Mount Pleasant through Fairview and Milburn to its end east of Indianola. GEOLOGIC SETTING Much of the following discussion about the Fair- view diapiric(?) fold is speculative; the available ground evidence is sparse and contradictory. Some evidence hints at the existence of a diapiric fold beneath the east fork of Sanpete, Valley. Thus, for example, test wells and seismic reflection profiles indicate that near Mount Pleasant (D—5) an inordi- nately large mass of Arapien Shale underlies the surficial deposits that floor Sanpete Valley. Further- more, the downwarp of the Cretaceous and Tertiary sedimentary strata that form the north end of the Wasatch monocline, essentially near and north of Milburn (B-5), seems most readily explained by dis- solution of salt from a diapir—the Fairview diapir— concealed beneath the surficial deposits. At the north end of the east fork of Sanpete Valley, coalesced alluvial fans partly bury westward-dipping, cuesta-like masses of Green River strata that have been much broken. Many of the smaller Green River masses are intensely brecciated, and locally appear as chaotically disrupted masses. A few of the larger masses, however, although greatly disrupted, still appear as entities. Runyon (1977b, p. 76) interpreted these disrupted masses to be part of a collapsed, dome-shaped diapir, which he called the “North San Pitch River Valley diapir.” Strata exposed west of the east fork of Sanpete Valley also dip westward at angles that range from about 15° to 20°. Directly west of the north end of the east fork of Sanpete Valley, North Horn, Flagstaff, Colton, and Green River strata are warped to form a south- plunging syncline best exposed east of Indianola (B—5) along the north side of Indian Hollow. DISCUSSION At the north end of the Wasatch monocline the Cretaceous and Tertiary beds flex down, and this DIAPIRIC STRUCTURES 99 NORTH SOUTH Wasatch monocline FIGURE 50.—Landslide and earthflow phenomena along Wasatch front. A, View eastward of earthflow (dashed outline), typical of those exposed along base of Wasatch monocline; about 6 km (4 mi) southwest of Ephraim. Detritus derived chiefly from the Colton Formation forms earthflow. The earthflow was em- placed at some time after the Wasatch monocline was formed. As salt was removed from the causative Sanpete—Sevier Valley salt diapir, which underlay Sanpete Valley, those sedimentary strata that overlay the diapir subsided into the resultant voids. The Wasatch monocline formed as a result of this downwarp, in my opinion, is the most telling bit of evidence supporting the existence of the Fairview diapiric(?) fold. Elsewhere, as in the Sixmile Canyon (F—4) area of the Wasatch Plateau, where the toe of the monocline has been breached, or in the Red Can- yon area (E—2) of the Valley Mountains, where the Valley Mountains monocline has been breached, the complex structural relations exposed in the breached areas seem reasonably explained only by invoking the repeated growth and collapse of causative salt diapirs (Witkind and Page, 1984, p. 152—155). Those causative diapirs, now concealed beneath surficial deposits, were once concealed beneath near-horizon- tal beds. Dissolution of salt from the diapirs resulted in subsidence of the Arapien mudstones into the newly formed voids, thus removing support from the near-horizontal beds. Inevitably, these strata failed and flexed down to form the monoclines. In my view, then, the process that formed the Wasatch and Valley Mountains monoclines was not differential uplift but rather subsidence, stemming from dissolution of salt in a system of diapirs including the proposed Fair- view diapir(?). Runyon (1977b, p. 76), discussing his North San Pitch River Valley diapir, also attributed its formation to subsidence as a result of dissolution of salt. I agree with Runyon about the existence of a diapir in the east fork of Sanpete Valley, but disagree with his interpretation that the jumble of disrupted Green Colluvium subsidence; probably the earthflow occurred shortly after in response to that downwarp. B, View northward near mouth of north valley wall of Manti Canyon. This exposure, about 0.8 km (1/2 mi) south of Temple Hill—the large detachment block composed of Green River and Crazy Hollow strata on which the Mormon temple at Manti is constructed—shows westward- inclined drag folds (directly beneath the colluvium) that proba- bly stem from the valleyward movement of comparable slide blocks that have since been eroded. River rocks at the north end of the east fork of San- pete Valley marks the site of a dome—shaped collapsed diapir. I believe rather that these brecciated Green River masses are ancestral landslide blocks that slid valleyward as the Wasatch monocline developed. The many large earthflows (fig. 50A), landslides, detachment blocks, and other mass-wasting deposits that mantle and flank the lower slopes of the Wasatch monocline probably stem from this down- warp. Most of these deposits consist of a chaotic jum- ble of fragmented rocks, derived chiefly from the breakup of the Colton Formation, which slid valley- ward off the tilted beds of the Flagstaff Limestone. Locally, however, large unbroken detachment blocks slid westward and came to rest at or near the base of the monocline. Perhaps the best example is Temple Hill, in Manti (E—4), on which the town’s striking Mormon temple is built. This block slid westward off the monocline, crossed steeply inclined Flagstaff and Colton strata (fig. 50B), and came to rest on the val- ley floor 150 m (500 ft) west of the monocline (fig. 51). The block, a crude oblong, trends west, and is about 1.4 km (0.9 mi) wide. It rises some 105 m (350 ft) above the adjacent valley floor, and is composed almost wholly of limestone beds of the Green River. These beds of Green River are overlain, along the north face of the block, by conglomerate beds of the Crazy Hollow Formation that were obviously carried “piggyback” on the Green River. 100 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH FIGURE 51.—Stereographic vertical aerial photographs of the Tiample Hill area, Manti, Utah. Temple Hill, a detachment block composed of Green River and Crazy Hollow strata, slid valleyward (westward) off the Wasatch monocline. From 1877 to 1888, early Mormon pioneers quarried oolitic limestone from the Green River Formation and constructed the temple at Manti. Some of the quarries used as a source of building stone are shown on the photograph; others are farther north near Ephraim. Still another detachment block, also composed of Green River and Crazy Hollow strata, is near the ancestral Willow Creek (G—3) area (Witkind, 1981). The presence of Crazy Hollow strata on these slide blocks implies that the downwarp responsible for the monocline and the accompanying sliding occurred during or after the late Oligocene. Some ground evidence, however, seemingly contra- dicts my view that a diapiric fold is concealed beneath the east fork of Sanpete Valley. So, Green River strata west of the east fork of Sanpete Valley dip westward (Witkind and Weiss, 1991). If, as I pro- pose, dissolution of salt from a concealed diapir caused subsidence of overlying near—horizontal strata to form the westward-facing Wasatch monocline, one would expect that strata west of the diapir would dip eastward and so form an eastward-facing monocline: in essence, paired, facing monoclines should result from the partial failure of the causative diapir. Such is not the case in this specific locality, and the west- ward dip of those rocks west of the east fork of San- pete Valley puzzles me. One possible explanation is that these strata west of the east fork of Sanpete Val- ley were tilted up to a westward dip at some time after the monocline was formed. Some support for this view is given by the south-plunging syncline near Indian Hollow. As Green River strata occupy the center of the syncline, the implication is strong that the deformation responsible for the development of the syncline occurred at some time after Green River strata were flexed down to form the Wasatch mono- cline. WEST HILLS DIAPIRICG) FOLD West Hills (D—2), and Long Ridge (B—2) to the north, are low, narrow, north-trending ridges com- posed of sedimentary and volcanic rocks that form the west side of Juab Valley (0—2). I suspect that a major salt diapir underlies the West Hills (fig. 16,, 5). GEOLOGIC SETTING Structurally, the West Hills are an elongate upwarp that trends about N. 20° E. and is about 24 km (15 mi) DIAPIRIC STRUCTURES long by 5 km (3 mi) wide. The fold extends from near Mills Gap (D—2) on the south, to near Utah State Highway 132 on the north (fig. 16), where it abuts an erosional remnant of the Charleston-Nebo overthrust. The fold is composed of Cretaceous and Tertiary strata (North Horn), and Tertiary strata (Flagstaff, Colton, and Green River Formations) that are unconformably overlain by volcaniclastic beds of the Eocene and Oli- gocene Goldens Ranch Formation. The volcanic units of the Goldens Ranch have been warped and faulted along with the underlying sedimentary units. In gen- eral, both flanks dip away from the crest of the fold at about 20° to 30°. In several places, elongate veins of banded calcite intrude the volcanic units. One of these veins, about 850 m (2,800 ft) long and 8 m (25 ft) wide, trends about N. 75° E. through C sec. 16, T. 13 S., R. 1 W. Other small calcite seams and veins, most of unknown length but ranging from 0.5 to 2.0 m (2 to 6 ft) in width, intrude volcaniclastic sediments that are exposed in small knolls in the E1/2 sec. 26, T. 13 S., R. 2 W DISCUSSION Although the Arapien Shale is nowhere exposed in the West Hills, recent drilling by Placid Oil Company on the crest of the fold (Howard Well No. l—A WXC, NW1/4NW1/4 sec. 5, T. 14 S., R. 1 W) (fig. 9) indicates that the fold has a core of Arapien Shale that con- tains many beds of both salt and anhydrite scattered through calcareous mudstone. The fact that the volcanics of the Goldens Ranch are deformed along with the underlying sedimentary rocks of Cretaceous and Tertiary age suggests that the folding must have occurred at some time after the middle Oligocene, the youngest age assigned to the Goldens Ranch Formation (Witkind and Marvin, 1989). As much salt is contained in the Arapien core of the fold, it seems reasonable to surmise that the folding may stem from movement of the salt. The calcite veins that intrude the volcanic mantle would seem to support the View that the deformation is the result of movement of the Arapien core. Presumably some of the evaporites of the buried Arapien were dissolved and then reprecipitated at some time after the volcanics were extruded, consoli- dated, and warped. Such dissolution and reprecipita- tion would seem most likely during episodes of diapiric deformation. VALLEY MOUNTAINS DIAPIRICG) FOLD The Valley Mountains (G—2) are a low, north- trending, oval mass about 45 km (28 mi) long and 101 some 11 km (7 mi) wide (fig. 2), bounded on the west by Scipio (E—1) and Round Valleys (F—2) and on the east by Sevier Valley (G—2). Sevier River, flowing north through Sevier Valley, bends around the north end of the Valley Mountains and is then impounded behind Yuba Dam (E—2) to form the Sevier Bridge Reservoir (Yuba Lake). On the south, the Valley Mountains end in a small saddle formed near a southeastward bulge of the Pavant Range (H—l). Highway US. 50 follows the west flank of the Valley Mountains southward from Scipio to Salina (G—3). The Valley Mountains may be the site of a diapiric fold (fig. 16, 6). GEOLOGIC SETTING The Valley Mountains, composed chiefly of Creta- ceous and Tertiary units, are an eastward—tilted fault block bounded on the west by a high-angle normal fault that trends north and dips steeply to the west. The crustal block west of the fault (greater Scipio Valley) is downthrown. The strata that form the crest of the mountains are nearly horizontal, and these are broken by many northward-trending high-angle nor- mal faults. Comparable fault patterns are found in the Wasatch Plateau (Gilliland, 1951, p. 61). Locally, several of these faults in the Valley Mountains are paired to form grabens; one of the larger grabens so formed is an unusually straight north-trending depression expressed topographically for part of its length as Japanese Valley. Japanese Valley is about 13 km (8 mi) long and 2 km (11/4 mi) wide. I believe, however, that the graben extends beyond the ends of Japanese Valley, possibly reaching from South Valley (G—2) northward almost to Red Canyon (E—2), a dis- tance of about 19 km (12 mi). As the nearly horizontal strata that form the crest of the Valley Mountains are traced eastward they gradually flex downward to form the eastward-facing Valley Mountains monocline. As in the Wasatch mon- ocline, far to the east, beds of the Flagstaff Lime- stone form much of the monoclinal slope. Younger beds, chiefly Colton, Green River, and Crazy Hollow strata, have been almost completely removed from this slope, but are preserved along and near the slope’s base where they appear as small eastward- dipping cuestas. Eastward-flowing consequent (but intermittent) streams have cut deep valleys that reach far back toward the crest of the mountains. Along the northeast and east edges of the Valley Mountains, the monocline has been breached to expose a structurally complex sequence of Cretaceous and Tertiary beds. I describe these exposures else- where in this Professional Paper (p. 62—66), and 102 attribute the structural complexity to recurrent movement of the Sevier Bridge Reservoir diapir, and the monoclinal downwarp to dissolution of salt from that diapir. DISCUSSION Although mudstones of the Arapien Shale are nowhere exposed in the Valley Mountains, they have been found in the Anschutz Corporation’s Monroe Fee No. 1 well (SE1/4SE1/4 sec. 14, T. 20 S., R. 2 W.), and Placid Oil Corporation's WXC—USA 1—2 well (NW1/4SW1/4 sec. 24, T. 19 S., R. 2 W.) (fig. 9). The Placid well is along the west flank of the mountains, and the Monroe well is in Round Valley. Although both wells penetrated the Arapien Shale, neither well cut beds of salt. Several factors hint that the mountains are a dia- piric fold somewhat similar to other diapiric folds in the area. Thus, the elongate shape of the mountains, the linear, collapsed graben (Japanese Valley) that follows the mountain crest, and the presence of Arapien mudstones in the core all favor the concept that the Valley Mountains are, or once were, under- lain by a salt diapir. The graben, in particular, sug- gests subsidence as a result of withdrawal of salt from a causative diapir. The many north-trending faults, so much like those that break the crest of the Wasatch Plateau, also favor dissolution of salt as an explanation for their origin. Although the two test wells failed to penetrate salt, this in itself does not necessarily mean that salt does not, or did not, underlie the Valley Mountains. Both wells, along the west flank of the fold, are consider- ably west of the crest of the fold, and thus could have missed the causative salt core. Previously, I have suggested (p. 12 and fig. 5) that most of the salt diapirs are long, narrow ridges of salt. 'I‘rusheim (1960, fig. 4), studying the Zechstein salt of northern Germany, has referred to comparable diapirs as “salt walls.” Wells drilled along the flanks of a diapiric fold could easily miss such thin salt ridges. GRAVITY DATA Gravity data are available for parts of the Sanpete— Sevier Valley area as a result of a Bouguer gravity survey completed between 1968 and 1974 by Brown (1975, fig. 5). Brown’s data were subsequently reeval- uated by Brown and Cook (1982), but this new appraisal included no new data. The gravity data reveal the general distribution pattern of the diapiric folds (fig. 52). The trends of SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH most folds closely coincide with the gravity lows, but the trends of a few folds seemingly diverge somewhat from the determined gravity lows. Such divergence may stem from the low density contrast between the Arapien Shale and the valley fill; the contrast seem- ingly is just too small to be easily recognized. Brown and Cook (1982, p. 123) commented: “The expected density contrast between it [the alluvium] and the Arapien Formation is too small to be detailed in this study. Hence, alluvium will be included with the Arapien in quantitative interpretations.” The gravity map shows three elongate, faintly sinu- ous lows more or less coincident with the Sevier (G—3), Sanpete (E—4), and J uab valleys (C—2). Farthest south is a narrow, deep trough that trends about N. 30° E., and that coincides with that part of Sevier Valley between Richfield (I—1) and Gunnison (F—3). Near Gunnison, the trough bifurcates to form two narrow lows—an eastern one that trends about N. 20° E. and that follows Sanpete Valley, and a western one that trends about N. 20° W. and that persists beneath Sevier Valley to underlie the Sevier Bridge Reservoir (E—2) sector. The third low, which follows Juab Valley, trends about N. 20° E.; the low’s south end joins the northwest-trending low beneath the Sevier Bridge Reservoir. All three gravity lows are remarkably alike— narrow, deep, and faintly sinuous, almost straight. Locally, as in the Sevier (Salina (Gh3)—Redmond (G—3) area) and Sanpete Valleys, intense gravity lows closely coincide with exposures of the Arapien Shale, strongly suggesting that at least in those areas the lows directly reflect the salt-rich diapiric cores. Else- where, however, the belts of Arapien mudstone, which I interpret to be the cores of the diapiric folds, are disturbingly distant from the gravity lows. For example, near Richfield (I—l) the gravity low follows the center of Sevier Valley, but the Arapien Shale exposures are some 10 km (6 mi) to the east, where FIGURE 52 (facing page).—Bouguer gravity anomaly map of part of central Utah on which are plotted the estimated traces of several major diapiric fold crests, which generally follow the trend of three major gravity lows. The Redmond diapiric fold follows the northern part of the low underlying Sevier Valley, between Rich- field and Gunnison. The Sanpete-Sevier Valley diapiric fold fol— lows the eastern lobe of the low extending northeast from Gunnison. The Sevier Bridge Reservoir diapiric fold follows part of the western low extending northwest beneath Sevier Bridge Reservoir. From data in Witkind and Marvin (1989), another diapiric fold as yet unrecognized may coincide with the branch of the low beneath Juab Valley. Fold crests dashed where inferred, queried where speculative. Gravity data from Brown, 1975. Contour interval 10 mGal; dashed where inferred; hachured to indicate area of closed low. 103 DIAPIRIC STRUCTURES 111°15’ 30’ 112°UU’ 112°15' 39 °45 Fountain Green 040m floaty oufil/ 2:: Gm/s/ NI osflmoro / 2mg 2203 39.0 30’— 39°00’ 38 °45’ 20 KILOMETEHS 1U 10 MILES 104 they form part of the eastern reaches of Sevier Valley. Brown and Cook (1982, p. 130) recognized this incon- sistency and attributed it to an anticline formed in pre-Arapien strata and concealed beneath the Arapien. Seemingly, the Arapien over the buried anti- cline is relatively thin; away from the anticline the Arapien thickens and forms definitive gravity troughs. A similar lack of agreement between a gravity low and the Arapien exposures is apparent in the Levan (C—3) area to the north. The gravity low follows the center of Juab Valley; the north—trending Arapien Shale outcrops, which mark the core of the Levan diapiric fold, are some 7.2 km (4.5 mi) to the east, where they form part of the west flank of the Gunni- son Plateau. Possibly, another diapiric mass under- lies Juab Valley (Witkind and Marvin, 1989). Furthermore, two major postulated diapiric folds, the Fairview and the Valley Mountains folds, seem- ingly are not shown at all by the gravity data. This lack, however, may be due to the sparsity of gravity data in those localities. DIAPIRIC DEFORMATION OF THE EAST FLANK OF THE CHARLESTON-NEBO THRUST PLATE Most of the diapiric folds discussed previously are distinctive and readily recognized. A causative salt diapir has warped up the surface rocks into near- vertical attitudes, and these upwarped rocks pre- cisely reflect the trend of the underlying diapir. By contrast, in this section I discuss how several of these diapirs, and their overlying diapiric folds, overridden by and concealed beneath the Charleston- Nebo thrust plate, subsequently deformed the over- riding plate and its mantle of younger rocks. I am convinced that both the Levan and the Thistle Creek diapirs have broken and warped the thrust plate (p. 69—75 and 83—86). Here, I summarize mate- rial that originally appeared in USGS Professional Paper 1170—F (Witkind, 1987), which described a series of geologic exposures along the eastern margin of the thrust plate that seemed most reasonably explained by diapiric uplift of the thrust plate and its sedimentary and volcanic cover. In brief, Cretaceous and Tertiary sedimentary and volcanic strata unconformably overlie the sinuous ero- sional escarpment (p. 83 and fig. 4) formed along the eastern margin of the thrust plate. Wherever these strata abut and overlie the escarpment they invari- ably dip away from it, regardless of the escarpment’s trend. For example, remnants along that part of the escarpment that trends northward dip generally east SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH or northeast; elsewhere, where the escarpment trends eastward the remnants dip south or southwest. Within short distances from the escarpment, however, the beds reverse dip and consistently dip toward the escarpment. A narrow to broad, ill-defined, sinuous syncline thus rims the escarpment. In my view, the tilted strata adjacent to the escarpment are the rem- nants of an upwarp formed when the east edge of the thrust plate was lifted up and arched long after the plate was emplaced, eroded, and buried beneath these younger Cretaceous and Tertiary strata. I attribute this uplift and warpage to upward movement of one or more diapiric folds concealed beneath the plate. I believe that the width of the marginal syncline at any one place is determined by the distance between the escarpment and one or another of several diapiric folds, described previously, that crop out east of the escarpment. In my earlier report (Witkind, 1987), I described nine localities marked by these upturned Cretaceous and Tertiary beds. Eight of these nine localities are alike, in that tilted beds of mudstone and elastic rocks of the North Horn Formation unconformably overlie Paleozoic and Mesozoic beds that form the escarp- ment cut on the thrust plate. In the ninth locality, the tilted beds that overlie the escarpment are volcanic rocks of the Moroni Formation. Of the nine localities marked by tilted strata, three—Salt Creek (fig. 54), Taylor Fork (fig. 56), and Red Lake (fig. 57)—are characterized by strata that dip eastward. In another three localities—Black Canyon (fig. 55), Payson Can- yon (fig. 58), and Thistle Creek (fig. 44)—the strata dip southeastward; and in two localities—Bennie Creek (fig. 58), and Loafer Mountain—the strata dip southwestward. In Santaquin Canyon (fig. 59), the North Horn strata dip northward. In all localities, no matter what the direction of dip, the strike of the overlying younger strata parallels the escarpment. This parallelism, coupled with these divergent direc- tions of dip, implies some structural relationship between the thrust plate and its mantle of younger Cretaceous and Tertiary rocks. For brevity, I omit descriptions of these localities in the present report, but do include a geologic map and cross section for eight of these localities. Photo- graphic overviews of various of these localities are given in figure 53, and figure 3 shows the locations of all nine. IMPLICATIONS OF THE TILTED STRATA Seemingly, four alternative interpretations reason- ably explain the deformation: DIAPIRIC DEFORMATION OF THE EAST FLANK OF THE CHARLESTON-NEBO THRUST PLATE 1. The tilt of beds in the North Horn Formation is the result of drag along one or more high-angle nor- mal faults that separate the North Horn from the escarpment. 2. Movement along the Wasatch fault zone has raised and tilted the Charleston-Nebo thrust plate eastward, resulting in eastward tilting of the overly- ing mantle of North Horn and younger rocks. 3. Uneven compaction, at time of deposition, of unconsolidated North Horn and younger sediments that were deposited across the eroded thrust plate resulted in the development of a pseudo-arch that reflected the buried plate. Erosion of the arch left tilted remnants of North Horn and younger beds. 4. One or more salt—generated structures— diapiric folds——developed beneath the thrust plate and arched parts of the plate and its overlying man- tle of younger rocks. DRAG ALONG NORMAL FAULT OR FAULTS I could find no evidence of normal faults separating the North Horn from the escarpment. Possibly such faults do exist, but if so they are concealed beneath debris and foliage. It seems unlikely, however, that a single unbroken fault extends along the length of the entire escarpment; such a fault would be marked by an extremely complex and sinuous trace having sev- eral right-angle bends. MOVEMENT ALONG THE WASATCH FAULT ZONE Clearly all sorts of attitudes are possible along a large, complex fault zone. Still, if the thrust plate was raised and tilted eastward as a result of move- ment along the Wasatch fault zone, all North Horn strata draped across the plate should dip eastward. In fact, some North Horn beds that are along the west side of the southern Wasatch Range (near San— taquin), but east of the Wasatch fault zone, dip west- ward (fig. 59). Moreover, although the North Horn along the east flank of the escarpment does dip east- ward, comparable units dip northward near the head of Santaquin Canyon, and southward in the Payson Canyon and Bennie Creek areas. UNEVEN COMPACTION OF UNCONSOLIDATED NORTH HORN FORMATION AND YOUNGER SEDIMENTS Uneven compaction of unconsolidated sediments deposited across the exposed, sloping, and eroded escarpment would result in beds of sedimentary rocks that dip away from the buried plate. As younger sediments were deposited on these rocks and 105 then unevenly compacted, the new units would have still lower dips. The end result would be a stack of sedimentary units with each younger unit marked by somewhat lower dips. This pattern is not apparent in the exposures discussed. The impression created is that all units in the sedimentary stack are parallel and were tilted concurrently. UPLIFT AS A RESULT OF SALT DIAPIRISM One or more diapiric folds, concealed beneath the thrust plate, raised and warped parts of the plate, and in so doing arched the overlying North Horn and younger strata. I believe that the Thistle Creek dia- piric(?) fold deformed the northern sector of the ero- sional escarpment cut across the plate, even as the Footes Canyon diapiric(?) fold (the middle fold of the three formed when the Levan fold trifurcated) deformed the southern sector. Although all four alternatives seem reasonable, it seems to me that only two—differential compaction of unconsolidated sediments, and salt diapirism—are acceptable alternatives. Inadequate exposures pre- clude complete acceptance of either. I believe, how- ever, that salt diapirism is the best explanation, and point to the deformation near Thistle as an example of such warpage of younger beds by uplift of the thrust plate. DISCUSSION Almost all the structural complexity in the Sanpete— Sevier Valley area is most reasonably and simply explained as the result of the repeated growth and collapse of salt-generated diapiric folds. These recur- rent episodes of salt diapirism, which began during the Mesozoic and have persisted into the Quaternary, have stamped a unique geologic pattern on this sector of central Utah. It seems unreaonable to assume that these diapiric folds are restricted only to that part of the area that lies in front of the thrust plate. The folds must be impressed on that part of the area overlain by the thrust plate; if so, the folds must have deformed the thrust plate, too. Still, some relationship must exist between the thickness of the “mother bed” of salt, the amount of overburden, and the degree of diapir- ism. Where the overburden is thick, as in those locali- ties overlain by the thrust plate, possibly the diapirism is restricted and diapiric features are few in number; where the overburden is thin, the diapirism is more active and as a result its features are widespread. 106 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH SOUTHWEST NORTHEAST South flank of Loafer Mountain PlPo EAST Santaquin V ‘ ' _» NORTHWEST NORTHEAST Canyon ‘ ‘ ‘ , ~. ’ a 3;!" F ‘ Thrslle (,reek U,S, HIGHWAYHS DEPOSITIONAL THINNING 107 FIGURE 53 (facing page).—Photographic overviews of localities ad- I propose that the Footes Canyon diapiric(?) fold jacent to the erosional escarpment bordering the Charleston- (fig. 16 13) and the Thistle Creek diapiric fold (fig. 16 Nebo thrust plate. In all localities, clastic beds of the North 11) raise d parts of the thrust plate after the plate was, Horn Formation unconformably overlie the escarpment formed on the Charleston-Nebo thrust plate. Dashed lines delineate an- emplaced, eI'Oded, and then covered by North Horn gular unconformity between the North Horn and underlying and younger strata. As a result, the overlying North units. The North Horn invariably dips away from the escarp- Horn and younger beds were more or less uniformly ment. A, View northward in Salt Creek Canyon showing east- arched ward-dipping sandstone beds of the North Horn Formation (TKn) unconformably overlying overturned beds of the Navajo I do h0t know how far to the north the F 001385 Can- Sandstone (Jn) and Twin Creek Limestone (Jtc). The Navajo yon fold continues beneath the plate. Possibly the and Twin Creek dip northwestward (away from viewer) and are concealed fold extends as far north as Santaquin part of the escarpment. The eastward dip of the North Horn Canyon, as suggested by isolated outcrops of tilted strata lessens and is almost horizontal near the right (east) . North Horn beds exposed on both Sides of the thrust edge of the photograph. Farther to the east, beyond the right edge of the photograph, the North Horn reverses dip and is in- Plate- Along the eaSt flank 0f the southern wasatCh clined westward toward the escarpment. See figure 54 for geo- Ran e, in the Ta lor Fork and Red Lake areas, the . . . . g y logic map of this locality. B, View northward along the east North Horn and younger beds dip eastward (fig_ 59)_ flank of Dry Mountain in Taylor Fork near the head of San- Directly to the west on the opposite side of the 1 taquin Canyon. Clastic beds of the North Horn Formation . . (TKn), which strike northward and dip eastward, unconformably mountalns’ patCheS 0f the North Horn Formatlon overlie beds of the Great Blue Limestone (Mgb), which is part of overlain by small erOded remnants 0f the FlagStalt the erosional escarpment formed on the Charleston-Nebo thrust Limestone dip westward. These opposing dips devel- plate. Volcanic units of the Moroni Formation (Tm) unconform- oped in North Horn and younger strata exposed on ably overlie the North Horn Formation, and seemingly are de- opposite sides of the mountains suggest that an anti- formed along with it. See figure 56 for geologic map of this . . locality. C, View southward along east flank of Dry Mountain, Chnal feld was formed In these younger beds above near Red Lake, showing eastward-tilted clastic beds of the an arched thrust plate, much as in the Thistle area. North Horn Formation (TKn) unconformably overlying east- And, as in the Thistle area, the deformation of the ward-tilted undivided Mississippian strata (Mu) that are part of rocks within the thrust plate obscures the simple, the escarpment on the Charleston-Nebo thrust plate. See figure later upwarping. 57 for geologic map of this locality. D, View eastward at expo- . sures near head of Payson Canyon. In this locality, the escarp- The attltUdeS assumed by the bowed-up North ment bends sharply to the northeast along a reentrant cut into Horn and younger beds were determined by the con- the thrust plate. As a result, the clastic beds of the North Horn figuration of that part of the erosional escarpment on Formation (TKn), which unconformably overlie the escarpment, which they rested. This would explain the general strike northeast and dip southeast. The escarpment is formed . on the Oquirrh Group (PIP 0), which also strikes northeast and eaStward tllt Of those North Horn and younger beds dips southeast. See figure 58 for geologic map of this locality. E, that reSt Oh that part Of the escarpment that trends View looking northwestward at a small hogback, near the head north, the northward dip Of North Horn strata in of Bennie Creek, along south flank of Loafer Mountain. The Santaquin Canyon Where these beds overlie the which is fg‘rmedthy (Stklhlivthnt-dlppmg 01:51:19 bet? 01f, thhte north flank of an eastward-directed protuberance of or - 0 H mm Ion a are cappe y a m lg the escarpment, and the southward and southwest- g'ray bed of the Flagstaff Limestone (Tf). The North Horn rests , . . unconformably on the Oquirrh Group (PlPo), which strikes ward dlps 0f Slmllar Strata eXPosed along the south northwestward and dips northeastward, and forms part of the flank of Loafer Mountain, where North Horn and east-trending escarpment See figure 58 for geologic map of this younger beds overlie the sinuous south flank of the locality. F, View northward along west valley wall of Thistle east-trending escarpment. Creek. The escarpment formed on the Charleston-Nebo thrust plate is exposed in a small gap eroded in a mantle of folded younger Cretaceous and Tertiary units. The escarpment is rep- resented by steep eastward-dipping beds of the Navajo Sand- DEPOSITIONAL THINNING stone (Jn) and the Twin Creek Limestone (Jtc). The folded Cretaceous-Tertiary mantle is represented by sedimentary beds _ . _ of the North Horn Formation (TKn) and the Flagstaff Limestone sequences 0f sedlmehtary unlts thlh and locally (Tf), and by volcanic units of the Moroni Formation (Tm). Only pinch out near the crests of the diapiric folds. Some remnants of the sedimentary cover are preserved along the base units wedge out by onlap against the flanks of the of the west valley wall of Thistle Creek, but the cover is exten- fold; other units thin but continue across the crests of sively exposed on the uplands both east and west of the creek. the folds. Both the pinchouts and the thinning pre- In general, the beds that form the cover west of the exposed . _ . . . escarpment dip westward; those that form the cover east of the sumably reSUlt from impeded depOSlthh- Thls depOSI- escarpment dip eastward. See figure 44 for geologic map of this tional thinning appears to influence sequences of locality. units rather than just one discrete unit in a 108 111°44’ 43' SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 42' 111°4‘I' 39°4B' Ev 4/4» is- ' ~‘ Ii +y/g . ,r . 39°43' “ ' FIGURE 54 (above and facing page).—Geology of Salt Creek area. Geology slightly modified from Witkind (1987, fig. 6). Base modified from US. Geological Survey 1:24,000 Nebo Basin (1979). Contour interval 200 ft. Overturned Paleozoic and Mesozoic strata that strike northeast and dip northwest mark the erosional escarpment formed on the Charleston-Nebo sequence. This thinning affects beds that range in age, at the least, from Middle(?) Jurassic to early Tertiary This widespread pattern of depositional thinning involving sequences of sedimentary units near the crests of folds provides some of the most compelling evidence that diapirism has played a significant role in the structural evolution of this part of central T125 2 KILOMETERS J 1 MILE thrust plate. These beds are mantled by beds of the North Horn (TKn) and Moroni (Tm) Formations. The North Horn strata that overlie the escarpment dip eastward; a short dis— tance away from the escarpment the strata reverse dip and are inclined toward the escarpment. See figure 53A for photo- graphic overview of this locality. Utah. If but one unit thinned as a result of onlap onto a static topographic high, younger sediments would, in time, bury the ancestral high. This is not the case in central Utah. All stratigraphic units near the crests of the folds thin, implying that a dynamic ancestral high—the diapiric fold—continued to move upward slowly even as the younger sediments were being deposited. DEPOSITIONAL THINNING 109 EXPLANATION Alluvium } Holocene Oligocene and Eocene } QUATERNARY Contact—Approximately located or inferred —-—-— lntrusive sedimentary contact—Oblongs on intrusive sedimentary unit J—u—‘—‘— Edge of erosional escarpment—Hachures point Moroni Formation TERTIARY 30 in general direction of inclination \ . TlJa) ‘ 1) Paleocene and 4—60 Strike and dip of inclined beds North Horn Formation j Upper Cretaceous CRETACEOUS —b— Strike and dip of overturned beds A , .7 Sh 1 } Middle rapien a e 4 x , Twin Creek Limestone Jurassrc > JURASSIC . } Lower Navajo Sandstone Jurassic 2 , } Upper and \ Ankareh Formation Lower Tria551c . Q t» “a > TRIASSIC Thaynes Limestone Lower Triassic Woodside Formation a 3941181’0441 111 a,“ . \ Unpublished reconnaissance Park City Formation mapplng-by .J. Wltklnd - PERMIAN Diamond Creek Sandstone Black and Kirkman Limestone (1965) am PENNSYLVANIAN Oquirrh Group Good examples of this depositional thinning are widespread; several are discussed following. SAN PETE—SEVIER VALLEY DIAPIRIC FOLD In Wales Gap (D—4) (along the east flank of the Gunnison Plateau), near the crest of the Sanpete— Sevier Valley diapiric fold, the Indianola Group, which is thousands of meters thick elsewhere, is but 35 m (115 ft) thick. Similarly, the Cedar Mountain Formation at Wales Gap is only 18 m (60 ft) thick but is almost 430 m (1,400 ft) thick away from the diapiric core of the fold. The Sixmile Canyon (F—4) area (along the west margin of the Wasatch Plateau) is just east of the crest of the Sanpete—Sevier Valley diapiric fold. The Price River, North Horn, and Flagstaff Formations are all extremely thin near the mouth of Sixmile Canyon but thicken markedly eastward away from the diapiric crest. The Flagstaff Limestone, for exam- ple, is about 30 m (100 ft) thick at the canyon mouth but at least 365 m (1,200 ft) thick some 10 km (6 mi) to the east along the top of the Wasatch Plateau. SOURCES OF GEOLOGlC DATA In various localities in Sanpete Valley, such as near ancestral Willow Creek (G—3), and in place after place along the west flank of the Gunnison Plateau, uppermost Green River strata unconformably overlie the Arapien Shale (Witkind, Weiss, and Brown, 1987). These localities are along the flanks of the dia- piric folds, and I interpret the stratigraphic relations to mean that units below the Green River, such as the North Horn, Flagstaff, and Colton, have pinched out against the flanks of the rising fold. The fact that uppermost Green River strata, unbroken but anoma- lously thin, mantle the fold’s crest, implies that lower Green River and older sediments pinched out against the fold’s flanks. Seemingly, during late Green River time deposition was rapid enough to surmount the rising mass of Arapien. SEVIER BRIDGE RESERVOIR DIAPIRIC FOLD Along the northeast flank of the Valley Mountains (G—Z), the North Horn, Flagstaff, Colton, and Green River Formations are anomalously thin where they form part of the southwest flank of the Sevier Bridge SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 110 lll°43’ 41' 40’ 111°39’ 39°52' ' A e T 11 s 4» 51’ 41 ¢ 3 o H 9 50 H 2 E [l l 2 KILUMETEBS l l I I ‘ w l | I | l I l I [J 1 MILE A E 4‘ A ' EXPLANATION > 8 FEET 5 (3 Contact—Approximately located 8000 ‘6 _§ - Oligocene or inferred; queried in cross sec- ; Z Moroni and Eocene TERTIARY tion where speculative 7000 \ K' Formation J—l—LJ—L Edge of erosional escarpment— . Paleocene Hachures point in general direc- 2 tion of inclination 8000 NW" H°"' _._ Strike and dip of inclined beds 111°43’ 111 039/ Formation Upper o ,_ Cretaceous CRETACEOUS —|—— Strike and dip of vertical beds 39 52 Unpublished ‘4 . lndianola reconnalssance . Group mapping by |.J. Witkind ‘ PERMlAN AND 39°50’ 0quth PENNSYLVANIAN SOURCE OF GEOLOGIC DATA Group DEPOSITIONAL THINNING Reservoir diapiric fold. So, for example, the North Horn is about 38 m (125 ft) thick, the Flagstaff about 11 m (37 ft), the Colton about 61 m (200 ft), and the Green River about 53 m (175 ft) thick. As these units are traced perpendicularly away from the crest of the fold, they thicken rapidly; within about a kilometer (0.6 mi) the North Horn has increased in thickness to about 91 In (300 ft), the Flagstaff to about 49 m (160 ft), the Colton to 82 m (270 ft), and the Green River to about 95 m (310 ft). The same pattern of depositional thinning is apparent in Red Canyon (E—2) (in the Valley Moun- tains) along the west flank of the Sevier Bridge Res- ervoir fold. The North Horn Formation, for example, is about 15 m (50 ft) thick near the canyon mouth, but more than 180 m (600 ft) thick 1.5 km (1 mi) to the west near the head of Red Canyon. Both along the northeast flank of the Valley Moun- tains and in Red Canyon, as far as I can determine, only the younger, upper parts of the formations are represented, implying that the older, lower parts of the formations pinched out against the flanks of the diapiric folds. POLE CREEK DIAPIRIC FOLD Units that are part of the southeast flank of the Pole Creek diapiric fold crop out in the Middle Fork Pole Creek (B—4) (fig. 39). These units, which include the Middle Jurassic Twist Gulch Formation and the Lower Cretaceous Cedar Mountain Formation, are vertical and anomalously thin. The Twist Gulch is only about 60 m (200 ft) thick; elsewhere in the Sanpete—Sevier Valley area, the 'IVvist Gulch is about 915 m (3,000 ft) thick. The Cedar Mountain, east of and conformably overlying the steeply dipping Twist FIGURE 55 (facing page).—Geology of an area along and near Black Canyon. Geology slightly modified from Witkind (1987, fig. 7). Base modified from US. Geological Survey 1224,000 Nebo Basin (1979). Contour interval 200 ft. Clastic beds of the North Horn Formation (TKn), which are juxtaposed against the escarpment formed on the thrust plate, strike northeast and dip southeast, and unconformably overlie units of the Oquirrh Group (PPO) of similar strike and dip. These North Horn units reverse dip west of Nebo Creek, reflecting the west flank of a diapiric fold (possi- bly a segment of the Thistle Creek fold (fig. 16, 11), part of which is exposed in sections 24 and 25. Cross section is not deep enough to include the Charleston-Nebo thrust fault, which is the sole of the thrust plate. 111 Gulch strata, is only about 245 m (800 ft) thick; else- where, the Cedar Mountain is as much as 430 m (1,400 ft) thick. THISTLE CREEK DIAPIRIC FOLD In the Thistle area, various of the Cretaceous and Tertiary units thin westward toward the crest of the Thistle Creek diapiric fold. This is perhaps best shown in Young's (1976) figure 5, which shows that all units from the North Horn to the Green River Formation thin westward toward Thistle. DISCUSSION Gundersen and Gilliland (1967) recognized this pat- tern of depositional thinning in various localities throughout the Sanpete—Sevier Valley area. As the most striking examples are near their Sanpete—Sevier Valley anticline (my Sanpete—Sevier Valley diapiric fold), their article concentrated on that part of the area. In a series of isopach maps, they demonstrated that three formations—the Price River and North Horn Formations, and the Flagstaff Limestone—thin anomalously toward the crest of the Sanpete—Sevier Valley fold; they commented (1967, p. 688): “* * * each formation thins markedly towards the anticline * * *.” Their isopach maps for the Price River (1967, fig. 2), North Horn (1967, fig. 3), and Flagstaff Limestone (1967, fig. 4) show that, on both flanks of the fold, the formations thin toward the fold crest. The Flagstaff Limestone, for example, thins westward from about 460 m (1,500 ft) along the top of the Wasatch Plateau to about 75 m (250 ft) near Sterling (F—4), which is along the east flank of the Sanpete—Sevier Valley dia- piric fold. Gundersen and Gilliland's isopach map of the North Horn Formation demonstrates a similar pattern of thinning. The North Horn, about 460 In ( 1,500 ft) thick along the top of the Wasatch Plateau, thins westward to only about 75 m (250 ft) near Manti (E—4), along the east flank of the Sanpete— Sevier Valley fold. Farther west, in and near the Valley Mountains (G—2), Gundersen and Gilliland’s isopach map (1967, fig. 3) shows the North Horn to be about 610 m (2,000 ft) thick near Scipio Lake (F—2) (west of the Valley Mountains), but to thin eastward to about 230 m (750 ft) near Redmond (G—3), which is along 112 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH T‘IUS T113 39°53' ’ ’ ' ' ' ‘ I ' " ' ’ RZE 1 2KILOMETERS I 1 MILE DEPOSITIONAL THINNING 113 EXPLANATION } Holocene } Oligocene and Eocene } QUATERNARY Contact—Approximately located or inferred -‘—‘—‘—‘—‘- Edge of erosional escarpment—Hachures point in general direction of inclination —; Fault—Approximately located; bar and ball Moroni Formation TERTlARY 2 on downthrown block i Paleocene —L Strike and dip of inclined beds North Horn ormation Upper Cretaceous CRETACEOUS 69 Horizontal beds " i i ’ PERMIAN Oquirrh GI'OIIP PENNSYLVANIAN Manning Canyon Shale Unpublished Great Blue Limestone Upper reconnaissance . ma in b Mississippian I J pWitEindl Metter ' ' Humbug Formation [ MISSISSIPPIAN (1955) Deseret Limestone < at _, Lower 39°5a' Gardison Limestone Mississippian SOURCES OF GEOLOGIC DATA Fitchville Formation Upper Devonian DEVONIAN c 0 Upper Cambrian rocks. undivided A g o g g E A ’ , , . FEET E g E 8 8 FEET . 9 , u, , 0000 g; 9 LC) ; .g 9000 Middle Cambrian rocks. undivided . 3 '3 § 5; ... < 0000 3 0000 Middle Cambrian Tintic Quartzite Late Proterozoic 7000 Big Cottonwood Formation FIGURE 56 (above and facing page).—Geology of Taylor Fork area near head of Santaquin Canyon. Geology slightly modified from Witkind (1987, fig. 8). Base modified from US. Geologi- cal Survey 1:24,000 Payson Lakes (1979). Contour interval 200 ft. In Taylor Fork, the escarpment formed on the Charles- ton-Nebo thrust plate trends north, and the overlying North Horn Formation (TKn) thus trends northward and dips east- the flank of their Redmond Hills anticline (my Red- mond diapiric fold). Willis (1986), working in the Salina Canyon area, astride the south end of the Sanpete—Sevier Valley diapiric fold, noted that North Horn and Flagstaff strata thin and locally pinch out near the crest of a north-trending “paleo-high,” essentially the Sanpete— Sevier Valley “anticline” (Willis, 1986, p. 9). Willis indicated that Colton and Green River strata also thin toward the axis of the paleo-high. ward (see fig. 533 for photographic overview of these rela- tions). As these beds of the North Horn are traced southeastward into Santaquin Canyon, they gradually assume an eastward strike and a northward dip reflecting an eastward bulge of the escarpment. Cross section is not deep enough to include the Charleston-Nebo thrust fault, which is the sole of the thrust plate. Gundersen and Gilliland (1967, p. 686) suggested that this anomalous thinning stemmed from the Sanpete—Sevier Valley and Redmond anticlines being topographically positive elements through much of Late Cretaceous and early Tertiary time. They attrib- uted the development of the Sanpete—Sevier Valley anticline to: “* * * compression during the early Lara- mide orogeny.” I disagree somewhat with Gundersen and Gilli- land’s interpretation. I suggest instead that the SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 114 111°41’ 42' 43' 2 KILUMETEHS 1 MILE DEPOSITIONAL THINNING 115 EXPLANATION ,i }Holocene }QUATERNARY Colluvrum Earthflow Oligocene and Eocene Alluvium Moroni Formation TERTIARY i Paleocene North Horn Formation Upper Cretaceous CRETACEOUS PERMIAN PENNSYLVANIAN Great Blue Limestone Upper Humbug ormation MiSSlSSipp‘an . , \ MISSlSSlPPIAN Deseret Limestone } Gardison Limestone Mississrppian Cmu Middle Cambrian rocks, undivided Middle Cambrian Tintic Quartzite A FEET 10,000— DRY MOUNTAIN 9mm — ‘ anon — , \ Eros' | t 7000— Iona escarpmen Contact—Approximately located or inferred; queried in cross section where speculative ——; Fault—Approximately located; bar and ball on downthrown block Fault—Indeterminate type; approximately located J—F‘A—L Edge of erosional escarpment—Hachures point in general direction of 2 inclination _I_ Strike and dip of inclined beds $ Horizontal beds 111°44’ 39°5a' 11141 Unpublished Metter reconnaissance (1955) mapping by |.J. Witkind 39 °55’ SOURCES OF GEOLOGIC DATA FEET 10,000 9000 5000 FIGURE 57 (above and facing page).—Geology of an area near Red Lake. Geology slightly modified from Witkind (1987, fig. 9). Base modified from US. Geological Survey 1:24,000 Payson Lakes (1979). Contour interval 200 ft. Clastic beds of the North Horn Formation (TKn) strike northward and dip eastward, and unconformably overlie a series of Mississippian strata that also depositional thinning so evident in the Sanpete— Sevier Valley area is due to slowly rising, dynamic, salt-cored diapiric folds that probably began rising in Middle Jurassic time and continued to rise slowly throughout the Cretaceous and into the middle Ter- tiary. Seemingly, Gundersen and Gilliland viewed strike northward and dip eastward. These Mississippian strata are part of the escarpment formed on the Charleston-Nebo thrust plate. Cross section is not deep enough to include the Charleston—Nebo thrust fault, which is the sole of the thrust plate. See figure 53C for general photographic overview of this locality. their Sanpete—Sevier Valley anticline as a dynamic feature—they demonstrated depositional thinning for at least three units. The conclusion seems inescap- able—depositional thinning is reasonably explained only by invoking a dynamic, rising body. As noted above, sediments deposited against the flanks of a 116 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°41’ 39°58’ , Ix++ga++ii 'l+{ ' T108 39%5' H2 E H a E 0 1 2 KILOMETERS II I I l i l I I II I I I | I I 4' g 1 MILE A A’ 111°41’ o ' FEET x LOAFER SEE: 39°5a’ m 38 9000 g MOUNTAIN Metter (1955) 8 A E 30”“ § anon Unpublished reconnaissance mapping by 7000 7300 LJ. Witkind 39°56' SOURCES OF GEOLOGIC DATA FIGURE 58 (above and facing page).—Geology of an area near Charleston-Nebo thrust block trends eastward, and the overly- head of Payson Canyon and Bennie Creek. Geology slightly ing North Horn Formation dips southward. Cross section is not modified from Witkind (1987, fig. 10). Base modified from US. deep enough to include the Charleston-Nebo thrust fault, which Geological Survey 1:24,000 Payson Lakes (1979). This area is the sole of the thrust plate. See figure 53D for a photographic encompasses the north edge of the broad, eastward-facing San- overview of the exposure at the head of Payson Canyon, and taquin embayment. As a result, the escarpment formed on the figure 53E for an overview of the Bennie Creek exposure. DIAPIRIC PROCESSES EXPLANATION } Holocene } QUATERNARY Alluvium } Oligocene Moron: ormation and Eocene Eocene -' TERTIARY Flagstaff Limestone and Colton Formation, Paleocene undivided North Horn Upper CRETACEOUS . Cretaceous Formation J l PERMIAN AND Oquirrh Group PENNSYLVANIAN Humbug Formation MISSISSIPPIAN Lower Mississippian Upper Mississippian Gardison Limestone Middle Cambrian rocks, undivided Contact—Approximately located or inferred F amt—Indeterminate type; approximately located -F‘—‘—‘—‘- Edge of erosional escarpment—Hachures point in general direction of inclination Strike and dip of inclined beds 50 _t_ static “anticline” would eventually bury that anti- cline. Younger strata, unchanged in thickness, would then pass over the buried anticline and show no pat- tern of depositional thinning. This anomalous thinning of the sedimentary units, although extremely localized, being confined to and near the crests of the diapiric folds, is found through- out the area. I have recognized it in the Valley Mountains (G—2) near the west end of the study area, throughout the center of the area, and to the east near Thistle (A—5). I interpret this widespread (but localized) depositional thinning to be evidence of the slow, continuous upwelling of salt in discrete dia- piric folds. Seemingly, the rate of upwelling was comparable to the rate of deposition; the folds kept coming up just about as fast as the sediments kept trying to bury them. In those places where the sedi- mentary beds wedge out against the flanks of the fold, the fold’s growth rate must have slightly exceeded the depositional rate of the sediments. Where thinned sediments overlie the crest of the fold 117 the depositional rate must have exceeded the fold’s growth rate. Sannemann (1968, p. 357), discussing the salt- stock families of northwestern Germany, suggested that salt, as it forms a salt stock (salt diapir), moves about 0.3 mm per year. Such movement would be dif- ficult to detect, but would be rapid enough to form a growing barrier that would impede the comparably slow deposition of sediments. The result would be wedgeout and thinning of sedimentary units along the flanks of the growing fold. It seems reasonable to conclude that as the folds grew they impeded sedimentary deposition through- out much of the Middle and Late Jurassic, Early and Late Cretaceous, and early Tertiary. Incomplete exposures prevent a definitive statement as to which units show this depositional thinning, but probably they include, at the very least, the sequence from the Twist Gulch Formation of Middle Jurassic age up to and including the Green River Formation of Eocene age. Two factors seem very significant: (1) Sequences of stratigraphic units thin near the crest of a diapiric fold, and (2) invariably, where criteria are adequate to permit determination, as in the Red Rocks area (p. 41), the beds that overlie the crest of the fold are the younger and uppermost parts of the formations involved; the older and lower beds of the formations pinch out against the flanks of the fold. DIAPIRIC PROCESSES GROWTH AND COLLAPSE OF DIAPIRIC F OLDS In place after place throughout central Utah, the structural complexity seems most reasonably explained by the repeated growth and collapse of dia- piric folds. GROWTH OF DIAPIRIC FOLDS The salt within the Arapien Shale has probably been moving since shortly after it was deposited. Some of this movement has been a slow upwelling that has resulted in the development of ancestral, linear to faintly sinuous topographic highs—paleo-highs—that impeded sedimentary deposition. At times, however, the salt, in the form of a linear, narrow salt diapir, seemingly has surged upward rapidly (in a geologic sense), and forcefully. These recurrent upward surges of the causative salt diapir have forced the overlying Arapien mudstone repeatedly to bow up and fold back 118 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 111°45’ T 10 S Foutz Matter (1960) (1955) 39°55' e SOURCES OF GEOLOGIC DATA (Modified somewhat on basis of unpublished reconnaissance mapping by l.J. Witkind) R l E [I 1 2 3 4 KILUMETEHS 0 1 2 MILES C o E 4: u.l E m 0 I A I g c E (l: DRY L: A was .9": a 3 //‘=;=—*\M°UNTA'N g9; METERS 3000 E5! 5 / i=3 \\ l~ 3000 2500 3 E g 375 2500 de “- Del 2000 QC, - 2000 “J 1500 « 1500 1000 1000 EXPLANATION I? « J Pfil ‘ I :| W ——— Contact—Approximately located or in- . . 0 V r . . _ 4 , , 5 ~‘ Holocene ferred; incross section, dashed where Earthflow Landslide Alluvium Colluvium Mass-wasting : inferred, queried where speculative deposits deposits deposits | > QUATERNARY -'—‘—‘—"—‘— Edge of erosional escarpment— : Pl . t Hachures point in general direction of Deposits of Lake Bonneville cycle a“ “we inclination 0 -‘—‘-‘—J— Fault—Approximately located; bar and " . . ’ -' Pliocenel?) ball on downthrown block; dotted Coalesced alluvial—fan deposits Laguna Springs - where concealed; hachures indicate modern fault scarp; barb shows Oligocene L downthrown block in cross section; and Eocene TERTIARY dashed in cross section where Volcanic Group Moroni 25 reconstructed above eroded surface Formation —l— Strike and dip of inclined beds Flagstaff Limestone Paleocene c ”3’” CRETACEOUS North Horn Formation 7 H re aceous Arapien Shale Mlddle JURASSIC Jurassic Paleozoic rocks, undivided DIAPIRIC PROCESSES the overlying sedimentary units into mushroom- shaped diapiric folds. SLOW UPWEILING The slow, upward movement of the salt diapir is expressed by the anomalous thinning of sedimentary units near the crests of the ancestral highs, much as discussed previously (p. 107—117). Locally, some of the units pinch out against the flanks of the high. Those units that continue unbroken across the crests of the highs, however, are the uppermost and younger parts of the formations. The lower and older parts of the formations presumably have pinched out against the slowly rising high. The fact that sequences of units thin must mean that the high was a dynamic feature growing continuously throughout lengthy episodes of geologic time. Were the paleo- high merely a static feature, the first units deposited against the flanks of the high might thin, but once the high was surmounted, subsequent units would pass over the crest of the high unchanged in thick- ness. This depositional thinning near the crests of the highs, found throughout the area, seems reason- ably explained only as the result of slowly rising salt diapirs. RAPID, UPWARD, FORCEFUL SURGES In contrast to the slow, continuous movement, it is the repeated, forceful upward surges of the causative salt diapirs that appear to have determined the structural pattern of this part of central Utah. Salt is the motive force: It forces up the Arapien mudstones, which, in turn, force up and deform the overlying sedimentary units. These deformed sedimentary units, and their contained folded angular unconformi- ties, reflect the repeated upward surges of the caus- ative salt diapir. Expectably, the Arapien mudstones show many signs of extreme deformation; their present attitudes, however, merely reflect the last diapiric episode. Subsequent episodes will deform them once again. FIGURE 59 (facing page).—Geology of an area near Dry Mountain. Geology slightly modified from Witkind (1987, fig. 12). Base modified from US. Geological Survey 1:100,000 Nephi (1981). Contour interval 250 In. An underlying diapir appears to have arched the Charleston-Nebo thrust plate. North Horn (TKn) strata that flank north-trending Dry Mountain, part of the Charleston-Nebo thrust plate, dip eastward east of the range and westward west of the range. These opposing dips in the younger strata suggest that the Charleston-Nebo thrust plate was arched by an underlying diapir (cross section A—A’). 119 COLLAPSE OF DIAPIRIC FOLDS After the major folds were bowed up by the intru- sive action of the Arapien Shale, they failed when salt was removed from the core of a diapiric fold. As the salt was removed, as a result of either extrusion or dissolution, the Arapien mudstone subsided into the newly formed void or voids. The failure probably occurred in small spasmodic movements, and not as a single catastrophic event. Failure of the folds seems to have occurred either by collapse of the crestal part of the fold between high-angle normal faults, or by gradual subsidence of strata (outside the normal faults) to form monoclines (fig. 60). In some places both modes of failure may have occurred—downthrow along a high-angle mar- ginal fault on one flank of a fold and downwarp on the opposite flank. Invariably, the downthrow or downwarp was toward the core of the fold. In the ancestral Willow Creek (G—3) area (fig. 27), and along the northeast border of the Valley Moun- tains (G—2) (fig. 30), the crestal part of the fold prob- ably collapsed between high-angle faults that formed along the fold’s flanks (fig. 60A). A long, linear gra- ben most likely resulted, probably much like those grabens that break the rocks along the crest and west flank of the Wasatch Plateau. This concept implies that the marginal faults that bound the gra- ben extend to the base of the Arapien Shale but do not cut through the underlying 'IVvin Creek Lime- stone on which the Arapien rests. My examination (through the courtesy of Chevron, USA) of seismic reflection profiles that cross the Wasatch Plateau convinces me that those faults that bound large gra- bens, such as the Joes Valley graben, do not, in fact, extend below the base of the Middle Jurassic Arapien Shale or its correlative, the upper part of the Carmel Formation. Elsewhere, as near the mouth of Sixmile Creek canyon (F—4), along the west flank of the Wasatch Plateau (fig. 21), and in Red Canyon (E—2), along the east flank of the Valley Mountains (fig. 31), the folds appear to have failed by gradual subsidence and so formed monoclines (fig. BOB; and Witkind and Page, 1984). Thus, I interpret the westward-facing Wasatch monocline, and the much smaller, unrelated, east- ward-facing Valley Mountains monocline, along the east flank of the Valley Mountains, to stem from such subsidence. As the diapiric core subsided, in response to the removal of salt, the overlying sedimentary and volcanic strata subsided into the resultant void to form a broad V, forming, thus, a pair of facing mono- clines. The resultant feature is best visualized as a 120 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH EAST WEST EAST EXPLANATION E i: S. : 3 I C Tertiary rocks, undivided—Includes, in descending order, Crazy Hollow Forma— tion, Green River Formation, and Colt— on Formation, and Flagstaff Limestone TKu Tertiary and Cretaceous rocks, undivided—Includes, in descending order, North Horn Formation and Price River Formation KJu ' Cretaceous and Jurassic rocks, undivided—Includes, in descending order, the undivided lndianola Group, Cedar Mountain Formation, and Twist Gulch Formation 7 Arapien Shale Holocene Eocene and Paleocene Upper Cretaceous Middle Jurassic } QUATERNARY W > TERTIARY > CRETACEOUS > JURASSlC DIAPIRIC PROCESSES collapse structure, for the formerly continuous strata that overlay the diapir were broken and disrupted as they subsided. The structure, thus, differs from a syncline, which is formed by downwarped but essen- tially unbroken strata. Doelling (1988, p. 45, figs. 46 and 49) referred to somewhat comparable collapse features developed in the Paradox Basin, and essen- tially similar in size to those within the Sanpete— Sevier Valley area, as “* * * v-shaped dissolution synclines * * *,” or “V-synclines.” PAIRED, FACING MONOCLINES If the monoclines in the Sanpete—Sevier Valley area are indeed the result of subsidence stemming from removal of salt, one would expect to find paired, fac- ing monoclines—one facing east even as its opposite number faces west. In places, that appears to be the case. So, the eastward-facing Valley Mountains mono- cline is paired with the westward-facing West Gunni- son monocline developed along the southwest flank of the Gunnison Plateau. Sevier Valley separates the two monoclines (fig. 61). In like fashion, the east- ward-facing West Hills monocline, which delineates the east flank of the West Hills, is paired with the northern part of the westward—facing West Gunnison monocline. Juab Valley separates the two monoclines. Farther to the east, the westward-facing Wasatch monocline then should be paired with another mono- cline across Sanpete Valley, one that faces east and FIGURE 60 (facing page).—Diagrammatic sections illustrating two alternative interpretations of how diapiric folds may fail. In each view, west is at left, east is at right. A, The crest of a fold collapses and a linear graben is formed. 1. Fan-shaped diapiric fold is formed as a result of the upward thrust (large arrow) of Arapien mudstones—a direct result of the upward movement of a salt diapir (not shown). II. With gradual removal of salt, by either extrusion or dissolu- tion, the underlying support for the Arapien mudstones is re- moved, and they and the overlying strata collapse (large arrow) along high-angle faults formed along both flanks of the fold’s crest (Barbs show relative movement along faults.) The end result is a long, linear graben comparable to those that break the rocks along the crest and west flank of the Wasatch Plateau. B, The central part of a fold gradually subsides, and facing monoclines are formed. I. A fan-shaped diapiric fold is formed. 11. With gradual removal of salt, the Arapien mudstones, lack— ing support, sink into the newly created voids; the overlying sedimentary strata founder and break into large masses. Ero- sion quickly destroys these fragmented blocks. III. Continued removal of salt and the concurrent subsidence of the Arapien mudstones eventually cause downward flexing of previously upturned beds to form paired, facing monoclines. 121 that delineates the east flank of the Gunnison Pla— teau. Rather than a monocline, however, a north- ward-trending belt of upturned and locally overturned Cretaceous and Jurassic rocks marks the lower flank of the plateau.4 All sedimentary units within this distinctive belt are anomalously thin. Analogous structures elsewhere in the area imply that this belt may once have lain beneath a former monocline. Similar, anomalously thin Cretaceous and Jurassic rocks are exposed in both the Wasatch and Valley Mountains monoclines, where the downwarped Tertiary beds have been breached (Witkind, 1992). In both those areas, the upturned “Cretacecus” rocks are complexly deformed, and all strata, upturned “Cretaceous” and downwarped Tertiary, are anoma- lously thin compared with their thicknesses else- where in the area. Specifically, where the foot of the Valley Mountains monocline is breached at its north end, the sedimentary units exposed at Red Canyon are both structurally complex and remarkably thin. Similarly, where the foot of the Wasatch monocline is breached at the mouth of Sixmile Creek canyon, the exposed rocks are both unusually complex structur- ally and atypically thin. Locally, this same pattern—downwarped Tertiary beds overlying upturned “Cretaceous” rocks—is exposed along the West Gunnison monocline. In that sector, too, the Cretaceous and Tertiary rocks display the anomalous thinness seen elsewhere, but not the striking structural complexity. I attribute this appar- ent absence of structural complexity to the fact that erosion has not cut deeply enough to expose the underlying vertical to overturned beds (fig. 62A). Weiss (in Witkind, Weiss, and Brown, 1987) and Mat- tox and Weiss (1987) have assigned the elastic beds beneath North Horn strata and exposed along the southwest flank of the Gunnison Plateau to the Indi- anola Group. I believe that the beds in question, rather than being part of the Indianola, are more cor- rectly part of the Price River Formation. In lithology, appearance, and attitude, the beds in question are very much like the Price River strata that overlie ver- tical to overturned beds of the Indianola Group exposed along the east flank of the Gunnison Plateau north of Wales (fig. 623, and fig. 17). Thus, in my view, erosion has not cut deeply enough along the west flank of the Gunnison Plateau to expose the 4The bowed up strata include, in various localities, Middle Jurassic (’IVvist Gulch Formation), Lower Cretaceous (Cedar Mountain Formation), Upper Cretaceous (Indianola Group, Price River Formation), and Upper Cretaceous and Paleocene units (North Horn Formation). For ease of discussion I group these beds and refer to them as “Cretaceous” in this discussion. SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 122 Emma? \ » 20w aqu .1 . . \. , _ . _ Ilr \ T . mz_40§_mz_353 m2”? 803 3U KILUMETERS 20 MILES 5 1D DIAPIRIC PROCESSES FIGURE 61 (facing page).——Paired, facing monoclines in the Sanpete—Sevier Valley area formed as the result of removal of salt from an underlying diapir. East-facing Valley Mountains monocline is paired with the west-facing West Gunnison mono- cline, across Sevier Valley. East-facing West Hills monocline is paired with north end of the west-facing West Gunnison mono— cline. A now completely eroded and removed monocline mark- ‘ ing the east flank of the Gunnison Plateau—the East Gunnison monocline—is postulated to pair with the Wasatch monocline. Of major Neogene monoclines trending northward through the Sanpete—Sevier Valley area, only the Wasatch and Valley mono- clines are essentially whole and only slightly eroded. Only remnants of the West Gunnison monocline are left to indicate its former extent, and the East Gunnison monocline, completely eroded, can only be inferred. Base modified from US. Coast and Geodetic Survey 1:500,000 Grand Junction (T—3) Sectional Aeronautical Chart (1954; rev.). 123 the monoclinal slope, are both anomalously thin and unusually complex structurally. It seems more than fortuitous that in three Widely separated areas—(1) Red Canyon in the Valley Mountains, (2) Sixmile Canyon along the west flank of the Wasatch Plateau, and (3) the lower flanks of the east side of the Gunnison Plateau—the exposed rocks display both unusual structural complexity and atypical thinness. The one great difference among the three areas is the absence of a monocline along underlying Indianola strata. Were those Indianola strata exposed, I believe their attitudes—vertical or dipping steeply toward the east—would mimic those exposures along the east flank of the plateau (fig. 62). Seemingly, the monoclines in the Sanpete—Sevier Valley area differ from most monoclines. A section through any monocline within the Colorado Plateau displays a sequence of stacked, layered beds that con- form in attitude to those beds that form the mono- clinal slope. It is much like a section through an onion. By contrast, a section through a monocline in central Utah does show the characteristic layered aspect in the upper and middle parts of the monocline, but not in the distal end—the foot—of the monocline. Those beds exposed at the foot of the monocline, beneath the downwarped Tertiary strata that define WEST EAST Suggested configuration of the _. / West Gunnison monocline /// > Flagsrarr L'Mestone Surficial deposiis/ / / s‘one unconformity FIGURE 62.—Diagrammatic cross sections showing suggested geo- logic relations along both east and west flanks of Gunnison Plateau, a southward-plunging syncline. A, West flank of the Gunnison Plateau. In general, Cretaceous strata that dip east- ward along the west flank of the plateau are overlain with angu- lar unconformity by westward-dipping Tertiary strata. These Tertiary beds form the much-dissected westward-facing West Gunnison monocline. Units here labeled Price River(?) Formation have been called the Indianola Group by Mattox and Weiss (1987). B, East flank of the Gunnison Plateau. In general, Creta- ceous strata dip westward along the east flank of the plateau. I contend that these strata were once overlain with angular uncon- formity by eastward-dipping Tertiary strata that formed the East Gunnison monocline, now completely eroded. C, East flank of the Gunnison Plateau. Locally, the Cretaceous beds that crop out along the east flank of the plateau have been warped up into vertical and overturned attitudes. Near Wales (D—4), for example, Price River strata, which dip gently westward near the mouth of Maple Canyon (E—3), are overturned and form a prom- inent ridge that parallels the front of the plateau. See figure 17, and figure 23A. For an explanation of how these relations developed, see figure 25. \ \lndianola Group, Cedar Mountain,\\\ i \ and Twist Gulch Formations,\ \ \ undivided \\‘_ A WEST EAST Flagstaff Limestone Suggested configuration of the East Gunnison monocline North Horn Formation Angular unconformity ) Formation Indianola Group, Cedar Mountain, and Twist Gulch Formations, l undivided \ price Riverll B WEST EAST mestone Hagstaff Li \ \\\ \\ \ \ Folded angular \?\\\ \\ \ unconformity \\\\\\ North Horn Formation SurficiaI Angular unconformity Indianola Group, Cedar Mountain, and \Twist Gulch Formations, undivided C 124 the east flank of the Gunnison Plateau; that absence can be attributed to erosion. It is this similarity between the beds exposed in the breached sectors of recognizable monoclines and comparable beds exposed along the east flank of the Gunnison Plateau that has led me to propose that the near-horizontal Tertiary units that cap the Gunnison Plateau once flexed down along the east flank of the plateau to form an eastward-facing monocline (fig. 62B). I refer to this monocline as the East Gunnison monocline, and it must have been every bit as impressive as the Wasatch monocline. During middle and late Tertiary time, then, the geomorphic pattern of the Sanpete—Sevier Valley area was probably dominated by at least four major north-trending monoclines (fig. 61). From east to west, these were (1) the Wasatch monocline, facing west; (2) the East Gunnison monocline, facing east; (3) the West Gunnison monocline, facing west; and (4) the Valley Mountains and West Hills monoclines, facing east. The Wasatch—East Gunnison monoclines formed a facing pair separated by Sanpete Valley; the West Gunnison—Valley Mountains and West Hills monoclines formed a second facing pair separated by the lowland formed by the collinear alignment of Sevier and Juab Valleys. DIAPIRIC STAGES AND EPISODES The diapiric folds have grown and collapsed repeatedly. Figure 63 illustrates this repeated growth and collapse of diapiric folds. In this figure, I have, for ease of understanding, assumed that the folds collapse between parallel crestal faults. As noted in figure 608, the folds may also fail by grad- ual subsidence. A diapiric fold grows and collapses in three succes- sive, interrelated stages, which together make up a diapiric episode. The first stage—the intrusive stage— is characterized by the rapid upwelling of a salt diapir that forces up the mobile mudstones of the Arapien Shale. These, in turn, acting much like a viscous magma, intrude, bow up, and fold back the overlying sedimentary beds (fig. 63, II). The resultant fan-shaped diapiric fold is probably partly destroyed, even as it rises, by gravity sliding and other forms of mass-wasting. Nevertheless, the end result is a topo- graphic high. This stage is followed almost immediately by the onset of the second stage, during which the fold fails, presumably owing to removal of the salt (fig. 63, III). The remnants of the collapsed fold are then eroded to form a broad, even-surfaced plain of low relief (fig. 63, IV). During this second stage—the erosional stage-— the salt diapir probably resumes its slow upwelling, SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH but its upward movement must be so slight that ero- sion is able to keep pace with whatever doming occurs. The third stage begins with the deposition of sedi- ments on this newly formed erosion surface (fig. 63, V). During this stage—the depositional stage—the salt diapir wells upward rapidly enough to restrict the amount of sediment deposited across the crest of the rising fold, resulting in depositional thinning. This third stage ends with a renewed upward surge of the salt diapir—the intrusive stage in yet another episode of salt diapirism (fig. 63, VI). I term each cycle of growth and collapse a diapiric episode; thus, each episode comprises three distin- guishable diapiric stages. Three such major diapiric episodes are well shown in the Red Rocks (F—3)— Sixmile Canyon (F—4) area along the east flank of the Gunnison Plateau, and in the Red Canyon (E—2) area of the Valley Mountains. 1. Late Cretaceous—early Paleocene episode: The first clearly recognized diapiric episode proba- bly began during the Late Cretaceous, after deposi- tion of the Indianola Group, and probably ended in the early Paleocene after deposition of the North Horn Formation but before deposition of the Flagstaff Limestone. The Twist Gulch and Cedar Mountain Formations, and the Indianola Group, bowed up during this first intrusive stage (fig. 63, II), were subsequently eroded to form a surface of low relief during the first ero- sional stage (fig. 63, IV). Later, the Price River and North Horn Formations were deposited on this surface of low relief during the first depositional stage (fig. 63, V). 2. Early Paleocene—late Oligocene(?) episode: The second episode probably began in early Pale— ocene time, after deposition of the North Horn For- mation, and ended after deposition of the Crazy Hollow Formation, possibly during the late Oligocene or Miocene. The North Horn and Price River Formations were bowed up during a second intrusive stage (fig. 63, VI). Subsequently, erosion reduced the newly formed dia- piric folds to a surface of low relief by the end of the second erosional stage (fig. 63, VIII). A sequence of Tertiary units, extending from the Flagstaff Lime- stone to at least the Crazy Hollow Formation, was deposited on this surface during the second deposi- tional stage (fig. 63, IX). 3. Late(?) Oligocene—Pliocene(?) episode: The third episode probably began during the late Oligocene or Miocene, after deposition of the Goldens Ranch and Moroni Formations, and may have ended during the Pliocene or Pleistocene. The evidence as to DIAPIRIC PROCESSES when this episode ended is fragmentary and incon- clusive. Locally, the Tertiary units (Flagstaff, Colton, Green River, and Crazy Hollow) were bowed up during a third intrusive stage (fig. 63, X). The folds failed in various ways, some by collapse (fig. 63, XI), and some by subsidence. Erosion, however, has not as yet completely beveled the diapiric folds, and most now appear in varying stages of dissection (fig. 63, XII). I believe that each of these three episodes was regional in extent, and that during each episode all the salt diapirs in central Utah reactivated and deformed the overlying beds. The evidence in the Gunnison Reservoir (F—3) area (fig. 28) suggests that a fourth, localized diapiric episode began and may have ended during the Pleistocene or Holocene. 125 Although all three stages of all three episodes are clearly shown in some exposures, elsewhere erosion has not cut deeply enough. Thus, in the ancestral Willow Creek (G—3) area (fig. 27), only that vestige of the Sanpete—Sevier Valley diapiric fold formed during the third diapiric episode (late Oligocene—Pliocene(?)) is exposed; erosion has not yet uncovered the earlier versions of the fold formed during the first (Late Cretaceous—early Paleocene) and second (early Paleocene—late(?) Oligocene) episodes. GEOLOGIC PATTERN The three major episodes of diapirism have stamped a geologic pattern on the area that is repeated in place after place. In its simplest form this pattern is represented by upturned conglomerate FIGURE 63 (following pages).—Schematic sections suggesting how the repeated growth and collapse of diapiric folds have deter- mined the structural pattern of central Utah. All sections rep- resent part of the west limb of a typical diapiric fold. I. Jurassic and Cretaceous sediments (KJu) were deposited on the Arapien Shale. Slow upwelling of the salt diapir (just east of area of section shown) pushed up the Arapien mudstones to form an elongate, north-trending arch, which impeded deposi— tion of the sediments. As the arch continued to rise, all sedi- ments that were deposited against its flanks or across its crest thinned or pinched out. First diapiric episode (Late Cretaceous to early Paleocene): II. Late Cretaceous intrusive stage. A sudden upward surge of the salt diapir (not shown) pushed up the mudstones and shales of the Arapien Shale (K(Ja)), which in turn bowed up and folded back (arrow) the overlying sedimentary strata (KJu) to form a fan-shaped fold. (Much of the overturned limb was soon de- stroyed by gravity sliding and other forms of mass-wasting.) III. Late Cretaceous erosional stage. Removal of the salt core (chiefly by solution) caused the central part of the fold to col- lapse, forming a graben between high-angle normal faults. Only the western fault (A) is shown here. IV. Late Cretaceous erosional stage. Erosion of fold remnants produced a surface of low relief. Persistent slow upwelling of the salt diapir arched the deformed strata (KJu) slightly. The fault (A), formerly vertical, is tilted. The rate of erosion either exceed- ed or at least kept pace with the rate of arching. V. Late Cretaceous—early Paleocene depositional stage. Upper Cretaceous sediments deposited on the eroded surface subse- quently were buried beneath lower Paleocene sediments (TKu). The continued slow upwelling of the salt diapir warped up the deformed strata (KJu), further tilting the previously vertical fault (A), and thinning those sediments (TKu) deposited across the crest of the fold. Second diapiric episode episode): VI. Early Paleocene intrusive stage. Reactivation of the salt di- apir during the early Paleocene resulted in a renewed diapiric fold, whose general trend and position followed that of the earli- er fold (II). The recently deposited Cretaceous and Paleocene strata (TKu) were flexed into a fan-shaped fold, and the older strata (KJu) were tilted to still steeper angles. Fault (A) was probably destroyed by the renewed movements of the mobile mudstones and shales of the Arapien Shale (T(Ja)); it is shown (early Paleocene—late Oligocene(?) here to emphasize the tilting of the strata. Here too, as for the earlier fold, the overturned limb of the developing fold was probably destroyed in great part by gravity sliding. VII. Middle(?) Paleocene erosional stage. Removal of the salt core, possibly during the middle Paleocene, resulted in collapse of the crest of the fold along high-angle normal faults. Only the western fault (B) of those faults that bound the graben thus formed is shown here. The pattern of collapse of the parental fold (III) is repeated. Near the core of the fold, the undivided Tertiary and Cretaceous strata (TKu) overlay the overturned un- divided Cretaceous and Jurassic strata (KJu) with profound an- gular unconformity. A short distance to the west the two units are disconformable, and still farther away they are conformable. VIII. Midd1e(?) Paleocene erosional stage. Erosion again re- duced the area to a widespread surface of low relief. The slow upwelling of the salt diapir resumed and the strata were again arched. Erosion kept pace with the upward bowing of the con- solidated units. IX. Late(?) Paleocene to late(?) Eocene depositional stage. The pattern recurs. Beginning in the late(?) Paleocene and continu- ing through the late Eocene and probably even into the Oli- gocene, sediments (Tu) were deposited on the newly formed erosion surface. The slow rise of the salt diapir arched the con- solidated strata (KJu, TKu), tilted the faults (A, B), and thinned the sequence of those sedimentary units being deposited across the axis of the fold. Third diapiric episode (late(?) Oligocene—Pliocene episode): X. Late(?) Oligocene intrusive stage. The salt diapir reactivated for a third time; again a new fold formed, and again it lay along the same site and had the same trend as that of the previous folds. The time of this reactivation may have been during the late(?) Oligocene or possibly even the Miocene. The newly depos- ited Tertiary strata (Tu) were raised and folded back by the re- mobilized mudstones of the Arapien Shale to form a fan-shaped fold. The overturned limb of the fold was concurrently destroyed by gravity sliding and mass wasting. XI. Late(?) Oligocene-Pliocene erosional stage. The newest formed fold was destroyed by collapse of the crest of the fold along high-angle normal faults. Fault C is the westernmost of the faults that bounded the newly formed graben. XII. Late(?) Oligocene-Pliocene erosional stage; ancestral topog- raphy. Erosion begar. to reduce the fold, even as the sedimenta- ry beds were raised and arched by continued slow upwelling of the salt diapir. 126 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH l<————‘—— Late Cretaceous—early Paleocene episode WEST EAST WEST EAST WEST EAST VII VIII Early Paleocene-late Oligocene(?) episode EXPLANATION Z Tertiary rocks. undivided—Includes, in descen- ding order, Crazy Hollow Formation, Green River Formation, Colton Formation, and Flagstaff Limestone L Eocene and Paleocene TKu Tertiary and Cretaceous rocks, undivided— lncludes, in descending order, North Horn and > er Cretaceous Price River Formations Upp KJu Cretaceous and Jurassic rocks, undivided— Includes, in descending order, lndianola Group, undivided, Cedar Mountain Forma« , » > Middle Jurassic tion, and Twist Gulch Formation JCJ 7 ’ " Arapien Shale , > TERTIARY CRETACEOUS > JURASSlC beds of the lndianola Group unconformably overlain Flagstaff Limestone. The two angular unconformities by thin Price River and North Horn Formations, commonly are folded, and they are distinctive in the which in turn are unconformably overlain by the stratigraphic sequence. This geologic pattern is well DIAPIRIC PROCESSES Late Cretaceous-early Paleocene episode EAST WEST WEST 127 t EAST WEST 1 Late(?) Oligocene-Pliocene(?) episode exposed at the mouth of Sixmile Creek canyon (F—4), in Red Canyon (E—2) (along the northeast flank of the Valley Mountains), and—not quite as easily rec- ognizable—along the east and west flanks of the Gunnison Plateau. How much of this geologic pattern is exposed depends to a great extent upon how deeply an area has been eroded. As exemplified in figure 64, if ero- sion has cut a deep valley through the “ancestral sur- face,” the geologic pattern is easily recognized— upturned beds of the Indianola Group and older rocks (KJu) unconformably overlain by thin Price River and North Horn sequences (TKu), which in turn are unconformably overlain by the Flagstaff Limestone and younger Tertiary strata (Tu). If, however, erosion has cut deeper and reached the “modern surface,” much of the structural complexity has been removed—the geologic pattern can only be inferred. The angular unconformities, in which near-vertical beds are overlain by near-horizontal beds, appear to be present only near the core of a diapiric fold. As one moves away from the core, the near-vertical beds lessen in dip and several kilometers (a mile or so) away are conformable with the overlying units. So, for example, in the Red Rocks (F—3) area, which is about 1 km (0.5 mi) west of the core of the diapiric fold, the lower angular unconformity (between the Price River and North Horn and the Indianola) is well exposed, but the upper unconformity (between the Flagstaff and North Horn strata) is not easily recognized (Spieker, 1949, p. 76). Here, the Flagstaff- North Horn contact appears as a disconformity; ero- sion has removed that part of the fold in which the angular unconformity between the Flagstaff and the North Horn was well displayed. By contrast, in the Sixmile Creek canyon (F—4) area, which is about 4 km (2.5 mi) east of the crest of the fold, the lower unconformity is not as impressive as it is in the Red Rocks area, for the Price River and units in the Indianola (Sixmile Canyon Formation, in particular) are separated by only a slight angular unconformity; the beds flatten rapidly eastward and are conformable only about 1 km (0.5 mi) away. The upper unconformity, however, does catch the eye, for 128 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH WEST FIGURE 64.—Cross section of typical diapiric fold in central Utah, illustrating how the extent of erosion can influence interpreta- tion of a geologic pattern. Vertical and overturned beds of the Indianola Group and older units are unconformably overlain by a Price River and North Horn sequence, which in turn is un- conformably overlain by a Tertiary sequence of which the Flag— staff Limestone is the oldest. Two distinctive angular the westward-tilted Flagstaff Limestone rests upon the upturned eastward—tilted beds of the Price River and North Horn sequence (fig. 21). The same geologic pattern is clearly visible in Red Canyon (E—2) along the northeast flank of the Valley Mountains. Near-vertical beds of the Indianola Group are overlain with angular unconformity by the North Horn Formation that dips west at a moderate angle. The North Horn, in turn, is overlain by beds of the Flagstaff Limestone that dip eastward (fig. 31). The exposure is a mirror image of the one in Sixmile Creek canyon (F—4) (Witkind and Page, 1984). Only part of the pattern is exposed along the east flank of the Gunnison Plateau. At and near the mouth of Maple Canyon (C—4), Price River strata, dipping gently to moderately westward, unconform- ably overlie vertical to overturned Indianola beds, duplicating stratigraphic relations found in the Red Rocks (F—3) area, and in the Red Canyon area of the Valley Mountains. Erosion, however, has removed much of the North Horn and all of the Flagstaff EAST Mme; ANNA» l W EXPLANATION }Holocene }QUATERNARY Alluvium \ 'u'flr'u' WW Tertiary rocks. undivided— W Includes, in descending order, Crazy Hollow Forma- tion, Green River Formation, Colton Formation, and Flagstaff Limestone ‘ ) $Eocene and Paleocene {TERTIARY TKu Tertiary and Cretaceous rocks, undivided—lncludes, in descending order, North Horn and Price River Formations Upper c lCRETACEOUS retaceous > Ara?pien < ‘ ‘ Shale i Cretaceous rassic rocks, undivided—Includes, in descending order, Indianola Group, undivided, Cedar Mountain Formation, and Twist Gulch Formation > Middle . JURASSlC Jurassrc U Unconformity —‘ Fault—Dashed where reconstructed toward ancestral surface; barb shows direction of relative movement unconformities are produced. If erosion is at the “ancestral sur- face” level, both unconforrnities are exposed and geologic rela- tions are unequivocal. If erosion has cut to the “modern surface” level shown, only one unconformity can be recognized, and the younger unconformity is removed or masked. Compare this il- lustration with figure 63, XII, and with photograph of the Red Rocks area, figure 18B. Limestone from the Maple Canyon area; the Flag- staff now crops out along the top of the plateau about 1.6 km (1 mi) to the southwest, far back from the crest of the diapiric fold. The Flagstaff, expectably, conformably overlies North Horn strata. Here too, then, much as in the Red Rocks area, that part of the fold (near the diapiric crest) where the Flagstaff and the North Horn were once separated by an angular unconformity has been removed by erosion. In a few localities, an additional complexity, stem— ming from the collapse of a diapiric fold, has some- what modified this geologic pattern. Along the northeast flank of the Valley Mountains, northwest of Painted Rock Canyon (E—2), younger beds are downthrown along a range-front, high-angle normal fault and abut the much older Indianola beds. Rela- tions are confused, but in general, it appears that elements of the North Horn, Flagstaff, Colton, and Green River formations are juxtaposed against the conglomerates of the Indianola Group (fig. 29B). I interpret these relations to result from the collapse of LOCALIZATION AND CAUSATIVE FORCES the crestal part of the Sevier Bridge Reservoir dia- piric fold. CYCLICAL ASPECTS The fact that the three diapiric episodes are repre- sented in single outcrops at several different locali- ties implies that ever-younger diapiric folds were formed time and again in the same structural zones and had the same trends as the earlier diapiric folds. In essence, the “parental” diapiric folds that were formed in Late Cretaceous time (and that are repre- sented by the beveled, steeply inclined beds of the Indianola Group) were the precursors of other folds formed still later, once during the Paleocene, and again during the late(?) Oligocene or Miocene. It is much as if the salt was confined to specific conduits and repeatedly used these conduits each time it surged upward. LOCALIZATION AND CAUSATIVE FORCES The diapiric folds in central Utah, the “salt anti- clines” (salt-cored anticlines) of the Paradox Basin, the elongate salt-cored structures of northern Germany (Trusheim, 1960; Sannemann, 1968), and northern Tunisia (Perthuisot, 1981), to select but a few examples, are all alike in that they are strikingly regular in distribution and orientation. This regular- ity of the salt structures in northern Germany was attributed by Trusheim (1957) to autonomous, isos- tatic salt movement, for which he coined the term “halo-kinesis.” In brief, he proposed that as soon as deeply buried salt begins to flow, it forms a low, swelling salt mass (Trusheim, 1960, p. 1524—1527). Adjacent salt from the “mother bed” of salt moves inward toward the salt mass, which begins to expand and forms a mound. Even as this occurs, the sedi- mentary rocks adjacent to these areas of inflowing salt subside to form rim synclines. Sedimentary material, deposited in these rim synclines, adds weight, which augments the inflow of the salt toward the salt mass. As the salt mass swells, it arches the overlying strata, and in time, the swelling salt mass, fed by a continuous supply of mother salt, intrudes the overlying sedimentary beds, starting the diapiric stage. With continued addition of salt, the diapir may breach the sedimentary cover, and flow out across the surface. A new rim syncline, formed adjacent to this diapir, is gradually filled as sediments accumulate in it. In time, these sediments are thick and dense enough to force the mother salt adjacent to the orig- inal “parent” diapir to migrate away from it and form 129 a new salt mass some distance away. With continued addition of mother salt, this new salt mass eventu- ally becomes a diapir; in essence, a second generation of salt structures develops. This process is repeated again and again with ever-younger generations of diapirs forming away from the parental diapir until the mother bed of salt is depleted. The cause of the initial movement of the salt is uncertain. It may be an inhomogeneity in the roof of the salt layer, a gentle warp in the basement rocks, or a tectonic impulse (Trusheim, 1960, p. 1523—1524; Sannemann, 1968, p. 268). In ’I‘rusheim’s interpreta- tion, autonomous, isostatic movement of the salt is the fundamental reason the salt diapirs developed. In a series of uniformly oriented, subparallel salt diapirs, then, the oldest is the central “parental” one. On each side, a second generation of daughter diapirs flanks this parental diapir; beyond these the succeed- ing diapirs represent ever-younger generations with the outermost diapirs being the youngest. This age sequence, however, is not apparent in central Utah. The oldest beds deformed (tilted verti— cally or overturned) as part of the westernmost diapiric fold (the Sevier Bridge Reservoir diaipiric fold (fig. 16, 4)) are conglomerate beds of the Indi- anola Group. Correlative beds of the Indianola Group have been tilted vertically or overturned in a central diapiric fold (the Sanpete—Sevier Valley diapiric fold (fig. 16, 1)) as well as in the easternmost diapiric fold exposed (Little Clear Creek diapiric fold (fig. 16, 9). Apparently, all the diapiric folds, no matter what their position in the diapiric cluster, were formed at the same time. The stratigraphic sequence at several localities indicates that the area has been deformed during at least three distinct diapiric episodes. And in each of these widely separated localities, the geologic evi- dence suggests that each of the three episodes began and seemingly ended at the same time. There is no evidence of progressive change of age from one diapir to another during any one of the three episodes. Moreover, the repetition of extremely localized angular unconformities, exposed in single outcrops at different localities, suggests repeated reactivation and destruction of ever-younger diapiric folds, which always occupied the same structural zones and had the same trends. As each reactivated salt diapir welled upward (seemingly using the same conduit as the previous diapir), a new diapiric fold was formed, at the same site and along the same trend as the previous fold. Each time the newly emplaced salt was removed, the newly formed fold collapsed. If, as sug- gested by the halokinetic hypothesis, the salt diapirs continuously form away from the parental diapir, it 130 is difficult to see how this central Utah pattern of diapiric folds being formed repeatedly and simulta- neously in all localities can be explained solely by halo—kinesis. Some other factor, or factors, must be involved. Although the central Utah salt diapirs may have been formed in part by halo-kinesis, I believe that tectonic forces are probably responsible for their development, and propose, therefore, that halo- tectonism (another term proposed by Trusheim (1957) to imply development of salt diapirs in response to tectonic forces) is a more plausible explanation. The diapiric folds are elongate, narrow, faintly sin- uous features that extend for many kilometers. This linearity suggests some form of structural control that determined not only the trends of the folds but also their distribution. The linearity of the folds plus the fact that they grew and collapsed repeatedly along the same axes suggests that well-established fault planes may have served as conduits for the salt and intermixed mudstones as they repeatedly welled upward toward the surface. This concept is supported by the fact that two of the diapiric folds align with major fault zones, and a third parallels such a zone (fig. 65). The Sanpete—Sevier Valley diapiric fold is collinear with the northeastward projection of the Sevier fault zone, and the Redmond fold aligns with the southward projection of the Wasatch fault zone. The Levan fold, which may be a northern segment of the Redmond fold, parallels the south end of the Wasatch fault zone. The Sevier fault zone extends northeastward from southwestern Utah into central Utah. Southeast of Richfield (I—l) it appears as a series of small scarps that break surficial deposits along the east side of Sevier Valley. The scarps end near Richfield; north- eastward beyond Richfield neither scarplets nor other features suggestive of the fault zone can be found. Even as the fault zone apparently ends, the elongate, narrow welt of Arapien mudstone beds, which marks the core of the Sanpete—Sevier Valley diapiric fold, begins and extends northeastward along the east side of Sevier Valley. The trend of the fault zone and the core of the fold are collinear. A similar alignment appears to exist between the trend of the Wasatch fault zone and the Redmond diapiric fold. The Wasatch fault zone can be traced southward from northern Utah into this area as a series of small scarps that break surficial deposits. The zone ends near Fayette (F—3) (Cluff, Brogan, and Glass, 1973), but about 6 km (4 mi) farther south, near Gunnison (F—3), a line of Arapien Shale out- crops—the core of the Redmond diapiric fold—begins and extends southward along the west valley wall of SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH Sevier Valley to Redmond (G—3). Here, too, even as the fault zone ends, the line of Arapien Shale out- crops begins and is collinear with the trend of the fault zone. Finally, from Nephi (B—3) southward, the Wasatch fault zone, marked by a series of small scarps, closely parallels the northward-trending welt of Arapien mudstone that crops out along the west flank of the Gunnison Plateau (fig. 65), and that I consider to be the core of the Levan diapiric fold. Possibly this collinearity between major fault zones and diapiric folds is fortuitous, but I do not think so. I believe the alignment is meaningful and propose that the position and extent of each parental diapiric fold was originally determined by a preexisting, deep- seated, fundamental structure. Other workers have commented on this apparent structural control of salt-generated structures. S0, Stokes (1948, p. 14), discussing the salt structures in the Paradox Basin, noted: “This regional uniformity of trend is evidently l [1 SH 100 KlLOMETERS I ‘ 0 50 MILES Great Salt Lake 41 ° L I | | 40°l’ WASATCH FAULT ZONE : Core of the Nephio Levan diapiric told I t s | Q' Fayette | 390'” Sevier k . I 16;: of the /Sanpete-5eVIferl;/alley ll IRedmond diapiric fold d'ap'm 0:, Richfield W‘“ \ L‘SEVIER FAULT ZONE I 38 ' EXPLANATION Cl Major outcrops of the Arapien Shale l ——-—' Fault zone—Dashed where l approximately located | Cedar Cityo _____ ——__._——__ _ .— FIGURE 65.—Alignment of several diapiric cores with major fault zones in central Utah. The core of the Sanpete—Sevier Valley diapiric fold begins where the Sevier fault zone ends and extends northeastward, collinear with the fault zone. In much the same fashion, the core of the Redmond diapiric fold begins where the Wasatch fault zone ends, near Fayette, and continues the southward trend. LOCALIZATION AND CAUSATIVE FORCES a reflection of important deep—seated breaks in the basement rocks* * *.” Cater (1955, p. 125), also impressed by the regularity of distribution of the salt-cored anticlines in the Paradox Basin, similarly speculated that deep-seated structures were responsi- ble for their parallelism. Cater and Elston (1963), on the basis of well data from the Paradox Basin, pro- posed that the larger diapirs were underlain by major pre-salt breaks. Baars and Stevenson (1981, p. 28) noted that past and recent seismic surveys in the Paradox Basin area “have left no doubt as to the existence of pre-salt faulting* * *,” which dictated the trend of the salt structures. Perthuisot (1981, p. 233), discussing the elongate salt diapirs of northern Tuni- sia, called upon deep movement of large basement blocks as an explanation for the preferred orientation of the diapirs. And Trusheim (1960, p. 1524) noted that the pattern of the northern German salt struc- tures may reflect “a network of faults in the pre- saline basement.” I suggest that in central Utah such basic deep- seated structures have continued to control and local- ize the younger reactivated versions of the diapiric folds. This would explain why these younger folds occupy the same sites and have the same trends as the older folds. Possibly each occurrence of crustal disturbance caused movement on one or more faults. Repeated movements along these faults have per- sisted at least from late Mesozoic time to the late Tertiary-Quaternary; each major movement has resulted in a major diapiric episode. It may be that the salt, under confining pressure as a result of static load, finds relief when movement along a fault opens a passageway. The salt, using the fault plane as a conduit, flows upward to form a long, near-linear salt diapir. In its upward movement the salt pushes up the overlying mudstones and shaly siltstones of the Arapien Shale and these, in turn, intrude and bow up the overlying sedimentary rocks. The end result is a faintly sinuous, near-linear, fan- shaped diapiric fold whose general trend, determined by the core of salt, reflects the fault plane now oblit- erated by the transported mudstones and siltstones. Repeated reactivation of the same fault results in repeated renewal of the same causative salt diapir. This would explain the near-linear shape of the major folds, the collinearity between known fault zones and several of these major folds, and the fact that similar folds have formed repeatedly in the same sites and with the same trends during all three major diapiric episodes. I suggest, therefore, that each of the major diapiric folds marks the position of a zone of weakness—a preexisting fundamental fault—that may have 131 formed in Precambrian time and that has been inter- mittently active ever since. These faults represent major flaws in the Earth’s crust. The fact that the hingeline (the east margin of the Cordilleran geosyn- clinal basin), the Jurassic Arapien basin in which the salt accumulated, the transition zone, and the zone of diapiric activity all, at one time or another, occupied the same geographic area must be more than mere coincidence. Movement along these fundamental faults during Paleozoic time led to the development of the hingeline, and, during much of Early and Middle Jurassic time, to the development and subse- quent growth of the saline basin of deposition in which the Arapien Shale with its contained salt and other evaporites accumulated. The striking break between the Colorado Plateaus and Basin and Range provinces probably reflects such fault movement. If this interpretation is valid, each intrusive stage of each of the three major diapiric episodes reflects reac- tivation of these deep-seated faults. As all the diapiric folds display a similar pattern of development—the postulated sequence of geologic events is the same for the Sanpete—Sevier Valley fold as it is for the Sevier Bridge Reservoir fold—movement probably occurred, more or less in concert, along all the faults in the area in response to the regional stresses applied. Presumably these faults first moved at some time after the Middle Jurassic, and were then used as conduits by the salt and intermixed mudstones of the Arapien Shale, which effectively obliterated the conduits. Subsequent tectonic pulses, probably once during the Late Cretaceous (post-Indianola Group— pre-Price River Formation), again during the Pale- ocene (post-North Horn Formation—pre-Flagstaff Limestone), and still again during the late(?) Oli- gocene or Miocene (post-Goldens Ranch Formation and post-Moroni Formation), triggered renewed movement along these faults, resulting in reactiva- tion of the salt diapirs; this renewed diapiric move- ment further masked any evidence of the former faults. Prior to the Paleocene, compressive forces from the west presumably caused movement along the faults. During the Late Cretaceous an eastward-directed thrust fault (stemming from the Sevier orogeny) may have triggered movement along these deep-seated faults and thus given rise to a diapiric episode. This may also explain the early Paleocene movement of the diapirs. Any movement along the faults since the Paleocene, however, must stem from the episode of crustal extension that began probably during late(?) Oligocene and Miocene time and that has persisted to the present. 132 ECONOMIC IMPLICATIONS The combination of multiple episodes of salt intru- sion and the resultant repeated upward movements of the Arapien Shale may have created a series of structural traps in which oil and gas could accumu- late, and in which mineral-rich, possibly saline, solu- tions could deposit their mineral content. OIL AND GAS The likelihood of finding economic pools of oil is enhanced if an area contains source rocks, reservoir beds, and suitable structural and stratigraphic traps. These three required elements appear to exist in this part of central Utah, and all seemingly have been influenced or modified in one way or another by the recurrent episodes of diapirism. SOURCE BEDS At least three major stratigraphic units in the area are potential source rocks—the Mancos Shale of Late Cretaceous age, the Manning Canyon Shale of Penn- sylvanian and Mississippian age, and the Arapien Shale of Middle Jurassic age. MANCOS SHALE The Mancos Shale is widely exposed along the east flank of the Wasatch Plateau, in Castle Valley (E—7) (between the Wasatch Plateau and the west flank of the San Rafael Swell), and in the barren lowlands that lie at the base of the curving mass of the Book Cliffs. The shale extends westward beneath the Wasatch Plateau and, although not exposed, underlies much of Sanpete Valley. Hale’s proposal (1972, p. 33) that Mancos sediments were deposited in a Sanpete Valley embayment of a shallow epicontinental seaway seems valid, and recent drilling has begun to give some indication of the thickness and extent of Mancos beds beneath Sanpete Valley. The Mancos forms a thick sequence in central San- pete Valley, but it probably thins rapidly westward and southward; I suspect that it does not extend much farther west than a north-trending line through Wales (D—4) (along the east flank of the Gunnison Plateau), nor much farther south than Manti (E—4). Three exploratory test wells drilled in the central part of Sanpete Valley, near Moroni (D—4) (fig. 9), penetrated black marine sedimentary rocks of the Mancos Shale. Together the well data indicate that the Mancos thins rapidly westward. The easternmost SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH test (fig. 9), Hanson Oil Corporation’s well Moroni AX—l (SE1/4NW1/4 sec. 14, T. 15 S., R. 3 E.) penetrated about 2,135 m (7,000 ft) of Mancos strata. About 2.4 km (11/2 mi) to the west the Tennessee Gas Transmis- sion Company’s J.W. Irons well No. 1 (C, SE1/4NE1/4 sec. 16, T. 15 S., R. 3 E.) penetrated only about 1,070 m (3,500 ft) of Mancos. The westernmost well, the Phillips Petroleum Company’s well Price “N” (SE 1/4 SE 1/4 sec. 29, T. 15 S., R. 3 E.), penetrated only about 610 m (2,000 ft) of Mancos Shale. These data empha- size this westward shoaling of the Mancos sea. The two westernmost wells also demonstrate the westward rise of the top of the Mancos. In the J.W. Irons well the Mancos top is at 6,268 ft, but in the next well to the west, the Phillips Price “N” well, the top is at 3,058 ft. Possibly this westward rise of the top of the Mancos may reflect the upward movement of the Sanpete—Sevier Valley salt diapir, which is west of the three wells and hugs the east flank of the Gunnison Plateau. Witkind and Sprinkel (1982, p. 317) interpreted these well data to mean that the Mancos sea occu- pied much of the present site of Sanpete Valley and probably had its shoreline close to what is now the east flank of the Gunnison Plateau. The Mancos penetrated by the test wells appears to be lithologically similar to its exposures to the east—a series of black marine and paludal shales and brown sandstones—seemingly an excellent source of hydrocarbons. MANNING CANYON SHALE The Manning Canyon Shale is a dark-gray to brownish—gray marine shale that contains interleaved lenses of brown quartzitic sandstone and bluish-gray limestone. It crops out in the Charleston-Nebo thrust plate; good exposures are east of Mona (B——3). Although the Manning Canyon, like the Mancos, is rich in an oil-generative type of organic material, it may be an unsuitable source rock because it has been subjected to high temperatures and is thermally supermature. Poole, Claypool, and Fouch (1983), dis- cussing episodes of petroleum generation in the northern Great Basin, indicated on their figure 5 that many of the Paleozoic rocks in central Utah have been subjected to temperatures of 300 °C (571 °F) or higher. Virtually all surface exposures of the Manning Canyon are included within the area of these elevated temperatures, which coincides, in general, with the extent of the Charleston-Nebo thrust plate. On the east flank of the Lake Mountains, along the west side of Utah Lake, several quarries have been opened in the Manning Canyon, and several clay ECONOMIC IMPLICATIONS beds in the shale are quarried extensively for the manufacture of brick and other ceramic products. The high-temperature clay minerals pyrophyllite and rectorite are principal constituents in these Manning Canyon exposures (Hall and Schnabel, 1985), and their presence reemphasizes the possibility that the Manning Canyon Shale is too mature, at least in that specific locality, for consideration as a promising source rock. ARAPIEN SHALE The calcareous mudstones that make up the bulk of the evaporite-rich Arapien Shale may also be potential source rocks for oil. Many geologists have noted the close association between evaporites and petroleum. Halbouty (1967), for example, discussing the salt domes along the Gulf Coast, demonstrated that large amounts of petroleum are associated with these domes. Weeks (1961) listed a multitude of basins in which petroleum accumulations are closely related to evaporite deposits. Kirkland and Evans (1981) proposed a new explanation for this close rela- tion. They suggested that although most organisms cannot survive high-saline (mesosaline) conditions—— characterized by brines in which the saline content ranges from 4 to 12 percent—some algae not only can exist under these circumstances but literally thrive. Vast amounts of such algae, for example, are found in present-day basins marked by such mesosaline conditions. Upon death, the algae sink into the deeper waters of the basin, where they are buried by fine sediments and preserved as fine-grained carbon- ates rich in organic matter. These carbonates are immature source rocks which, upon maturation, pro- duce petroleum. It seems probable that the calcareous mudstones that make up most of the Arapien Shale developed under such mesosaline conditions. Presumably, marine waters from an open sea flowed periodically into the broad and extensive land-locked saline Arapien basin, which overlay much of central Utah during Middle Jurassic time. Continued evaporation resulted in increased salinity of the brines, and in time mesosaline conditions prevailed. If large amounts of organic matter did flourish in the Arapien basin, much of that organic matter must have been preserved in the bottom sediments, implying that the Arapien Shale is a possible source rock. Regrettably for the hydrocarbon potential, total organic carbon in the Arapien is low (R.J. Coskey, Forest Oil Company, oral commun., 1982); despite this, probably the one factor that detracts from the Arapien as a promising 133 source rock is its low maturation level (D.A. Sprinkel, Placid Oil Company, oral commun., 1983). RESERVOIR BEDS Of the various units suitable for the accumulation of oil and gas, the most promising would be those sandstone beds that make up the Ferron Sandstone Member of the Mancos Shale. The Ferron produces both hydrocarbon and carbon dioxide gas in the Clear Creek area to the east along the crest of the Wasatch Plateau (Walton, 1963). Comparable reservoir beds, however, could be any of the sandstone beds of the Emery Sandstone Member of the Mancos Shale. Likely, some of the units in the stratigraphic section may be good reservoir beds because they are highly fractured and not because of any inherent primary porosity. POTENTIAL TRAPS The stratigraphic column in this sector of central Utah can be visualized as consisting of two parts: the salt-bearing and younger beds, which extend from the base of the Arapien Shale to the surface, and the pre-salt beds, which include the 'IVvin Creek Lime- stone and older strata. The salt-bearing and younger beds are locally intensely warped and form the many diapiric folds described in the previous sections of this Professional Paper. By contrast, the pre-salt units, although deformed, may not be as severely contorted as the overlying younger units. I believe that structural traps suitable for the accumulation of commercial amounts of oil and gas are in both sequences of rocks. SALT-BEARING AND YOUNGER STRATA The upward thrust of the salt diapirs may have resulted in a series of structural traps, the most favorable of which would be those confined to areas underlain by the Mancos Shale. I recognize four types of traps related to the diapiric folds: (1) those that are along the flanks of a diapiric fold, (2) those that are along the crest of a fold, (3) those that are wholly within a diapiric fold, and (4) those that resulted from the collapse of a fold. Traps along the flanks of the folds.——It seems prob- able that any diapirs formed beneath the Mancos Shale would have intruded and bowed up the Man- cos. Such upwarped beds, juxtaposed against the intrusive Arapien mass, would seem to be ideal structural traps for the accumulation of oil and gas. 134 The Arapien, in most localities a somewhat impervi— ous mudstone, would serve as a barrier, trapping the oil and gas migrating up the upturned Mancos beds. ’D‘aps along the crest of a fold.—A second type of potential trap may be those sedimentary beds that are draped across the crests of the diapiric folds. Examples are common in the Gulf Coast (Halbouty, 1967), but there, the draped, deformed beds directly overlie the salt core of the salt domes. In central Utah, the salt has pushed up the mudstones and shales of the Arapien Shale and these, in turn, have bowed up the overlying sedimentary beds. I consider these domed sedimentary beds likely targets. Although they have been extensively eroded and almost completely removed from the crests of many of the major diapiric folds, in several places, the crests of some of the larger folds (such as the north end of the Sanpete—Sevier Valley fold) are still man- tled by surficial deposits. Suitable targets may underlie these surficial deposits. Traps wholly within a diapiric fold—Other poten- tial oil traps may be wholly Within a diapiric fold. The salt core of the diapir penetrated by the Argo- naut-Federal well consisted almost completely of salt; little or no anhydrite was found. By contrast, various oil tests in this part of central Utah have drilled through an alternating sequence of salt and anhydrite. If the anhydrite beds in a diapiric fold were much fractured as a result of the repeated growth and collapse of that fold, they would have become quite porous. The salt, however, being more plastic and mobile, would retain its nonporous char- acter. The result would be porous zones of anhydrite sealed by nonporous salt. Traps resulting from collapse of a diapiric fold.— Other structural traps may have formed as a conse- quence of the collapse of the diapiric folds. Although it is clear that some of the folds collapsed by gradual subsidence, much as shown in figure 60B, others appear to have collapsed along high-angle faults (fig. 60A). These latter folds are ones that may be worthy of investigation, for the downthrown limbs, either overturned or right-side-up (as, for example, in the ancestral Willow Creek (G—3) area, fig. 27), are probably sealed against the marginal faults, and thus become suitable traps for the accumulation of oil and gas. An inherent uncertainty in this type of trap, however, is how much the downthrown limb was fragmented. The limb was probably dropped thou- sands of meters, and most likely this occurred as many small spasmodic events; each event may have fractured and offset the once-continuous beds. Although the offset during each event may have been SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH minor, the cumulative effect of many such offsets may be sizeable. Previously, I have suggested that the zero line of the Mancos Shale is approximately along a north- trending line through Wales (D—4)—essentially along the east flank of the Gunnison Plateau—and that the Mancos thickens eastward (p. 132). In my View, then, those diapiric folds that are east of the Gunnison Plateau are the most favorable; they underlie the Mancos Shale, a good source rock, which also con- tains adequate reservoir rocks. By contrast, those folds west of the plateau are probably somewhat less favorable; they are distant from suitable source rocks. PRE-SALT STRATA Although the most feasible oil traps appear to be related in one way or another to the salt diapirs, other traps, concealed beneath the masking blanket of diapirically folded rocks, may have formed in the older pre-salt-bearing strata. Such traps seemingly would be unrelated to the diapiric deformation, which is confined to the salt—bearing and younger strata. OVERTHRUST BELT AND SALT DIAPIRS Salt diapirism may have had a profound effect on the position of oil pools, for whatever oil pools did form may have been displaced as a result of intrusion by the Arapien Shale. Much of the search for oil has centered on the overthrust belt, and overturned folds have been prime targets. In this sector of central Utah, for exam- ple, an overturned fold (possibly a remnant of the Charleston-Nebo thrust plate) well exposed along the west flank of the Gunnison Plateau in Chicken (D—2) and Pigeon (C—3) Creeks (east of Levan), was tested by Standard Oil of California’s Levan Unit 1 (fig. 9) and by American Quasar’s Chicken Creek Fed. No. 16—34. Ample evidence, however, demonstrates that the fold, after it was emplaced, was deformed and intruded by both gypsum beds and mudstones of the Arapien Shale (figs. 33, 34). It seems clear that diapirism, throughout central Utah, has modified the thrust-related features. In the Gardner Canyon—Red Canyon (B—3) area, for exam- ple, the Arapien Shale broke, raised, and locally tilted the overturned fold that forms the upper plate of the Charleston-Nebo thrust (fig. 35). In the Thistle area, a northeast segment of the same overturned fold, plus its overlying mantle of Cretaceous and Tertiary units, has been arched to form an elongate north-trending upwarp (fig. 44). The causative agent appears to have SUMMARY been the Arapien Shale. If oil pools did form in over- turned strata in this part of central Utah, they have probably been displaced during one or more episodes of salt diapirism. In essence, displacement of an oil pool may be a simple migration because of secondary deformation imposed on the original overturned fold. MINERAL DEPOSITS Base-metal deposits appear to be localized chiefly along the contact between the Arapien Shale and the country rock. For example, in the ancestral Willow Creek (G—3) area, a small mine known as the “Red- mond silver mine” produced zinc ore intermittently from the time of World War I until about 1950, when it was closed owing to lack of ore. The mine, about 5 km (3 mi) east of Redmond (G—3), is in a small cuesta that occupies parts of secs. 4 and 5, T. 21 S., R. 1 E., Sevier County, Utah. The bulk of the oxi- dized zinc ore (chiefly hydrozincite and smithsonite) is concentrated in shattered Green River rocks next to a narrow “fault zone” (Heyl, 1963, 1978) that fol- lows the contact between Arapien Shale on the east and the Green River Formation to the west. The geologic relations near the mine (Witkind, 1981) can be interpreted in two ways: as a fault zone in which the block west of the fault has been downthrown, or as an intrusive contact between the Arapien Shale and the bowed-up Green River Forma- tion (fig. 66). Although Heyl (1963, 1978), who exam- ined the mine when it was open, favored the fault interpretation, I favor the second alternative because the Arapien Shale and Green River Formation rela- tions here are identical to intrusive relations between these two units elsewhere in the area. The source of the mineral-rich solutions is uncer- tain. They may stem from a volcanic center in the East Tintic Mountains, essentially the site of the East Tintic Mining District. Morris and Lovering (1979, p. 68—69) and Laughlin and others (1969) noted a significant igneous episode in that area dur- ing the Miocene. Still another possibility is that Arapien saline brines may have furnished the zinc and lead minerals. Thus, the Arapien Shale may be the ultimate source of these ore deposits. Whatever their source, these mineral-rich solutions were then deposited in the fractured rocks of the Green River Formation. SUMMARY Multiple episodes of salt diapirism seem the most reasonable explanation for the intense, localized 135 deformation that marks the disturbed zone between the Colorado Plateaus and Basin and Range prov- inces in central Utah. The salt (halite), as well as other evaporites such as gypsum and anhydrite, is in the Arapien Shale of Middle Jurassic age. The salt, in large amounts and much of it now probably in the form of narrow, steep-walled diapirs, welled upward repeatedly, and in so doing forced the calcareous mudstones and gypsiferous shaly siltstones of the Arapien Shale to intrude, arch, and fold back the overlying sedimentary beds. The Arapien, thus, is best visualized as an intrusive sedimentary unit. Repeatedly forced upward by the reactivated salt dia- pirs, the soft and mobile Arapien mudstones have acted much like a viscous magma. Perhaps the best analogy is that of a hydraulic car jack. The salt rep- resents the hydraulic fluid, the Arapien mudstones and shales, the bearing platform of the jack, and the uplifted younger strata, the car. Upward movement of the concealed, elongate salt diapirs formed a series of generally north trending, subparallel diapiric folds, fan-shaped in cross section. Removal of the salt either by dissolution or extrusion resulted in failure of these folds. The general struc- tural pattern, thus, resulted from the repeated growth and collapse of salt diapirs and those folds formed over them. Each time the salt diapirs reactivated, the newly formed folds occupied the same sites and fol- lowed the same trends as the earlier folds. The many signs of tectonic unrest——angular unconformities, steeply tilted to overturned beds—emanate from this recurrent growth and collapse of the reactivated salt diapirs and their overlying folds. As a result of these recurrent disturbances, the Arapien has different “ages.” Its depositional age is Middle Jurassic; its emplacement ages—the geologic age of movements—however, have changed repeat- edly. In places, the Arapien deforms Cretaceous beds, elsewhere Eocene or Oligocene beds, and in several places it probably has deformed Pliocene or Quater- nary beds. If one considers the age of the Arapien Shale to be solely Middle Jurassic, critical structural and economic relations are masked. The contact relations between the Arapien Shale and the overlying beds are neither unconformities nor strip-thrusts, but rather intrusive contacts. I question whether the Arapien Shale is undisturbed anywhere in central Utah. The Arapien mudstones have been pushed about so many times by the con- tained salt that it seems unlikely that their present attitudes in any way reflect the attitudes of the sedi- mentary units that underlie them. This recurrent movement of the salt emphasizes the critical fact that the stratigraphic section is divisible 136 FiiE i KILOMETER n 1/2 MILE A Fault with gouge 2 METERS 0 5 FEET B FIGURE 66.—Two alternative interpretations of the geologic relations near the abandoned zinc-producing “Redmond silver mine,” secs. 4 and 5, T. 21 S., R. 1 E., Sevier County, Utah. Base modified from US. Geological Survey 1224,000 Redmond (1966). Contour inter- val 100 it. A, Mine is in a small, isolated cuesta about 5 km (3 mi) east of Redmond. Geologic relations are from Witkind (1981). B, One interpretation suggests that the Green River Formation (“Eocene limestone”) is downthrown against the Arapien Shale (“Jurassic red shale”) along a normal fault. The ore is localized into two parts—an upper part consisting of the salt- bearing and younger strata, and an underlying, lower part consisting of the pre-salt older units. The intense localized deformation so visible on the surface is con- fined solely to the salt-bearing and younger units. The underlying pre-salt units, although deformed, have not been deformed as a result of the repeated salt movements. SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH EXPLANATION } Holocene, Pleistocene} QUATERNARY Coalesced alluviai- and Pliocene(?) fan deposits Crazy Hollow Formation Eocene TERTIARY Green River Formation _ : Middle JURASSIC Arapie Jurassic Shale —-—- intrusive contact—Oblongs on intrusive unit 45 —‘— Strike and dip of inclined beds X‘Z" Abandoned mine (zinc) FEET HEDMDND FEE 0000 sum MINE 6000 5500 _ 5500 5000 5000 4500 4500 4000 4000 i KILOMETEH 0 1/2 MILE C in the Green River adjacent to the fault. Illustration from Heyl (1963, 1978). Barbs show direction of relative fault movement. C, An alternative interpretation, which I favor, is that the area was deformed in the late(?) Oligocene by the intrusive action of the Arapien Shale. At this time, mineral—rich saline solutions moved up a brecciated zone formed along the intrusive contact between the Green River and the Arapien Shale and deposited their base— metal content along that contact. Bedding dashed within units; contacts dashed and queried to indicate uncertainty. Sequences of sedimentary formations thin toward the crests of the diapiric folds, and discrete units within these sequences either pinch out against the flanks of the folds or are anomalously thin across the crests of the folds. This depositional thinning of sequences of units suggests that the salt diapirs welled upward very slowly but continuously, and in so doing have acted like dynamic barriers, impeding SUMMARY deposition. All units, from the Twist Gulch Formation of Middle Jurassic age up to and including the Green River Formation of Eocene age, display this deposi- tional thinning. I believe that even younger units thin toward the diapiric crests, but because of inade- quate exposures, I currently lack evidence to demon- strate this. Probably, these salt diapirs are rising today at a slow, almost imperceptible rate. Rapid upward surges of the salt diapirs sporadically inter- rupted this persistent upward movement. Each surge marked the beginning—the intrusive stage—of a new diapiric episode. Once the surge ended, the slow, con- tinuous rise of the diapirs resumed. The growth and collapse of a diapiric fold occur in three interrelated stages that together make up a diapiric episode: An intrusive stage, during which a salt diapir surges upward rapidly and forcibly drives up the overlying mudstones of the Arapien Shale, which in turn push up and fold back the overlying strata to form a diapiric fold, fan-shaped in cross sec- tion; an erosional stage, during which the diapiric fold fails (presumably as a result of partial removal of the salt) and its remnants are then eroded to an almost featureless plain; and a depositional stage, during which younger sediments are deposited on the newly formed erosional surface. This depositional stage is ended by a renewed upward surge of the salt diapir—the intrusive stage of the next younger dia- piric episode. I recognize at least three major diapiric episodes: 1. A Late Cretaceous to early Paleocene episode. The first clearly recognized diapiric episode probably began during the Late Cretaceous, after deposition of the Indianola Group, and ended in the early Pale- ocene after deposition of the North Horn Formation but before deposition of the Flagstaff Limestone. 2. An early Paleocene to late(?) Oligocene episode. The second episode probably began in early Pale- ocene time, after deposition of the North Horn For- mation, and ended after the Eocene (possibly during the late Oligocene or Miocene) after deposition of the Goldens Ranch and Moroni Formations (of late Eocene to middle Oligocene age). 3. A late(?) Oligocene to Pliocene(?) episode. The third episode probably began during the late Oli- gocene or Miocene, after deposition of the Goldens Ranch and Moroni Formations, and may have ended during the Pliocene or Pleistocene. The evidence as to when this episode ended is inconclusive. Some evidence suggests that a fourth, localized diapiric episode began and may have ended during the Pleistocene or Holocene. The crests and flanks of many diapiric folds dis- play a distinctive structural pattern that reflects the 137 three episodes of salt diapirism. In its simplest form this pattern consists of vertical to overturned beds of the Indianola Group at the base of an exposure. These upturned Indianola beds are unconformably overlain by a sequence of gently to moderately inclined Price River and North Horn strata. The Price River and North Horn Formations, in turn, are unconformably overlain by a stack of downwarped Tertiary beds, consisting chiefly of the Flagstaff, Colton, andGreen River Formations. During the first diapiric episode the Indianola beds were pushed up to vertical or overturned attitudes. During the second episode the Price River and North Horn sequence also was bowed up, but in most places not as drasti- cally as the Indianola beds. The crest of the upwarp formed during this second episode coincides, more or less, with the crest of the previous upwarp. During the third episode the Flagstaff and younger Tertiary beds were deformed. Locally, these younger Tertiary strata have been bowed up to vertical attitudes, but in most places they are warped down and define the great monoclines that mark the Sanpete—Sevier Valley area. The general geologic pattern is best expressed by the phrase: Upturned Cretaceous and Jurassic strata overlain by downturned Tertiary beds. (See also p. 8.) 'va0 major angular unconformities, thus, are exposed in single outcrops—one between the Indi- anola and the overlying Price River and North Horn sequence, and a second between the Price River and North Horn sequence and the overlying Flagstaff Limestone. These angular unconformities represent the periods of erosion during which the upturned, deformed beds were beveled to surfaces of low relief. As the strata above and below these angular uncon- formities are traced laterally, away from the folds, they gradually lessen in dip, and in distances as short as 0.8 km (1/2 mi) are conformable. Most likely, if exposures were adequate, the same structural pattern would be found in all the diapiric folds. The repetition of this pattern—it has been found in the western, central, and eastern sectors of the area—suggests that during each of the three major diapiric episodes all the salt diapirs in the area were reactivated more or less concurrently. This implies that the causative forces were regional in extent. Although all the salt diapirs apparently acted more or less in unison during each of the three major diapiric episodes, some evidence suggests that during the late Tertiary or Quaternary, small cells of these larger salt diapirs reactivated independently and deformed parts of the previously formed diapiric folds. The Red Knolls (p. 30), west of Redmond, are 138 composed of the Arapien Shale and form topographic prominences that rise above more durable units. These knolls of the easily eroded Arapien must have been pushed up in the recent geologic past or they would have long since been eroded. Overturned folds, part of the Charleston-Nebo thrust plate, were intruded, broken, tilted, and prob- ably arched by the intrusive action of the Arapien Shale. The field evidence suggests that the Charleston-Nebo thrust plate was emplaced at some time after Middle Jurassic (Bathonian) time but before Late Cretaceous (Maastrichtian) time. Farther north, south of the Uinta Mountains, Bryant and Nichols (1988, p. 420) concluded, based on strati- graphic evidence, “* * *that major movement on the Charleston thrust occurred in Campanian time* * *.” Erosion partly destroyed the thrust plate during its eastward movement. Subsequently, the deeply eroded plate was buried beneath near—horizontal younger Cretaceous and Tertiary rocks. Later, salt diapirs, overridden and concealed beneath the thrust plate, welled upward and arched the thrust plate and its overlying mantle of Cretaceous and Tertiary sedi- mentary rocks. Since then, erosion has removed many of these younger sedimentary rocks, leaving their tilted remnants as a reflection of the former arched sedimentary cover. Whatever oil pools formed in these overturned beds of the Charleston-Nebo thrust plate possibly were displaced or dissipated as a result of this diapiric activity. The salt diapirs, and the diapiric folds formed over them, may be structurally controlled. The folds are elongate, faintly sinuous, northward-trending upwarps that parallel the major fault systems in the area. Two of the largest diapiric folds are collinear with major fault zones. Possibly, renewed movement along preexisting faults reactivated the salt diapirs, which then forced the Arapien mudstones and shales into the fault planes. These planes acted as conduits along which the mudstone moved upward toward the surface; in time, the rising mudstone effectively oblit- erated the fault planes. In this interpretation, the former trace of a fault plane is now expressed as a northward-trending, slightly sinuous belt of Arapien mudstone—the core of a diapiric fold. The forces responsible for the movement of the salt are unknown; important factors were probably buoy- ancy, static load, regional lateral compression, crustal extension, or some combination of these. The slow but persistent upwelling of the salt diapirs possibly reflects sedimentary loading in those areas adjacent to the diapirs. By contrast, the rapid upward surges of the salt diapirs may have been in response to fault SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH movement that was triggered, during pre-Paleocene time, by pulses of compression (thrust faulting) from the west, and during post-Paleocene time, by crustal extension. Static load was important, for it kept the salt under compression; the reactivated faults merely offered avenues of escape for the tightly confined, mobile salt. The emplacement of the salt diapirs and the result- ant upward bowing of the intruded rocks may have created structural traps between the diapirs and the country rock in which oil and gas could accumulate. The most promising sites for such traps would be where the diapirs deformed the Mancos Shale. Base-metal deposits, probably deposited from mineral-rich, possibly saline solutions, may be con- centrated along parts of the contact between the country rock and the intrusive mudstones of the Arapien Shale. 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Geological Survey Miscellaneous Investigations Map I—1631. Young, GE, 1976, Geology of Billies Mountain quadrangle, Utah County, Utah: Brigham Young University Geology Studies, v. 23, pt. 1, p. 205—280. A Aerial views of east flank Gunnison Plateau 39 Aggie Creek ............................................ Alignment between faults and folds ..... Alternative interpretations (“Redmond Silver Mine”) .............................. 136 Ancestral course of Willow Creek ........... 29, 31 Ancestral San Pitch River ...24 Ancestral Sevier Lake 24 Ancestral Sevier River .. ...24 Ancestral surface, geologic pattern ...127, 128 Ancestral Willow Creek .................. 29, 109, 125 Ancestral Willow Creek area ..... 20, 41, 51—55, 67, 100, 119, 134, 135 Ancient Ephraim fault .. ....23 Angular unconformities .11, 135, 137 Anhydrite ................................... 18, 135 Anomalous depositional thinning ............. 57, 63 Anschutz Corporation’s Monroe Fee No. 1 well ..... 102 Arapien basin .............. .7, 11, 23, 25, 131, 133 Arapien deformation ....................................... 86 Arapien embayment .......... Arapien salt ......... Arapien Shale Age ............... Areal extent ........................... Aspects ............................................ Contact relations . Contained salt .. Deformed beds .. ...28 Depositional age ............................... 25, 135 Geologic aspects ......................................... 18 Gypsum in .......... 18, 19, 135 Intrusive aspects .. 27, 30, 85 Lithology ............ 18, 23 Lower contact ............................................ 19 Nomenclature .................................. Oil potential... Thickness Upper contact Arapien sill .......................... 91 Arapien Valley ........................................... 37, 38 Argonaut»Federal well 23, 24, 134 Autochthonous plate Axtell Formation ........ B Barton No. 1 well, Placid Oil Company .......... 25 Base-metal deposits ..138 Basement rocks . 11 Basin and Range provmce .2, 8, 11, 135 Bennie Creek area ................. 104, 105, 106, 107 Billies Mountain ..................................... 84 “Billies Mountain” area.. .. 29, 84, 85, 86 Birch Creek ....74 Birdseye ......... ...92 Black Canyon ........................ 104, 111 Block faulting ........................ Book Cliffs ............................. INDEX {Italic numbers refer to illustrations] Bouguer gravity anomaly map ..................... 103 Boundary Ridge Member of Twin Creek Limestone 23, 25 Brines ........................ ....133 Buoyancy ...................... 138 C Calcite ............................................................... 18 Canyon Mountains 11, 21, 23 Carmel Formation 20, 21 Castle Valley .......................... 9, 132 Causative forces of deformation ..................... 137 Cedar Hills ................................... .. 8, 10, 81 Cedar Mountain Formation .. 3, 18, 50, 75, 77, 86, 93, 95, 96, 109, 111, 124 Cedar Mountain road ...................................... 51 Centerfield ........................................ Charleston thrust fault. . .. Charleston-Nebo overthrust ............ ....101 Charleston-Nebo thrust fault ................. 8, 9, 69 Charleston-Nebo thrust plate ........... 12, 20, 21, 29, 38, 69, 70, 74, 75, 81, 83, 92, 93, 104, 105, 132, 134, 138 Chevron U.S.A. Chriss Canyon well ........................... 24, 25 Salina Unit No. 1 well .......... 24 Chicken Creek area . ..18, 19, 20, 134 Chriss-Mellor graben . 6, 76 Christianburg ................................................... 41 Clear Creek area ............................................ 133 Code of Stratigraphic Nomenclature ....... 16 Collapse of diapiric folds ..... 8, 119, 120 Collapse structure ................ 120, 121 Colorado Plateaus province ........ 2, 8, 9, 11, 135 Colton Formation ......................... 29, 51, 63, 86, 98, 99, 109, 137 Complex structural relations (Sevier Bridge Reservoir diapiric fold) Conduit for diapiric sediments .......... Contained salt, Arapien Shale Cordilleran geosyncline ..... Crab Creek ......................... Craton, Paleozmc Crazy Hollow Formation ...29, 35,51, 55, 63, 99, 100, 124 Cross section of typical diapiric fold ...128 Crustal extension ........................................ 138 Cuesta north of Redmond .................. Curtis Formation ................................ D Dairy Fork graben ........................ 38. 96, 97, 98 Deformed gravels near Gunnison Reservoir ..... Delta ............... 23, 24 Depositional age (of Arapien Shale) .. ...25 Depositional stage (of diapiric episode) .............................................. 124, 137 Depositional thinning .............................. 63, 76, 107—117, 119, 136 Pole Creek diapiric fold ........................... 111 Sanpete—Sevier Valley diapiric fold ....... 109 Sevier Bridge Reservoir diapiric fold ....................... 109—111 Thistle Creek diapiric fold .. Diagrammatic cross sections of Red Rocks area ................................................. 45 Diagrammatic sketches of Red Canyon area, Valley Mountains ................ 68 Diapiric activity ...................................... 131 Diapiric core ............ 12, 13, 37, 38, 130 Diapiric deformation in Thistle area .............. 92 Diapiric episodes .. 124, 126—127, 129, 131, 137 Diapiric folds (salt-cored anticlines) .......... 3, 12, 13, 21, 25, 28,37, 57, 67, 93, 102, 105, 108, 117, 119, 124, 125, 129, 130, 131, 134, 135, 136, 137, 138 Collapse ............... 119—121 Cross section ..................... 13 Distribution pattern ............... 36‘ Growth ................................ 117—119 Localization ..... 129-131 Diapiric processes .................. 117 Causative forces. .. 129—131 Cyclical aspects.. ...... 129 Geologic pattern... ..... 125—129 Diapiric shale ................................. 12 Diapiric sheath ...................... 12, 13 Diapiric stage ........................................ 124, 129 Diapiric stages and episodes . ...... 124 Diapiric structures 18, 27 Diapirism ................... 27—29 Dinoflagellate assemblages ............................ 25 Disturbed zone ........................................ 11, 135 Dixel Resources well ........................................ 25 Dog Valley .......................................................... 9 Dome near ancestral Willow Creek .. 29 Dry Canyon ............................................... 28 Dry Hollow ...81, 83, 96 Dry Hollow diapiric fold ............... 38, 81, 83, 95 Development ........................................ 86, 87 Dry Mountain .......................... 107, 118, 119 Dynamic ancestral high ................................ 108 Dynamic barriers .......................................... 136 E East Fork of Sanpete Valley ..... East Gunnison monocline .. East ’I‘intic Mining District East ’I‘intic Mountains Eastern Sevier Valley ..... Economic implications of diapirism Elongate salt structures Elsinore ............................ Emery Sandstone Member of the Mancos Shale ........................................ 133 Emplacement ages of the Arapien Shale ...................... Entrada Sandstone. Ephraim .................... Erosional escarpment .............. 9, 10, 21, 29, 84, 92, 93, 104 Erosional stage of diapiric episode ....... 124, 137 Escarpment fault ..................... .. 76 Evaporites ..... 13 Extensional tectomsm .................................... 35 F Fairview ........................................................... 98 Fairview diapir(?) ...... 98, 99 Fairview diapiric(?) fold 38, 98—100 Fault plane used as conduit. 130, 131 Fault zone ...................................................... 130 Fayette ..................................................... 38, 130 Ferron Sandstone Member of the Mancos Shale .......................... 133 Flagstaff Limestone ........ 20, 29, 41, 45, 51, 53, 62,85, 92, 93, 98, 101, 107, 109, 111, 124, 128, 137 Footes Canyon ........................................... 69, 81 Footes Canyon diapiric(?) fold .......... 21, 38, 75, 81—83, 105, 107 Fountain Green . 38, 41 Freedom ........................................................... 38 G 0—24 well (Union Oil Company) ................... 98 70, 74 Gardner Canyon ............................. Gardner Canyon—Red Canyon area .. . 134 General stratigraphy ................................ 12—16 Geologic maps of areas discussed in the report ................................................ 7 Geologic pattern .................................... 125—129 Geologic relations Along both flanks of Gunnison Plateau 123 Near Middle Fork Pole Creek .................. 80 Near “Redmond Silver Mine” ................ 136 Geology near Black Canyon ................................... 110, 111 Dry Mountain .......... 118, 119 Head of Payson Canyon. ..... 116 Head of Santaquin Canyon 113 Red Lake .................................................. 115 Wales, Utah ............................................... 52 Geology of Ancestral Willow Creek Area . . 58 Dry Hollow area ............... 84 Hjorth Canyon area .................................. 95 Little Clear Creek area ..................... 96, 97 Pole Creek—Hop Creek area, Cedar Hills. 77, 78 Red Rocks area 42 Salt Creek area ............................ 108 Sixmile Creek Canyon area .................... 46 Thistle area .................................. 88, 89, 90 Giraffe Creek Member of Twin Creek Limestone ............ 19 Goldens Ranch Formation ....... 67, 75, 101, 124 Gordon Creek well .................................... 21 Grabens ............................................... 11, 21, 76 Gravity data .......................................... 102-104 Great Basin Section of Basin and Range province ...................... 11, 132 Great Salt Lake ........................................... 24 Great Western Salt Company ........................ 23 Greater Scipio Valley .................................... 101 Green River Formation ......... 20, 23, 29, 31, 84, 92, 96, 98, 99, 100, 109, 113, 117, 135, 137 Growth and collapse of diapiric folds ....117—121 INDEX Gulf Coast ................................................ 12, 134 Gunnison ....................... 21, 38, 41, 57, 102, 130 Gunnison Plateau (San Pitch Mountains) ..... 10, 11, 18, 19,21, 24, 27, 28, 29, 37, 38,41, 4 8, 50, 69, 75, 76, 77,81, 98, 104, 109, 121, 123, 124, 128, 130, 132, 134 Gunnison Reservoir area ..... 41, 55—57, 61, 125 Gypsum ............................................................. 19 Gypsum Spring Member of Twin Creek Limestone ................................. 19, 23 H Halite (salt) ....................................................... 24 Halo-kinesis ............................................. 25, 129 Halo-tectonism ...... ........ 25, 130 Hanson Oil Corporation‘s Moroni A—1 well ........................................ 132 Hanson wells ......................................... 25 High-saline conditions, Arapien Shale ......... 133 Hingeline (Paleozoic) ........................ . 11, 131 Hjork Creek dome ...93 Hjorth Canyon area... .93, 95, 96 Hjorth Canyon diapiric fold ................ 38, 93—96 Hjorth Canyon salt diapir ....................... 95 Hogbacks in eastern Sevier Valley Hop Creek Hop Creek Ridge Howard 1—A WXC well (Placid Oil Company) ............................ 24, 101 Hydraulic car jack (analogy) ..... I Index map of central Utah Indian Hollow ........................ Indianola ............................... 8, 9, 21, 38, 93, 98 Indianola Group .29, 41, 50, 57, 62, 75, 77, 81, 83, 93, 95, 96, 109, 121, 124, 129, 137 Ingram Canyon ............................... 74 Intrusive sedimentary beds .. 12, 27 Intrusive stage of diapiric episode ........ 124, 137 Iranian diapirs .......................... 24 Isoclinal fold, Red Rocks area Isopach map of salt deposits ......... J J.W. Irons well No. 1 ..................................... 132 Japanese Valley ..... .38, 101 Joes Valley graben . 119 Juab .................... .8, 19, 102 Juab County .................................................... 20 Juab Valley ........................................... 9, 24, 69, 100, 102, 104, 121, 124 Jurassic marginal basin .................................. 23 K KOA Campground area ...................... 18, 77, 81 L Lake Bonneville, ancestral .............................. 24 Lake Fork ............... 83, 98 Lake Mountains ........................... 132 Landslide and earthflow phenomena .............. 99 Leamington trans-current fault ....................... 9 Leeds Creek Member of Twin Creek Limestone ...... 19, 20, 23, 25 Levan ............................ 9, 21, 69, 104, 134 Levan area ....... Levan diapir Levan diapiric core Levan diapiric fold .. 74, 75, 76, 77, 81, 104, 130 Levan Unit 1 well (Standard Oil of California) .............................. 69, 134 Linear upwarps .............................. 12 Little Clear Creek .. ...38, 95, 96, 98 Little Clear Creek diapiric fold .............. 38, 95, 96—98, 129 Little Salt Creek ...... 24, 69, 75 Loafer Mountain 92, 104, 107 Locality file (Index map of central Utah) ..... 6—7 Localization and causative forces ...... 129 Long Ridge ............................................. 100 M Major fault zones ............................. Major test wells in central Utah ..... Mancos Shale ......... 132, 133, 134 Oil potential ..... Manning Canyon Shale Oil potential ............... Manti ......................... ........ 26 Maple Canyon area ...... 128 Maturation level 133 Mayfield .................. 18, 33, 38, 57 Mesocordilleran anticline ............................... 23 Micrite, Arapien Shale .................................... 18 Middle Fork Pole Creek ....... 20, 77, 80, 81, 111 Middle Jurassic (Callovian) (Twist Gulch Formation) ..................................... 18 Middle Rocky Mountains province Milburn ............... Mills Gap ...... Mineral deposits Minor structures Mobilization of plastic mudstone beds ............ 3 Mona .......................................................... 9, 132 Monoclines . 121—124, 137 Paired, facmg 121—124 Monroe 13—7 well (Placid Oil Co.) ............ 25, 69 Monroe Fee No. 1 well (Anschutz Corp.) ..... 102 Mormon temple in Manti ................................ 99 Moroni ................................................ 38, 93, 132 Moroni AX—l well (Hanson Oil Corp.) ......... 132 Moroni Formation ........................ 75, 77, 81, 84, 92, 95, 96, 124, 137 Moroni wells .............................................. 25, 41 “Mother bed” of salt ................ 105, 129 Mount Nebo ............................. Mount Pleasant .......................... Multiple episodes of orogeny .. Multiple episodes of salt diapirism N Navajo Sandstone (Nugget Sandstone) ......... 19, 29, 74 Nebo Loop Road ....................... 77 Nebo thrust fault ...... 8 Nephi ............ 8, 9, 18, 24, 70, 81, 130 Ninemile Reservmr ................................... 35, 37 North American Stratigraphic Code ............. 16 North Fork Salt Creek ............................. 18, 24 North Horn Formation 29, 38, 76, 84, 85, 86, 92, 93, 95, 96, 98, 107, 109, 111, 124, 137 North San Pitch River Valley diapir ....... 98, 99 144 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH Northeast flank Valley Mountains .............. 62 Northern Tunisia, salt structures .............. 129 Nugget Sandstone (Navajo Sandstone) ..... 19, 92 0 Oak Creek .............. . Oil and gas accumulation of. Oil and gas, source beds ............. Oquirrh Group ........................................... 70, 74 Orogenic forces Osiris Tuff ........... Overthrust belt ........................................ P Painted Rock Canyon .................................... 128 Paired, facing monoclines ....100, 121—124 Paleo-high 81, 83, 92, 113, 117 Paradox Basin ...7, 121, 129, 130, 131 Paxton No. 1 test well (Placid Oil Company) ..................... 21 Pavant Range ............................... 11, 21, 23, 101 Payson Canyon area ........ 21, 104, 105, 107, 116 Phillips Petroleum Company’s Price “N” Well ............ 24, 25, 41, 132 Photographic overviews near erosional escarpment ............................ 106, 107 Photographs of Thistle area ........................... 90 Physiographic provinces in central Utah . ....3 Piercement structures ..................................... 12 Pigeon Creek ............. Pigeon Creek area ............................ Placid Oil Company Howard 1—A WXC well ..................... 24, 101 Monroe 13—7 well ...... .. 25, 69 Paxton No. 1 test well.. ..... 21 WXC—USA 1—2 well ................................ 102 Pole Creek area ........................................... 77, 81 Pole Creek diapiric fold ............... 21, 38, 69, 77—81, 83,111 Potential oil and gas traps ...... ....134 Overthrust belt ........................................ 134 Pre-salt strata ................................... Salt-bearing and younger strata .. Salt diapirs ., Pre-salt beds ...... .16,133, 134,136 Preuss Sandstone ............................. 21 Price “N" well (Phillips Petroleum Company) ................... 24, 25, 41, 132 Price River and North Horn sequence ..... 45, 62 Price River Formation ................... 9, 38, 41, 45, 50, 67, 75, 109, 111, 121, 137 Provo ........................ 9, 23, 83 Pyrophyllite .................................................... 133 R Rectorite ......................................................... 133 Red Canyon area (Southern Wasatch Range) .......... 20, 57, 63, 70, 74, 75, 101, 111, 119, 123, 124, 127, 128 Red Canyon area, Valley Mountains ............. 63, 66, 68, 99 Red Knolls ........................... Red Knolls area ................... Red Lake ........................................ 104, 107, 115 Red Rocks area (Christianburg) .......... 28, 41, 45, 50, 51, 75, 117, 124, 127, 128 Red Rocks-Sixmile Canyon area ....... 41, 51, 55 Redmond .......................... 18, 21, 23, 24, 30, 31, 57, 67, 102, 111, 130, 135, 137 Redmond diapiric fold ........................ 21, 31, 38, 57, 67, 113, 130 Redmond Hills anticline ............... 57, 113 “Redmond Silver Mine”... 135, 136 Rees Flat ..................... .74, 75 Regional lateral compressmn . 138 Reservoir beds, oil and gas ............................ 132 Rich Member of the Twin Creek Limestone ...................................... 19, 23, 25 Richfield ................. 21, 38, 102, 130 Rim syncline .. ......................... 129 Rock salt (halite) ..... ...3, 13, 18 Round Valley ........... S St. George ........................................................... 3 Salina ..... 18, 20, 23, 24, 30, 33, 38, 51, 57, 101 Salina Canyon - ...................... 23 Salina Creek Canyon . .9, 113 Saline basin ............................................. 11, 131 Saline solutions ............................................. 138 Salt (halite) ........... .119,135 “Salt anticlines” (salt-cored anticlines) .......... 2, 37,129 Salt-bearing and younger strata .......... 133, 136 Salt-cored anticlines (diapiric folds) ................ 3, 12,20,131 Salt cores .. 12 .18 21, 24,69, 81, 104 Salt Creek ..... Salt Creek Canyon ............................ 18, 21, 107 Salt Creek Fanglomerate ............................... 77 Salt diapir ........................ 12, 13, 16, 23, 24, 25, 45, 117, 119, 124, 129, 131, 135, 138 Salt diapirism ............................... 3, 8, 76, 135 Salt diapirs ....... 12, 16, 25, 119, 135, 138 Salt—generated diapiric folds ......... Salt-generated structures Salt-cored dome Salt-stock families... Salt stock (salt diapir) .................... Salt stocks ............. Salt structures... Salt structures in northern Germany ........... 129 Salt structures in northern Tunisia" Salt walls ................. San Pitch Mountains (Gunnison Plateau) ..... 10 San Pitch River ..................................... 9, 10, 57 ..18, 20 .. 132 .23 23 San Rafael Group ...... San Rafael Swell . Sanpete County Sanpete—Sevier rift .................. Sanpete—Sevier Valley and Redmond anticlines ..................... 113 Sanpete—Sevier Valley anticline ........ 29, 38 111, 113, 115 Sanpete—Sevier Valley area ...... 3, 9, 12, 20, 37, 55, 76, 111, 115, 124, 137 Sanpete—Sevier Valley diapiric fold ........ 21, 29, 38—57, 67, 98, 109, 111, 113, 129, 130, 131, 134 Sanpete—Sevier Valley salt diapir ..... 55, 56, 132 Sanpete Valley ............................ 8, 9, 21, 38, 48, 57, 62, 98, 102, 109, 124, 132 Sanpete Valley embayment ...... 132 Santaquin .................................... 9, 105 Santaquin Canyon ........................ 104, 107, 113 Scipio ............................................. Scipio Lake .. Scipio Valley Scofield Reservoxr ...... Seismic reflection profiles ..... Seismic surveys .................................. Selenite crystals in Arapien Shale. Sevier Bridge Reservoir (Yuba Lake). . Sevier Bridge Reservoir area ............ 57,69,102 Sevier Bridge Reservoir diapiric fold ............ 38, 57—69, 109, 111, 129, 131 Sevier Bridge Reservoir salt diapir . 63, 69, 102 Sevier County, Utah ......................... 20, 23, 135 Sevier Desert ................................... Sevier fault zone .......... Sevier orogeny ............. Sevier River Sevier thrusting ............................................... 55 Sevier Valley ............................ 8, 19, 21, 30, 37, 38, 101, 102, 104, 121, 124, 130 Side Canyon 98 Sigurd ............. ...38 Sixmile Canyon ....... 99,109,119,121,123,127 Sixmile Canyon area ......................... 41, 45, 48, 62, 109, 124, 127 Sixmile Canyon Formation ..... 127 Sixmile Creek canyon ..... 29, 48, 50 Skinner Peaks ................. Skinner Peaks area ................................... 75, 81 Sliderock Member of Twin Creek Limestone ................. 19, 23, 25 Small-scale features of Arapien Shale (photographs) .................................. 33 Smiths Reservoir ............................................. 98 Soldier Creek ........... 9, 83, 84, 85, 86 Soldier Creek Canyon ..................................... 83 Source rocks (oil and gas) .............................. 132 South Valley ................................................... 101 South wall of Red Canyon (Southern Wasatch Range) .............................. 76 Southern Wasatch Range ....... 8, 9, 70, 105, 107 Southwest flank of the Sevier Bridge Reservoir diapiric fold .................. 64 Spanish Fork Canyon . Spanish Fork River ....... Standard Oil of California Levan unit 1 well ..... State No. 1 well Static load ...... Static topographic high . Sterling ............ 8, 18, 23, 28, 29, 38, 41, 57, 111 Stratigraphy .............................. 12—26 Strip- thrust fault ...... Structural and stratigraphic traps Structural complexity and diapiric folds ........ 63 Structural pattern of central Utah .............. 125 Structural traps (oil and gas) .......... 133 Summerville Formation ............. T Taylor Fork .......... Taylor Fork area Temple Hill, Manti . Tertiary thrusting ....... Test wells in central Utah ........... The Washboard ................................................ 69 Thickness of salt . .24 Thistle ................................. 8,9,19,20,21, 23,29, 81,83, 111, 117 Thistle area ........... 83, 84, 92, 93, 107, 111, 134 Thistle Canyon fault ....................................... 92 Thistle Creek ....................... 84, 86, 92, 104, 107 Thistle Creek diapiric(?) fold .................. 21, 38, 83—93, 104, 105, 107, 111 Thistle landslide ...................... 29, 86 Transition zone ................................... 2, 11, 131 Twelvemile Canyon Member of the Arapien Shale .......................... 16, 27 Twelvemile Creek ........................................... 57 Twin Creek Limestone ...... 19, 20, 23, 29, 69, 70, 71, 74, 86, 91, 92, 119, 133 Boundary Ridge Member 19 Giraffe Creek Member ............................. 19 Gypsum Spring Member 19 Leeds Creek Member .. .. 19 Rich Member ...... .. 19 Sliderock Member ..... .. 19 Watton Canyon Member ..... 19 Twist Gulch Formation ......... 16, 18, 20, 50, 51, 77, 86, 93, 95,96, 111, 117, 124, 137 Aspects (photographs) ..... Thickness ......................... Twist Gulch Member of Arapien Shale .. . 16 U Uinta Mountains ..................................... 23, 138 Union Oil Company’s No. G—24 well .............. 98 Unnamed hill near Ninemile Reservoir. .. 35 USGS Professional Paper 1170—F .......... . 104 US Highway 6 and 89 ....... Utah, central, index map Utah, central, physiog'raphic provinces ............ 3 Utah Lake ..................................................... 132 INDEX Utah State Highway 132 ............................... 101 Utah Valley ......................................................... 8 V Valley Mountains ................... 10, 21, 23, 24, 27, 30, 38, 57, 61, 67, 101, 102, 109, 111, 117, 119, 123, 124, 127, 128 Valley Mountains diapiric(?) fold ...38, 101—102 Valley Mountains monocline ................... 63, 69, 98, 99, 101, 119, 121 Vertical aerial photographs of Temple Hill area, Manti .............. 100 Views Along east flank Dry Mountain ..... 106, 107 Along west valley wall of Thistle Creek ....................... 106, 107 In Salt Creek Canyon ..................... 106, 107 Near head of Bennie Creek ............ 106, 107 Near head of Dry Hollow .......................... 86 .106, 107 .106, 107 Near head of Payson Canyon. Near Red Lake Ancestral Willow Creek area Volcanic gravels of Gilliland (1948) . V-shaped dissolution synclines ..... V-synclines ............................................ W Wales .............................................. 121, 132, 134 Wales Canyon ........................................... 50 Wales Gap ................ 41, 50, 55, 57, 98, 109 Manuscript approved for publication March 13, 1992 Published in the Central Region, Denver, Colorado Edited by Lorna Carter Photocomposition by Marie F. Melone Graphic design by Patricia L. Wilber Cartography by Henry Williams fiU.S. CDVERNdI-NT PRINTDI; OFFICE: 1994-673-046/86056 145 Wasatch and Valley Mountains monoclines .............................. 69, 99 Wasatch fault zone ..................... 9, 11, 105, 130 Wasatch monocline 9, 37, 48, 51, 62, 64, 98, 99, 100, 101, 119, 121, 124 Wasatch Plateau ........... 8, 9, 21, 23, 38, 48, 51, 76, 99, 101, 109, 119, 123, 132, 133 Wasatch Range ............................................ 8, 10 Watton Canyon Member of Twin Creek Limestone ...... 19, 23, 25 West Fork of Sanpete Valley 98 West Gunnison monocline ....... 69, 75, 76, 121, 124 West Hills ..................... 9, 21, 24, 100, 101, 121 West Hills diapiric(?) fold 38, 100—101 West Hills monocline .................. 121, 124 Western Interior of the United States .......... 37 White Hills ............ 18, 37, 51, 57 Willow Creek ....................... 51 Willow Creek gap ................................ 41, 51, 53 Willow Creek road .................................... 53, 55 Y Yuba Dam .............................. 23, 62, 67, 69, 101 Z Zechstein salt .......................................... 12, 102 Z-fold ................................................................ 28 SELECTED SERIES OF US. 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