JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 91, NO. B12, PAGES 12,587-12,631, NOVEMBER 10, 1986
Earthquakes,Quaternary Faults, and SeismicHazard in California
STEVEN G. WESNOUSKY 1
SeismologicalLaboratory, California Institute of Technology
Data describingthe locations,slip rates, and lengthsof Quaternary faults are the primary basisin this work for constructingmaps that characterizeseismic hazard in California. The expectedseismic moment Moe and the strengthof groundshaking resulting from the entire rupture of each mapped fault (or fault segment)are estimatedusing empirical relations between seismic moment Mo, rupture length, sourceto site distance,and strong ground motion•s. Assuminga fault model.whereby the repeattime T of earthquakesoneach fault equals Moe/M•o (where the moment rate Mo g is propor- tional to fault slip rate), it is observed that the moment-frequency distribution of earthquakes predictedfrom the geologicdata agreeswell with the distributiondetermined from a 150-yearhistori- cal record. The agreementis consistentwith the argument that the geologicrecord of Quaternary fault offsetscontains information sufficientto predict the averagespatial and size distribution of earth- quakesthrough time in California. The estimatesof r for each fault are the foundationfor con- structingmaps that depict the average return period of >• 0. lg peakhorizontal ground accelerations, and the horizontal componentsof peak acceleration,peak velocity, and the pseudovelocityresponse (at 1-periodand 5% damping) expectedto occur at the level of 0.1 probability during a 50-year period of time. A map is alsoformulated to showthe probabilitythat >• 0. lg horizontalground accelera- tions will occur during the next 50 years. The maps serveto illustratethe potential value of Quater- nary fault studiesfor assessingseismic hazard. Interpretationof availableslip ratesindicates that the largestand most frequent occurrenceof potentially destructivestrong ground motions are associated principally with the San Andreas, San Jacinto, Calaveras,Hayward, and Ventura Basin fault zones. Other regionsof similarly high hazard may yet remain unrecognized. This inadequacyresults pri- marily from an incompletedata set. Numerous faults, for example, are mapped along the coastal region of northern California and within the Modoc Plateau, but relativelyfew studiesrelating to fault slip rate are reported. A similar problem existsfor other stretchesof coastalCalifornia where marine reflectionstudies provide evidenceof active faulting offshoreyet yield little or no information of fault slip rate. Geologicaland geophysicalfield studiescan work to remove thesedeficiencies. A concerted effort to locate and define ratesof activity on all faults in California is the most promisingmeans to further quantify presentlevels of seismichazard in California.
INTRODUCTION describethe averagerates of offsetacross Quaternary faults, The causalrelation betweenearthquakes and faulting was with an aim toward developingmaps that depict long-term well describedsome 100 yearsago by Gilbert [1884] during seismic hazard in California: specifically,the average size his discussion of earthquakes in the Great Basin. Koto and spatialdistribution of earthquakesthrough time and, of [1893] independentlynoted the samecausality during his more practicalconsequence, the expectedoccurrence rate of study of the great 1891 Nobi earthquake of Japan. Later the resultingstrong ground motions. field investigationsof the great 1906 California earthquake The motivation for this study residesin the uncertainties inherent to more conventional forms of seismic hazard by Lawson[1908] and his colleaguesremoved most remain- ing doubt of the close connection between faulting and analysis,which are basedprimarily on earthquakefrequency earthquakes.Moreover, Reid's [1910] geodeticstudy of statistics obtained from historical catalogues of seismicity. The uncertainty in such analyses is large that same earthquakeprovided a physicalmodel to explain when the historical record is too short to define secular rates the occurrenceof earthquakefaulting, the now well-known of seismicity,which is the usual case,particularly when rela- concept of elastic rebound. These observationsprompted Willis [1923] to suggestas earlyas 1923 that a fault map of tively small regionsare considered. In contrast to historical data, the geologicrecord of Quaternary fault offsetscontains California was a good indicator to the sitesof future earth- information on the occurrence of earthquakes through quakes. Since these studies,knowledge of the mechanicsof periods of time many orders longer than the averagerepeat earthquake faulting has continued to grow, moderate to time of large earthquakeson individual faults and orders of large earthquakeshave consistentlybeen observedto rup- magnitude greater than periods covered by historical ture along mapped faults, and faults that break Quaternary depos{tsare now commonly accepted as sources of seismic records. Observations such as these have recently led a number of investigatorsto argue that geologicinformation hazard. The purpose of this work is to use our current of fault offset rates may be used to reduce uncertainties understanding of fault mechanics to interpret data that associatedwith estimates of long-term seismicity and, in turn, seismic hazard [e.g., Allen, 1975; Anderson, 1979; Molnar, 1979]. The following exerciseis thus an attempt at 1Now at Tennessee Earthquake Imormation Center, Memphis placing this idea into a quantitative framework for analysis State University. of seismic hazard in California. The approach I will take Copyright 1986 by the American GeophysicalUnion. follows that developedin a recent study of seismichazard in Japan [Wesnouskyet al., 1984]. The underlyingpremise of Paper number 5B5769. that work was that moderate to large earthquakes occur on 0148-02;•7/86/005B-5769505.00 mappable Quaternary faults and that the occurrencerate of
12,587 12,588 WESNOUSKY'.SEISMIC HAZARD INCALIFORNIA
ß
MODOC PLATEAU m•(, 195L•.•.• •x, CALIFORNIAEA R T H Q U A K E S Cape Mendocino 194•
Pt. Arena
SAN sA FRANC•,SCO FRANClSC
MONTEREY MONTEREY
PARKFIELD 'EHACHAPI MOJAVE •947(6.2)• Pac/Hc SANTAMARIA GABRIEL DESERTSAN BERNARDINO Ocean Pt.Arg MOUNTAINS •ENTURABASIN SANTA PalosVerdes
SANDIEGO SANDIEGO
Fig.1. (a)Major active faults, physiographic features, and (b) locations of historically recorded moderate to large earthquakesthathave occun-ed in California. Faults that have produced coseismic surface ruptures are stippled. Onshoreand offshoreevents of M>•6.2 are listedin Tables1 and 3, respectively.
earthquakeson eachfault is proportionalto the Quaternary seismicityto ratesof seismicityaveraged over longer periods fault slip rate. of geologictime hasnow been observed for the regions It is the parameterof seismicmoment Mo that allowsthe encompassingsouthern California [Anderson, 1979], Utah quantitativeassessment of seismicityrates from fault slip [Doserand Smith,1982], and intraplate Japan [ Wesnousky rate data [Brune,1968]. The seismicmoment Mo is a more et al., 1982],as well as a numberof plateboundaries fundamentalmeasure of eaChquakestrength than is earth- [Brune,1968; Davies and Brune,1971]. The observed quakemagnitude M and,like M, maybe measureddirectly coincidencein seismicityrates over these broad regions pro- from a seismogram.Mo, however,may be relateddi,rectly videssupport for the suggestion[Allen, 1975; Anderson, to physicalparameters that describethe earthquakesource, 1979]that the geologic record of Quaternaryfault offsets is whereasM canonly be indirectlyrelated through its empiri- well suitedfor estimatinglong-term rates of seismicityand cal relationwith Mo [e.g.Hanks and Kanamori,1979]. henceseismic hazard in regionscharacterized by shallow Specifically,seismic moment Mo is definedto equalI4. UA, seismicity,Quaternary faulting, and a shortrecorded his- whereg is the shearmodulus, A is the faultarea, and U is tory. Californiapossesses each of theseattributes. Let me the averageslip occurringacross the fault [e.g.,Aki and thenbriefly review the availabledata concerning seismicity, Richards,1980]. Thus,for a fault on whicha numbern of faulting,and fault slip rates in California. earthquakeshave occurred during a periodof time T•, the DATA AND OBSERVATIONS rate of seismicityon the fault may be characterizedby the seismic moment rate Earthquakesand Faulting Earthquakesin California,and in otherregions of similar tectonicsty]v, generally rupture along faults that show evi- dence of prior Quaternarymovements [Allen, 1975; Further,if a geologicmarker of ageT2 is displacedacross Matsuda, 1977]. It is alsogenerally recognized in Califor- the faultby distanceU, the lo.ng-termrate of seismicityon nia that the occurrenceof earthquakesis limited primarily thefault may be ,expressedasMo--gA (U/T2) [Brune,1968]. to theupper 15 km of theearth's crust [e.g., Sibson, 1982]. This assumesthat fault displacementsare not the resultof Theepicentral distribution of moderateto largeearthquakes aseismiccreep but ratherare the cumulativeresult of many that have occurredin Californiaduring historical time is earthquakesthrough geologic time. Usingthe conceptof picturedon a simplifiedfault map of Californiain Figure1. seismicmoment, a near coincidenceof historicalrates of Onshoreearthquakes of M >/ 6.2 arefurther listed in Table WESNOUSKY.'SEISMIC HAZARD IN CALIFORNIA 12,589
TABLE 1. Earthquakes Onshore California Mappable Surface Date Location Magnitude* Faultt Rupturet References April9, 1857 SanAndreas 7.9õ Yes Yes 1 March 26, 1872 Owens Valley 7.8 Yes Yes 2,21 April18, 1906 SanAndreas 7.7õ Yes Yes 3 July21, 1952 KernCouqty 7.3õ Yes Yes 4 Jan.22, 1923 Humboldtn 7.2 .... 9,25 June 1838 San Andreas 7.0 Yes Yes 5 Dec.8, 1812 LosAngeles # 6.9 .... 7 May19, 1940 ImperialValley 6.9õ Yes Yes 6 June 10, 1836 Hayward 6.8 ? ? 5,7 Oct. 21, 1868 Hayward 6.8 Yes Yes 3 April 21, 1918 San Jacinto 6.8 Yes -- 7,8 Nov. 23, 1873 Oregon border 6.7 .... 18 Feb. 24, 1892 San Diego County 6.7 .... 7 Dec. 25, 1899 San Jacinto 6.6 Yes -- 8,9 July 1, 1911 Santa Clara 6.6 Yes -- 7,11 Feb.9, 1971 SanFernando 6.6õ Yes Yes 12 July 22, 1899 Cajon Pass 6.5 .... 7,8 Nov. 4, 1908 Inyo 6.5 .... 9 March 10, 1922 Parkfield 6.5 Yes ? 13,23 Oct. 21, 1942 San Jacinto 6.5 Yes -- 7,8 Dec. 4, 1948 Desert Hot Springs 6.5 ? ? 14 Dec. 21, 1954 Humboldt 6.5 .... 18 April9, 1968 BorregoMountain 6.5õ Yes Yes 15 April 19, 1892 Winters 6.4 .... 16 Oct.15, 1979 ImperialValley 6.4õ Yes Yes 19 May 2, 1983 Coalinga 6.4 No No 20 May 25, 1980 Mammoth 6.4,6.3 ? ? Oct. 8, 1865 San Jose 6.3 .... 7 Feb. 9, 1890 San Jacinto 6.3 .... 7,8 May 28, 1892 San Jacinto 6.3 .... 7,8 July 23, 1923 Riverside 6.3 .... 8,9 March 11, 1933 Long Beach 6.3 Yes No 17 March 15, 1946 Walker Pass 6.3 ? ? 21 May 27, 1980 Mammoth 6.3 ? ? 10,26 April 12, 1885 Salinas 6.2 .... 7 April 21, 1892 Winters 6.2 .... 7 June 20, 1897 Gilroy 6.2 Yes ? 7 March 31, 1898 RodgersCreek 6.2 .... 7 April 10, 1947 Manix 6.2 Yes Yes 21 March 19, 1954 Santa Rosa Mountain 6.2 Yes -- 8,22 April 24, 1984 Morgan Hill 6.2 Yes No 24
* Magnitudesare from Toppozadaet at. [1981], Toppozadaand Parke [1982], and Toppozadaet at. [1986] for the periodsprior to 1900, 1900 to 1950, and post-1950,respectively. •' Answersare providedto (1) whether or not instrumental,isoseismal, or field studiesindicate that the earthquakewas associatedwith displacementalong a mappablefault, and (2) whether or not the earthquakeproduced tectonic surfaceruptures along the fault trace. Observations,particularly for older events,are often equivocal and, in such cases,are marked by a query. Pair of dashesindicates that data are insufficientto considerpossible association of event to a specificmapped fault. * 1, Sieh [1978b];2, Whitney [1872]; 3, Lawsonet at. [1908]; 4, Buwatdaand St. Amand [1955]; 5, Louderback[1947]; 6, Brune and Allen [1967]; 7, Toppozadaet at. [1981]; 8, Sandersand Kanamori [1984]; 9, Toppozadaand Parke, [1982]; 10, Taylor and Bryant [1980]; 11, Reasenberg and Ellsworth[1982]; 12, Barrowset at. [1973]; 13, Bulletin of the SeismologicalSociety of America [1924]; 14, Richter et at. [1958]; 15, Clark [1972]; 16, Wong [1984]; 17, Barrows [1974]; 18, Toppo- zada et at. [1986]; 19, Sharp et at. [1982]; 20, Clark et at. [1983]; 21, Richter [1958]; 22, Magistrate et at. [1984]; 23, Bakun and McEvitty [1984]; 24, Cockerhamand Eaton [1984]; 25, Lajoie and Keefer[ 1981]; 26, Clark and Yount [ 1981]. õMagnitude determined from seismic moment Mo viaempirical relation M--2/3xlogMo-10.7 [Hanksand Kanamori, 1979 ], assumingvalue of Mo listedin Table2. # Near coast,possibly offshore.
1. The data in Table 1 serveto illustratethe closeassocia- upon this observation. Similarly, further examination of tion betweenearthquakes and Quaternaryfaults. Examina- Table 1 showsthat the moderateevents of magnitudeM < tion of Table 1 showsthat as a generalrule, earthquakesof 6.5 may also generallybe demonstratedto be the resultof M/>---6.5 produceobservable surface ruptures along preex- displacementalong faults with mappable surficial traces, isting and mappableQuaternary faults, when attention is thoughsurface ruptures are not commonlyin evidence. limited to those earthquakesfor which data exist to bear The distribution of onshorefaults with Quaternary dis- 12,590 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
TABLE 2. Earthquake Data
Moment Length Type{} Date Location 1019 Reference* Data • km Reference* Data * N-m North America Jan.6, 1857 SouthernCalifornia 53-90 1,16 d 360-400 1,16 h S P May3, 1887 Sonora,Mexico 7-15# 61 d 76 61 h N I April18, 1906 NorthernCalifornia 35-43 1,29 d 420-470 1,29 h S P Oct.2, 1915 PleasantValley, Nevada 3-8# 17 d 34 17 h N I June7, 1934 Parkfield,California 0.15 6 b 20 7 g S P May19, 1940 Imperial,California 2.6#- 8 8,9,5 d,b 60 8,9 h S P July21, 1952 KernCounty, California 11 10 d 75 10 f R I July6, 1954 FallonRainbow, Nevada 0.3 4 a 18 19 h N I Aug.23, 1954 FallonStillwater, Nevada 0.7 4 a 30 19 h N I Dec.16, 1954 DixieValley, Nevada 1 4 a 40 18 h N I Dec.16, 1954 FairviewPeak, Nevada 5.3 4 a 45 18 h N I July10, 1958 SoutheastAlaska 44 59 d 350 25 g S P Aug.17, 1959 HebgenLake,Montana 10 58 a 26 20 h N I April9, 1966 Borrego,California 0.7-1.1 11,12 a 30-45 13,14 h,g S P June27, 1966 Parkfield,California 0.15 2 b 37 3 h S P Feb.9, 1971 SanFernando, California 0.8-1.9 23,24 b,a 14-22 21 g,h R I Oct.15, 1979 Imperial,California 0.6 52 b 30 15 h S P April2, 1983 Coalinga 0.54 60 b 25 46 g R I Oct.28, 1983 BorahPeak 2.1-3.5 56,57 a,b 36 35,41 g,h N I Japan Oct.28, 1892 Nobi,Japan 15 37 d 80 39 h S I Aug.31, 1896 Rikuu,Japan 14 39 d,e 36-50 38,39 fih R I March27, 1927 Tango,Japan 4.6 40 d 33 40 fig S I Nov.25, 1930 N. Izu,Japan 2.7 42 d,e 22 42,43 fih S I Sept.21, 1931 Saitama,Japan 0.7 44 b 20 44 g S I July11, 1935 Shizuoka,Japan 0.22 45 a 11 45 g S I Aug.11, 1940 Shakotan,Japan 21 50 b 170 50 i R I Sept.10, 1943 Tottori,Japan 3.6 40 a,e 33 40 e S I Jan.31, 1945 Mikawa,Japan 0.9 47 e 12 47 f R I June28, 1948 Fukui,Japan 3.3 40 a,e 30 40 g S I Aug.19, 1961 Kita-Mino,Japan 0.9 51 a 12 51 fig S I March26, 1963 WakasaBay, Japan 0.33 49 a 20 49 g S I May7, 1964 OgaPen., Japan 4.6 50 b 50 50 g R I June16, 1964 Niigata,Japan 32 48 b 80 48 g R I Jan14, 1968 Izu-Oshima,Japan 1.1 55 a,b 17 55 g S I Sept.9, 1969 Gifu,Japan 0.35 53 c,e 18 53 fig S I Oct. 16,1970 Akita,Japan 0.22 55 c,e 14 54 g R I May8, 1974 Izu-Hanto-oki,Japan 0.6 42 e 18 42 g S I Elsewhere Dec.26, 1939 Erincan,Turkey 45 59 d 350 30 h S P Dec.20, 1942 ErbaNiksar, Turkey 2.5 59 d 50 30 h S P Feb.1, 1944 Gerede-Bolu,Turkey 24 59 d 190 30 h S P March18, 1953 Gonen-Yenice,Turkey 7.3 59 d 58 30 h S P Dec.4, 1957 Gobi-Altai,Mongolia 130-180 31,32 b 270-300 31,32 g S I July22, 1967 Mudurnu,Turkey 3.6-8.8 11,59 a,d 80 30 h S P Aug.31, 1968 Dashte Bayaz,Iran 6.7 11 a 80-110 34 h,g S I Oct. 16, 1974 GibbsFracture Zone 4.5 62 b 75 62 g S P Feb.4, 1976 Guatemala 26 27 b 240-300 27,28 g,h S P July27, 1976 Tangshan,China 18 33 b 140 33 g S I
* Referenceto published estimates of seismic moment and fault rupture length: 1, Sieh [1978b ]; 2, Tsaiand Aki [1969]; 3, Brownand Vedder[1967]; 4, Doser(unpublished manuscript, 1986); 5, Doserand Kanamori [1986]; 6, Bakunand McEvilly[1984]; 7, Wilson[1936]; 8, Bruneand Allen [1967]; 9, Trifunac[1972]; 10, Stein and Thatcher [1981]; 11, Hanks andWyss [1972]; 12, Burdick and Mellman [1976]; 13, Clark [1972]; 14, Hamilton [1972]; 15, Sharp et al. [1982];16, Hanksand Kanamori [1979]; 17, Page[1935]; 18, Slemmons[1957]; 19, Tocher[1956]; 20, Witkind[1964]; 21, Sharp [1975];22, Allen et al. [1975];23, Wyss[1971]; 24, Canitez and Toksoz [1972]; 25, Sykes [1971]; 26, PlaJker et al. [1978]; 27,Kanamori and Stewart [1978]; 28, Bucknam et al., 1978;29, Kanamori and Stewart [1976]; 30, Ambraseys [1970]; 31, Okal[1976]; 32, Chenand Molnar [1977]; 33, Butler et al. [1979];34, Ambraseys and Tchalenko [1969]; 35, Croneet al. [1985];36, Matsuda[1974]; 37, Mikumoand Ando [1976]; 38, Matsudaet al. [1980];39, Thatcheret al. [1980];40, Kanamori[1973]; 41, Richins et al. [1985];42, Abe [1978]; 43, Matsuda [1972]; 44, Abe [1975a]; 45, Takeoet al. [1979]; 46, Urhammeret al. [1983];47, Ando[1974]; 48, Abe[1975b]; 49, Abe [1974]; 50, Fukao and Furumoto [1975]; 51, Kawasaki[1975]; 52, Kanamori and Regan [1982]; 53, Mikumo [1973]; 54, Mikumo [1974]; 55, Shimazaki and Somerville [1979];56, Doserand Smith [1985]; 57, Tanimotoand Kanamori [1986]; 58, Doser[1985]; 59, Sykesand Quittmeyer [1981];60, Kanamori [1983]; 61, Herd and McMaster [1982]; 62, Thatcher[1975]. WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,591 placement is shown in Plate 1. The location of onshore ANALYSIS faults is basedprimarily on the work of Jennings[1975] and Clark et al. [1984]. Also shown in Plate 1 is the distri- Fault Length and Earthquake Size bution of major offshore faults which are known from The seismicmoment rate 21)Io characterizes the average marine seismic reflection or drillhole studies to reach to or rate of seismicactivity on a fault. The releaseof seismic near the seafloor and hence may also be characterizedby moment on a fault occurs, however, in the discrete form of Quaternarydisplacement. The offshorefault distributionis earthquakes. Hence seismichazard analysisrequires an esti- adaptedfrom severalseparate studies. Offshorefaults south mate of both the expected size and the occurrencerate of of PalosVerdes are reportedby Legg and Kennedy[1979] earthquakeson faults in a region of interest. Empirical rela- and Greeneet al. [1979], offshoreSanta Monica by Junger tions betweenearthquake magnitude M and rupture length l and Wagner[1977], north of Ventura to Point Arguelloby derived from recent earthquakesare commonly the basisfor Yerkes et al. [1981], and northward of Point Arguello to estimating the expected size of earthquakes on mapped CapeMendocino by Field et al. [1980]. faults [e.g., Albee and Smith, 1966; Slemmons, 1977; Bonilla et al., 1984], with the inferencethat the size of an Fault Slip Rates earthquake on a fault will be proportional to the mapped Recent years have witnessedan increasedeffort toward fault length. A similar approach is taken here, except the the recognitionof Quaternaryfaults and the collectionand measure of seismic moment is substituted for earthquake use of fault slip rate data. Anderson[1979] compiledslip magnitude. Seismic source parameters for earthquakes ratesfor a studyof seismicrisk in southernCalifornia. Bird from California and other regions of similar tectonic style and Rosenstock[1984] made a similar compilation to con- are presentedin Table 2. The seismicmoment 214oversus struct a kinematic model of deformation in southern Cali- rupture length I of each event is plotted in Figure 2. The fornia. The most comprehensivecollection of slip rate solid symbols in Figure 2 indicate events that occurred on information currently availableis the result of an effort by major plate boundingfaults generallycharacterized by slip geologistsat the U.S. GeologicalSurvey [Clark et al., rates of about a centimeter per year or more. The open 1984]. It is thesethree works that provide the primary data symbols represent earthquakes that occurred on faults with base for this study. Faults in California for which some lesser slip rates. In spite of significant scatter, the two information on slip rate has been inferred from either groupsform distinct populations. Empirically, the separa- Quaternary displacementsor offsetsof older Pliocene to tion indicatesthat for two faults of similar length, earth- Miocene age units are marked in Plate 1. Plate 1 shows quakesrupturing the more slowly slippingfault will produce that estimates of slip rate exist for most of the major a greater amount of slip and hence a greater seismic onshorefault zones,whereas virtually no slip rate informa- moment. The physical consequencesof this separation are tion exists for the offshore faults. Rates of slip determined discussedby Scholz et al. [1986] and Kanamori and Allen from older Pliocene and Miocene deposits may be less [1986]. For present purposes, lines of the form representativeof presentrates of seismicactivity than are logMo--A + B x log I are fit through the two groups of rates assessedfrom the offset of younger deposits. In this data and shall provide the basisfor estimatingthe expected work, slip rates derived from offset Pliocene and Miocene earthquakesize from mapped fault length (Figure 2). For units are used only when rates determined from younger the sake of completeness,the earthquakesin Table 2 are depositsare not availableand, initially, attention is limited also divided according to the earthquake mechanism. It is to earthquakesand faulting onshoreCalifornia. found that strike-slip,reverse, and normal faulting eventsdo Slip rate estimatesare generallycoupled with large uncer- not form distinct populations when Mo is plotted versus tainties. For that reason, slip rates of individual faults are rupture length (Figure 2). most often reported as a range of values which bracket the The estimation of expectedearthquake size from mapped investigator'sbest estimate. Frequently, only a maximum fault length is simple in concept but difficult in practice. or minimum value is reported. Uncertainties inherent to Earthquakesin California commonly do not rupture along slip rate estimatesare detailedby Clark et al. [1986], are the entire extent of the faults on which they occur. Thus significant,and shouldbe consideredwhen interpretingthe there arisesthe critical problem of identifying the segments maps resultingfrom this analysis.The range of slip rates of faults that will be the source of future earthquakes. A reportedfor onshorefaults in Plate 1, referencesto the data, growing body of empirical evidence indicates that the end and the value of slip rate used for each fault in calculations points of earthquakeruptures are controlledby structuralor are provided in Table A1 of the appendix. Faults in Table physical discontinuitiesalong fault strike. This is clearly A1 for which no slip rate data are available are assigneda demonstrated on the San Andreas fault by the rupture very low slip rate of 0.01 mm/yr. characteristicsof the 1906 and 1857 earthquakes. Each of
•' Moment estimatedwith a, long-periodbody waves;b, long-periodsurface waves; c, short-periodbody waves;d, rupture parametersdetermined from geologicobservations; or e, rupture parametersdetermined from geodeticobservations. * Rupturelength inferred from f, geodeticdata; g, aftershockdistribution; h, extentof surfaceoffsets; or i, tsunamaidata õ Earthquakedisplacment predominantly S, strike-slip;N, Normal;or R, reverse. Earthquakeoccurred on P, plate boundary or I, intraplateor plate boundaryrelated fault inferred to have long-termslip rate greaterthan or lessthan about 1 cm/yr, respectively. # Estimatedhere from rupture parameterssummarized in respectivereferences. 12,592 WESNOUSKY.'SEISMIC HAZARD IN CALIFORNIA
•u n., ults
o 1- qu. t- n. Rate ' lio-Mioc- n- Rate . No 'at
Plate 1. Distribution of faults in and offshore California that dis- placeQuaternary rocks (Table A1) and nearseafloor marine depo- Plate 2. Contour map showsthe number of mapped,onshore sits,respectively. Fault slip rate estimates assessed from Quaternary Quaternaryfaults capable of producing>• 0.1g peak horizontal offsetsand displacedPliocene to Mioceneage rocks have been re- groundaccelerations at any localityin California. ported for sites along the faults marked in yellow and orange, respectively. Distribution of onshore faults adapted primarily from Jennings[ 1975] and Clark et al. [ 1984]. Referencesto distribution of offshorefaults provided in text.
i!i > 1 ooo .o O0 - 1000 0.01- 0 1 O- 99 O. -0, 100 - 9 0 0 O- 99 O. -0 o o. -lO
Plate 3a Contour map showsthe averageexpected return time of Plate 3b. Contour map showsestimated probability that onshore •O. lg peak horizontalground acceleration expected due to the re- Quaternaryfaults mapped in Californiawill producepeak horizon- peatedoccurrence of earthquakeson mappedQuaternary thults tal groundaccelerations of •O. lg duringthe next50 years. onshore California. WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,593
County earthquake,shows that the fault ruptureis overrid- 100 SLIPR4,TE (cm/yr) den on the southwestby the Pleito thrust fault and ter- >•1 <•1 minates on the northeast at an abrupt northward bend in [] Norraol the fault zone. En echelonsteps along strike-slipfaults have i A Reversei ß o Str•ke-Sl•p been observedto be controllingfactors in the rupture length of the 1966 Parkfield [Lindh and Boore, 1981], 1968 Borrego Mountain [Clark, 1972], 1979 Coyote Lake [Reasenbergand Ellsworth,1982], and 1984 Morgan Hill [Bakun et al., 1984] earthquakes.Physical explanations of the controllingnature of en echelonsteps on the fault rup- ture processhave been suggested in the work of Segalland Pollard [1980] and $ibson [1986]. The observations and argumentsgiven above are the basisin this studyfor assum- A/ ' 23.26, B: 1.75 ing that certainfaults in Californiaare segmentedand that the segmentswill produceearthquakes independently. The observations and decisions used to characterize the seg- 23.75,B: 1.73 mented nature of each of the major fault zonesin Califor- / nia are discussedfurther in the appendix. Some of the deci- / sions regardingfault segmentationare largely subjective. / Nonetheless,the decisionsused here are an estimateof the future behavior of faults based on our current understand- lO lOO lOOO ing of geologyand the faulting process. RuplureLenglh (km) Fig. 2. Seismicmoment M o versusrupture length l for earthquakes OccurrenceRate of Earthquakes listedin Table 2. Solidsymbols indicate earthquakes on major plate Estimates of the occurrencerate of earthquakeson faults, boundaryfaults generally characterized to haveslip rates of 1 cm/yr or greater.Earthquakes on faultswith lesserslip rates are shownby from geologicdata of fault length and fault slip rate, require open symbols.Lines of form log M o -- A +Bxlog! are fit the assumption of a fault model. Seismologicalliterature throughthe solidand open symbols,respectively. Squares, trian- includes two extremes of thought concerning the mechani- gles,and circlescorrespond to normal,reverse, and strike-sliptype cal behaviorof faults. A number of investigators[e.g., Nur, earthquakes,respectively. The verticaland horizontalbars of the 1978; Hanks, 1979; Andrews, 1980; von $eggern, 1980] crossin lowerright comer of plot correspondto a factorof 3 in M o and 50% in l, respectively. have assumedthat seismicity particular to a single fault or fault segment satisfiesthe relation log N--a-bM, where N is the number of events with magnitude greater than or the events ruptured different segmentsof the San Andreas. equal to M, and a and b are empirical constants[e.g., Ishi- The 1906 and 1857 rupture zones are separated by the moto and Iida, 1939; Gutenbergand Richter, 1944]. A creepingsection of fault extendingfrom San Juan Bautista consequenceof this assumption is that during the repeat to Parkfield. The southernmargin of the 1857 rupture is time T of one maximum magnitude earthquake on a fault, a site marking the complex juncture of several different some fault slip is also accommodatedby the occurrenceof fault zones(i.e., the Cucamonga,San Jacinto, San Andreas, smaller though potentially hazardous earthquakes. A Cleghorn fault zones).The northern end of the 1906 rup- separateview of fault behavior, initially implied in the work ture is at the junction of the San Andreas with the Mendo- of geologists[e.g., Allen, 1968; Wallace, 1970; Matsuda, cino escarpment. It seemslikely that these points of tec- 1977], is that faults or fault segmentsproduce earthquakes tonic complexitywill mark the end of fault ruptures along of a characteristicsize that is a function of fault length and the San Andreas in the future. Another example is the tectonic setting and that these events together with their Sierra Madre fault systemthat producedthe 1971 San Fer- foreshocksand aftershocksaccount for all seismic slip on a nando earthquakerupture. The 1971 event ruptured only a fault. For the sake of consistency with earlier papers 20-km segmentof this system. Detailed examinationof the [Wesnousky et al., 1983, 1984], this latter behavior is Sierra Madre fault zone has shown that the freshness of referred to here as the maximum magnitude earthquake scarpsor recencyof faulting varies along different segments model. of the zone [Crook et al., 1986]. In addition, investigators The assumption of which model best depicts fault have noted that the Sierra Madre fault zone appears to be behavior is of both scientific and practical significanceand segmentedinto a seriesof arcuate salientsconvex toward hasbeen discussed at lengthby Wesnouskyet al. [1983]. A the San Gabriel Valley [e.g.,Procter et al., 1972]. These growing body of seismologicaland geological observations observationshave led investigatorsto arguethat segmentsof points to the maximum magnitude earthquake model as the the San Gabriel range, each 15-25 km in length, behave as more accurate picture of the mechanical behavior of indivi- independentseismic entities [Crook et al., 1986]. Similarly, dual faults. Allen [1968], for example, examined the Wallace and Whitney [1984] studied the distribution and seismiccharacter of the San Andreas and noted that the seg- ,c•c,,•y...... of range •-'•o,,.,u,.,u,,.,•; -'•:-• ,au,•'"' t scarpsin central Nevada ments of the fault which ruptured in historical time are and suggestedthat individual mountain blocksmay at times essentially devoid of seismicity down as far as the behaveindependently and that block boundariesmay deter- microearthquake level. He suggestedthat this behavior mine the extent of future surfacefaulting. Examination of is typical of the past and future behavior of thesefault seg- the White Wolf fault, which produced the 1952 Kern ments. A number of investigationsalong convergent plate 12,594 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA margins report evidenceto suggestthat plate boundaries 6.1 6.5 6.9 '7.3 '7.7 generallyrupture along specificsegments and that rupture 1.0 of the segmentsoccurs cyclically [e.g., Kelleher, 1970, 1972; Ando, 1975;Sykes and Quittmeyer,1981]. Earthquakefre- quency statistics,where compiled for various segmentsof the world plate margins, show that the earthquake fre- quencydistribution along each segment is dominatedby the repeatedoccurrence of main shocksand the accompanying 0.1 m aftershocks[Utsu, 1971;Singh et al., 1981, 1983;Lahr and Stephens,1982; Davisonand Scholz, 1985]. Bath [1981] interpreted earthquake frequency statisticsobserved for regionsof Europe in a similar manner. Site-specificgeolo- gic investigationsare also consistentwith the maximum magnitudemodel. Sieh and Jahns [ 1984] interpreteddis- O.Ol - placed geomorphic features along segmentsof the San Predicted,=2.3x109 N-m/yr ß Andreas fault to indicate the repeatedoccurrence of similar o sizedevents. Schwartzand Coppersmith[1984] arrivedat a Observed,o=1.Cox1019 N-m/yr o similar conclusionduring their study of the Wasatch range (1835to 1985) front in Utah. They interpretedthat future earthquakerup- o.ool I I I turesalong the Wasatchwill be limited to specificsegments o.ol o.1 1.o lO of the range front, based on the existenceof structural discontinuitiesand differing values of repeat time that they MOMENT(102oN-m) estimated from trench studies at sites along strike of the Fig. 3. Earthquakefrequency distribution expected from slipon all frontal fault zone. Trenching[Schwartz and Crone, 1985] mappedQuaternary faults onshoreCalifornia (open symbols)com- and scarp morphology[Salyards, 1985] studiesalong the paredto the distribution(solid circles) computed from the 150-year historicalrecord of seismicityin Table 1. Magnitudesof eventsin recent 1984 Borah Peak earthquake fault have also been Table 1 are converted to seismic moment with the empirical rela- used to suggestthat that fault has previously ruptured in a tion logM o -- 1.5M + 16.1 [Hanksand Kanamori, 1979], except similar fashion during late Quaternary time. In Japan, for those eventswhere direct measurementsof M o are available Wesnouskyet al. [1983] observedthat the earthquakefre- (Table 2). quency distribution predicted from geologicdata describing the slip rates of Quaternary faults, and with the assumption that faults behave according to a maximum magnitude and c are empirical constants. A correct analysis of model, matched well with the distribution derived from a regionalseismic hazard must incorporatethis observation. 400-year record of seismicity. In this work then it is The expectedmoment-frequency distribution of earthquakes assumedthat the mechanicsof faulting is describedby the resultingfrom slip on all mappedfaults in Californiamay maximum magnitude model. be computedfrom the informationof fault lengthand slip The maximum magnitude model of fault behavior may rate compiled in Table A1. The seismic moment Moe be cast in terms of seismicmoment. The averageexpected expectedfor an earthquakerupturing the entire lengthof repeat time of earthquakeson a fault that is describedby each fault or fault segmentin Table A1 is considereda the maximum magnitude model can be approximated to functionof fault lengthand is computedwith the empirical equal relationsin Figure 2. Themoment rate Mo • -- glwitof each fault is a function of the mapped fault length l and the r -- Mo•IM•e (1) respectivefault slip rate/t and is determinedassuming that the width w of each fault is 15 km and that the shear years, where the seismicmoment Moe of the expectedevent modulusg of thecrust is equalto 3 x l0 TMdyn/cm 2. Inser- on the fault is proportional to the fault length and the geo- tion of the estimatesof Moe and Mo• into equation(1) logicallyassessed moment rate Mo • of thefault is a functiondefines the averagerepeat time T of Moe earthquakesfor of the fault slip rate. Estimation of average earthquake each of the mappedfaults. The cumulativerate of seismi- repeat times in this manner is conceptuallyconsistent with city, computedin this manner,resulting from slip on all the well-known and supported concept of elastic rebound onshorefaults listed in Table A1 is compared in Figure 3 to [e.g., Imamura, 1930; Fitch and Scholz, 1971; Kanamori, the historical rate of seismicityaveraged over the last 150 1973; Shimazaki, 1974; Thatcher, 1975; Scholz and Kato, years. The observedand predictedearthquake frequency 1978]. Hence in equation(1), Moe is a measureof the aver- distributionsexhibit a similar shapeand indicate earthquake agestrain drop during an earthquakeand Mo • is a function occurrencerates that generallyagree to within a factor of of the strain accumulation rate, and it is assumed that the about 2. Speculationas to the causeof the differencesin two parameters remain constant for each fault through the predictedversus observed curves is not warranted,since time. the differencesare small with respect to the uncertainties associatedwith this analysis. The cumulative seismic PredictedVersus Observed Seismicity momentrate •/o predictedfrom the geologic data (2.1 x The size distribution of earthquakesin a region generally 1019N -m/yr) is alsofound to differby lessthan a factorof obeys the relationship log N -- a - c x log Mo, where N is 2 from the rate computed from the historical record (1.6 x the number of events with seismic moment >/ Mo and a 1019N -m/yr). The similaritybetween the observedand WESNOUSKY: SEISMICHAZARD IN CALIFORNIA 12,595
Ace-l-ratio (.). Ve!oc!t,y,( rn.... see) <00 <0 0.0 - 0.09 06- 19 O.lO- o.19 0-39 O. 0-0. 9 O- 9 0.30 - 0. 9 60 9 >0 0 >8O
Plate4. Contourmaps show the (a) peakhorizontal ground acceleration and the (b) peakhorizontal ground velocity at 1-secondperiod expected to beexceeded on rocksites at the 10%probability level during a 50-yearperiod of time dueto earthquakeson Quaternaryfaults mapped onshore of California.
Plate 5. Contour maps show the peak horizontal ground accelerationexpected at the 10% probability level during a 50-year period in southern California assumingthat (a), in addition to slip rates reported for onshore faults, mapped offshorefaults further accommodate---2 cm/yr of slip and (b) total relative plate motion between the Pacific plate and North America is 5.6 cm/yr and primarily accommodatedby onshore faults accordingto the model of Bird and Rosenstock[ 1984]. SeePlate 4a for color key. 12,596 WESNOUSKY: SEISMICHAZARD IN CALIFORNIA predictedvalues of •r•o as wellas the earthquakefre- components of peak acceleration, peak velocity, and the quency distributions computed with the two data sets is peak pseudovelocityresponse (at 1-period and 5% damping) encouraging, for it is in accord with the hypothesisthat expectedto occur at level of 0.1 probability during a period current knowledge of Quaternary fault offsets and fault of 50 years. mechanics provides sut•cient information to predict both the average spatial and size distribution of earthquakesin Maps DepictingSeismic Hazard Due to OnshoreFaults California through time. The suite of maps in Plates 2-4 and Figure 4 help provide a synoptic view of our current understanding of seismic Constructionof SeismicHazard Maps hazard in California. A detailed assessmentof the maps The data reviewed thus far are consistent with the idea requires a comprehensive understanding of the geological that in areascharacterized by shallow seismicityand surface and seismologicaldata used in compiling Table A1. Discus- faulting, rates of seismicityderived from fault slip rate data sion is limited here to a description of the major features are representativeof present-dayrates. Evidence also points that characterizethe maps. Specific faults and geographic to a simple model of fault behavior, whereby the average regionsare discussedin the appendix. repeat time of earthquakes on a fault can be approximated Plate 2 portrays the number of mapped faults capable of to equalT--Moe/Mo g years (equation (1)). Thus a founda- producing ground shaking at levels of peak horizontal tion is set upon which we may begin to base estimates of acceleration >/ 0.1 gravity at any locality in California. A long-term seismic hazard. Specifically,with empirical rela- peak horizontal acceleration of 0.1g is the level at which tions between seismic moment, source to site distance, and older structuresand some modern structuresnot engineered strongground motions [Joynerand Fumal, 1985], the equa- to withstand earthquake shaking are susceptible to tion (1) and data describingthe length and averageslip rate significantdamage. The contours in Plate 2 thus provide a of faults in California are used to compute the average picture of the relative density of faults that constitute a expectedfrequency f of occurrenceof seismicshaking over a source of seismic hazard. The greatest concentrations of range of different strengths. The valuef, for a given level of faulting are within the Transverseranges of southern Cali- strong ground motion at site location j, is defined by the fornia, the southernMojave, and adjacentto the juncture of relation the San Andreas and Calaveras fault systems in northern California. Sites in these regionsare commonly susceptible N 1 to ground accelerations>/0.1g originating from a dozen or more faults. Significantconcentrations of Quaternary faults are also evident in northern California, along the coast where Ti are the average repeat times of the N faults that north of Cape Mendocino and inland within the Modoc are capable of producing a specific strength of ground Plateau. The relative concentration of Quaternary faults, motion at site location j. The probability of occurrenceof however, provides only an incomplete measure of seismic a given ground motion is a function of the frequency of hazard. The picture of seismichazard is altered significantly occurrence of the specified ground motion and the time when the geologicrate of slip on each fault is further taken period for which one is concerned. More concisely,the into account. probability that the occurrencetime S of a certain strength A second map, shown as Plate 3a, depicts the average of strong ground motion will occur during the period of expected return time of peak horizontal accelerations time from t l to t2 conditional to t l years having elapsed exceeding0. lg. The expectedreturn period of >•0. lg peak since the last occurrenceof similar ground shaking is gen- horizontal ground accelerationsis less than 50 years in erally expressedas severalregions of California (Plate 3a). The shortestvalues are generally associatedwith the San Andreas, Calaveras, Hayward, and San Jacinto fault systems. This is reasonable Sg(t)dt since it is these faults that accommodate much of the P(tl•
Velocity within the Peninsularranges are the San Jacintoand Elsi- (at 1 Sec) nore fault zones. Within the westernTransverse Range, slip
> 06 cm/sec rate information points to high hazard within the Ventura Basin region. 06 - 19 cm/sec Attention so far has centered upon the regions character-
20- 39 cm/sec ized by high levelsof seismichazard. Examination of the parametersthat lead to low levels of seismichazard being 40- 59 cm/sec predicted for various regions is equally important when
60- 79 cm/sec interpretingthe hazard maps. Plate 2, for example, indi- cates that the eastern Mojave, Great Valley, and Central > 80 cm/sec Coast near Point Arguello are characterizedby few or no mappedQuaternary faults. The low levelsof strongground motion predicted for these regions is contingent upon the detail of geologicmapping. The Modoc Plateau,unlike the Great Valley and easternMojave, is the site of numerous Quaternaryfaults (e.g., Plate 2). Plate 1 shows,however, that little data regardingfault slip rate is available in the area. The small values of strong motion predicted within the Modoc Plateau (Plate 4 and Figure 4) may then not be real but rather a consequenceof assigningvery low slip rates to those faults which have not been the subject of detailed geologicstudy. The same is likely true for other regionsof California that are characterizedby Quaternary faults but for which slip rates are unknown. Hence other regions of relatively high seismic hazard may remain Fig. 4. Peakhorizontal pseudovelocity response at 1-secondperiod expectedto be exceededon rock sitesat the 10% probabilitylevel unrecognized.This observation,however, should be tem- during a 50-yearperiod of time due to earthquakeson Quaternary peredby the realizationthat geologistshave generallyaimed faults mapped onshoreof California. their efforts toward those faults recognized to be most active.
Potential Hazard Due to OffshoreFaults city and the pseudovelocityresponse registered at 1-period with a 5% dampingcoefficient, respectively. Plate 4, unlike The hazard maps constructedthus far consideronly faults Plates2 and 3a, simultaneouslydisplay information bearing onshore and within the political boundaries of California. upon both the expected size and the frequency of A consequenceis that the predicted levels of hazard are earthquake-inducedstrong ground motions. The strong underestimatedalong the boundaries of California where ground motionscontoured in Plate 4 are characterizedby active faults lie outsidebut near the border. The problem is an averagereturn period of •<475 years,as may be seenby most acute along coastal California where population insertion of the appropriatevalues of At=t2-t• (50 years) centers are greatest, historical records describe the and probability(0.1) into equation(4). The contoursof occurrenceof severalmoderate to large offshoreearthquakes higheracceleration or velocityin thesemaps may, for con- (Table 3), and both geologicaland geophysicalinvestiga- venienceof discussion,be consideredto encloseregions pos- tions have been the basis for suggestingrapid rates of slip ing the greaterseismic hazard. The maps in Plate 4 show and high seismicpotential on offshorefault structures[e.g. the San Andreas fault to be a principal contributor to high Anderson, 1979; $ieh and Jahns, 1984; Minster and Jordan, levels of seismic hazard in California. Contours of strong 1984; Weldon and Humphreys, 1986, Heaton and groundmotion along strike of the San Andreasare uni- Kanamori, 1984]. Observedrates of seismicityoffshore and formly high, exceptalong a small segmentin centralCali- north of Cape Mendocino are, for example, comparable to fornia where slip occurs primarily by aseismic creep. rates observedonshore in southernCalifornia [e.g., Toppo- Several other regions are also characterizedby levels of zada et al., 1981; Toppozada and Parke, 1982; Rogers, seismichazard that approach levels predicted adjacent to 1980]. Seismicityoffshore of the coastnorth of Cape Men- the San Andreas. Relatively rapid rates of slip along the Calaveras,Hayward, and associatedlesser faults are inter- pretedto indicatesignificant levels of hazardin the regions TABLE 3. EarthquakesOffshore California adjacentto San FranciscoBay. The likely transferof slip northward from the Hayward to the Healdsberg, Rogers Date Location Magnitude* References Creek, and Maacama fault zones implies a zone of high Dec. 12, 1812 SantaBarbara 7.1 7 seismichazard extending north of San Francisco Bay as April 15, 1898 Point Arena 6.4 7 June29, 1925 SantaBarbara 6.3 9 well. To the south, reportedrates of slip acrossthe Pleito, Nov. 4, 1927 SantaBarbara 7.5 9 White Wolf, and Garlock faults (Figure A6) indicate the June 6, 1932 Humboldt 6.4 9 northernboundary of the Mojave Desert as a zone of rela- Oct. 3, 1941 Humboldt 6.4 9 tively high hazard. The southernMojave is mapped as a Nov. 8, 1980 Humboldt 6.9 18 region of comparativelyhigh hazarddue to a number of * See Table 1. faults with moderate slip rates. Major sourcesof hazard p See Table 1. 12,598 WESNOUSKY.'SEISMIC HAZARD IN CALIFORNIA docino is generallyattributed to the relativemotion taking north-south transect is 2 cm/yr. Between Point Arguello place between the Gorda plate and North America. and San Francisco, the 2 cm/yr of slip is assumed to Interpretationsof seafloor magnetic lineations show that transferto the San Gregorio-Hosgrifault system. The San relative motion between North America and the Gorda Gregorio-Hosgrifault system is the only major offshore plate is between3 and 5 mm/yr [e.g.Minster and Jordan, structure mapped along the stretch of coast between Point 1978; Riddihough, 1980]. Observeddistortion of magnetic Arguello and San Francisco. No major fault systemsare lineations and the distributed nature of seismicitywithin the mapped offshoreof the coastextending farther north from Gorda plate indicatethat a significantportion of the relative San Franciscoto Cape Mendocino that may accommodate motion may be taking placeas internaldeformation of the significantamounts of plate motion. The possibilityexists Gorda plate [Silver, 1971]. Interpretationsof geophysical that the proposed2 cm/yr of slip is transferredonshore near data with the assumptionthat the Gorda plate is rigid sug- San Francisco,but geodeticand geologicstudies along the gestthat relative motion is being accommodatedby either San Andreas near Point Reyes do not support such an idea strike-slipmotion [Riddihough,1980] or thrustingof the [Prescottand Yu, 1986;Hall et al., 1983]. Becauseof these Gorda plate beneath North America [Minster and Jordan, enigmas,Plate 5a encompassesonly the part of California 1978]. The potential of large thrust earthquakesoccurring south of San Francisco. The obviousresult of assigning along the north coast is discussedin detail by Heaton and large valuesof slip to offshorefaults is a significantincrease Kanamori [1984]. It is beyond the scopeof this work to in the expectedlevel of strongground motion for the entire examine the effect of assumingthe different interpretations coastalregion reachingsouth of San Franciscoto the Mexi- of plated•formation on predictedlevels of hazardalong the can border (Plate 5a). coast north of Cape Mendocino. A different picture of seismic hazard results when the Faultingalong the coastsouth of Cape Mendocinois gen- constraint is imposed that 5.6 cm/yr of plate motion in erally interpreted to accommodate right-lateral transform southern California is taken up principally by mapped motion between the Pacific plate and North America. Min- onshore faults (Plate 5b). Bird and Rosenstock [1984] ster and Jordan [1978] estimatedthe plate velocityvector divided southernCalifornia into a set of blocksbounded by alongthe Californiaplate margin to equal 5.6 cm/yr and to mapped Quaternary faults. Within the limitations imposed parallel the strike of the central San Andreas. Their rate is by publishedfault slip rate data, they constructeda model the result of a global inversionof plate velocitydata and is of block movement that satisfies the restriction that the averagedover the last few million years. It has sincebeen total plate motion acrossCalifornia is 5.6 cm/yr. The block recognized that the cumulative geologic slip rate across model constructed[see Bird and Rosenstock,1984, Figure major mappedfaults in most regionsof the westernUnited 3] satisfiesabout 80% of the limits imposedby geological Statesis only 3-4 cm/yr, insufficientto account for the rate fault slip rate studies,though in many casesthe assigned predictedby Minster and Jordan [1978] [Sieh and Jahns, block movement rates are near the extreme limits rather 1984; Minster and Jordan, 1984; Weldonand Humphreys, than the preferredvalues of slip rate reportedby geologists. 1986]. Either of two conclusionsmay be drawn from this The map in Plate 5b is constructedwith the slip rates used discrepancyif it is acceptedthat the ratespredicted by Min- by Bird and Rosenstock [1984] in their block model ster and Jordan [1978] are representativeof present-dayanalysis. The Bird and Rosenstockmodel assigns5.1 of the plate rates. The first is that geologicdata are now incom- total 5.6 cm/yr of plate motion in California to occur plete and that further onshorefield investigationswill reveal onshore across the San Andreas and San Jacinto faults. The the missing1-2 cm/yr of slip. The secondpossibility is that most obvious consequence,with respect to Plate 5a, is a the missing slip is being accommodatedby offshorefault decreasein the predicted values of strong ground motion structures.Data are insufficientto conclusivelyargue either along the south coast.Also, predicted levels of strong of the interpretations. The two interpretations,however, ground motion are higheralong the San Gabriel rangefront predict markedly different distribution of seismic hazard and the Garlock fault zone. The large strong ground along the southerncoast of California. The maps in Plate 5 motions predicted along the San Gabriel range front result illustrate these differences. from the kinematic constraint of the block model that ---5 Plate 5a is a contour map of the peak acceleration cm/yr of slip must be taken up by convergencewithin the expectedto occur in southernCalifornia at the 10% proba- Transverseranges, a significantportion of which is assigned bility level during a 50-year period. The data and method to the San Gabriel rangefront fault system. Such large (> 1 used to construct Plate 5a are identical to those used earlier cm/yr) slip rates imposedalong the range front are, how- for Plate 4, except that 2 cm/yr of additional slip is ever, in conflict with the geologicstudy of Crook et al. assumed to be equally distributed across faults that have [1986] whichsuggests that the repeattime of rupturealong been identified with marine seismic reflection methods many individual segmentsof the range front is of the order offshoreof southernCalifornia (Plate 1). Specifically,south of 5000 years. of about SantaMonica, 2 cm/yr of slip is distributedalong The disparatepatterns of seismichazard depictedin Plate the major fault structureswest of and includingthe Palos 5 underscorethe importanceof furtheringour knowledgeof Verdes, Newport-Inglewood,and Rose Canyon fault zones both the distribution and rate of slip acrossQuaternary (Plate 1 and Figure A2). Deformation in the offshore faults in California. The exerciseof constructingthe maps region north of Santa Monica to about Point Arguello is also points to a number of problems that should be the con- characterizedby folding and reversefaulting that indicatea tinued targets of geophysicaland geologicalinvestigation northerly contractionof the crust [Yeats, 1983a; Yerkeset during the immediate future. A fundamental problem is al., 1981]. Slip rates are assignedto faults within this determining whether or not the 5.6 cm/yr of plate move- offshoreprovince so that the cumulativeslip rate alongany ment that Minster and Jordan [1978] found representative WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,599 of the last few million years is actually representativeof 1.0 I present-dayplate rates. Satellite-basedmethods of geodetic measurementmay ultimately provide a corroboration of the 5.6 cm/yr rate of plate motion [e.g., Christodoulidiset al., 1985]. Ground-basedgeological and geodetic studiesare, however, also necessaryto document the spatial distribution .5- and total amount of fault displacement occurring across California. Little is known, for example, about the activity P(t•
SeismicHazard as a Function of Time where the standard deviation o is assignedto representthe confidencegiven to a predictedvalue of Rv. The likelihood A major assumption underlying the hazard maps in that the rupture time R of a fault will occur during the next Plates4 and 5 and Figure 4 is that the occurrenceof ground At--t2-t• years conditional to t• years having elapsedsince shakingat a given site is a Poissonprocess. As a result, the Rl can then be expressedas the conditionalprobability maps convey an estimate of hazard that remains constant through time and independentof the recent history of large t2 earthquakes. This is evident when noting that the probabil- f n(t)dt ities resultingfrom equation (4) and used to constructthe P( t•
TABLE 4. Poisson Versus Conditional Estimates of Seismic Hazard: An Illustration Earthquake Estimated Probabilityt
Fault Rl ReturnyearsTime,* Poisson Conditional San Andreas (Carrizo Plain) 1857 345 0.1 <0.1 San Andreas(Hwy. 166 to Cajon Pass) 1857 170 0.3 0.4 San Andreas (Chalome to Hwy. 58) 1857 115 0.4 >0.9 Hayward 1868 556 <0.1 <0.1 Owens Valley 1872 3364 <0.1 <0.1 San Jacinto (Casa Loma segment) 1899 128 0.3 0.3 San Andreas (Los Altos to San Juan Bautista) 1906 95 0.4 0.8 San Andreas (Shelter Cove to Los Altos) 1906 300 0.1 < 0.1 San Jacinto (Claremont segment) 1918 107 0.4 0.6 White Wolf 1952 300 0.2 <0.1 San Andreas (Slack Canyon to Cholame) 1966 22 0.9 >0.9 San Jacinto (BorregoMountain) 1968 150 0.3 <0.1 San Fernando 1971 200 0.2 <0.1 Imperial 1979 700 0.8 >0.9 Calaveras(segment A - Coyote Lake) 1979 82 0.5 0.2 Calaveras(segment B - Morgan Hill) 1984 150 0.3 <0.1
* Return times RT are taken to equal values of T listed for respectivefaults in Table A1. •' Probability that earthquakewill repeat during the next 50 yearsassuming Poisson (equation (4)) and conditional (equation (6)) modes of earthquake recurrence.
bility for many of the faults. The differenceswork to illus- (Table A1) is again taken to satisfya Poissondistribution trate the potential benefit of including the time dependence (equation (4)), and the probabilitiesare computed accord- of the earthquakecycle in hazard assessment. ingly. Plate 3b demonstrateshow the added knowledgeof The maps that display the value of strongground motion where in time faults reside with respectto the earthquake expected at the 10% probability level during a 50-year cyclemay be incorporatedinto a map of seismichazard. period of time (e.g., Plate 4) are a convenient basis for ini- The map indicatesthat the likelihoodof shakingis generally tially examining Table 4. Information leading to an greatestalong various segments of the SanAndreas and San increase or decrease of the probability of given levels of Jacinto fault zones. Interpretation of Plate 3b, as with the ground motion to above or below 10% probability, respec- mapsconstructed previously, is contingentupon an under- tively, will result in changesin the map contours. Assump- standingof the assumptionsand data on which it is tion of a time-dependent, rather than Poisson, behavior founded. Withstandingthe uncertainties,Plate 3b conveys resultsin drops in probability from above to below 10% for information in a format that may prove usefulfor decisions 6 of the fault segmentsin Table 4: The Carrizo Plain and regardingthe sitingof hazardmitigation procedures and the Shelter Cove to Los Altos segmentsof the San Andreas deploymentof seismicinstrumentation. (Figure A11) that ruptured in 1857 and 1906, respectively; the BorregoMountain fault that broke in 1968; the segment DISCUSSIONAND CONCLUSIONS of the Calaveras fault that ruptured in 1984; and the White Wolf and San Fernando faults that broke in 1952 and 1979, This paper demonstrateshow we may begin to use geolo- respectively. In no case does the reverse occur. Seismic gic data and current understanding of the mechanics of hazard adjacent to these six fault segmentsmay then be less earthquakefaulting to characterizeseismic hazard in Calfor- than depictedin Plates 4 and Figure 4, if the respectiveesti- nia. The resultingmaps provide usefulinformation regard- mates of RT and o are accepted as representative of the ing the distribution of seismichazard in California, but cau- faults. The decreasesin probability realized by the use of tion should be exercisedin their interpretation. Slip rate the conditional probability function reflect an interpretation data are presentlyincomplete. Further geologicstudies will that the six fault segmentsare now in the early stagesof likely prove some of the slip rates in Table A1 incorrect, or their respectivestrain accumulation cycles. Conversely,the inapplicable to the present. A significant number of two segmentsof the San Andreas that extend from Los Quaternary faults probably remain unrecognized. Lack of Altos to San Juan Bautista and Cholame to Hwy. 58 near geologic data pertaining to the locations and slip rates of the Carrizo Plain (Figure A11) are estimated to have aver- faults in a region may result in an apparently low and age repeat times that are nearly equivalent to the time since incorrect characterizationof seismichazard in that region. the faults last ruptured. The conditional estimates reflect It should be further emphasized that the hazard maps this observationby yielding probabilitiesthat are markedly presentedare not the result of a rigorous statistical treat- greaterthan the respectivePoisson estimates. ment. Errors and uncertainties, for example, associated A contour map of the estimated probability that mapped with individual slip rate estimates for each fault are gen- faults will produce >0.1g ground accelerationsduring the erally large and have not been used in construction of the next 50 yearsis displayedin Plate 3b. For constructionof maps. Rather, specificvalues within the range of reported the map, equation (6) is used to compute the conditional rates have been used. The resulting estimates of seismic probability of fault rupture for those faults in Table 4. The hazard may in certain regionsbe altered sharplyby use of occurrence of shaking expected from the remaining faults other acceptableslip rates within the range of presently WESNOUSKY: SEISMICHAZARD IN CALIFORNIA 12,601 reported values. Similarly, uncertainties in the empirical seismicity [e.g., Algermissenet al., 1982]. Conventional relationship between seismic moment and rupture length forms of seismichazard analysisare, as a consequence,asso- (Figure 2) usedto estimatethe expectedsize of future earth- ciated with large uncertaintieswhen historical data are not quakes are not incorporated into the analysis. A rigorous sufficientto define secular rates of seismicity. In contrast, treatment of the errors will surely be desirable in the future the geologic record of Quaternary fault offsets contains development of these maps. It is unwise, however, to think information on the occurrence of earthquakes through that such treatment will substitutefor inadequate geologic periodsof time many orderslonger than coveredby histori- data. The greatestcontribution that can be made to reduc- cal records. This work and that describedby Wesnouskyet ing uncertaintiesassociated with this type of analysiswill be al. [1983, 1984] are supportive of the hypothesisthat a the further acquisitionand understandingof geologicaland complete knowledge of the geologic record of Quaternary geophysicaldata relating to the locations, offset rates, and fault offsetsis sufficient to predict both the spatial and size faulting histories of Quaternary faults. It is perhaps this distribution of earthquakesthrough time in a region charac- ability to actively collect data that representsthe greatest terized by shallow seismicityand active faulting. California advantage over conventional forms of seismic hazard is characterizedby each of these attributes. This analysis analysis,which are limited by the existing and limited his- and the resulting maps illustrate how quantitative estimates torical data set [e.g.,Algermissen et al., 1982]. A concerted of the long-term seismic hazard in California may eventu- effort to increase studies of active faulting, both onshore ally be basedprimarily on geologicdata describingthe aver- and offshore, may well be the most efficient means of age slip rates and repeat times of Quaternary faults, rather increasingour understandingof seismichazard in Califor- than the historical record of seismicity. Use of geologic nia. data in this manner should, at minimum, provide a firm Fundamental research toward understanding the complement to estimates of seismic hazard based on earth- phenomenawhich control the lateral extent of earthquake quake statisticsand may, as more and better data become ruptures is clearly of critical importance to the further available, provide a better characterization of the seismic developmentof this work. The studiesof Segall and Pol- hazard resulting from moderate to large earthquakes on lard [1980], Sibson[1986], and King and Nabelek [1985] Quaternary faults in California. are steps in this direction. The historical record of earth- quakesclearly indicates that the entire length of major fault APPENDIX zones in California does not rupture during a single earthquake. A number of observations have been drawn The seismichazard maps developedin this study are the upon in this study to suggestthat the extent of earthquake result of a specific interpretation of the seismic behavior of ruptures is strongly controlled by structural or physical each mapped fault in California. The purpose of this discontinuities along fault strike. These observations, in appendix is to summarize as concisely as possible the data conjunction with knowledgeof the location of past earth- and assumptionsused to interpret that behavior. The faults quake ruptures, provided the basis for estimating which are grouped accordingto geographicprovince (Figure A1), fault segmentswill rupture independently during future and listed accordinglyin Table A 1. Table A1 referencesgeo- earthquakes. It should be recognized, however, that the logic maps and reports on the location and slip rate for each fault and further summarizes the results of those studies. specificdecisions regarding fault segmentlength (Table A1) used in constructingthe hazard maps are largely tentative Also included in Table A1 are the specific estimates of the and coupled with large uncertainties, since there are now expected moment magnitude M and estimated average relatively few data on which to rest such decisions. repeat time T of earthquakes on each fault which were used It is useful to briefly examine how the maps developed in constructingthe seismichazard maps. Major faults and here might have fared if constructed40 years ago. Several fault zones in each province are discussedseparately. Maps large earthquakeshave occurredduring the subsequentspan accompany the discussion to illustrate the location and of time, including the 1952 Kern County and 1971 San mapped length of each fault and fault segment listed in Table A 1. Fernando earthquakes. Neither of the faults that these events ruptured were known to displace Quaternary rocks PeninsularRange-Salton Trough prior to the occurrenceof the earthquakesand thus would not have been included in estimates of the seismic hazard of San Jacinto fault zone. The San Jacinto fault zone their respectiveregions. It is, however, now recognizedthat (SJFZ) is historicallythe most seismicallyactive fault zone thesefaults did show mappable evidenceof Quaternary dis- in California. Extensive summaries and interpretations of placements before the earthquakes occurred. The the earthquakehistory along SJFZ are given by Thatcher et occurrenceof events like the 1952 and 1971 earthquakes al. [1975] and Sanders and Kanamori [1984]. Epicenters does not then negate the premise upon which this work is of earthquakeswith magnitudes >/6 that occurredalong San built but, rather, emphasizesthat the extent to which the Jacinto sinceabout 1890 are denoted by starsin Figure A2. maps represent seismic hazard is a direct function of the Offsets across the SJFZ are predominantly right-lateral. amount and quality of field investigationsthat have been Geologicdata presentedby Sharp [1981] placea minimum conducted in an area. limit of 8-12 mm/yr of slip along the SJFZ near Anza (Fig- To summarize,seismic hazard analysesare fundamentally ure A2) during the last 0.73 m.y. South of Anza, along the based on estimatesof the averageoccurrence rate of earth- fault trace that ruptured during the 1968 BorregoMountain quakes in a region of interest. Estimates of this parameter earthquake(Table 2), Sharp [1981] interpretsgeologic rela- are conventionally made with earthquake frequency statis- tions to show slip has averaged 2.8-5.0 mm/yr and 1.6-2.2 tics obtained from data listed in historical cataloguesof mm/yr during the last 400+ and 6000 q- years,respectively, 12,602 WESNOUSKY: SEISMICHAZARD IN CALIFORNIA
The Lytle Creek-Glenn Helen-Claremont segment of the SJFZ here refers to the stretch of the SJFZ that extends northwest into the San Gabriel mountains from a point near San Jacinto (Figure A2), where the fault trace showsa major right-step [Matti et al., 1985]. Isoseismaland instrumental evidencehave led investigatorsto suggestthat the July 22, 1899 (M -- 6.5), the July 23, 1923 (M -- 6.3), and the April 21, 1918 (M -- 6.8) earthquakes ruptured along this segment of the SJFZ [Thatcher et al., 1975; Sandersand Kanamori, 1984]. No firm evidenceof surface rupture is known for any of these events, however, and the large uncertainties associatedwith locating such historical events do not eliminate the possibility that one or more of the earthquakes were the result of slip on other nearby faults. This segment of the SJFZ is mapped as a narrow zone as it trends northwest from San Jacinto until it reaches the San Gabriel Mountains where it splaysinto several or more strands, forming a wider zone of about 3.5 km that includes the Glenn Helen and Lytle Creek faults. Mezger and Weldon [1983] interpret offsetterrace depositsto indi- cate a maximum horizontal slip rate of 2.5 mm/yr across the Lytle Creek fault, but this rate probably does not reflect the entire deformation rate acrossthis segmentof the SJFZ [e.g., Morton, 1975]. For this analysis,the Lytle Creek- Fig. A 1. Geographicprovinces of California (adaptedfrom Clark et Glenn Helen-Claremont segment is treated as a single al. [1984]). Discussionand tabulationof fault data in the appendix and Table A 1, respectively,are indexed accordingto the geographic seismogenicsource that is accumulating the equivalent of province where the faults are located. 10 mm/yr of slip. The Casa Loma fault is the right step and southwardcon- tinuation of the Claremont fault (Figure A2). The Casa but some question existswhether these rates reflect the total Loma fault appears continuous with the Clark fault to the deformation across the SJFZ at that latitude. Thatcher et southeast,the trace of each being separatedonly by some al. [1975] determined and summed the seismic moments of very young alluvial deposits[Sharp, 1967]. For this work, earthquakesalong the entire fault zone since about 1890 to the Casa Loma and Clark faults are treated as a single determine a seismic slip rate of about 8 mm/yr. Brune earthquake source and referred to as the Casa Loma-Clark [1968] computed a slip rate of about 15 mm/yr basedon segment. This segmentwas a possiblelocus for the magni- similar calculations and a lesser data base. Geodetic and tude 6.6 earthquake of December 25, 1899 [Sanders and trilateration measurementsspanning the periods 1969-1975 Kanamori, 1984; Thatcher et al., 1975]. Moderate-sized and 1973-1981 are consistent with 11-18 mm/yr of slip earthquakesof about magnitude 6 also occurredalong this being stored elasticallyin a 10-15-km-thick crust [Savage section of the SJFZ on March 25, 1937, and March 19, and Prescott,1976; King and Savage, 1983]. In summary, 1954 [Figure A2; Thatcher et al., 1975; Magistrale et al., geologic, geodetic, and seismologic observationsgenerally 1984], but neither can definitelybe attributedto displace- point to an average slip rate of at minimum 8-12 mm/yr ment along the major mapped faults in this area. Geologic across the SJFZ during late Quaternary time. Though a relations near Anza indicate that slip along this segmenthas higher rate cannot be ruled out, the hazard maps are con- averaged 8-12 mm/yr or greater during the last 0.73 m.y. structedwith the assumptionthat right-lateral the slip rate [Sharp, 1981], at least along the reach northwestof Anza. acrossthe entire SJFZ averages10 mm/yr. The entire segmentis assigneda 10 mm/yr slip rate for the The historical record of earthquake ruptures [e.g., hazard analysis. Thatcheret al., 1975] and mapped complexitiesand discon- The Hot Springsand Thomas Mountain faults strike sub- tinuitiesalong strike of the fault zone [e.g.,Sharp, 1975a,b] parallel to the Casa Loma fault [Hill, 1981]. Sharp [1967] give reason to consider the zone as consistingof many briefly discussesthe character of displacementalong these separatesegments, each of which may rupture in separate two faults but reports no evidence of slip rates. He notes earthquakes. For this analysis,the fault zone is divided into that the rounded topographiccharacter of scarpsalong the nine segments (Figure A2). Where individual segments Hot Springsfault suggeststhat little movement has occurred strike subparallel, the constraint is imposed that the cumu- in recent geologictime and that no evidenceof Quaternary lative slip rate acrossthe segmentssums to near 10 mm/yr. movement was found along the Thomas Mountain fault The expected seismic moments Moe and repeat times T of except at a point near Burnt Valley where Pleistocene earthquakesfor each segment that are listed in Table A 1 are deposits are cut by a thin gouge zone. The faults are computed using the relation in Figure 2 that correspondsto included in this analysisbut each is assigneda very low slip major plate boundary faults. Data describingthe location, rate of 0.01 mm/yr. extent, slip rate, and earthquake history of each fault seg- South of Anza, displacement along the SJFZ is also ment are summarized in Table A1 and discussed in more accommodatedby the Buck Ridge and Coyote Creek faults. detail below. The fault nomenclaturefollows approximately Each fault strikes subparallel to the Clark fault. Sharp that usedby Jennings[1975]. [1967] reports that total horizontal separation acrossthe WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,603
TABLE A1. Quaternary Faults
SlipRate a Fault Location* St L* M õ C# mm/yr T** D tt A** Referenceõõ lat Ion Mn Mx Pr
PeninsularRanges and Salton Trough Chino 34.0 117.7 rr? 28 6.8 B 0.0 0.2 0.1 v q Yerkes et al. [ 1965 ]b Heath et al. [1982]c ElsinoreA (Whittier) 33.8 117.7 rl 74 7.3 A 0.6 9.0 4.0 730 h h seesegment D Elsinore B 33.5 117.2 rl 51 7.1 A 0.6 9.0 4.0 553 h h seesegment D Elsinore C 33.2 116.7 rl 64 7.2 A 0.6 9.0 4.0 651 h h seesegment D ElsinoreD 32.8 116.2 rl 69 7.2 A 0.6 9.0 4.0 694 h h seeappendix and Crowell and Sylvester[1979 ]b Lamar et al. [ 1973 ]a Lowman [1980]b Sage [ 1973]a Weber [ 1977 ]a Pinault and Rockwell [ 1984] Imperial-Brawley 32.8 115.5 rv? 40 6.7 AA 20.0 32t* t h seethe appendixand (1979 rupture) Sharp [1980]c Sharp [1982]c Sharp et al. [1982]c Sharp and Lienkaemper [1982]c Clark et al. [ 1984] Imperial-Brawley 32.7 115.4 rv 69 6.9 A 8.6 700t* h h see1979 segment (1940 rupture) La Nacion 32.7 117.1 19 6.6 C Jennings[ 1975] Newport- InglewoodA 33.7 118.1 rv? 34 6.9 A 0.1 6.0 1.0 1650 v h seesegment B Newport- InglewoodB 33.9 118.3 rv? 28 6.8 A 0.1 6.0 1.0 1454 v h seethe appendixand Castle [ 1960]c Castle and Yerkes [1976]c California Department Water Resources [ 1968 ]c Poland and Piper [1956]c Wright et al. [1973]a Yeats [ 1973 ]b Palos Verdes 33.8 118.3 rr? 45 7.0 A 0.02 0.7 0.7 2905 v h Yerkeset al. [1965]a,b Darrow and Fisher [1983]c RoseCanyon 32.8 117.2 rr? 50 7.1 A 0.0 2.2 1.5 1458 t q Artim and Streiff [ 1981] Ferrand et al. [ 1981 ] Kennedy [ 1975a]b Kern [ 1977 ]c Moore and Kennedy[ 1975]c San Jacinto Fault Zone Sharp [1981] (referencesummary) Bartholomew [ 1970]b Clark et al. [ 1972 ] Savage and Prescott[1976] King and Savage[1983] Sharp [1967] Thatcher et al. [ 1975 ] Brune [1968] San Jacinto(Lytle Creek- 34.5 117.2 rl 78 7.0 AA 10.0 107 h q seethe appendix Glenn Helen - Claremont) SanJacinto (Hot Springs) 33.7 116.8 29 6.8 C see the appendix San Jacinto 33.6 116.6 15 6.5 C see the appendix (Thomas Mountain) San Jacinto(Casa Loma - 33.5 116.6 rl 100 7.1 AA 8.0 10.0 128 h q seethe appendix Clark) SanJacinto (Buck Ridge) 33.5 116.5 fi 35 6.6 A 2.0 294 h q seethe appendix SanJacinto (Coyote Creek) 33.3 116.4 rl 38 6.6 A 2.0 314 h q seethe appendix SanJacinto (Borrego 33.1 116.1 rl 30 6.5 A 1.6 5.0 2.0 150t* h h seethe appendix Mountain) San Jacinto 32.9 115.8 rl 26 6.4 A 1.0 468 h q seethe appendix (SuperstitionMountain) San Jacinto 33.0 115.8 rl 22 6.4 A 1.0 422 h q seethe appendix (SuperstitionHills) 12,604 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
TABLE A 1. (continued) SlipRate a Fault Location* St L* M õ C# mm/yr T** D ttA*' Referenceõõ lat lon Mn Mx Pr
Transverse Ranges Arrastre Canyon Narrows 34.4 117.1 11 6.3 C Meisling [ 1984] Arrowhead Springs ß 34.2 117.2 11 6.3 C Jennings[ 1975] Arroyo Parida 34.4 119.5 44 7.0 B 0.35 0.4 5350 v q Rockwell(1983 ]c Rockwell et al. [ 1984] Beaumont Fault Zone 33.9 117.0 n 8 6.1 C Matti et al. [1985] Benedict Canyon 34.1 118.3 r? 11 6.3 C Weber [ 1980] Big Pine 34.7 119.3 11 67 7.2 A 0.8 2.0 1.0 2699 h p Kahleetal. [1966]b Lamar et al. [ 1973 ]a Chatsworth Reservoir ß 34.2 118.6 12 6.3 C Jennings[ 1975] Clearwater 34.6 118.6 33 6.9 C Jennings[ 1975] Cleghom 34.3 117.4 20 6.6 A 1.5 18.0 3.0 380 h q Meisling [1984] Crofton Hills 34.0 117.1 21 6.6 C Matti et al. [1985] Cucamonga 34.2 117.6 20 6.6 A 2.9 6.4 700t* t h Mortonet al. [1982]c Weldon and Sieh [ 1980]c Weldon [1983 ]c Matti et al. [1982] EagleRock - San Rafael 34.1 118.2 r? 11 6.3 C Weber [ 1980] Frazier Mountain North 34.8 119.0 r 13 6.4 C Jennings[ 1975] Frazier Mountain South 34.7 119.0 r 11 6.3 C Jennings[ 1975] Glen Annie 34.4 119.8 21 6.6 C Sylvesterand Darrow [ 1979] Hollywood 34.1 118.3 r? 14 6.4 B 0.3 0.8 1627 v h Weber [1980]c Holser 34.4 118.7 19 6.6 C Jennings[ 1975] Yeats [1983a] Javon Canyon 34.3 119.4 r 8 6.2 C 0.7 2.5 0.01 t h seethe appendixand Sarna-Wojcickiet al. [1979]c, Yeats[1982]c Lavigia 34.4 119.7 9 6.2 C Yeats and Olson [ 1984] Malibu Coast 34.0 118.7 r 34 6.9 C 0.04 0.09 t q Clark et al. [1984] Mesa 34.4 119.7 7 6.1 C Yeats and Olson [ 1984] Mission Hills 34.3 118.5 r? 8 6.1 C Weber [ 19801 More 34.4 119.8 19 6.6 C Yeats and Olson [ 1984] Morongo Valley 34.1 116.6 11 18 6.5 C Jennings[ 1975] Northridge Hills 34.3 118.6 r? 21 6.6 C Weber [ 1980] Oak Ridge (onshore) 34.3 119.0 r 39 6.9 A 3.5 521 t q Yeats [1983a] Ocotillo Ridge (fold) 34.4 117.1 r 14 6.4 C Meisling [ 1984] Ord Mountain 34.4 117.2 r 11 6.3 B 1.2 0.1 v q Meisling [1984] Pine Mountain 34.6 119.1 59 7.1 C Jennings[ 1975] Pinto Mountain 34.1 116.3 11 73 7.3 A 0.3 5.3 1.0 2885 h m Dibblee [1968a]b Dibblee [1975]a Garfunkle[ 1974]a Raymond 34.1 118.1 lr? 22 6.7 B 0.1 0.2 3000t* v h Yerkesetal. [1965]a,b Allen et al. [ 1978 ]b Crook et al. [1986] Red Hill 34.1 117.6 14 6.4 C Jennings[ 1975] Red Mountain 34.4 119.4 r? 25 6.7 A 0.9 2.3 831 d q Lajoie et al. [1982]c Lee et al. [ 1979 ]c Sarna-Wojcickiet al. [1979]c Yeats et al. [ 1982]c Sarna-Wojcicki and Yerkes [1982] San Antonio North ß 34.2 117.6 18 6.6 C Jennings[ 1975] San Antonio South ß 34.2 117.6 18 6.5 C Jennings[ 1975] San Cayetano 34.4 119.0 49 7.1 A 0.9 9.0 5.0 429 d q Yeats [1983a] Rockwell [1983] San Fernando ( 1971) 34.3 118.4 r 17 6.5 A 200t* h Bonilla[ 1973] San Gabriel A 34.6 118.7 rl 47 7.0 B 5.0 h m seesegment B San Gabriel B 34.4 118.4 rl 24 6.7 B 5.0 h m Ehlig [ 1973]ab Crowell [ 1973 ]a San Gorgonio Mtn. ß 34.1 116.8 20 6.6 C Jennings[ 1975] San Jose 34.1 117.8 23 6.7 C Jennings[ 1975] Santa Ana Fault ß 34.2 117.1 16 6.5 C Jennings[ 1975] WESNOUSKY; SEISMICHAZARD IN CALIFORNIA 12,605
TABLE A1. (continued)
SlipRate • Fault Location* St L* M õ C# mm/yr T** D tt A** Referenceõõ lat Ion Mn Mx Pr
Santa Cruz Island 34.1 119.9 r 94 7.4 B 0.2 0.9 0.9 4035 h q Jungerand Wagner[1977] Patterson [1979 ]c Yerkes et al. [ 1981 ] Santa Monica 34.1 118.4 r? 24 6.7 B 0.1 1.0 0.3 3955 v q Yerkes et al. [1965]b Lamar [ 1961 ]b McGill [ 1981,1982]b,c Yerkes and Wentworth [1965]a Santa Rosa Island 34.0 120.2 47 7.0 Yerkes et al. [ 1981 ] Santa Susana 34.4 118.6 38 6.9 A 1.2 4.5 630 d q Barnhart andSlosson [1973]a Yeats [ 1979 ] Santa Ynez (west) 34.5 120.1 lv 46 7.0 B 0.2 0.6 0.4 5152 v h Clark et al. [1984] Santa Ynez (east) 34.5 119.4 11 84 7.3 B 0.1 6.7 1.0 3195 t h Sylvesterand Darrow [1979[b Dibblee [ 1966 ]b Gordon [ 1979 ]b Keaton [1978]c Clark et al. [ 1984 ] Saw Pit Canyon 34.2 118.0 13 6.4 C Jennings[ 1975] Sierra Madre A 34.3 118.2 r? 14 6.4 A 5000t* v h Crooket al. [1986] Sierra Madre B 34.3 118.2 r? 17 6.5 A 0.4 4.0 5000t* q Crook et al. [1986] Sierra Madre C 34.2 118.1 r? 15 6.5 A 5000t* q Crook et al. [1986] Sierra Madre D 34.2 117.9 r? 14 6.4 A 5000t* q Crook et al. [1986] Sierra Madre E 34.1 117.8 r? 14 6.4 A 5000t* see the appendix Simi 34.3 118.9 36 6.9 C Yeats [1983b] Sky High Ranch 34.4 117.0 rl 11 6.3 A 0.3 15.0 1.3 578 h q Meisling [1984] (Fifteen Mile Valley) Slide Peak ß 34.2 117.0 20 6.6 C Jennings[ 1975] Soledad 34.5 118.3 11 6.3 C Jennings[ 1975] Summit Valley 34.3 117.3 r 16 6.5 C Meisling [ 1984] Tunnel Ridge Lineament 34.3 117.2 10 6.3 C Meisling [ 1984] Ventura 34.3 119.3 lr 7 6.1 C 0.8 2.4 0.01 d p $arna-Wojcickiet al. [1976]c Gardner and Stahl [1977]c Lee et al. [ 1979 ]c Yerkes and Lee [1979]c $arna- Wojcicki and Yerkes [ 1982 ]c Verdugo 34.2 118.3 r? 21 6.6 Weber [ 1980 ] Walnut Creek 34.1 117.9 16 6.5 Jennings[ 1975] Waterman Canyon 34.2 117.2 18 6.6 Jennings(1975)
Mojave Desert Avawatz Mountain 35.5 116.2 16 6.5 C Jennings[ 1975] Baker * 35.3 116.1 15 6.5 C Jennings[ 1975] Bitter Spring A * 35.2 116.5 17 6.5 C Jennings[ 1975] Bitter Spring B * 35.2 116.6 12 6.4 C Jennings[ 1975] Blake Ranch 34.8 117.6 27 6.8 C Jennings[ 1975] Blackhawk Springs 34.3 116.8 12 6.4 C Jennings[ 1975] Blackwater 35.3 117.3 42 7.0 B 0.4 4746 h P Dibblee [1968a]b Blue Cut 33.9 116.1 27 6.8 C Hope [ 1969]b Bristol Mountain 34.7 115.8 40 7.0 B 0.3 3.0 1133 h p Dokka[1983] Miller and Mortorj [ 1980] Bullion A 34.5 116.3 27 6.8 Jennings[ 1975] Bullion B 34.3 116.0 39 6.9 Jennings[ 1975] Bullion C 34.1 115.9 19 6.6 Jennings[ 1975] Bullion D 34.5 116.3 13 6.4 Jennings[ 1975] Bullion Mountain A ß 34.5 116.2 17 6.5 Jennings[ 1975] Bullion Mountain B * 34.4 116.0 21 6.6 Jennings[ 1975] Bullion Mountain C * 34.4 115.9 9 6.2 Jennings[ 1975] Bullion Mountain D * 34.3 115.8 8 6.1 Jennings[ 1975] Cady 34.9 116.5 21 6.6 Jennings[ 1975] Calico A 35.0 116.9 12 6.4 0.4 5.0 1.0 786 h P inferredfrom segmentB 12,606 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
TABLE A 1. (continued)
SlipRate a Fault Location* St L* M õ C# mm/yr T** D tt A** Referenceõõ lat Ion Mn Mx Pr
Calico B 34.8 116.7 rl 34 6.9 A 0.4 5.0 1.0 1657 h P Dokka [1983]c Miller and Morton [ 1980] Garfunkle[ 1974]a Calico C 34.6 116.4 rl 44 7.0 A 0.4 5.0 1.0 1983 h p inferredfrom segmentB Camp Rock 34.7 116.7 rl 32 6.8 A 0.8 2.0 1.0 1580 h p Dokka[1983]c Morton et al. [ 1980]c Garfunkle[1974]a Covington Flat ß 34.1 116.3 16 6.5 C Jennings[ 1975] Coyote Lake A 35.1 116.9 19 6.6 C Jennings[ 1975] Coyote Lake B 35.1 116.6 25 6.7 C Jennings[ 1975] Deep Spring 34.9 117.6 26 6.8 C Jennings[ 1975] Dome Mountain ß 35.4 117.5 12 6.4 C Jennings[ 1975] Emerson A 34.5 116.6 rl 27 6.8 B 0.6 1.2 1544 h m Garfunkle[1974]a Emerson B 34.4 116.4 rl 22 6.7 B 0.6 1.2 1351 h m Garfunkle[ 1974]a Emerson C 34.3 116.3 rl 12 6.4 C Jennings[ 1975] Emerson D 34.2 116.3 rl 13 6.4 C Jennings[ 1975] Emerson E 34.5 116.5 d 10 6.3 C Jennings[ 1975] Garlic Spring 35.2 116.6 12 6.4 C Jennings[ 1975] Garlock (west) 35.1 118.4 d 103 7.4 A 0.7 30.0 7.0 527t* h h seeGafiock (east) Gafiock (east) 35.5 117.2 rl 148 7.6 A 0.7 30.0 7.0 685t* h h Astiz and Allen [ 1983] Burke and Clark [ 1978 ]c Carter [ 1980,1982]c Clark and Lajoie [1974]c La Violette et al. [ 1980]c Michael [ 1966 ]a Smith [ 1962 ]a Smith [1975]c Garlock Splay A ß 34.9 118.6 18 6.6 Jennings[ 1975] Gafiock Splay B ß 34.9 118.4 20 6.6 Jennings[ 1975] Goldstone ß 35.3 117.0 32 6.8 Jennings[ 1975] Granite Mountain A ß 35.5 116.8 39 6.9 Jennings[ 1975] Granite Mountain B ß 35.5 116.5 26 6.7 Jennings[ 1975] Harper A 35.2 117.5 30 6.8 0.2 6302 h p inferredfrom segmentB Harper B 35.1 117.2 25 6.7 0.2 5582 h P Dibblee [1968b]b Harper C 35.0 117.0 17 6.5 0.2 4223 h p inferredfrom segmentB Helendale A 34.8 117.3 26 6.7 0.2 1.5 1.0 1379 h p Dokka [1983] Miller and Morton [ 1980]c Morton et al. [ 1980]c Helendale B 34.5 117.1 39 6.9 0.2 1.5 1.0 1835 h p inferredfrom segmentA Helendale C 34.3 116.8 29 6.8 0.2 1.5 1.0 1479 h p inferredfrom segmentA Hidalgo 34.3 116.3 30 6.8 Jennings[ 1975] Hidalgo East 34.3 116.2 14 6.4 Jennings[ 1975] Homestead 34.4 116.5 24 6.7 Jennings[ 1975] Johnson Valley 34.4 116.6 37 6.9 Jennings[ 1975] Lenwood 34.6 116.8 51 7.1 0.1 2.5 1.0 2234 h p Dokka[1983] Miller and Morton [ 1980]c Garfunkle[1974]a Lockhart 35.0 117.4 ss 76 7.3 0.9 2.5 1742 h m Garfunkle[1974]a Ludlow 34.7 116.1 67 7.2 Jennings[ 1975] Manix 35.0 116.5 20 6.6 Jennings[ 1975] Mesquite Lake 34.2 116.1 22 6.7 Jennings[ 1975) Mirage Valley 34.7 117.7 32 6.8 Jennings[ 1975] Old Woman Springs 34.4 116.7 35 6.9 Jennings[ 1975] Pipes Canyon 34.2 116.6 rl 23 6.7 Jennings[ 1975] Pisgah 34.7 116.4 rl 34 6.9 0.3 7.0 1.0 1668 h P Dokka [1983] Miller and Morton [ 1980]c Garfunkle[1974]a Rock Creek ß 34.6 117.8 21 6.6 Jennings[ 1975] Red Pass Lake ß 35.2 116.3 18 6.6 Jennings[ 1975] Rodman 34.7 116.5 16 6.5 0.3 0.7 0.5 1891 h p Dokka [1983] Miller and Morton [ 1980]c Garfunkle[1974]a Soda Mountains ß 35.3 116.2 14 6.4 Jennings[ 1975] WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,607
TABLE A 1. (continued)
SlipRate a Fault Location* S• L* M õ C# mm/yr T** D tt A** Referenceõõ lat Ion Mn Mx Pr
South Lockhart 35.0 117.5 25 6.7 C Jennings[ 1975] Tiefort Mountain A ß 35.3 116.6 30 6.8 C Jennings[1975] Tiefort Mountain B ß 35.3 116.8 11 6.3 C Jennings[ 1975] Tiefort Mountain C ß 35.3 116.4 14 6.4 C Jennings[ 1975] Tiefort Mountain D ß 35.3 116.5 15 6.5 C Jennings[1975]
Sierra Nevada- Great Basin
Auburn Shear 39.0 121.1 13 6.4 C 0.07 v q see Swains Ravine (Dewitt fault) Auburn Shear(Rescue 38.9 121.1 29 6.8 C 0.07 v q Woodward-Clyde fault) Consultants [1977]c Harwood and Helley [ 1982]c Borchardt et al. [1978]c Harden and Marchand [ 1980 ]c Auburn Shear zone 39.3 121.4 n? 32 6.8 C .01 v q Woodward-Clyde (SwainsRavine fault) Consultants [1977]c Borchardt et al. [1978]c Harden and Marchand [ 1980]c Auburn Shear zone 39.0 121.3 n 31 6.8 C 0.07 v q see Swains Ravine (Spencevillefault) Battle Creek 40.4 122.0 n 33 6.9 B 0.1 1.0 0.4 5412 t q Harwood et al. [ 1980, 1981]c Helley et al. [ 1981]c CarsonValley 38.7 119.8 n 35 6.9 A 0.7 1.6 1.0 1684 t q Clarketal. [1984] Fish Springs 37.2 118.3 n 28 6.8 B 0.1 1.4 0.4 3623 t q Bachman [1974]b Clark [ 1979 ]c Clark et al. [1984] Furnace Creek 36.9 117.2 d 139 7.6 B 0.7 6574 h m Wrightand Troxel[ 1967]b Hartley Springs 37.8 119.1 n 23 6.7 B 0.1 0.2 0.2 8424 t h Clarketal. [1984] Hilton Creek Fault 37.6 118.8 n 19 6.6 A 1.3 2.6 2.0 554 t h Clarkand Gillespie[1981]c Independence 36.7 118.2 n 65 7.2 B 0.1 0.2 0.1 t q Gillespie [1982]c Inyo Mountains ß 37.3 118.0 22 6.7 C Jennings[ 1975] KeoughSprings ß 37.3 118.4 17 6.5 C Jennings[ 1975] Mt. Humphreysß 37.3 118.6 16 6.5 C Jennings[ 1975] MonoLake 38.1 119.1 n 27 6.8 C 1.8 3.3 2.5 557 t h Clarket al. [1984] North Death Valley 37.5 118.0 43 7.0 C Jennings[ 1975] OwensValley 36.7 118.1 rn 91 7.4 A 0.3 2.0 1.0 3364 t h Lubetkin(1980)c Lubetkin and Clark [1980]c Owl Lake 35.7 116.8 20 6.6 C Jennings[1975] PanamintValley (East) 36.3 117.3 n? 35 6.9 C Jennings[ 1975] PanamintValley (West) 36.2 117.4 n? 30 6.8 C Jennings[ 1975] PanamintValley (South) 35.8 117.1 rn 56 7.1 A 1.0 2.6 2.0 1192 t h Smith [1979]c Parker Lake 37.9 119.2 n 31 6.8 B 0.2 0.8 0.5 3083 t q Clark[1979]c Pleito Thrust 34.9 119.1 r 44 7.0 A 0.2 14.0 1.4 1470 t h Clarket al. [1984] Hall [1984]a Round Valley 37.5 118.7 n 30 6.8 A 0.7 1.4 1.0 1503 t h Clarket al. [1984] SalineValley (North) 36.7 117.9 25 6.7 C Jennings[ 1975] SalineValley (South) 36.6 117.6 36 6.9 C Jennings[1975] SouthDeath Valley(East) 36.3 116.8 rv 52 7.1 A 0.2 5.7 761 h q seesouth segment SouthDeath Valley 35.8 116.6 rv 55 7.1 A 0.2 5.7 800 q m Troxel and Butler [1980]b (South) Hooke [ 1972 ]b SouthDeath Valley(West) 36.2 116.9 62 7.2 C Jennings[ 1975] Sierra Nevada A 36.1 118.0 n? 58 7.1 A 0.3 2.7 1633 v q SaintAmandand Roquemore [ 1979]b Roquemore [1981 ]c Duffield and Smith [1978]c Christensen [ 1966 ]a Sierra Nevada B 35.7 117.9 n? 24 6.7 1.5 850 v P inferred from segmentA Sierra Nevada C 35.4 118.0 n? 25 6.7 1.5 897 v P inferred from segmentA Tank Canyon 35.7 117.3 n 18 6.5 0.5 1.6 1.0 1031 t h Smith et al. [1968]c West Walker 38.6 119.5 n 22 6.7 0.3 0.9 0.6 1996 t q Clark [1967] White Mountain 37.3 118.3 n? 56 7.1 0.8 2956 v h Wallace [1978]b 12,608 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
TABLE A1. (continued)
SlipRate • Fault Location* S• L* M õ C# mm/yr T** D ppA** Referenceõõ lat lon Mn Mx Pr
White Wolf 35.2 118.8 r 62 7.2 A 3.0 8.5 300 d q Stein and Thatcher [1981 ] Lamar et al. [ 1973 ]a Wilson Canyon 35.8 117.5 37 6.9 C Jennings[1975]
Modoc Plateau
Honey Lake 40.1 120.3 52 7.1 C Jennings[1975] Likely 41.3 120.6 94 7.4 C Jennings[1975] Suprise 41.5 120.1 n 102 7.4 A 0.8 2.7 1.0 3669 v q Hedel [1980]c Susanville 40.4 120.6 rn 33 6.9 B 0.1 0.4 0.2 8096 t q Roberts and Gross [1982]c
Central Coast Carmel ß 36.6 121.9 28 6.8 C Jennings[1975] Cuyama Valley ß 35.0 119.8 44 7.0 C Jennings[1975] Hosgri 35.6 121.3 rv 199 7.8 A 4.6 9.0 7.0 852 h q Weber [1981]c King City 36.0 121.6 57 7.1 C Jennings[1975] La Panza 35.4 120.4 33 6.9 C Jennings[1975] Lions Head 34.8 120.5 26 6.7 C Sylvesterand Darrow [1979] Little Pine 34.7 120.0 r 31 6.8 C Jennings[1975] Los Alamos-Baseline 34.7 120.1 44 7.0 C Sylvesterand Darrow [1979] Ozena 34.8 119.5 36 6.9 C Jennings[1975] Rinconada 35.8 120.9 rl 136 7.6 A 2.4 12.0 2.4 1883 h p Durham [1965]b Hart [1976]b San Gregorio 37.1 122.3 rl 190 7.7 A 7.0 19.0 7.0 824 h q Weber and Cotton [1981]c Weberand Lajoie [ 1981]c Clark et al. [ 1984]c Weber and Cotton [ 1981 ]c San Juan 35.4 120.1 69 7.2 Jennings[1975] Santa Maria 34.9 120.4 23 6.7 C Sylvesterand Darrow [1979] Seaside ß 36.5 121.7 23 6.7 C Jennings[1975] North Coast and Great Valley Antioch A 38.1 121.8 10 6.3 C Jennings[1975] Antioch B 38.0 121.8 19 6.6 C Jennings[1975] Bay Entrance 40.7 124.2 r 20 6.6 A 1.4 2.2 1.8 632 d q Woodward-Clyde Consultants [ 1980] Bear River 40.4 124.2 30 6.8 C Carver et al. [ 1982 ] Big Valley 39.0 122.9 rl 16 6.5 B 0.3 2675 h q Hearn etal. [1976]c Clark et al. [ 1984] Blue Lake 40.8 123.9 r 65 7.2 A 1.1 1.6 1965 t q Carver [1985] BrownsValley ß 36.9 121.3 29 6.8 C Jennings[ 1975] Burdell Mountain 38.1 122.6 21 6.6 C Jennings[ 1975] CalaverasA (CoyoteLake) 37.0 121.5 rl 28 5.7 A 17.0 82p* h h Prescottet al. [1981] Savageet al. [ 1979] CalaverasB (MorganHill) 37.3 121.7 fi 28 6.3 A 7.0 17.0 150•* h h Prescottet al. [1981] Savageet al. [ 1979] Calaveras C 37.5 121.8 rl 31 6.3 A 7.0 150•* h seethe appendix Calaveras D 37.7 122.0 rl 23 6.3 A 7.0 150•* h h seethe appendix Collayami 38.9 122.8 rl 18 6.6 B 1.0 0.1 h q Hearn etal. [1976]c Concord 38.0 122.0 rl 24 6.7 A 4.0 319 seethe appendixand Harsh and Burford[ 1982] Cordelia 38.3 122.1 22 6.7 C Herd and Helley [ 1977] Corral Hollow ß 37.7 121.6 17 6.5 C Jennings[ 1975] Fickle Hill 40.7 123.9 rr 63 7.2 0.4 0.8 4335 t q Carver([1985] Freshwater 40.8 124.1 32 6.8 C Jennings[ 1975] Goose Lake 40.6 124.2 rr 22 6.7 B 0.3 1.0 1.0 6108 t q Carver et al. [1982] Clark et al. [ 1984] Woodward-Clyde Consultants [ 1980]c Green Valley 38.2 122.1 35 6.9 A 4.0 424 seethe appendixand Herd and Helly [ 1977] Frizzell and Brown [ 1976 ] Greenville 37.7 121.7 rv 28 6.8 B 0.1 0.7 3585 h h Wrightetal. [1982] WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,609
TABLE A1. (continued)
SlipRate a Fault Location* St L* M õ C# mm/yr T** D ttA** Referenceõõ lat lon Mn Mx Pr
Grogan's 41.0 123.8 94 7.4 Carver et al. [ 1982] Hayward A 37.2 121.7 11 18 6.6 A 4.0 264 h h seethe appendix (Coyote and Silver Creek faults) Hayward B 37.4 121.8 rl 25 6.7 A 4.0 335 h h seethe appendix (Evergreenfault) Hayward C 37.6 122.1 fi 51 7.1 A 6.0 8.0 4.0 556 h h Prescott et al. [1981] Prescott and Lisowski [1982] Hayward D 37.9 122.3 rl 25 6.7 A 4.0 336 h h seethe appendix Healdsberg 38.6 122.8 rl 32 6.8 A 7.0 228 seethe appendixand Jennings[ 1975] Lagoons 40.9 123.8 89 7.3 Carver et al. [ 1982] Lake Mountain- 39.9 123.4 94 7.4 A 7.0 494 seethe appendixand Island Mountain Herd [1978] Carver et al. [ 1982 ] Las Positas 37.6 121.7 In 10 6.3 B 0.04 1.6 872 t q Carpenterand Clark [1982]c Herd and Brabb [ 1979 ] Little Salmon 40.6 124.1 r? 29 6.8 A 1.8 3.0 2.4 609 d q Woodward-Clyde Consultants [ 1980]c Carver et al. (1982) Livermore 37.7 121.8 8 6.2 C Jennings[1975] Los Altos 37.3 122.1 14 6.4 C Jennings[1975] Los Gatos 37.2 121.9 15 6.5 C Jennings[1975] Maacama 39.1 123.1 151 7.6 A 7.0 696 seethe appendixand Pampeyanet al. [ 1981] Herd [1978] Herd and Helley [1977] Mad River 40.7 123.9 64 7.2 B 0.6 1.1 3075 Carver [1985] Mckinleyville 40.8 123.9 rr 67 7.2 B 0.2 0.7 6017 t q Woodward-Clyde Consultants [ 1980]c Carver [1985] Midway 37.7 121.6 r 11 6.3 B 0.1 0.5 2651 t q Shedlocketal. [1980]c Oneill 36.9 121.0 r 18 6.5 A 0.3 1.8 984 t q Lettis [1982]c Ortigalita A 37.1 121.2 ? 25 6.7 C 0.01 0.04 10000•'* v q Andersonet al. [1982] Clark et al. [ 1984 ] Ortigalita B 37.0121.1 ? 18 6.6 C 0.01 0.04 10000•'* v q seesegmentA Ortigalita C 36.9121.0 ? 18 6.6 C 0.01 0.04 10000•'* v q seesegmentA Ortigalita D 36.7120.9 ? 21 6.6 C 0.01 0.04 10000•'* v q seesegment A Paicines 36.8 121.3 rl 36 6.9 A 5.0 13.0 1.0 1726 h seethe appendixand Harsh and Pavoni [1978] Ellsworth [ 1975 ] Savageet al. [1973] Lisowski and Prescott [ 1981 ] Panoche Pass 36.6 121.1 22 6.6 C Jennings[1975] Pleasonton 37.7 121.9 9 6.2 C Jennings[1975] Rogers Creek 38.3 122.6 38 6.9 A 7.0 255 seethe appendixand Jennings[ 1975] Russ 40.5 124.2 30 6.8 Carver et al. [1982] San Benito 36.6 121.1 rl 24 6.7 A 5.0 13.0 1.0 1291 see Paicines fault San Joaquin 36.9 120.8 ? 21 6.6 A 0.2 2.0 1083 v q Lettis [1982]c Sargent-Berrocal 37.0 121.7 rr 51 7.1 A 4.0 1.0 h Savageet al. [ 1979] Hay et al. [ 1980] Tolay 38.2 122.5 14 6.5 C Jennings[1975] Trinidad 40.8 123.9 r 74 7.3 0.1 0.9 5900 t q Clarket al., [1984]c Carver [ 1985 ] Vaca 38.3 122.0 rl 7 6.1 A 0.3 4.0 260 h q Knuepfer[1977]c Verona 37.6 121.8 r 8 6.2 B 0.02 0.1 0.1 9735 t q Herd and Brabb [1980]c West Napa 38.3 122.3 17 6.5 C Herd and Helley [1977] Zamora 38.8 121.9 n 21 6.6 A 0.2 0.5 0.3 4631 v q Harwoodet al. [1981]c Harwoodand Helley [ 1982]c Zayante-Vergales 37.0 121.8 rr 50 7.1 B 0.1 1.3 3130 t q Coppersmith[1979]c Dupre [ 1975]c 12,610 WESNOUSKY.'SEISMIC HAZARD IN CALIFORNIA
TABLE A 1. (continued)
SlipRate a Fault Location* St L* M õ C# mm/yr T** D tt A** Referenceõõ lat Ion Mn Mx Pr
San Andreas SanAndreas (Shelter Cove 38.5 122.8 rl 420 7.8 AA 6.9 30.0 12.0 300t* h h Hall [1984]b to San Juan Bautista) Cummings[ 1968] Prescott and Yu [ 1986 ] Addicott [ 1969] Clark et al. [ 1984] SanAndreas- (Los Altos 37.1 121.9 rl 85 7.0 AA 12.0 140•* h h Prescottetal. (1981) to San Juan Bautista) Hall [1984]b SanAndreas (San Juan 36.6 121.2 rl 86 7.0 AA 10.0 39.0 5.0 228 h h seethe appendixand Bautista to Bitterwater) Burfordand Harsh [ 1980] Clark et al. [1984] SanAndreas (Bitterwater 36.2 120.7 rl 51 33.9 0.01 Burfordand Harsh [ 1980] to Slack Canyon) SanAndreas (Slack 35.9 120.4 rl 37 6.6 AA 33.9 28•* h h Bakunand McEvilly [1984] Canyon to Cholame) SanAndreas (Slack 35.7 120.2 rl 85 7.0 AA 33.9 140t* h h Sieh[1984] Canyon to Hwy 58) Sieh and Jahns [ 1984] SanAndreas (Slack 35.2 119.0 rl 337 7.7 AA 5.8 67.0 33.9 345p* h h Rust[1982a,b]c Canyon to Cajon Pass) Sieh [1984] SanAndreas (Hwy. 166 34.6 118.4 fi 177 7.4 AA 360t* h Sieh[1978a, 1984] to Cajon Pass) SanAndreas (Cajon 33.9 116.7 rl 210 7.5 AA 10.0 35.0 25.0 170?* h h Weldon and Sieh [1985] Passto Salton Sea) Rasmussen [ 1982] Keller et al. [ 1982] K. E. Sieh (personalcommunication, 1986)
* Locationof fault. Coordinatesmark approximatelatitude (øN) and longitude(øW) of fault midpoint. ß Fault name assumed without reference to earlier studies. • Fault type (e.g., reverse(r), normal (n), right-lateral(rl), left-lateral(11), right-reverse (rr), left-reverse(lr), right-vertical(rv), left-vertical(rv), right-normal(rn), left-normal(In)). * Fault length (kilometers). õ Moment-magnitudeM w of earthquakeexpected for ruptureof entirefault length, estimated with sliprate dependent empiri- cal relationsbetween seismic moment M o and faultlength in Figure2, and assumingthe empiricalrelation log M o - 1.5Mw + 16.1 [Hanks and Kanamori, 1979]. # Slip rate class:AA >• 10 mm/yr; A >• 1 mm/yr; B >• 0.1 mm/yr; C >• 0.01 mm/yr. Faultsare assumedto be classC when no slip rate data are availableand assigneda slip rate equalto 0.01 mm/yr for hazardmap development. 15The minimum (Mn) and maximum(Mx) valuesof sliprate reportedby referencedinvestigators. The preferred(Pr) valueof rate, when listed, is used for estimatingT. Otherwise,T is estimatedwith either the minimum, maximum, or averageof the minimum and maximum reportedrates, depending on which limits are placedon the respectivefaults. ** Repeattime of rupture for each fault estimatedwith equation(1) unlessmarked by •* . Repeattimes estimatedto be greaterthan 10,000 years are not listed. • The reportedslip rate is determinedprimarily from the horizontal(h), vertical(v), dip-slip(d), or the total (t) componentof displacement. ** Youngestfeature usedto determineslip rate and/or repeat time along entire fault zone; Holocene(h), Pleistocene(q), Pliocene(p), or Miocene(m). Rangeof slip ratesmay reflectrates determined from olderoffsets as well. õõReferences regarding location, slip rate, and repeattime of each fault. A letter a, b, or c followingthe referenceindicates that valuesof sliprate listedare thosereported by a, Anderson[1979]; b, Bird and Rosenstock[1984]; and c, Clark et al. [1984], respectively. •, Basedon historicalinformation, trenching studies, or other geologicalinferences, rather than equation(1). Casesare discussedin the appendix.
Clark fault is about 19 km, whereastotal horizontal separa- ore Creek faults are accordingly assignedslip rates of 2.0 tion acrossthe Coyote Creek and Buck Ridge faults is about mm/yr for the hazard analysis. 5-6 km. For the hazard analysis,slip rates of the individual The 30-km sectionof fault that broke during the magni- faults are assumedto be approximately proportional to the rude 6.8 earthquake in April of 1968 (Table 2) is here total separationdocumented across each fault, though it is referredto as the BorregoMountain fault (Figure A2). The recognizedthat no evidence is reported to document the Borrego Mountain fault is the only major mapped fault relative youth of the three faults. The Buck Ridge and Coy- strand to continue immediately south of the Clark, Coyote WESNOUSKY: SEISMICHAZARD IN CALIFORNIA 12,611
GLENHELEN F.\ ./'/'-•½ .•• "•...... :":• Browley r SANGABRIEL •O+:Y•L • • E Lomo•a?•.c•nl•d•99 Linde -•- C•ALOMA F.Anzo ß COYOTE...... CREEKF ß .• • F•UL•CREEK_• S•N d•CINTO F•ULT • • Riv•rsid•
' " • E/smote LL ' •• ]Z --
WHITTIER - ELSINORE FAULT ZONE " N•WPORT-INGLEWOOD FLT
• 1933
I • • •L• • POo/f/'c O 'u•• DiegoSon %0
KILOMETERS
Fig. A2. Map showinglocation of Quaternaryfaults and fault segmentswithin the PeninsularRanges which are listed in Table A1 and used in the developmentof seismichazard maps. Limits of assumedsegment lengths for the Whittier-Elsinorefault and Newport-Inglewoodfault zones are denoted by brackets. Epicentersof historicalearth- quakeswith M•6 are shownby stars.The faultsthat producedsurface rupture during the 1968 BorregoMountain and the 1940 and 1979 Imperial earthquakesare hatchered. Teeth are placedon hangingwall side of thrust and re- verse fault traces.
Creek, and Buck Ridge faults. Clark et al. [1972] estimated subparallel Superstition Hills and Superstition Mountain an averagerecurrence interval of about 200 years for tec- faults. Aseismic creep of 0.5 mm/yr is documented by tonic events like that of the 1968 by comparing vertical Louie et al. [1985] at a site along the SuperstitionHills components of displacement in 1968 with earlier move- fault between May 1968 and 1979. Surface displacements ments recorded in offset sediments of ancient Lake Cahuilla ranging up to about 20 mm were also triggered on the that ranged in age from 860 to 3080 years. With the SuperstitionHills fault by the 1968 Borrego Mountain and assumptionthat earthquakesalong this fault prior to 1968 1979 Imperial Valley earthquakes(Table 2), respectively were associatedwith the ratio of horizontal to vertical slip [Fuis, 1982]. However,no geologicevidence that limits the observedin the 1968 event, Clark et al. [1972] further slip rate of either fault over longer periods of time is interpreted vertical rates of deformation to suggesta right- recorded in the literature. Lacking firm evidence, it is lateraloffset rate of about 3 mm/yr. Sharp [1981] citesnew speculatedthat the cumulative seismic slip rate for these stratigraphic features found in a series of trenches and two faults is approximatelyequal to the 1.6-2.2 mm/yr further reinterpretsthe observationsof Clark et al. [1972] assessedby Sharp [1981] just to the north along the to estimatethat the rate of slip has averaged2.7-5.0 mm/yr Borrego Mountain fault. Thus the seismicslip rate of each duringthe last 435 years. In light of Sharp• [1981] data, fault is assumedfor the hazardanalysis to equal 1.0 mm/yr. Clark et al.'s [1972] observations are consistent with a lesser Imperial Fault. The Imperial fault strikes southward repeat time than they originally reported, with best esti- from near Brawley to acrossthe Mexican Border. The fault mates ranging roughly between about 100 and 200 years. was the site of large earthquakesin 1940 and 1979 (Table Sharp [1981] also reportsa right-lateraloffset of 10.9 m 2), each of which producedprimary surfaceruptures north measured on a buffed stream channel that is between 5060 of the U.S.-Mexico border. A minimum slip rate of 20 and 6820 years of age, yielding the most direct measureof mm/yr is inferred for the section of fault that broke in horizontal slip rate along this segment equal to 1.6-2.2 1979, when it is assumedthat strain releasedduring the mm/yr. Louie et al. [1985] report that aseismiccreep at a 1979 earthquakewas accumulatedduring the period subse- site along the fault has averagedabout 5 mm/yr since 1971 quent to the 1940 earthquake [Clark et al., 1984]. but acknowledgethat the rate may partly reflect triggered Isoseismalstudies also yield some evidence that an earth- slip due to the 1968 BorregoMountain and 1979 Imperial quake in 1915 rupturedthe northernextent of the Imperial earthquakes. All of the reported rates of slip are less than fault [Toppozadaand Parke, 1982]. The averagereturn the rate found farther to the north by Sharp [1981]. The time betweenthe three earthquakesis 32 years. It is, how- discrepancyimplies that a significantamount of deforma- ever, important to note that surfaceruptures during 1979 tion at this latitude is being taken up along faults or struc- were limited to the fault north of the border [Sharp, 1982], tures that are not presentlyrecognized or understood. For whereas the 1940 earthquake also ruptured some 30 km constructionof the hazard maps, this segmentis assumedto into Mexico [Bruneand Allen, 1967; Trifunac, 1972]. Prel- rupture each 150 years. iminary resultsof a trenchingstudy along the fault trace Strike-slip deformation south of the Borrego Mountain south of the 1979 rupture imply that no slip occurreddur- segmentis apparently accomodatedby the motion along the ing at leastthe 700 yearspreceding the 1940 event [Clark et 12,612 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
al., 1984]. Clark et al. [1984] note that this result and approximately 30-km segment of the fault extending observations of maximum observed surface offsets in 1940 northwestof the epicenter[Benioff, 1938; Richter, 1958]. It imply a maximum slip rate of 8.6 mm/yr just south of the is assumed here that the 1933 aftershocks delimit a charac- 1979 surface rupture. The hazard maps are constructed teristic rupture length for earthquakesalong the Newport- assuming that the Imperial fault ruptures in events Inglewood fault zone. Thus, in Figure A2, segmentA of equivalent in location and length to the 1979 and 1940 the Newport-Inglewood fault marks the inferred extent of earthquakeseach 32 and 700 years, respectively. rupture during 1933, and segmentB is assumedto be capa- Elsinore fault zone. The Elsinore fault zone (including ble of producing an event of size similar to the 1933 earth- the Whittier fault) strikes northwest from the Mexican quake. Right-lateral slip has averaged0.3-0.8 mm/yr since border a distance of about 250 km (Figure A2). Displace- the Pliocene[Anderson, 1979; Bird and Rosenstock,1984]. ment acrossthe fault zone is predominantly fight-lateral. It Estimates of slip rate from offset features of Holocene to may be inferred from the relations in Figure 2 that com- Pleistoceneage range between 0.1 and 6.0 mm/yr, with plete rupture of this fault zone would produce average cose- averageand better limited valuesequal to about 0.6 mm/yr ismic offsets of 2.5-7.0 m. Pinault and Rockwell [1984] [Clark et al., 1984]. These latter values, however, reflect recently interpreted offset geomorphic features along the only the vertical component of slip, and hence the total rate southern Elsinore to indicate the repeated occurrence of may be greater[Clark et al., 1984]. The hazardanalysis is several earthquakesduring prehistorical time. The average made assumingthat the slip rate equals 1.0 mm/yr. coseismic offsets inferred for the earthquakes were inter- The Palos Verdes fault also strikes southeast and offshore preted to equal 1.4 m, less than would be expected from a of Palos Verdes Peninsula (Figure A2). The onshore reach complete rupture of the Elsinore fault. With this scant evi- of the fault is assumedto be the central portion of a fault dence, it is assumed that the Elsinore fault is characterized segment capable of producing earthquakesalso similar in by moderate-sized earthquakes that do not rupture the size to the 1933 Long Beach event. The segmentextends entire extent of the fault zone and that the location and from north of the Palos Verdes peninsula southward across extent of future earthquake ruptures will correspond to the the peninsulato about 15 km offshore(Figure A2), where segmentslabeled A-D in Figure A2. The segmentsare beds consideredof Holocene age are recognizedby marine chosen so that each is separatedby a major step or bend in reflection methods to be offset by the fault [Darrow and the fault trace. The range of slip rates reported for the Elsi- Fisher, 1983]. Reportedslip ratesrange between 0.02 and nore fault range from about 1 to 9 mm/yr (Table A1). Lim- 0.7 mm/yr but reflect only the vertical component of move- itations placed upon the rate of slip acrossthe Elsinore have ment (Table A1). The total may be greater [Clark et al., generally been imposed by the displacement of features 1984]. The upper bound of 0.7 mm/yr is used for the older than Quaternary age (Table A1). The only rate hazard analysis. inferred from displacement of rocks of Quaternary age or The Rose Canyon fault zone traversesSan Diego and younger was recently reported by Pinault and Rockwell extendsoffshore to the northwest(Figure A2). Greeneet al. [1984]. They inferred a slip rate of 4 mm/yr along segment [1979] mapped the northward extension of the fault zone D. The rate of 4 mm/yr is assumedhere as representative with marine seismic reflection techniques. The northern- of the entire fault trace, though it is emphasized that data most point of the fault zone shown in Figure A2 beating on the extrapolation of this rate along the entire correspondsto a pronouncedright step in the fault system. fault length are few and conflicting. For example, Clark It is assumedfor the analysisthat the 50-km stretch of the [1982] discussesgeomorphic evidence to suggest fault fault displayedin Figure A2 is capableof rupture during a activity is relatively lessto the north of segmentD. Prelim- single earthquake. Anderson [1979] and Bird and Rosen- inary reports of work along segment A, however, appear stock [1984] site offsetPliocene rocks reported by Kennedy consistentwith slip rates of similar order to those reported [1975] to imply a 1-2 mm/yr right-lateralslip rate. Marine along segment D. Specifically, Millman and Rockwell terracesof Pleistoceneage offsetin a right-reversesense sug- [1985] recognizea 1.6-km offset of alluvial depositsthey gesta 1.2-1.5 mm/yr slip rate [Clark et al., 1984]. Prelim- interpret to be mid-Quaternary in age and Rockwell et al. inary reports of trenching across strands within the fault [1985] interpret sedimentsexposed in trenchesto suggesta zone indicate no movement during about the last 1-8 200- to 300-year recurrenceinterval for ground rupturing thousand years [Artim and Streiff, 1981; Ferrand et al., earthquakes. 1981], but it is not clear whether the trenchesspan the Displacementacross the Chino fault is right-reverse[e.g., entire zone of faulting. The maps are constructedassuming Heath et al., 1982]. Heath et al. [1982] concludethat the a 1.5 mm/yr slip rate. Chino fiault is not the principal extension of the Elsinore fault zone. Reported values of slip rate are low, ranging TransverseRange from 0.02 to 0.2 mm/yr. The hazard maps are constructed assuming0.1 mm/yr of slip acrossthe Chino fault. Central area. The Raymond, Hollywood, and Santa Newport-Inglewood,Palos Verdes, and Rose Canyon Monica faults strike southwesterlythrough the Los Angeles faults. The Newport-Inglewoodfault strikessoutheast and region(Figure A3). Each fault is assumedcapable of com- offshoreof Palos Verdes peninsula (Figure A2). Attention plete rupture during a singleearthquake for constructionof is limited here primarily to where the fault is exposedon the hazard maps. The Raymond fault was most recently land. The fault producedthe magnitude6.3 Long Beach studiedby Crooket al. [1986]. Data obtainedfrom excava- earthquakeof March 10, 1933 [Richter, 1958]. The epi- tions acrossthe fault trace led them to estimatean average center of that event is shown in Figure A2. Aftershocksof repeat time of rupture equal to 3000 years. The slip rates the 1933 earthquake apparently concentratedalong the listed in Table A1, interpreted within the framework of WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,613
_,•"" • "•/% SANGABRIEL MOUNTAINS
...... •...... • EAGLEROCK, ••/e- VALLEY ' . SANRAFAEL FAULTS • '•X MADRE'•
NNN• •o © ß RAYMONU
• •_. s• Angeles:,, •elOoo o •• I KILOMETERS117I• 30 " Fig. A3. Map showinglocation of Quaternaryfaults and fault segmentsin centralTransverse Ranges which are listed in Table A1 and usedin the developmentof seismichazard maps. Discontinuitiesbetween segments of SierraMadre and associatedfault zonesare largely schematic.
equation (1), are used to estimate the occurrence rate of The Cucamongafault is the easternmostsegment of the rupture along the Hollywood and Santa Monica faults. Sierra Madre fault system.Geomorphic expression of fault The Sierra Madre fault zone. The southern base of the relatedfeatures along this fault imply a muchgreater degree San Gabriel mountains is composedof a seriesof north dip- of activitythan found for segmentsimmediately to the west ping thrust and reverse faults (Figure A3), one of which [e.g., Matti et al., 1982]. Estimates of the vertical com- ruptured in the magnitude 6.6 San Fernando earthquakeof ponentof slip acrossthe fault rangefrom 2.9 to 6.4 mm/yr February 9, 1971 (Table 1). The 1971 earthquake ruptured (Table A1). Matti et al. [1982] concluded that the the along a 20-km segmentof the range front, labeled the San height and age distribution of fault scarps along the Fernandofault in FigureA3. Procteret al. [1972] observed Cucamongafault zone is consistentwith an averagerepeat that the Sierra Madre fault zone is composed of a number time of 2-m displacementseach 700 years. of discretearcuate segments,each separatedby a transverse Westernarea. Slip rates are reported for but a few faults structuraldiscontinuity. Ehlig [1975] argued that due to in the westernTransverse Ranges (Figure A4). A 3-4.5 the differencein structuralcharacter of the segments,it is mm/yr slip rate acrossthe SantaSusana is impliedby 3-4.5 unlikely that a single earthquake will be associatedwith km of reverseseparation of a 1-m.y. horizon [ Yeats, 1979]. rupture along more than one of the segments. The observa- Similar observationsindicate reverse slip on the San Caye- tion of Crook et al. [1986] that the freshness of fault related tano and Oak Ridge faults has averagedabout 9.0 mm/yr morphology varies significantlybetween different segments and 3.5 mm/yr during the last 1 m.y., respectively[Yeats, lendssupport to Ehlig's [1975] hypothesis.These observa- 1983a]. Analysisof faulted alluvial fans by Rockwell tions and argumentsare acceptedin this analysis. Accord- [1983],however, suggests that slip alongthe San Cayetano ingly, the segmentation of the Sierra Madre fault zone in has averageda minimum of 2-3 mm/yr during the Holo- Figure A3 and Table A1 is based on the work of Procter et cene, and about 9 mm/yr during the last 160-200 thousand al. [1972] and Ehlig [1975]. years.The San Cayetanois assigneda 5 mm/yr slip rate for Sitesalong the San Fernando fault (Figure A3) were exca- the hazard analysis. Marine platformsoffset by the Red vated immediately following the 1971 earthquake by Mountain fault are interpretedto showreverse slip hasaver- Bonilla [1973]. He reportedevidence of a prior rupture aged0.9-2.3 mm/yr during the last 45-60 thousandyears along the same trace between 100 and 300 years ago. A (TableA1). Estimatesof latePleistocene slip rates along the 200-year repeat time is assignedto the San Fernando fault. Javon Canyon and Ventura faults range between about 1 Crook et al. [1986] searched for evidence of Holocene dis- and 3 mm/yr. Yeats [1982], however,argues that these placementsalong segmentsof the Sierra Madre labeled 'A,' latter two faults are not seismogenic.For that reason the 'B,' 'C,' and 'D' in Figure A3. They recognized abundant two faultsare here assigneda very low seismicslip rate of evidence of late Pleistocenefault activity but observed no 0.01 mm/yr, though the argument of Yeats [1982] is not Holocene displacements. Crook et al. [1986] inferred from without question[Sarna- Wojcicki and Yerkes, 1982]. The their studies that a 5000-year repeat time was probably Santa Ynez fault is treated here as two separatesegments representativeof the return time of rupture along each seg- and dividedat the Baselinefault intersection,approximately ment. Such is the basis for assigninga 5000-year repeat where total offsetacross the fault differsmarkedly to the time for segmentsA, B, C, and D of the Sierra Madre fault east and west, respectively[Sylvester and Darrow, 1979]. zone. The same return time is assumed for segment E, Slip ratesof 1.0 mm/yr and 0.4 mm/yr are assignedto the thoughsite-specific studies of the Quaternary activity of this eastand westsegments of the SantaYnez fault, respectively, segment are not known to the author. basedon studiessummarized by Clark et al. [1984]. The 12,614 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
:K E
BIG FRAZIER MTN. FLTS
GIBRALTAR RES. SANTA Y SAN GLENN ANNIE F. CAYETANO F.
MORE RANCH '-•SOLEDADCYN. F. LAVIGIA F. RED MTN. E Santa SAN FERNANDO F. Barbara /SIERRAMADRE ,•Ventur( Santo Barbara Channel
MALIBU COAST F. 54 ø N SANTAROSAF./ • SAN'•u••UziS.F. Chonnel œslonds o 50 I i I KILOMETERS
120øW 119ow
Fig.A4. Map showinglocation of Quaternaryfaults and fault segments within the western Transverse Ranges which arelisted in TableA 1 andused in thedevelopment of seismichazard maps. Teeth are placed on hangingwall side of thrustand reversefaults. Senseof lateraldisplacement is indicatedby half-sidedarrows.
I r_,•LLORIOGœ•0 % MOJAVEDESERT •,/" c'<•.•X e •"'•% EASTERN •?,•-- •'/' • X BLACKHAWK TRANSVERSE
,,•, •a L OH OR N p•, • NNO RANGE •+Z MOUNTAINS•
. '. '. __-% -%• •. '•0 • •%
- Riverside • ' ' • 34ø0'N-
•ooN•o.- SANN• •• • s• •o• - '.•+ I KILOMETERS ll7ø15IwI •
Fig.A5. Map showinglocation of Quaternaryfaults and fault segments within the eastern Transverse Ranges which arelisted in TableA 1 andused in thedevelopment of seismic hazard maps. Fault notation is explained in FigureA4. WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,615
118 ø 116ø 5O I KILOMETERS GRANITEMT•,o - NAVAWATZ •'• .... ø. • zo~• •MVNS.•. '• ..... RTMTN_.• X • •_ FAULTSD .SODA•TN E LAKE /X '
GARLOCK SPLAYS
SAN BERNARDINO PIPES ' FAULTS MOUNTAINS MESQUITE OF THE LAKE F, 34 ø -- MOJAVE DESERT
Fig.A6. Mapshowing location of Quaternaryfaults and fault segments within the Mojave Desert which are listed in TableA1 and usedin the developmentof seismichazard maps. Fault notationas in FigureA4.
0.35-0.40mm/yr rate assignedto the Arroyo Paridafault tural discontinuitiesalong strike are the basisfor dividing (TableA1) is the verticalslip rate assessedby Rockwell some of the more major fault zonesinto smaller segments, [1983] from a study of Ventura River terracesthat are each of which is consideredto behave independently. The offsetby the fault. A speculativeoffset rate of 1 mm/yr is faultsand fault segmentsused in computationof the hazard assignedto the Big Pine fault basedon the documentedmaps are picturedin Figure A6. offsetsof Pliocenerocks (Table A1). Dokka [1983] documents right-lateral displacements Eastern area. The eastern Transverse Range consists alongthe Lenwood(1.0-5.0 km), Calico(7.0-9.0 km), Rod- principallyof the San BernardinoMountains (Figure A5). man and Pisgah(6.4-14.4 km), and Camp Rock (1.6-4.0 Quaternaryfaulting along the northernSan Bernardinokm) faults. He furthercites Miller andMorton [ 1980]and rangefront was studiedby Meisling[1984]. Meisling Miller [1980] for documenting simultaneousoffsets along [1984] documentedQuaternary displacements across the the Helendale (3.0 km) and Bristol Mountains (6.0 km) majorfaults that boundthe the SanBernardino Mountains faults. The time when these displacementsinitiated is not to the north(Figure A5) but succeededin establishinglimits well determined [Dokka, 1983] and may have been any- of sliprate only for the Cleghorn,Ord Mountain,and Sky wherebetween about 2 m.y. and 20 m.y. ago [Clark et al., HighRanch faults (Table A1). The authoris not awareof 1984]. It is these values which provide the limits on the any publishedstudies relating to the slip rate of faults slip rateslisted for thesefaults in Table A1. Slip rateshave within the southern San Bernardino mountains, and hence also been estimated for the Blackwater, Emerson, and Lock- theyare assigned a low sliprate of 0.01 mm/yr. Fartherto hart faults on the basis of offset Pliocene or older rocks the east,slip alongthe Pinto Mountainfault hasreportedly (Table A1). averaged0.3-5.3 mm/yr sinceabout the Miocene(Table The Gadock fault defines the northern boundary of the A1), anda sliprate of 1.0 mm/yr is assumedfor the hazard Mojave desert,extends about 250 km in an easterlydirec- analysis.The San Gorgonio,Banning, and Mill Creek tion, and showsleft-lateral displacement. Estimates of fault faults are discussedlater in the section concerning the San slip rate rangefrom 1 to 30 mm/yr (Table A1). Astiz and Andreas fault system. Allen [1983] providean extensivesummary and discussion of studiesrelating to the earthquakehistory and slip rate of Mojave Desert the Gadock fault during Holocene time. Their summary Quaternaryfaults in the Mojave region generallyshow suggeststhat the bestcurrent estimate of the fault sliprate is fight-lateraldisplacements and are characterizedby anasto- 7 mm/yr, which is assumedfor this analysis,and that the mosingand en echelonsegments. The locationsof struc- averagerecurrence interval of largeearthquakes is probably 12,616 WESNOUSKY: SEISMICHAZARD IN CALIFORNIA
Nevada - - NO. •u k .."'": SP6.F. /,/4, LUNE
:• •.-" VALLEY
•F ' • •.•• //•."' HILTON / • CRK. XL• ...... ••• o,.. •'o•/ -•,,•H • '••••ouF,, "ARTLEYSPRINGS •,P•REYS• FAULT ..... SIERRA
o•
GREAT t
/• / Fig. A7. Map showinglocation of Quaternaryfaults and fault segmentswithin the SierraNevada and Great Basinpro- vinceswhich are listedin Table A 1 and usedin developmentof the seismichazard maps. Limits of assumedassumed segmentlengths for the SierraNevada fault zone are denotedby brackets.
1000+500 years. The segmentsof the fault that strike to the junctionof the SierraNevada, Transverse Range, and the east and west of a major step in the fault tract near CentralCoast geographic provinces (Figure A6). The White Koehnlake (FigureA6) showdistinctly different geological Wolf faultruptured during the magnitude7.3 Kern County characteristicsand seismicbehavior during historical time earthquakeof 1952 (Table 2). Stein and Thatcher [1981] [Astizand Allen, 1983] and are treatedseparately in estimatea 3-9 mm/yr vertical slip rate for the fault based developmentof the hazardmaps (Table A1). on their inferenceof the age (0.6-1.2 m.y) and total dis- placetnentof an ashlayer that intersectsthe fault at depth. Sierra Nevada-Great Basin A 300-yearrepeat time is here assignedto the White Wolf Few Quaternary faults are mapped within the Sierra fault. Basedon Steinand Thatcher's[1981] observation, a Nevada(Figure A1). In contrast,many Quaternaryfaults fault displacementrate of 3-9 mm/yr overa periodof 170- are recognizedalong the easternedge of the SierraNevada 450 yearsis sufficientto accumulatedisplacement equal to and within the Great Basin(Figure A7). The faultsgen- that producedin 1952. Clark et al. [1984] interpretthe erally trend northerly,show normal and right-lateraldis- work of N. T. Hall to indicatethat slip alongthe Pleito placements,and commonlymark the edgeof long linear thrusthas averaged between 0.2 and 14 mm/yr duringthe mountainranges. The largesthistorical earthquake in this late Quaternary,though Hall [1984a] reportsthat a 1.3-1.4 regionoccurred in 1872, producingsurface displacements mm/yr is mostrepresentative for the last 1500years. for a distanceof about100 km alongthe OwensValley fault zone [Whitney,1872]. Other largeevents, such as Modoc Plateau thoserecorded in Nevadaduring this century(Table 2), producedrupture lengths ranging from about 20 to 50 km. Quaternary faults mapped within the Modoc Plateau are Wallaceand Whitney [1984] examinedthe distributionof shownin FigureA8. Faultsin this provincegenerally strike range-boundingfault scarps in centralNevada and suggested northwestward. Only faults for which fault slip rate studies that discontinuities between individual mountain blocks are reportedare listedin Table A 1 and labeled,according to may controlthe extentof futuresurface faulting events. It fault name,in FigureA8. Thosefew faultsgenerally show is that observationthat providesreason here to consider normal displacement.Slip ratesthat are reportedare gen- severalof the majorfault zones in the areato be segmented.erally lessthan 1 mm/yr (Table A1). A slip rate of 0.01 The location,segment lengths, and slip ratesof faultsused mm/yr is assignedto the other mapped faults in the area. in this work are summarizedin FigureA7 and Table A1. A consequenceof the data and assumptions,when analyzed Only faultsor faultsegments of lengthgreater than about within the frameworkof equation(1), is that the expected 10 km are includedfor the hazardanalysis, though a repeattimes for the separatefaults in the regionare largely on the order of severalor more thousandsof years(Table myriadof faultsof lesserlength are present and may be the A•). sourceof smallerearthquakes. It also shouldbe notedthat the easternboundary of the SierraNevada has been marked by volcanismduring Pleistocene to recent time [e.g.,Kil- Central Coast bourneet al., 1980]. Hencesome question exists whether Quaternaryfaults mapped along the centralcoast are pic- the recurrenceof earthquakesin thisregion is primarilytured in FigureA9. Geologicstudies regarding fault slip controlledby regionaltectonic processesor localizedvol- rate are reportedonly for the Rinconada,San Gregorio, and canic activity. Hosgri fault zones. Bird and Rosenstock [1984] cite the The White Wolf and Pleito thrust faults are locatednear work of Durham [ 1965] and Hart [1976] to indicate that WESNOUSKY.' SEISMICHAZARD IN CALIFORNIA 12,617
SCALE I00 km I
I GROGAN FAULT ZONE 2 LAGOON'S FAULT ZONE 3 TRINIDAD FAULT
4. BLUE LAKE MAD RIVER 5 McKINLEYVILLE FAULT FAULT ZONE 6 MAD RIVER FAULT 7 FICKLE HILL FAULT 8 FRESHWATER FAULT
9 LITTLE SALMON FAULT ZONE GOOSE LAKE FAULT ZONE I0 41 ø - II RUSS FAULT ZONE 12. BEAR RIVER SHEAR ZONE
i? """'""•BATTLECREEK I SUSANVILLE LAKEMOUNTAIN FAULT FA U LT 40 ø AULTZONE
ISLAND MOUNTAIN FAULTZONE MAACAMAFAULTZONE Fig. A8. Map showinglocation of Quaternaryfaults and fault segmentswithin the Modoc Plateauand partsof the North Coast and Sierra Nevada geographicprovinces (see Figure A1) that are listed in Table A1 and used in the developmentof seismichazard maps. Queries indicate which southwardextent of coastalthrust and reversefault sys- temsis not yet mapped[Carver, 1985; Carver et al., 1982].Unnamed faults are from Jennings[1975] and not listedin Table A1. Faultsmarked by thinner traceare not includedin hazardanalysis. Fault notationas in FigureA4. right-lateralslip along the Rinconadafault zone has aver- den Gate where it joins the San Andreas [e.g. Graham and agedbetween 2.4 and 12 mm/yr sincethe Pliocene. The Dickinson, 1978]. South of Point Ago Nuevo, seismic minimum value is assumed for input to the hazard maps. profiling showsthe fault to crossouter Monterey Bay and It is, however,important to emphasizethat estimatesof slip into Carmel submarine canyon near Point Sur [Greene et rate basedon Quaternaryor youngerdeposits are neededto al., 1973]. Greene et al. [1973] inferred that the San Gre- confirm whether sucha rate is presentlycharacteristic of the gorio trace turns landward near Point Sur to join the Palo fault zone. Colorado fault. More recently, Graham and Dickinson The San Gregorio and Hosgri fault zones strike a com- [1978] interpretedgeologic relations to indicate that dis- bined distanceof nearly 400 km along the California coast placementsalong the San Gregorio fault are not transferred south of San Francisco(Figure A9). Much of the fault zone to the Palo Colorado fault but, rather, are conveyedsouth- is located offshore,and for that reason there remain uncer- ward acrossPoint Sur. Silver [1978] reviewedaeromagnetic taintiesregarding details of the fault location,the continuity data to conclude that "the bulk of evidence at present of the fault zone, the offsethistory, and the rate of displace- favors, or at least allows, the continuation of the fault zone ment acrossthe zone during Quaternarytime. A synopsis through and to the south of the San Simeon region." The of theseproblems is recountedby Silver [1978]. Estimates southernterminus of the San Gregorio-Hosgrifault zone is of the total right-lateraloffset across the San Gregoriofault not known. It has been proposed that the fault bends into range from 80-115 km since Miocene time [Graham and the TransverseRanges and motion is there taken up by Dickinson,1978; Silver, 1974]. Hall [1975] arguesfor 80 compression[e.g., Hamilton and Willingham, 1977]. Silver to 100 km of post-Mioceneoffset along the Hosgri fault, [1978] reportsthe suggestionthat the fault is offsetby east though his estimatehas been questioned[e.g., Hamilton trending faults in the Santa Barbara Basin. Crouch et al. and Willingham,1977]. The San Gregoriofault wasorigi- [1984] recently interpreted seismic reflection profiles nally mapped on that section of land between Point A•o offshoreof Point Arguello to indicate major post-Miocene Nuevo and the town of San Gregorio[Branner et al., 1909; deformation that may mark the continuation of the San Graham and Dickinson, 1978]. Marine seismic reflection Gregorio-Hosgrisystem, though their observationsindicate data are interpreted to show that the fault extends offshore thrust movement, in contrast to indications that the to the north, through Pillar Point, to a point near the Gol- predominant mode of displacementto the north is right- 12,618 WESNOUSKY: SEISMICHAZARD IN CALIFORNIA
THECENTRAL COAST •.&•-•
A F •/"•--'• mN•r
Fig. A9. Map showinglocation of Quaternaryfaults and fault segmentswithin the CentralCoast province of Califor- nia which are listed in Table A1 and usedin the developmentof seismichazard maps. Reasonsto infer offshore (dashed)extent of the San Gregorio and Hosgri fault zonesare summarizedin text.
lateral [e.g.,Graham and Dickinson,1978]. For the hazard mm/yr of fight-lateral slip acrossthe section of Calaveras analysisthe junction of the two fault zones is placed at fault locatedsouth of the Haywardfault. Interpretationof Point Sur, and eachis treatedas a continuousand indepen- geodeticmeasurements indicates that to the north, the 17 dent seismic source. mm/yr of slip is dividedbetween the the Hayward(7 + 1 Fault slip rate estimatesalong the San Gregofio fault mm/yr) and Calaveras(7 + 1 mm/yr) faults, with the zone are the result of studiesnear Point Afio Nuevo, where remainderof motionbeing taken up by rotationof a large the fault strikes onshore and is composedof severalsub- block to the east of the Calaverasfault [Prescottet al., parallel strands[Clark et al., 1984]. Summation of the late 1981]. Quaternaryoffset rates across the activestrands range from Calaverasfault. Sitesalong the Calaverasfault are known about7 to 19 mm/yr of fight-lateralmovement (Table A 1). to creepaseismically at ratesof severalmillimeters per year The estimatesconsidered most reliablegenerally lie at the or more [e.g., Savageand Burford, 1973; Burford and lower boundof that range[Clark et al., 1984]. Alongthe Sharp, 1982; Prescottand Lisowski,1982]. Analysesof Hosgfi fault zone, slip rate studies are limited to the geodeticfigures also show that little or no strain is accumu- onshore stretch of the zone near San Simeon Point. lating within the crust adjacentto the Calaverasfault zone Ancientmarine shorelines that are offsetby the Hosgrifault [e.g.,Prescott et al., 1981;Prescott and Lisowski,1982]. A zone are interpretedto indicate5-9 mm/yr of fight-vertical consequenceof these observations is that the likelihood of a movementduring the late Quaternary(Table A1). For the major rupture extendingthe length of the Calaverasfault hazard maps the San Gregofio and Hosgri fault zonesare zone appearsvery small [e.g.,Prescott and Lisowski,1982]. eachassigned a 7 mm/yr slip rate. The Calaveras,however, has been the site of three moderate (M•-6) earthquakesduring historicaltime [Bakun et al., North Coast 1984; Toppozadaet al., 1981]. The apparentcontradiction impliesthat the presentconfiguration of geodeticnetworks Calaveras-Haywardfault system. Estimatesof the Holo- is insufficientto resolvestrains accumulated over a 10-year cene and historic slip rate of the San Andreas decrease interval that are associatedwith the preparationof events northward from 32 mm/yr near Bitterwater [Burford and on the Calaverasof about magnitude 6. Moreover, it Harsh, 1980; $ieh and Jahns, 1984] to about 12 mm/yr appears,and is assumedin this analysis,that the charac- along the San Francisco peninsula [Hall, 1984a]. The teristicsize event along the Calaverasis aboutmagnitude 6. decrease in rate reflects a partitioning of slip to the The extent of historicalearthquake ruptures and the loca- Calaveras-Haywardfault system(Figure A10). A minimum tion of mapped discontinuitiesin fault strike are thus used slip rate of 1.4-7.1 mm/yr is estimated for the Calaveras to dividethe Calaverasfault zone into four separateseg- fault from the offset of 3.5-m.y.-old volcanic rocks north of ments, each assumedcapable of producingmoderate sized Hollister [Herd, 1979; Page, 1982; Nakata, 1977]. I am earthquakes.The segments,labeled A-D in FigureA 10, are aware of no geologicestimates of slip rate for the Hayward about 25-30 km in length and are discussedseparately fault. The transfer of slip from the San Andreas to the below. Calaveras-Hayward system is best evidenced by geodetic Segment A corresponds to the zone of aftershocks measurementsthat spanthe last 10-20 years [Savageet al., registeredby the magnitude5.9 CoyoteLake earthquakeof 1973, 1979; Prescott et al., 1981]. Geodetic observations August 6, 1979 [Reasenbergand Ellsworth, 1982]. The show that at the latitude of the southernSan FranciscoBay, northern end of this segmentis approximatelycoincident the cumulative rate of relative motion across the San with the bifurcationof the Calaverasand Haywardfault Andreas, Hayward, and Calaveras faults is equivalent to zones. The southern terminus is located at the fault inter- about 32 mm/yr of fight-lateraldisplacement [e.g., Prescott sectionwith the small left-lateralBusch fault, site of the et al., 1981; Savageet al., 1973, 1979]. Geodolitemeasure- magnitude 5.1 ThanksgivingDay earthquakeof 1974 ments of Savage et a! [1979] are consistentwith 17 + 2 [Reasenbergand Ellsworth,1982]. The seismicmoment of WESNOUSKY: SEISMICHAZARD IN CALIFORNIA 12,619
123 ø 122 ø 121 ø • AUBURNSHEARZONE
'•G VALLEYF. *•OLLAYAMI F. MORAF.
ß Sacramento
GREEN VALLEY F.
CORDELIA F.
38 ø B ANTIOCH FAULTS
ONCORD F, PL EASONTON F. Son Francisco \ \ MIDWAY F. CORRAL HOLLOW F. ILLE E POSITAS F. •RE F'.
Poc/'f/'c
SAN 37 ø
SanJuan Boutlsto o 50 IOO BUSCHF. I I KILOMETERS PASS F, •, Monterey SAN BENITO F,
Fig. A10. Map showinglocation of Quaternaryfaults and fault segmentswithin part of the North Coastgeographic provincewhich are listedin Table A1 and usedin the developmentof seismichazard maps. Limits of assumedseg- ment lengthsfor the Calaverasand Haywardfault zonesare denotedby brackets.Fault notationas in FigureA4. the 1979 earthquakewas 4-6x1019 N -m [Urhammer, lateral extent of rupture in 1984 is interpreted to be con- 1980; Liu and Helmberger, 1983; Ekstrom and Dziewonski, trolled by mappedcomplexities in the fault trace [King and 1985]. Analysis of short-periodinstrumental data shows Nabelek, 1985; Bakun et al., 1984]. Geodetic data recorded that coseismicslip during the 1979 event was primarily lim- for the Morgan Hill earthquake are consistent with a ited to a patch of the fault 6-14 km in length [Bouchon, seismicmoment equal to about 3x1018N -m [Bakunet 1982; Liu and Helmberger, 1983]. Little or no slip al., 1984]. Analysis of strong ground motion data and occurredoutside the patch, apparently becausestrain release long-period surface waves yield a similar result (H. outside the patch is primarily accommodatedby aseismic Kanamori, personal communication, 1986; Hartzell and creep. Maximum coseismicslip on the patch during 1979 Heaton, 1986). Hartzell and Heatoh's (1986) study of was 1.2 m [Liu and Helmberger, 1983]. The geodetically strong ground motion recordsshows that coseismicslip dur- determined rate of slip acrossthe fault is about 17 mm/yr ing the Morgan Hill earthquakewas, much like observedfor [Savageet al., 1979], sufficientto produce 1.2 m of slip the 1979 Coyote Lake earthquake, confined primarily to each 70 years. Historical data also show that a similar sized two patchesalong the fault plane, each no more than about earthquake ruptured this segmentof the Calaveras 82 years 5 km in dimension. Maximum coseismicslip on the fault ago on June 20, 1897 [Toppozadaet al., 1981; Reasenberg plane was about 1 m. It is at this latitude that slip along and Ellsworth, 1982]. The hazard maps are constructed the Calaveras appears to be partially transferring to the assuming that this segment will produce earthquakes of Hayward fault zone, but the exact kinematics of the slip Mo--5x1017 N-m each82 years. transfer are not fully understood. Slip of about 1 m will Segment B extends the length of the aftershock zone accumulateover a period of about 60 to 150 years assum- [Cockerhamand Eaton, 1984] of the magnitude 6.1 Mor- ing slip rates that range from 7 to 17 mm/yr. The last gan Hill earthquake that occurred April 24, 1984. The event comparable in size to the 1984 earthquake to occur 12,620 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
on this segmentof the Calaverastook place in 1911 [Top- ratesof 8-11 mm/yr duringhistorical time [Ellsworth,1975; pozada, 1984; Bakun et al., 1984], 73 years prior to the Savageet al., 1973; Lisowskiand Prescott,1981]. Near- Morgan Hill earthquake. The hazard maps are constructed fault measurementsfrom alignment arrays [Harsh and assumingthat an earthquakewith Mo=3xle •8 N-m will Pavoni, 1978] and short-range distance measurements rupture this segmentof fault each 150 years. [Lisowski and Prescott,1981 ] show 5-13 mm/yr of slip at The Calaveras fault extends another 55 km northward of various sites along the faults. The general agreement segmentB (Figure Ale). Though geodeticdata suggestthat betweenthe long and shortbaseline measurements might be little, if any, elastic strain is accumulatingalong the fault in interpretedto indicatethat most slip is taking place aseismi- this region [e.g.,Prescott and Lisowski, 1982], the possible cally, ratherthan beingaccumulated as elasticstrain. The occurrenceof earthquakessimilar in size to the Morgan Hill data are too few, however,to yield any firm conclusioncon- earthquake of 1984 cannot be ruled out. A moderate-sized cerning the seismicbehavior of these faults. For present event is, in fact, reported to have produced 8 km of surface purposes,the faults are speculativelyassigned a 1 mm/yr rupture along the northern end of the Calaveras in 1861 seismicslip rate. [Toppozada et al., 1981]. For computation of the hazard The Concord and Green Valley faults are the right-step maps, the northern 55 km of the Calaveras fault zone is northward continuation of the Calaverasfault zone [Page, further divided into two segments(C and D in Figure Ale), 1982]. Alignmentarray measurementsshow an averageof each similar in length to segmentsA and B. Segment C 4 mm/yr of fault creep at a site along the Concord fault strikes north from segmentB to a relatively sharp left bend [Harshand Burford,1982]. Sharp [1973] alsodocuments a in the fault that, in turn, coincides approximately with the number of offset cultural features within the city of Con- point where the Verona fault strikesinto the Calaveras. For cord that may be interpretedto indicate a similar or greater the hazard analysis, segmentsC and D are treated identi- value of creep. For the hazard analysis,the assumptionis cally to segmentB. made that the faults are accumulating slip at a rate of 4 Hayward fault zone. The Hayward fault zone splaysoff mm/yr, but it is emphasizedthat there are presentlyno geo- the Calaveras fault at a point south of San Francisco Bay, logic data available that directly bear upon the correctness strikingnorthwestward a distanceof about 120 km (Figure of this assumption. Ale). Motion across the fault is predominantly right- North of San Francisco bay, the Rogers Creek, lateral, except along the southern reach where the fault trace Healdsberg,Maacama, Lake Mountain, and Island Moun- is more complex and is characterizedby reverse displace- tain fault zones (Figures A8 and Ale) exhibit landforms ments [Page, 1982; Bryant, 1982]. Prescottand Lisowski indicativeof geologicallyrecent strike-slip movement [Herd, [1982] determinedstrain rates from both small (1-2 km) 1978; Herd and Helley, 1977; Pampeyanet al., 1981], but and large (10-30 km) aperture geodetic networks that strad- geologicslip ratesfor the faults are not reported. The faults dle the Hayward fault north of about Los Altos. They con- appear to mark the northward continuation of the Hayward clude that no more than 4 mm/yr of slip is presentlyaccu- fault zone [Herd, 1978]. Prescottand Yu [1986] report mulating as elastic strain in rocks adjacent to the fault, geodetic observationsspanning a l e-year period that are whereasthe total rate of displacementmeasured geodetically consistent with such an interpretation. They observe that is about 8 mm/yr [Prescottet al., 1981]. The hazard maps total right-lateral displacementdistributed acrossa 6e-km- reflect the assumption that such behavior is characteristicof wide zone north of San Francisco that extends between and the entire fault zone over the long term and that the seismic includesthe San Andreas and Green Valley faults is, within slip rate averages4 mm/yr. The consequencesof assuming uncertainties,equivalent to the rate determined by Prescott other than a constant slip rate are detailed by Prescottand et al. [1981] for the San Andreas-Hayward-Calaverasfault Lisowski [1982]. It is further assumedthat the Hayward system south of San Francisco. An isolated measure of fault zone is composed of four segments,labeled A-D in fault creep equal to 2 mm/yr along a strand of the Figure Ale. The segmentationis based on the location of Maacamma fault zone near 39.5øN is reported by Harsh et historicalearthquake ruptures, mapped discontinuitiesalong al. [1978]. The geodeticdata reportedby Prescottand Yu fault strike, and the senseof displacementregistered across [1986] prohibit large amounts of fault creep,at least south the fault. Segments A and B include the Silver Creek- of about 39øN. Geodetic data indicate that right-lateral slip Coyote Creek and Evergreen fault systems, respectively alongthe Haywardfault occursat about 7 mm/yr [Prescott [Aydin, 1982], show predominantly reverse-typemotion et al., 1981]. For the hazard analysis,the same rate is [e.g., Bryant, 1982; Page, 1982], and are 18-25 km long. assumed to be characteristic of the northward extensions of The 5e-km segment of the Hayward fault that probably the Hayward fault zone. ruptured in a magnitude 6.8 earthquake on October 21, Quaternary faults north of Cape Mendocino and within 1868 [Toppozada and Parke, 1982] shows offset right- the coastal region are predominantly west to northwest lateral [Prescottet al., 1981] and is labeledC in FigureAle. trending,northeast dipping, reverseand thrust faults (Figure There are also reports that a similar sized event also rup- A8) Carver et al., 1982; Carver, 1985]. The distancethe tured along segmentC in 1836 [Toppozadaet al., 1981], faults extend offshore is unknown, though a number of though evidence for the actual location of the 1836 event is faults showingsimilar strike are identified offshoreby Field scant. Segment D is the northernmost extension of the et al. [1980]. It appearsthat this set of coastalreverse and Hayward fault zone. thrust faults marks a northward continuation of the Lake Extensions of Calaveras-Haywardfault system. The Mountain-IslandMountain fault zone [Herd, 1978], though Paicines and San Benito faults are the southernmost exten- more mapping is necessaryto determine the exact relation sion of the Calaverasfault zone (Figure Ale). Relatively betweenthe two fault regimes[Carver, 1985]. To construct long geodolite line measurementsindicate right-lateral slip the hazard maps, only the onshore extent of the faults as WESNOUSKY: SEISMICHAZARD IN CALIFORNIA 12,621 picturedin Figure A8 is considered.Carver [1985] reports Francisco and Los Altos and from that inferred a 224 _+ 25 that the cumulative displacementrate acrossthe Mad River year averagerepeat time for 1906-type earthquakes. Hall et fault zone has averagedabout 4 mm/yr during late Quater- al. [1983] conducted trench studies of the San Andreas near nary time. Geologicwork relating to fault slip rate is also Point Reyesand estimatedthe maximum return time of slip reportedfor the Little Salmon, Goose Lake, and Mad River eventsto equal 360 + 25 years. The averagerepeat time of fault zones(Figure A8) and summarizedin Table A1. rupture along this fault segmentestimated with equation (1) is 313 years, assumingthat 12 mm/yr is representativeof San Andreas Fault the slip rate along the entire length of the fault segment. The average of these three estimates, 300 years, is used in The San Andreas fault is perhaps the most studied fault formulating the seismichazard maps. in California. The fault produces right-lateral offsets and Los Altos to San Juan Bautista. The smaller coseismic extends from Cape Mendocino to the Salton Sea, a distance offsets(0.5-1.5 m) observed along this segment in 1906, as of about 1000 km. Seismological,geodetic, and geological compared to north of Los Altos (2.5-5.0 m), give reason to information has led a number of investigatorsto conclude further examine this stretch of the fault. Geologic and geo- that the seismic behavior of the San Andreas varies detic data indicate that slip to both the north and south of markedly along strike [e.g., Allen, 1968; Sieh and Jahns, Los Altos occurs at about 12 mm/yr. If, as observed in 1984]. The San Andreas, for example, displacesstream 1906, it is assumedthat coseismicoffsets along this segment channelsin the Cardzo Plain. Geomorphologic and geolo- of the fault are characteristically smaller than occur to the gic analyses of the displaced channels indicate that slip north of Los Altos, it also requires that coseismicoffsets be across the fault in the Cardzo Plain takes place during relatively more frequent along this segment. For input to earthquakes that occur every 240-450 years and produce the hazard maps, it is assumedthat this segment also rup- displacementsof the order of 8 m. Earthquake displace- tures during the interseismic period between 1906-type ments are, however, much smaller and more frequent along events. It may be interpretedwith equation (1), assuminga a stretch of the San Andreas near Parkfield. Rupture of the 12 mm/yr slip rate, that this 85-km segment will accumu- San Andreas near Parkfield since 1857 is reported to occur late sufficient strain to produce an earthquake on average on averageevery 22 years [Bakun and McEvilly, 1984]. each 95 years. For the hazard maps then, rupture limited Seismological and geodetic analysis of the more recent to this segment is assumed to occur each 140 years. Thus, earthquakesin this sequenceshows that coseismicslip dur- in combination with the occurrenceof 1906-type events, the ing the Parkfield eventsis characteristicallyan order of mag- hazard maps reflect an interpretation that this segmentwill nitude lessthan observedin the Cardzo Plain, averagingnot experiencelarge earthquakeseach 95 years. more than about 30 cm [Scholz et al., 1969]. The San Historical documents provide evidence that a major Andreas may be characterized as a number of segments earthquake also ruptured along the Los Altos to San Juan based on observationssuch as these, each segmentbeing Bautistasegment of the fault in 1838 [Louderback,1947]. characterizedby a different mode of seismicbehavior and, The 1838 earthquake is important for two reasons. The in turn, posing a different long-term seismic hazard. The relatively short period of 68 years between 1838 and 1906 location, length, and expectedrepeat time of rupture of the provides support for the mode of fault behavior assumed for segmentsused as input to the hazard maps are illustratedin this region. Further, accommodationof slip in this segment Figure A11 and, from north to south, are discussedbelow. during 1838 may in part explain the relatively small cose- Shelter Cove to San Juan Bautista. This segmentof the ismic slip observed here in 1906 as compared to farther fault broke during the San Francisco earthquake of 1906 north. This latter interpretation is, however, compli- [Lawson, 1908; Sieh, 1978b; Thatcher, 1975]. Coseismic cated and uncertain. Louderback's [1947] account of the displacements in 1906 averaged 2.5-5.0 m between Los 1838 event indicates the event extended to the north of Los Altos and Point Arena and a significantlyless 0.5-1.5 meters Altos as well, perhaps even to the north of San south of Los Altos. Northward of Point Arena the fault is Francisco. Louderback [1947] further noted that the predominantly offshore, except for a small segment at intensity of shaking in Monterey was greater in 1838 than Shelter Cove, where no information of the average cose- in 1906 and on that basis, suggestedthat rupture during ismic slip exists.Hall [1984b] interpretsa displacedchannel 1838 may have even extended south of San Juan on the San Francisco Peninsula, about 20 km north of Los Bautista. Nonetheless, the extent and variations in slip Altos to suggesta late Holocene fault slip rate of about 12 observedfor the 1906 earthquakeare reason to suggestthe mm/yr. Offsets of a facies of the Santa Clara formation mode of fault behavior differs in this segmentas compared between San Juan Bautista and San Francisco has led Cum- to north of Los Altos. mings [1983] to estimate that the average rate of offset San Juan Bautista to Bitterwater Valley. A late Holo- acrossthe San Andreas has averagedabout 8 + 3 mm/yr cene slip rate of about 34 mm/yr is estimated by Sieh and during the last ---450,000 years.Recent geodetic surveys Jahns [1984] for the San Andreas fault within the Carrizo spanning the fault near Los Altos, during the period of Plain. Aseismiccreep is occurringat rates up to 32 mm/yr 1970-1980, show strain rates that imply that 12 mm/yr of betweenBitterwater Valley and Slack Canyon [Burfordand slip deficit is presently accumulating along the fault Harsh, 1980]. North of about San Juan Bautista,however, [Prescottet al., 1981]. Recent geodeticsurveys near Point both geologicand geodeticstudies provide evidence of only Reyes,show similar results [Prescott and Yu, 1986]. about 12 mm/yr of slip. [Hall, 1984b; Prescott et al., Hall [1984b] noted that approximately five 1906-type 1981]. This fault segmentappears to mark a transition offsets are necessary to explain the total offset of a zone where a portion of the slip occurring along the San 1130 + 160 year old stream channel located between San Andreas is transferred northward to the Paicines-Calaveras- 12,622 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
Hayward fault system. Such an interpretation is supported by the geodeticmeasurements of Prescottet al. [1981] that show the cumulative slip rate to the north of San Juan Bautista across the San Andreas, Hayward, and Calaveras faults (Figure A10) is also 33 mm/yr, as well as by observa- Cape tions of fault creep along the Paicines fault [Harsh and Mendocino Pavoni, 1978; Lisowski and Prescott,1981]. The slip rate Shelter Cove along this fault segment thus increases southward from about 12 to 34 mm/yr. It is not, however, understoodwhat ! portion of the slip is accumulating as elastic strain versus Pt. Arena being released by aseismic slip. Louderback's [1947] account of the large 1838 earthquake providessome sugges- tion that this segmentmay sustain significantlevels of elas- 300y tic strain, though the largestearthquake recordedalong the Pt.Reye segmentin recenttime doesnot exceedmagnitude 5.2 [Bur- San ford and Harsh, 1980]. To computethe hazard maps,it is Francisco speculativelyassumed that 5 mm/yr of slip is being stored Los as elastic strain energy and that the extent of the segment 140y behavesas a singleseismogenic source. JuanSon Baut t Bitterwater Valley to Slack Canyon. Alignment array sur- veys dating back to the mid-1960s show this segment to d 250y creepaseismically at about 32 mm/yr [Burfordand Harsh, BitterwaterValle' 1980]. The geologicrate of slip as averagedover the late Holocene determined at a site within the Carrizo Plain is SlackC•n' p•' virtually identical to this value [Sieh and Jahns, 1984]. It 28y Oh thus appears that elastic strain is not accumulating along 140y this segment [Burford and Harsh, 1980; Sieh and Jahns, H Carrlzo 545y 1984]. The hazard maps are constructedassuming that •Hw negligiblepotential exists for a large earthquaketo rupture this segment. 60y Slack Canyon to Cajon Pass--The 1857 rupture zone. The northern and southernends of this segmentare placed Pallet, near Slack Canyon and Cajon Pass, respectively, and correspondto the probable rupture length of the great 1857 earthquake estimated by Sieh [1978b]. Sieh and Jahns [1984] estimatedthat the late Holoceneslip rate within the SanGorg 170y Carrizo Plain has averaged33.9 ñ 2.9 mm/yr. A review of geomorphicevidence by Sieh and Jahns [1984] showsthat the past three earthquakesthat producedruptures along the San Andreas in the Carrizo Plain resulted in surface offsets 0 100 KM of between9.5 and 12.3 m. Using thesevalues and the late Holocene slip rate, Sieh and Jahns [1984] estimated the averagetime interval between the occurrenceof such offsets Fig. A 11. Map illustratingassumed mode of rupture along the San is between 240 and 450 years. Hence it is assumedthat the Andreasthat satisfiesexisting data and is assumedfor development averagereturn time of rupture for this segmentis 345 years. of seismichazard maps. Solid bars adjacent to fault trace extend The largest offsetsduring the 1857 earthquakeoccurred length assumedto rupture during singleearthquakes. Overlapping of bars indicatessegments of the fault that, at different times, are in the Carrizo Plain [Sieh, 1978b]. Displacementsduring associatedwith earthquakesof different magnitude and hence rup- 1857 to both the north and the south of the Carrizo Plain ture length. Expectedaverage repeat times of rupture listed next to were considerablyless [Sieh, 1978b]. An assumptionthat each segmentare in years. Observationsindicate that elastic strain the long-term rate of slip is maintained along strike of this accumulationis now largely being releasedby aseismiccreep along segment requires that earthquakesbe more frequent in segmentmarked by infinity. those regionsthat experiencedsmaller offsetsin 1857. This requisite is, of course, also dependent on the assumption that earthquake displacementson sectionsof the fault are have occurredrelatively frequentlyalong this segment. A always of a characteristic size. The long-term seismic moderate-sizedevent in 1966 produced tectonic surface behavior interpreted for the San Andreas and used here to ruptures extending from between Slack Canyon and construct the hazard maps is based on these assumptions. Parkfield to Cholame [Brown and Vedder, 1967]. For that reason,it is useful to further examine segmentsof Isoseismaldistributions determined from studyof historical 1857 rupture zone that extend to the north and south of the documents have been interpreted to suggestthat similar Carrizo Plain. sized events also occurred here in 1881, 1901, 1922, and Slack Canyon to Cholame. Subsequentto the 1857 1934 [Sieh, 1978c;Bakun and McEvilly, 1984]. Analyses earthquake,moderate-sized earthquakes are also reportedto of seismogramsfor the 1922, 1934, and 1966 eventssup- WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA 12,623 port this argument, showingthat the seismicmoments for occur every 150-200 years. Preliminary work by K.E. Sieh the three events differ at most by 20% [Bakun and (personal communication, 1986) along the San Andreas McEvilly, 1984]. The averagetime intervalbetween the six near the Salton Sea presently appears consistent with a earthquakesis 22 years. To reflect that observationin the 170-yearrepeat time for large earthquakes. Other scenarios, hazard maps, it is assumedthat ruptures limited to this seg- as well as this one, have previously been put forth to ment occur on averageeach 28 years. Thus, in combina- explain the existingdata [Weldon and Sieh, 1985], and all tion with the occurrenceof larger earthquakesthat extend similarly infer the occurrenceof large earthquakeson aver- along this reach of the fault (Figure A11), the effective age each 150-200 years. Finally, it is not clear how slip repeat time between earthquakes along this segment is along the San Andreas is transferred through the San Gor- placed at 22 years. goniopass region (Figure A11) [Matti et al., 1985]. For the Slack Canyon to Hwy. 58. Offsets along this segment hazard maps, it is assumedthat slip occurssimultaneously averaged3-4 m directly to the south of Cholame during the along the Mill Creek, San Gorgonio-Banning,and San Ber- great 1857 event, whereasoffsets further to the south along nardino fault strands (Figure A5) during a rupture of the the Carrizo Plain were on average8-10 m [Sieh and Jahns, Cajon Passto Salton Sea segments. 1984]. Immediately to the south of this segment,$ieh and Jahns [1984] assessedthe fault slip rate to have averaged Acknowledgements. I give special thanks to Kerry Sieh and 33.9 + 2.9 mm/yr for the past 3700 years. The San Clarence Allen, whose support and interest were instrumental to the Andreas is creeping at a virtually identical rate just to the completion of this study. I also thank Luciana Astiz, Malcolm north of this segment[e.g., Burford and Harsh, 1980]. At Clark, Hiroo Kanamori, and Kerry Sieh for reviews of the manuscript,Rob Clayton for accessto computer graphicshardware, that rate, sufficient slip is accumulatingto produce a 3.5-m Gene Humphreys for contouring programs, and David Brillinger, offsetabout every 100 years. To reflect that observationin Gary Carver, Jim Lienkaemper, Mike Lisowski, Dave McCulloch the hazard maps, ruptures limited to this segment are Tom Rockwell, Mike Rymer, Robert V. Sharp, Ray Weldon, and assumedto occur each 140 years. In conjunction with the Bob Yeats for comments and discussionregarding treatment of the geological data. Edith Huang and Barbara Pallant kindly helped assignedrepeat time (345 years) of 1857-type ruptures then, prepare the manuscript. This research was supported by U.S.G.S. the resultant repeat time of earthquakesalong this segment contracts 14-08-0001-21980 and 14-08-0001-G 1184. Contribution is set to 100 years. 4253, Division of Geological and Planetary Sciences, California Hwy. 166 to Salton Sea. Surfacerupture during the 1857 Institute of Technology. earthquakeextended as far southas about Cajon Pass[Sieh, 1978b. Studies by Sieh [1978a, 1984] provide evidence REFERENCES that rupture of the San Andreas occurs at Pallett Creek on Abe, K., Fault parameters determined by near- and far-field data: averageevery 145-200 years. Davis [1983] has argued,on The Wakasa Bay earthquake of March 26, 1963, Bull. Seismol. the basisof data gatheredfrom trench studiesabout 20 km $oc. Am., 64, 1369-1382, 1974. south of Hwy. 166, that rupture did not extend north into Abe, K., Static and dynamic fault parametersof the Saitama earth- quake of July 1, 1968, Tectonophysics,27, 223-238, 1975a. the Carrizo Plain for every earthquake documented at Pal- Abe, K., Reexamination of the fault model for the Niigata earth- lett Creek, as it did for the 1857 earthquake. No historical quake of 1964, J. Phys. Earth, 23, 349-366, 1975b. evidence of large earthquakes exists on the San Andreas Abe, K., Dislocations, source dimensions and stressesassociated south of Cajon Pass. There are, however, reports of 1-4 m with earthquakesin the Izu Peninsula,Japan, J. Phys. Earth, 26, 253-274, 1978. offsetsof young geomorphicfeatures at sitesalong the reach Addicot, W. O., Late PleistoceneMollusks from San Francisco Pen- of the San Andreas south of Cajon Pass that may reflect insula, California, and their paleogeographicsignificance, Proc. prehistoric earthquake displacements[e.g., Weldon and Calif Acad. $ci., 37, 57-93, 1969. Sieh, 1985; Keller et al., 1982; Sieh, 1978b ] The lack of Aki, K., and P. G. Richards, Quantitative Seismology: Theory and historicalrupture south of Cajon Passimplies a repeat time Methods, 932 pp., W. H. Freeman, New York, 1980. Albee, A. L., and J. L. Smith, Earthquake characteristicsand fault on the order of at least 150 years,the approximatelength of activity in southernCalifornia, in EngineeringGeology in South- the historical record. ern California, edited by R. Lung and R. Procter,pp. 9-33, Asso- Toward reconciling available observations,it is assumed ciation of EngineeringGeologists, Glendale, Califi, 1966. that the San Andreas between Hwy. 166 and the Salton Sea Algermissen,S. T., D. M. Perkins, P. C. Thenhaus, S. H. Hanson, and B. L. Bender, Probablistic estimates of maximum accelera- is composedof two separatesegments. The first segmentis tion and velocity in rock in the contiguousUnited States, U.S. taken to extend from Hwy. 166 to just north of Cajon Pass. Geol. Surv. Open File Rep., 82-1033, 99 pp., 1982. The average repeat time of rupture of this segment is Allen, C. R., The tectonic environments of seismicallyactive and assumed to equal 360 years. Such a mode of behavior inactive areasalong the San Andreasfault system,in Proceedings satisfiesSieh's [1984] conclusionthat the average return Conferenceon GeologicProblems of San Andreas Fault System, edited by W. R. Dickenson and A. Grantz, pp. 70-82, Stanford time of large earthquakesat Pallett Creek is between 145 University Press,Stanford, Calif., 1968. and 200 years. That is, the previouslycalculated occurrence Allen, C. R., Geological criteria for evaluating seismicity, Bull. of 1857-type earthquakeseach 345 years, in conjunction $eismol. $oc. Am., 86, 1041-1057, 1975. with a rupture confined between Hwy. 166 and Cajon Pass Allen, C. R., L. T. Silver, and F. G. Stehli, Agua Blanca Fault-A major transversestructure of northern Baja California, Mexico, each 360 years, is consistentwith the occurrenceof earth- Geol. $oc. Am. Bull., 71, 457-482, 1960. quakes at Pallett Creek on average every 170 years. A Allen, C. R., T. C. Hanks, and J. H. Whitcomb, Seismologicalstu- repeat time of 170 years is also assignedto the remaining dies of the San Fernando earthquake and their tectonic implica- southernmost segment of the fault. The 170-year repeat tions, Bull. Calif. Div. Mines Geol., 196, 257-262, 1975 time is chosen to satisfy the geomorphologicand geologic Allen, C. R., R. Crook, Jr., B. Kamb., C. M. Payne, and R. J. Proctor, Evidence for faulting recurrence in the Raymond and analysisof sedimentsalong the San Andreas in Cajon Pass Sierra Madre fault zones, southern California, Eos Trans. AGU, by Weldonand Sieh [1985] that indicateslarge earthquakes 59, 1210, 1978. 12,624 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
Ambraseys,N., Some characteristicfeatures of the Anatolian fault Bouchon,M., The rupture mechanismof the Coyote Lake earth- zone, Tectonophysics,9, 143-165, 1970 quake of August 6, 1979 inferred from near field data, Bull. Ambraseys, N. N., and J. S. Tchalenko, The Dasht-e Bayaz (Iran) Seismol.Soc. Am., 72, 745-757, 1982. earthquake of August 31, 1968: A field report, Bull. Seismol. Branner, J. C., J. F. Newson, and R. Arnold, Descriptionof the Soc. Am., 59, 1751-1792, 1969. SantaCruz quadrangle,in GeologicalAtlas, Folio 163, 11 pp., Anderson, J. G., Estimating the seismicityfrom geologicalstructure U.S. GeologicalSurvey, Reston, Va., 1909. for seismic-riskstudies, Bull. Seismol. Soc. Am., 69 p. 135-158, Brown, R. D., Jr., and J. G. Vedder, The Parkfield-Cholame Cali- 1979. fornia earthquakesof June-August1966: Surfacetectonic frac- Anderson, L. W., M. H. Anders, and D. A. Ostena, Late Quater- tures along the San Andreasfault, U.S. Geol. Surv. Prof Pap., nary faulting and seismichazard potential,eastern Diablo Range, 5 79, 2-22, 1967. California, ProceedingsConference on Earthquake Hazards in Brune, J. N., Seismicmoment, seismicity, and rate of slip along the Eastern San FranciscoBay Area, edited by E. W. Hart et al., major fault zones,J. Geophys.Res., 73, 777-784, 1968. Calif Div. Mines Geol. Spec.Publ. , 62, 197-206, 1982. Brune, J. N., and C. R. Allen, A low stress-drop,low-magnitude Ando, M., Faulting in the Mikawa earthquake of 1945, Tectono- earthquakewith surface faulting: The Imperial, California, physics,22, 173-186, 1974. earthquakeof March 4, 1966, Bull. Seismol. Soc. Am., 57, 501- Ando, M., Source mechanismsand tectonic significanceof histori- 514, 1967. cal earthquakesalong the Nankai trough, Japan, Tectonophysics, Bryant, W. A., Southern Hayward fault zone, Alameda and Santa 27, 119-140, 1975. Clara counties,California, ProceedingsConference on Earth- Andrews,D. J., A stochasticfault model, 1, Static case,J. Geophys. quakeHazards in the EasternSan FranciscoBay Area, editedby Res., 85, 3867-3877, 1980. E. W. Hart et. al., Calif Div. Mines Geol. Spec.Publ. 62, 35-44, Artim, E. R., and D. Streiff, Trenching in the Rose Canyon fault 1982. zone, San Diego, California, Summ. Tech. Rep., 13, p. 113, Nat. Bucknam, R. C., G. Plafker, and R. V. Sharp, Fault movement Earthquake Hazards Reduct. Program, U.S. Geol. Surv., Menlo (afterslip)following the Guatemalaearthquake of February4, Park, Calif., 1981. 1976, Geology,6, 170-173, 1978. Astiz, L., and C. R. Allen, Seismicityof the Garlock Fault, Califor- Bulletinof the SeismologicalSociety of America,14, Seismological nia, Bull. Seismol.Soc. Am., 73, 1721-1735, 1983. notes, 169-170, 1924. Aydin, A., The East Bay hills, a compressionaldomain resulting Burdick,L., and G. R. Mellman, Inversionof the body wavesfrom from interaction between the Calaveras and Hayward-Rodgers the BorregoMountain earthquaketo sourcemechanism, Bull. Creek faults, ProceedingsConference on Earthquake Hazards in Seismol.Soc. Am., 66, 1485-1499, 1976. the Eastern San FranciscoBay Area, edited by E. W. Hart et al., Burford, R. D., and P. W. Harsh, Slip on the San Andreasfault in Calif Div. Mines Geol. Spec.Publ. 62, 11-21, 1982. centralCalifornia from alignementarray surveys,Bull. Seismol. Bachman, S. B., Depositionaland structuralhistory of the Waucobi Soc. Am., 70, 1233-1261, 1980. Lake bed deposits, Owens Valley, California, M.S. thesis, 129 Burford, R. D., and R. V. Sharp, Slip on the Hayward and pp., Univ. of Calif., Los Angeles, 1974. Calaverasfaults determined from offsetpowerlines, Proceedings Bakun, W. H., and T. V. McEvilly, Recurrence models and Conference on Earthquake Hazards in the Eastern San Francisco Parkfieldearthquakes, J. Geophys.Res., 89, 3051-3058, 1984. Bay area, editedby E. W. Hart et al., 261-269, 1982. Bakun, W. H., M. M. Clark, R. S. Cockerham,W. L. Ellsworth,A. Burke,D. B., and M. M. Clark,Late Quaternaryactivity along the G. Lindh, W. H. Prescott,A. F. Shakal, and P. Spudich,The Gafiock fault at Koehn Lake, California,Eos Trans.A GU, 59, 1984 Morgan Hill, California, earthquake,Science, 225, 288-291, 1126, 1978. 1984. Butler, R., G. S. Stewart,and H. Kanamori,The July 27, 1976 Barnhart, J. T., and J. E. Slosson,The Northridge Hills and associ- Tangshan,China earthquake-Acomplex sequence of intraplate ated faults-a zone of high seismic probability?,in Geology, events,Bull. Seismol.Soc. Am., 69, 207-220, 1979. Seismicityand EnvironmentalImpact, editedby D. E. Moran, J. Buwalda,J.P., and P. St. Amand, Geologicaleffects of the Arvin- E. Slosson,R. O. Stone, and C. A. Yelverton, pp. 253-256, Asso- Tehachapiearthquake, Bull. Calif Div. Mines Geol.,171, 41-56, ciation of EngineeringGeologists, University Publishers,Los 1955 Angeles,Calif., 1973. CaliforniaDepartment of Water Resources,Sea-water intrusion, Barrows,A. G., A review of the geologyand earthquakehistory of Bolsa-Sunsetarea, Orange County, Bull. Calif Dep. Water the Newport-Inglewood structural zone, southern California, Resour., 63-2, 167 pp., 1968. Spec.Rep. Calif Div. Mines Geol., 114, 115 pp., 1974. Canitez,N., and M. N. Toksoz,Static and dynamicstudy of earth- Barrows,A. G., J. E. Kahle, F. H. Weber, Jr., and R. B. Saul, Map quakesource mechanism: San Fernando earthquake, J. Geophys. of surface breaks resulting from the San Fernando, California, Res., 77, 2583-2594, 1972. earthquakeof Feb. 9, 1971, in San Fernando,California Earth- Carpenter,D. W., and R. J. Clark, Geologicstudies for seismic quake of Feb. 9, 1971, pp. 127-136, U.S. Department of Com- hazardassessment, Las Positasfault zone, ProceedingsConfer- merce, National Oceanic and Atmospheric Administration, enceon EarthquakeHazards in the EasternSan FranciscoBay Washington,D.C., 1973. Area, editedby E. W. Hart et al., Spec.Rep. Calif Div. Mines Bartholomew, M. J., The San Jacinto fault zone in the northern Geol., 62, 147-154, 1982. Imperial Valley, California, Geol. Soc. Amer. Bull., 81, 3161- Carter, B. A., Quaternarydisplacement on the Garlock fault, Cali- 3166, 1970. fornia,in Geologyand Mineral Wealthof the CaliforniaDesert, B•ith, M., Earthquakerecurrence of a particulartype, Pure Appl. DibbleeVolume, edited by D. L. Fife andA. R. Brown,pp. 457- Geophys.,119, 1063-1076, 1981. 466, SouthCoast Geological Society, Santa Ana, Calif., 1980. Benioff,H., The determinationof the extent of faultingwith appli- Carter,B., Neogenedisplacement on the Garlockfault, California, cation to the Long Beach earthquake, Bull. Seismol. Soc. Am., Eos Trans.AGU, 63, 1124, 1982. 28, 77-84, 1938. Carver,G. A., Quaternarytectonics of the MendocinoTriple Junc- Bird, P., and R. W. Rosenstock,Kinematics of presentcrust and tion, the Mad River fault zone,in AmericanGeomorphological mantle flow in southern California, Geol. Soc. Am. Bull., 95, Field Trip GroupGuidebook, edited by H. M. Hulsey,T. E. 946-957, 1984. Lisle,and M. E. Savina,pp. 155-167,American Geomorphologi- Bonilla, M. G., Trench exposuresacross surface fault rupturesasso- cal FieldGroup, University of California,Berkeley, 1985. ciated with San Fernando earthquakein San Fernando,Califor- Carver,G. A., T. A. Stephens,and J. C. Young,Quaternary reverse nia, earthquakeof February 9, 1971, vol. 3, pp. 173-182, U.S. andthrust faults, Mad Riverfault zone, in Late CenozoicHistory Department of Commerce,Washington, D.C., 1973. and Forest Geomorphologyof HumboldtCounty, California: Bonilla, M. G., R. K. Mark, and J. J. Leinkaemper,Statistical rela- Friends of the Pleistocene,Pacific Cell, Field Trip Guidebook, tions among earthquakemagnitude, surface rupture, and surface editedby D. R. Harden,D.C. Marron,and A. McDonald,pp. fault displacement,Bull. Seismol.Soc. Am., 74, 2379-2411, 1984. 93-97, 1982. Borchardt,G. A., S. Rice, and G. Taylor, Fault featuresin paleosols Castle,R. O., Geologicmap of the BaldwinHills area,California, overlying the Foothills fault system near Auburn, California, scale1:12,000, U.S. Geol. Surv. OpenFile Rep., 1960. Calif Div. Mines Geol. OpenFile Rep., 78-16, 125 pp., 1978. Castle, R. O., and R. F. Yerkes, Recent surfacemovements in the WESNOUSKY'. SEISMICHAZARD IN CALIFORNIA 12,625
Baldwin Hills, Los AngelesCounty, California, U.S. Geol. Surv. in southernCalifornia, Proceedingsof the Conferenceon Tec- Prof Pap., 882, 125 pp., 1976. tonic Problemsof the San AndreasFault System,edited by R. L. Chen, W.P., and P. Molnar, Seismic moments of major earth- Kovach and A. Nur, Stanford Univ. Publ. Geol. Sci., 13, 125- quakesand the averagerate of slip in Central Asia, J. Geophys. 135, 1973. Res., 82, 2945-2969, 1977. Crowell, J. C., and A. G. Sylvester,Tectonics of the juncture Christensen,M. N., Late Cenozoic crustal movementsin the Sierra betweenthe San Andreasfault systemand the Salton Trough, Nevada of California, Geol. Soc.Am. Bull., 77, 163-182, 1966. southeasternCalifornia, report, Dep. of Geol. Sci., Univ. of Christodoulidis, D.C., D. E. Smith, R. Kolenkiewicz, S. M. Calif., Santa Barbara, 1979. Klosko, M. H. Torrence, and P. J. Dunn, Observing tectonic Cummings,J. C., The Santa Clara Formation and possiblepost- plate motions from satellitelaser ranging,J. Geophys.Res., 90, Pliocene slip on the San Andreas fault in central California, 9249-9263, 1985. Proceedingsof the Conferenceon Geologic Problemsof the San Clark, M. M., Pleistoceneglaciation of the drainageof the West AndreasFault System,edited by W. R. Dickinsonand A. Grantz, Walker River, Sierra Nevada, California, Ph.D. thesis, 130 pp., Stanford Univ. Publ. Geol. Sci., 11, 191-207, 1968. Stanford Univ., Stanford, Calif., 1967. Cummings, J. C., The Woodside facies, Santa Clara Formation and Clark, M. M., Surfacerupture along the Coyote Creek fault, The late Quaternary slip on the San Andreas fault, San Mateo BorregoMountain Earthquake of April 9, 1968, U.S. Geol.Surv. County, California, paper presentedat 58th Annual Meeting, Prof Pap., 787, 55-86, 1972. Pac. Coast Sect., Soc. of Econ. Paleontol. and Mineral., Clark, M. M., Range-front faulting: Cause of the difference in Sacramento, Calif., 1983. height between Mono Basin and Tahoe moraines at Walker Darrow, A. C., and P. J. Fisher, Activity and earthquakepotential Creek,in Field Guide to RelativeDating MethodsApplied to Gla- of the Palos Verdes fault, final technical report, contract 14-08- cial Depositsin the Third and Fourth Recessesand Along the 001-19786, 90 pp., U.S. Geol. Surv., Menlo Park, Calif., 1983. Eastern Sierra Nevada, California, With SupplementaryNotes on Davies, G. F., and J. N. Brune, Regional and global fault rates Other California Localities: The Friends of the Pleistocene, from seismicity,Nature Phys.Sci., 229, 101-107, 1971. PacificCell, Field Trip Guidebook,edited by R. M. Burke and P. Davis, T. L., Late cenozoicstructure and tectonichistory of the W. Birkeland, pp. 54-57, 1979. western"Big Bend"of the San Andreasfault and adjacentSan Clark, M. M., Map showingrecently active breaks along the Elsi- Emigdio Mountains,Ph.D. thesis,580 pp., Univ. of Calif., Santa nore and associatedfaults, Clalifornia, between Lake Henshaw Barbara, 1983. and Mexico, U.S. Geol. Surv. Misc. Invest. Ser. Map, 1-1329, Davison, F.C., Jr., and C. H. Scholz,Frequency moment distribu- 1982. tion of earthquakesin the Aleutian Arc: A test of the characteris- Clark, M. M., and A. R. Gillespie, Record of the late Quaternary tic earthquakemodel, Bull. Seismol. Soc. Am., 75, 1349-1362, faultingalong the Hilton Creek fault in the SierraNevada, Cali- 1985. fornia (abstract),Earthquake Notes, 52, 46, 1981. Dibblee, T. W., Jr., Geologyof the centralSanta Ynez mountains, Clark, M. M., and K. R. Lajoie, Holocenebehavior of the Garlock Santa BarbaraCounty, California, Bull. Calif. Div. Mines Geol., fault (abstract), Geol. Soc. Am. Abstr. Programs, 6, 156-157, 186, 99 pp., 1966. 1974. Dibblee, T. W., Jr., Existenceof major lateral displacementon the Clark, M. M., and J. C. Yount, Surface faulting along the Hilton Pinto Mountain Fault, southeasternCalifornia, Spec. Pap. Geol. Creek fault associated with the Mammoth Lakes, California Soc. Am., 115, 322, 1968a. earthquakesof May 1980, Earthquake Notes, 52, 45-46, 1981. Dibblee, T. W., Jr., Geology of the Fremont Peak and Opal Clark, M. M., A. Grantz, and M. Rubin, Holocene activity of Mountain quadrangles,California, Bull. Calif Div. Mines Geol., the Coyote Creek fault as recorded in sediments of Lake 188, 64 pp., 1968b. Cahuilla, The Borrego Mountain Earthquake of April 9, 1968, Dibblee, T. W., Jr., Late Quaternary uplift of the San Bernardino U.S. Geol. Surv. Prof. Pap., 787, 55-86, 1972. Mountains on the San Andreas and related faults, Spec. Rep. Clark, M., K. Harms, J. Lienkaemper,J. A. Perkins, M. J. Rymer, Calif Div. Mines Geol., 118, 127-146, 1975. and R. V. Sharp, The searchfor surfacefaulting, The Coalinga Dokka, R. K., Displacementson late Cenozoic strike-slipfaults of EarthquakeSequence of May 2, 1983, U.S. Geol. Surv. Open File the central Mojave Desert, California, Geology, 11, 305-308, Rep., 83-511, 8-11, 1983. 1983. Clark, M. M., K. K. Harms, J. J. Lienkaemper, D. S. Harwood, K. Doser, D. I., Source parameters and faulting processesof the 1959 R. Lajoie, J. C. Matti, J. A. Perkins,M. J. Rymer, A.M. Sarna- Hebgen Lake, Montana, earthquake sequence,J. Geophys.Res., Wojcicki, R. V. Sharp,J. D. Sims,J. C. Tinsley and J. I. Ziony, 90, 4537-4555, 1985. Preliminary slip-ratetable for late Quaternaryfaults of California, Doser, D. I., and H. Kanamori, Long period surfacewaves of four U.S. Geol. Surv. Open File Rep., 84-106, 12, 1984. western U.S. earthquakesrecorded by the Pasadenastrainmeter, Clark, M. M., A. C. Darrow, K. K. Harms, J. J. Lienkaemper, and Bull. Seismol.Soc. Am., in press,1986. R. H. Patterson, Uncertainties in slip rates, manuscript in Doser, D. I., and R. B. Smith, Seismic moment rates in the Utah preparation, 1986. Region, Bull. Seismol.Soc. Am., 72, 525-552, 1982. Cockerham, R. S., and J.P. Eaton, The April 24, 1984 Morgan Doser, D. I., and R. B. Smith, Source parameters of the 28 October Hill earthquakeand its aftershocks:April 24 through September 1983 Borah Peak, Idaho, earthquake from body wave analysis, 30, 1984, Calif. Div. Mines Geol. Spec.Publ. 68, 215-236, 1984. Bull. Seismol.Soc. of Am., 75, 1041-1051, 1985. Coppersmith,K. J., Activity assessmentof the Zayante-VergelesDuffleld, W. A., and G. I. Smith, Pleistocenehistory of volcanism fault, central San Andreas fault system,California, Ph.D. thesis, and the Owens River near Little Lake, California, U.S. Geol. 210 pp., Univ. of Calif., Santa Cruz, 1979. Surv. J. Res., 6, 395-408, 1978. Crone, A. J., M. N. Machette, M. G. Bonilla, J. J. Lienkaemper, K. Dupre, W. R., Quaternary history of the Watsonville lowlands, L. Pierce, W. E. Scott, and R. C. Bucknam, Characteristics of north-central Monterey Bay region, California, Ph.D. thesis, 145 surfacefaulting accompanyingthe Borah Peak earthquake, cen- pp. Stanford Univ., Stanford, Calif., 1975. tral Idaho, U.S. Geol. Sur. Open File Rep., 85-290, 43-58, 1985. Durham, D. L., Evidence of large strike-slipdisplacement along a Crook, R., Jr., C. R. Allen, B. Kamb, C. M. Payne, and R. J. Proc- fault in the southernSalinas Valley, California, U.S. Geol. Surv. tor, Quaternary geology and seismic hazard of the Sierra Madre Prof. Pap., 525-D, D 106-D 111, 1965. and associatedfaults, western San Gabriel Mountains, California, Ehlig,P. L., History,seismicity, and engineeringgeology of the San RecentReverse Faulting in the TransverseRanges, California, U. Gabriel fault, Geology, Seismicityand EnvironmentalImpact, S. Geol.Surv. Prof Pap.,in press,1986. pp. 247-251, Associationof EngineeringGeologists, University Crouch, J. K., S. B. Bachman, and J. T. Shay, Post-Miocene Publishers,Los Angeles,Calif., 1973. compressionaltectonics along the central California margin, in Ehlig, P. L., Geologicframework of the San Gabriel mountains, Tectonicsand SedimentationAlong the CaliforniaMargin, edited Bull. Calif Div. Mines Geol., 196, 7-18, 1975. by J. K. Crouch and S. B. Bachman, pp. 37-54, Pacific Coast Ekstrom, G., and A.M. Dziewonski, Centroid-momenttensor solu- Section,Society for EconomicPaleontologists and Mineralogists, tionsfor 35 earthquakesin westernNorth America(1977-1983), Bakersfield,Calif., 1984. Bull. Seismol.Soc. Am., 75, 23-40, 1985. Crowell,J. C., Problemsconcerning the San Andreasfault system Ellsworth,W. L., Bear Valley, California earthquakesequence of 12,626 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
February-March 1972, Bull. SeismoL Sod Am., 65, 483-506, Hanks, T., and H. Kanamori,A momentmagnitude scale, J. Geo- 1975. phys.Res., 84, 2348-2350, 1979. Ferrand, G. T., C. G. Bemis, and L. T. Jansen, Radiocarbon dates Hanks, T. C., and M. Wyss,The useof body-wavespectra in the of alluvium, Rose Canyon fault zone, San Diego, California, determinationof seismic-sourceparameters, Bull. Seismol.Soc. Geol. $oc. Am. Abstr. Programs,13, 55, 1981. Am., 62, 561-589, 1972. Field, M. E., S. H. Clarke, Jr., and M. E. While, Geologyand Geo- Harden,J. W., and D. E. Marchand,Quaternary stratigraphy and logic Hazards of offshore Eel River Basin, northern California interpretationof soil data from Auburn, Oroville, and Sonora continentalmargin, U.S. Geol. Surv. Open File Rep., 80-1080, 80 areasalong the Foothillfault system,western Sierra Nevada, Cali- pp., 1980. fornia, U.S. Geol.Surv. OpenFile Rep., 80-305, 39 pp., 1980. Fitch, T. J., and C. H. Scholz, Mechanisms of underthrusting in Harsh, P. W., and R. O. Burford, Alignment-array measurements southwest Japan: A model of convergent plate interactions, J. of fault slip in the easternSan FranciscoBay area, California, Geophys.Res., 76, 7260-7292, 1971. ProceedingsConference on EarthquakeHazards in the Eastern Frizzell, U. A., Jr., and R. D. Brown, Jr., Map showing recently San FranciscoBay Area, editedby E. W. Hart et al., Calif. Div. active breaks along the Green Valley fault, Napa and Solano of Mines Geol.Spec. Publ., 62, 251-260, 1982. counties, California, U.S. Geol. Surv. Map, MF-743, 1976. Harsh, P. W., and N. Pavoni, Slip on the PacinesFault, Bull. Fuis, G. S., Displacementon the superstitionHills fault triggeredby $eismol. $oc. Am., 68, 1191-1193, 1978. the earthquake,U.S. Geol. Surv. Prof Pap., 1254, 145-154, 1982. Harsh, P. W., E. H. Pampeyan,and J. M. Coakley,Slip on the Wil- Fukao, Y., and M. Furumoto, Mechanisms of large earthquakes lits fault, California,Earthquake Notes, 49, 22, 1978. along the eastern margin of the Japan Sea, Tectonophysics,25. Hart, E. W., Basicgeology of the Santa Margarita area, San Luis 247-266, 1975. ObispoCounty, California, Bull. Calif. Div. Mines Geol.,199, 45 Gardner, D. A., and I. Stahl, Geotechnical-seismicinvestigation of pp., 1976. the proposed 330 zone water storage reservoir and water condi- Harwood, D. S., and E. J. Helley, Preliminary structure-contour tioning facilitiessite for the City of San Buenaventura,California, map of the SacramentoValley, California,showing major late Rep. V77151, 19 pp., Geotech. Consult., Inc., Ventura, Calif., Cenozoic structural features and depth to basement, scale 1977. 1:250,000, U.S. Geol. Surv. Open File Rep., 82-737, 1982. Garfunkle, Z., Model for the late Cenozoic tectonic history of the Harwood,D. S., E. J. Helley, J. A. Barker,and E. A. Grit•n, Prel- Mojave Desert, California, and for its relation to adjacentregion, iminary geologicmap of the BattleCreek fault zone, Shastaand Geol. Soc. Am. Bull., 85, 1931-1944, 1974. Tenama counties,California, scale 1:24,000, U.S. Geol. Surv. Gilbert, G. K., A theory of earthquakes of the Great Basin with Open File Rep., 80-4 74, 1980. practical applications,A.M. J. $ci., 27, 49-53, 1884. Harwood,D. S., E. J. Helley, and M.P. Doukas,Geologic map of Gillespie, A. R., Quaternary glaciation and tectonics in the the Chico monocline and northeasternpart of the Sacramento southeastern Sierra Nevada, Inyo County, California, Ph.D. Valley, California,scale 1:62,500, U.S. Geol. Surv. Misc. Invest. thesis,695 pp., Calif. Inst. of Tech., Pasadena,1982. Map, 1-1238, 1981. Gordon, S. A., Relations between the Santa Ynez fault zone and Hay, E. A., W. R. Cotton,and N. T. Hall, Shearcouple tectonics the Pine Mountain thrust fault system,Piru Mountains, Califor- and the Sargent-Berrocalfault systemin northernCalifornia, Stu- nia, Geol. Soc.Am. Abstr. Programs,11, 80, 1979. dies of the San Andreas Fault Zone in Northern California, Spec. Graham, S. A., and W. R. Dickinson, Apparent offsetsof on-land Rep. Calif. Div. Mines Geol., 140, 41-50, 1980. geologicfeatures across the San Gregorio-Hosgrifault trend, Spec. Hearn, B.C., Jr., J. M. Donelly, and F. E. Goff, Preliminarygeolo- Rep. Calif. Div. Mines Geol., 137, 13-23, 1978. gic map of the Clear Lake volcanicfield, Lake County,Califor- Greene, H. G., W. H. K. Lee, D. S. McCulloch, and E. E. Brabb, nia, scale1:24,000, U.S. Geol. Surv. Open File Rep., 76-751, 3 Faults and earthquakesin the Monterey bay region, California, plates., 1976. U.S. Geol. Surv. Misc. Field Maps, MF-518, 14, 1973. Heath, E.G., D. E. Jensen, and D. W. Lukesh, Style and age of Greene, H. G., K. A. Bailey, S. H. Clarke, J. I. Ziony, and M.P. deformation on the Chino fault, in Neotectonicsin Southern Cal- Kennedy, Implicationsof fault patternsof the inner California ifornia, compiled by J. D. Cooper, pp. 123-134, Geological continental borderland between San Pedro and San Diego, in Societyof America, Cordilleran Section,Anaheim, Calif., 1982. Earthquakeand Other Perils in the San Diego Region,edited by Heaton, T. H., and H. Kanamori, Seismic potential associatedwith P. L. Abbot and W. J. Elliot, pp. 21-28, GeologicalSociety of subductionin the northwesternUnited States,Bull. Seismol. Soc. America, Boulder, Colo., 1979. Am., 74, 933-941, 1984. Gutenberg,B., and C. F. Richter, Frequencyof earthquakesin Cal- Hedel, C. W., Late Quaternary faulting in western SurpriseValley, ifornia, Bull. Seismol.Soc. Am., 34, 185-188, 1944. Modoc County, Calif., M.S. thesis,113 pp., San JoseState Univ., Hall, C. A., Jr., San Simeon-Hosgrifault system,coastal California: San Jose, Calif., 1980. Economic and environmental implications, Science, 190, 1291- Helley, E. J., et al., Geologic map of the Battle Creek fault zone 1294, 1975 and adjacentparts of the northern SacramentoValley, California, Hall, N. T., Holocene history of the San Andreas fault between scale 1:62,500, U.S. Geol. Surv. Misc. Field Stud. Map, MF- Crystal SpringsReservoir and San Andreas Dam, San Mateo 1298, 12 pp., 1981. County,California, Bull. Seismol. Soc. Am., 74,281-300,1984b. Herd, D. G., Intracontinental plate boundary east of Cape Mendo- Hall, N. T., Late Quaternary history of the easternPleito thrust cino, Calif Geol., 6, 721-725, 1978. fault, northern transverseranges, California, Ph.D. thesis,89 pp., Herd, D. G., Neotectonic framework of central California and its Stanford Univ., Stanford, Calif., 1984. implications to microzonation of the San Francisco Bay region, Hall, N. T., W. R. Cotton, and E. A. Hay, Recurrencefrequency of U.S. Geol. Surv. Circ., 807, 3-12, 1979. large earthquakeson the San AndreasFault near Dogtown and Herd, D. G., and E. E. Brabb, Evidence for tectonic movement on on the San FranciscoPeninsula, paper presentedat AGU Chap- the Las Positas fault, Alameda County, California, U.S. Geol. man Conference on Fault Behavior and the Earthquake Genera- Surv. Open File Rep., 79-1658, 7 pp., 1979. tion Process,AGU, Snowbird, Utah, 1983. Herd, D. G., and E. E. Brabb, Faults at the General Electric test Hamilton, D. H., and C. R. Willingham, Hosgri fault zone; struc- reactor site, Vallecitos Nuclear Center, Pleasanton, California, ture, amount of displacement,and relationshipto structuresof U.S. Geol. Surv. Admin. Rep., 77, 1980. the westernTransverse Ranges, Geol. Soc. Am. Abstr. Programs, Herd, D. G., and E. J. Helley, Faults with Quaternary displacement 9, 429, 1977. northwestern San Francisco Bay region, California, U.S. Geol. Hamilton, R. M., Aftershocksof the BorregoMountain earthquake Surv. Misc. Field Stud. Map, MF-818, 1977. from April 12 to June 12, 1968, The BorregoMountain Earth- Herd, D. G., and C. R. McMaster, Surface faulting in the Sonora, quake of April 9, 1968, U.S. Geol. Surv. Prof Pap., 787, 31-54, Mexico, earthquakeof 1886, Geol. Soc.Am. Abstr. Programs,14, 1972. 4, 1982. Hanks,T., [3values and c0• seismicsource models: Implications for Hill, R. I., Geology of Garner Valley and Vicinity, in Geologyof tectonic stressvariations along active crustal fault zonesand the the San Jacinto Mountains, Field Trip Guideb. 9, edited by A. R. estimationof high-frequencystrong ground motion, J. Geophys. Brown and R. W. Ruff, pp. 90-99, South Coast Geological Res., 84, 2235-2242, 1979. Society, Irvine, Calif., 1981. WESNOUSKY: SEISMICHAZARD IN CALIFORNIA 12,627
Hooke,R. L., Geomorphicevidence for late Wisconsinand Holo- Lajoie, K. R., and D. Keefer, Investigationsof the 8 November cene tectonicsdeformation, Death Valley, California, Geol. Soc. 1980 earthquake in Humboldt County, California, U.S. Geol. Am. Bull., 83, 2073-2098, 1972. Surv. Open File Rep., 81-397, 30 pp., 1981. Hope, R. A., The Blue Cut fault, southeastern California, U.S. Lajoie, K. R., A.M. Sarna-Wojcicki,and R. F. Yerkes, Quaternary Geol. Surv. Prof. Pap. 650-D, D 116-D 121, 1969. chronologyand rates of crustal deformation in the Ventura area, Imamura, A., Topographic changesaccompanying earthquakes or California,in Neotectonicsin SouthernCalifornia, compiled by J. volcanic eruptions, Publ. 25, pp. 1-143, Earthquake Invest. D. Cooper, pp. 43-51, Geological Societyof America, Cordilleran Comm. on Foreign Languages,Tokyo, 1930. Section, Anaheim, Califi, 1982. Ishimoto, M., and K. Iida, Observationssur les seismsenregistre Lamar, D. L., Structural evolution of the northern margin of the par le microseismographconstruite dernierment (I), Bull. Earth- Los AngelesBasin, Ph.D. thesis,Univ. of Calif., Los Angeles,142 quake Res. Inst., Univ. Tokyo, 17, 443-478, 1939 pp., 1961. Jennings,C. W., Fault map of California, California geologicdata Lamar, D. L., P.M. Medfield, and R. J. Proctor, Earthquake map series,Dep. of Conserv.,San Francisco,Calif., 1975. recurrence intervals on major faults in southern California, in Joyner, W. B., and T. E. Fumal, Predictive mapping of earthquake Geology,Seismicity and Environmental Impact, edited by D. E. ground motion, Evaluating Earthquake Hazards in the Los Moran, J. E. Slosson,R. O. Stone, and C. A. Yelverton, pp. Angeles Region-An Earth-Science Perspective,edited by J. I. 265-275, Associationof EngineeringGeologists, University Pub- Ziony, U.S. Geol. Surv. Prof. Pap., 1360, 203-220, 1985. lishers,Los Angeles,Califi, 1973. Junger,A., and H. C. Wagner, Geology of the Santa Monica and La Violette, J. W., G. E. Christenson,and J. C. Stepp, Quaternary San Pedro basins,California continentalborderland, U.S. Geol. displacementon the western Gafiock fault, southern California, Surv. Misc. Field Stud. Map, MF-820, 1977. in Geologyand Mineral Wealth of the California Desert, Dibblee Kahle, J. E., Megabrecciasand sedimentarystructures of the Plush Volume, edited by D. L. Fife, and A. R. Brown, pp. 449-456, Ranch Formation, northern Ventura County, California, M. A. South Coast GeologicalSociety, Santa Ana, Calif., 1980. thesis,125 pp., Univ. of Calif., Los Angeles, 1966. Lawson, A. C., et al., The California earthquake of April 18, 1906, Kanamofi, H., Mode of strain releaseassociated with major earth- in Report of the State Earthquake Investigation Commission, quakesin Japan,Annu. Ray. Earth Planet. Sci., 1, 2i3-239, 1973. vol. 1-2, 451 pp., Carnegieinstitution of Washington,Washing- Kanamofi, H., Mechanism of the 1983 Coalinga earthquakedeter- ton, D.C., 1908. mined from long-periodsurface waves, Calif Div. Mines Geol. Lee, W. H. K., R. F. Yerkes, and M. Samirenko, Recent earth- Spec.Publ., 66, 233-240, 1983. quake activity and focal mechanismsin the western Transverse Kanamori H., and C. R. Allen, Earthquake repeat time and average Ranges,California, U.S. Geol. Surv. Circ., 799-A, 37 pp., 1979. stressdrop, in Earthquake SourceMechanics, Geophys. Monogr. Legg, M. R., and M.P. Kennedy, Faulting offshoreSan Diego and Ser., vol. 37, edited by S. Das, J. Boatwright, and C. Scholz, pp. northern Baja California, in Earthquake and other Perils in the 227-235, AGU, Washington,D.C., 1986. San Diego Region, edited by P. L. Abbot and W. J. Elliot, pp. Kanamori, H., and J. Regan, Long-periodsurface waves, U.S. Geol. 29-46, GeologicalSociety of America, Boulder, Colo., 1979. Surv. Prof. Pap. 1254, 55-58, 1982. Lettis, W. R., Late Cenozoic stratigraphyand structure of the Kanamori, H., and G. S. Stewart, Mode of strain releasealong the western margin of the central San Joaquin Valley, California, Gibb's fracture zone, Mid-Atlantic Ridge, Phys. Earth Planet. U.S. Geol. Surv. Open File Rep., 82-526, 203 pp., 1982. Inter., I1, 312-332, 1976. Lisowski, M., and W. H. Prescott,Short-range distance measure- Kanamofi, H., and G. S. Stewart, Seismologicalaspects of the ments along the San Andreas fault system in central California, Guatemalaearthquake of February4, 1976, J. Geophys.Res., 83, 1975 to 1979, Bull. $eismol. $oc. Am., 71, 1607-1624, 1981. 3427-3434, 1978. Lindh, A. G., Preliminary assessmentof long-term probabilitiesfor Kawasaki, I., The focal processof the Kita-Mino earthquake of large earthquakes along selected fault segments of the San August 19, 1961, and its relationshipto a Quaternary fault, the Andreas fault system in California, U.S. Geol. Surv. Open File Hatogayu-Koikefault, J. Phys.Earth, 24, 227-250, 1975. Rep., 83-63, 1-15, 1983. Keaton, J. R., Geomorphic evidencefor late Quaternary displace- Lindh, A. G., and D. M. Boore, Control of rupture by fault ment along the Santa Ynez fault zone, Blue Canyon, eastern geometryduring the 1966 Parkfield earthquake,Bull. Seismol. Santa Barbara County, California (abstract), Geol. Soc. Am. Soc. Am., 71, 95-116, 1981. Abstr. Programs,10, 111, 1978. Liu, H., and D. V. Helmberger,The near-sourceground motion of Kelleher, J. A., Space-timeseismicity of the Alaska-Aleutianseismic the 6 August 1979, Coyote Lake, California,earthquake, Bull. zone, J. Geophys.Res., 75, 5745, 1970. Seismol. Soc. Am., 73, 201-218, 1983. Kelleher, J. A., Rupture zones of large south American earthquakes Louderback,G. D., Central California earthquakesof the 1830's, and somepredictions, J. Geophys.Res., 77, 2087-2103, 1972. Bull. Seismol.Soc. Am., 37, 33-74, 1947. Keller, E. A., M. S. Bonkowski, R. J. Korsch, and R. J. Salemon, Louie, J. N., C. R. Allen, D.C. Johnson,and P. C. Haase, Fault Tectonic geomorphologyof the San Andreas fault zone in the slip in southernCalifornia, Bull. Seismol.Soc. Am., 75, 811-834, southernIndio Hills, CoachellaValley, California, Geol. Soc. Am. 1985. Bull., 93, 46-56, 1982. Lowman, P. D., Vertical displacement on the Elsinore fault of Kennedy, M.P., Geology of the San Diego metropolitan area, Cali- southernCalifornia: Evidencefrom orbital photographs,J. Geol., fornia, Bull. Calif Div. Mines Geol., 200, 1-39, 1975. 88, 415-432, 1980. Kern, J.P., Origin and historyof upper Pleistocenemarine terraces, Lubetkin, L. K. C., Late Quaternaryactivity alongthe Lone Pine San Diego, California, Geol. Soc.Am. Bull., 88, 1553-1566, 1977. fault, OwensValley fault zone, California,M.S. thesis,85 pp., Kilbourne, R. T., C. W. Chesternman, and S. W. Wood, Recent Stanford Univ., Stanford Calif., 1980. volcanism in the Mono Balin-Long Valley region of Mono Lubetkin, L. K. C., and M. M. Clark, Late Quaternaryactivity County, California, Spec.Rep. Calif Div. Mines Geol., 150, 7-22, along the Lone Pine fault, eastern California (abstract),Eos, 1980. Trans. AGU, 61, 1042, 1980. King, G., and J. Nabelek, Role of fault bends in the initiation and Magistrale,H., C. Sanders,and H. Kanamori, The rupturepatterns termination of earthquake rupture, Science,228, 984-987, 1985. of large earthquakesin the San Jacinto fault zone, Eos Trans. King, N. E., and J. C. Savage, Strain-rate profile acrossthe Elsi- AGU, 65, 992, 1984. nore, San Jacinto, and San Andreas faults near Palm Springs, Matsuda, T., Surfacefaults associatedwith Kita-Izu earthquakeof California, 1973-81, Geophys.Res. Lett., 10, 55-57, 1983. 1930 in Izu Peninsula,Japan (in Japanese),in Izu Peninsula, Knuepfer, P. L., Geomorphic investigationsof the Vaca and editedby M. Hoshinoand H. Aoki, pp. 73-93, Tokai University Antioch fault systems,Solano and Contra Costa counties,Califor- Press,Tokyo, 1972. nia, M.S. thesis, 53 pp., Stanford Univ., Stanford, Calif., 1977. Matsuda, T., Surface faults associatedwith Nobi (Mino-Owari) Koto, B., On the causeof the great earthquake in central Japan, J. earthquake of 1891, Japan, Spec. Bull. Earthquake Res. Inst., Coll. Sci. Imp. Univ. Tokyo, 5, 295-353, 1893. Univ. Tokyo, 13, 85-126, 1974. Lahr, J. C., and C. D. Stephens,Alaska seismic zone: Possible Matsuda, T., Estimation of future destructiveearthquakes from example of non-linear magnitude distribution for faults, Earth- active faults on land in Japan, J. Phys. Earth, 25, suppl., S251- quake Notes, 53, 66, 1982. S260, 1977. 12,628 WESNOUSKY: SEISMICHAZARD IN CALIFORNIA
Matsuda, T., H. Yamazaki, T. Nakata, and T. Imaizumi, The sur- Morton, D. M., J. C. Matti, and J. C. Tinsley, Quaternaryhistory face faults associatedwith the Rikuu earthquake of 1896, Bull. of the Cucamongafault zone, southern California, Geol. Soc. EarthquakeRes. Inst., Univ. Tokyo, 55, 795-855, 1980. Am. Abstr. Programs, 14, 118, 1982. Matti, J. C., and D. M. Morton, Geologic history of the Banning Nakata, J. K., Distributionand petrologyof the Anderson-Coyote fault zone, southernCalifornia, Geol. Soc. Am. Abstr. Programs, Reservoir volcanic rocks, M.S. thesis, 105 pp., San Jose State 14, 184, 1982. Univ., San Jose,Calif., 1977. Matti, J. C., J. C. Tinsley, D. M. Morton, and L. D. McFadden, Nur, A., Nonuniform friction as a physical basis for earthquake Holocene faulting history as recorded by alluvial stratigraphy mechanics,Pure Appl. Geophys.,116, 1-26, 1978. within the Cucamongafault zone: A preliminary view, in Late Okal, E. A., A surface wave investigation of the Gobi-Altai Quaternary Pedogenesisand Alluvial Chronologiesof the Los (December 4, 1957) earthquake,Phys. Earth Planet. Inter., 12, Angeles and San Gabriel Mountain Areas, Southern California, 319-328, 1976. and Holocene Faulting and Alluvial Stratigraphy Within the Page, B. M., Basin-Rangefaulting in PleasantValley, Nevada, J. CucamongaFault Zone, edited by J. C. Tinsley, L. D. McFad- Geol., 43, 690-707, 1935. den, J. C. Matti, pp. 21-44, Geological Society of America, Cor- Page, B. M., Modes of Quaternary tectonic movement in the San dilleran Section,Anaheim, Calif., 1982. Francisco Bay region, California, ProceedingsConference on Matti, J. C., D. M. Morton, and B. F. Cox, Distribution and geolo- EarthquakeHazards in the Eastern San FranciscoBay Area, gic relations of fault systems in the vicinity of the Central editedby E. W. Hart, Calif Div. Mines Geol. Spec.Publ., 62, 1- TransverseRanges, southern California, U.S. Geol. Surv. Open 16, 1982. File Rep., 85-365, 27 pp., 1985. Pampeyan,E. H., P. W. Harsh, and J. M. Coakley,Recent breaks McCulloch, D. S., H. G. Greene, and K. S. Heston, A summary of along Maacana fault zone, Laytonville to Hopland, California, the geology and geologic hazards in proposed lease sale 53, cen- U.S. Geol. Surv. Map, MF-1217, 1981. tral California outer continental shelf, U.S. Geol. Surv. Open File Patterson,R. H., Tectonic geomorphologyand neotectonicsof the Rep., 80-1095, 76 pp., 1980. SantaCruz Island fault, Santa Barbaracounty, California, M. A. McGill, J. T., Recent movement on the Potrero Canyon fault, thesis,Univ. of Calif., SantaBarbara, 141 pp., 1979. Pacific Palisadesarea, Los Angeles,California, U.S. Geol. Surv. Pinault, C. T., and T. K. Rockwell, Rates and senseof Holocene Prof Pal)., 1175, 258-259, 1981. faulting on the southern Elsinore fault: Further constraints on McGill, J. T., Preliminary geologic map of the Pacific Palisades the distribution of dextral shear between the Pacific and North area, City of Los Angeles, California, scale 1:4800, U,S. Geol. American plates, Geol. Soc. of Am. Abstr. Programs,16, 624, Surv. Open File Rep., 82-194, 15 pp., 1982. 1984. Meisling, K. E., Neotectonicsof the north frontal fault system of Plafker,G., T. Hudson,T. Bruns,and M. Rubin, Late Quaternary the San Bernardino Mountains, southernCalifornia: Cajon Pass offsetsalong the Fairweatherfault and crustalplate interactionsin to Lucerne Valley, Ph.D. thesis, 394 pp., Calif. Inst. of Tech., southernAlaska, Can. J. Earth Sci., 15, 805-816, 1978. Pasadena, 1984. Poland, J. F., and A.M. Piper, Ground water geologyof the coastal Mezger, L., and R. J. Weldon, Tectonic implicationsof the Quater- zone Long Beach-Santa Ana area, California, U.S. Geol. Surv. nary history of lower Lytle Creek, southeastSan Gabriel Moun- Water SupplyPap., 1109, 126 pp., 1956. tains, Geol. Soc.Am. Abstr. Programs,15, 418, 1983. Prescott,W. H., and M. Lisowski,Deformation along the Hayward Michael, E. D., Large lateral displacementon Garlock fault, Cali- and Calaverasfaults: Steady aseismic slip or strain accumulation, fornia, as measured from offset fault system, Geol. Soc. Am. ProceedingsConference on Earthquake Hazards in the Eastern Bull., 77, 111-114, 1966. San FranciscoBay Area, editedby E. W. Hart, Calif Div. Mines Mikumo, T., Faulting mechanism of the Gifu earthquake of Sept. Geol. Spec.Publ., 62, 261-269, 1982. 9, 1969, and some relatedproblems, J. Phys. Earth, 21, 191-212, Prescott, W. H., and S.-B. Yu, Geodetic measurement of horizontal 1973. deformationin the northern San FranciscoBay region, Califor- Mikumo, T., Some considerationson the faulting mechanismof nia, J. Geophys.Res., 91, 7475-7484, 1986. the southeasternAkita earthquakeof October 16, 1970, J. Phys. Prescott, W. H., M. Lizowski, and J. C. Savage, Geodetic Earth, 22, 87-108, 1974. measurementof crustal deformation on the San Andreas, Hay- Mikumo, T., and M. Ando, A searchinto the faulting mechanism ward and Calaveras faults near San Francisco, California, J. Geo- of the 1891 great Nobi earthquake,J. Phys. Earth, 24, 63-87, phys. Res., 86, 10,853-10,869, 1981. 1976. Proctor, R. J., R. Crook, Jr., M. H. McKeown, and R. L. Moresco, Miller, F. K., and D. M. Morton, Potassium-argongeochronology Relation of known faults to surfaceruptures, 1977 San Fernando of the easternTransverse Ranges and southernMojave Desert, earthquake, southern California, Geol. Soc. Am. Bull., 83, 1601- southernCalifornia, U.S. Geol. Surv. Prof Pap., 1151, 30, 1980. 1618, 1972. Miller, S. T., Geology and mammalian biostratigraphyof a part of Rasmussen,G. S., Geologicfeatures and rate of movementalong the northern Cady Mountains, Mojave Desert, California, U.S. the south branch of the San Andreas fault, San Bernardino, Cali- Geol. Surv. Open File Rep., 80-8 78, 122 pp., 1980. fornia, in Neotectonicsin SouthernCalifornia, compiledby J. D. Millman, D. E., and T. K. Rockwell, Lateral offset of mid and late Cooper, pp. 109-114, GeologicalSociety of America, Cordilleran Quaternary deposits along the northern Elsinore fault, southern Section, Anaheim, Calif., 1982. California, Geol. Soc.Am. Abstr. Programs,17, 370, 1985. Reasenberg,P., and W. L. Ellsworth, Aftershocksof the Coyote Minster, J. B., and T. H. Jordan, Present-dayplate motions,J. Geo- Lake, California, earthquake of August 6, 1979: A detailed phys. Res., 83, 5331-5354, 1978. study,J. Geophys.Res., 87, 10,637-10,655, 1982. Minster, J. B., and T. H. Jordan,Vector constraintson Quaternary Reid, H. F., The California earthquake of April 18, 1906, the deformation of the western United States,in Tectonicsand Sedi- mechanicsof the earthquake,in The State EarthquakeInvestiga- mentationAlong the California Margin, edited by J. K. Crouch, tion Committee Report, vol. 2, 192 pp., Carnegie Institute of and S. B. Burcham, pp. 1-16, Pacific Coast Section, Society for Washington, D.C., 1910. Economic Paleontologistsand Mineralogists,Bakersfield, Calif., Richins,W. D., R. B. Smith, C. J. Langer,J. E. Zollweg,J. J. King, 1984. and J. C. Pechman, The 1983 Borah Peak, Idaho, earthquake: Molnar, P., Earthquake recurrence intervals and plate tectonics, Relationshipof aftershocksto the main shock,surface faulting, Bull. Seismol. Soc. Am., 69, 115-134, 1979. and regionaltectonics, U.S. Geol. Surv. Open File Rep., 85-290, Moore, G. W., and M.P. Kennedy, Quaternaryfaults at San Diego 285-310, 1985. Bay, California: J. Res. U.S. Geol. Surv., 3, 589-595, 1975. Richter, C. F., Elementary Seismology,768 pp., W. H. Freeman, Morton, D. M., Synopsisof the geologyof the easternSan Gabriel New York, 1958. Mountains, southern California, Spec. Rep. Calif Div. Mines Richter, C. F., C. R. Allen, and J. M. Nordquist, The Desert Hot Geol., 118, 170-176, 1975. Springs earthquakes and their tectonic environment, Bull. Morton, D. M., F. K. Miller, and C. C. Smith, Photo- $eismol. $oc. Am., 48, 315-337, 1958. reconnaissancemaps showingyoung-looking fault featuresin the Riddihough, R., Gorda plate motions from magnetic anomaly southern Mojave Desert, California, U.S. Geol. Surv. Misc. Field analysis,Earth Planet. Sci. Lett., 51, 163-170, 1980. Stud. Map, MF-1051, 1980. Roberts, C. T., and T. L. T. Gross, Late Cenozoic extensional WESNOUSKY.' SEISMICHAZARD IN CALIFORNIA 12,629
strain ratesand directionsin the Honey Lake-EagleLake region, Schwartz, D. P., and K. J. Coppersmith, Fault behavior and charac- northeastCalifornia, Eos, Trans.AGU, 63, 1107, 1982. teristic earthquakes: Examples from the Wasatch and San Rockwell, T. K., Soil chronology,geology, and neotectonicsof the Andreas fault zones,J. Geophys.Res., 89, 5681-5698, 1984. north-central Ventura basin, California, Ph.D. thesis, Univ. of Schwartz, D. P., and A. J. Crone, The 1983 Borah Peak earth- Calif., Santa Barbara, 1983. quake: A calibration event for quantifying earthquake recurrence Rockwell, T. K., E. A. Keller, M. N. Clark and D. L. Johnson, and fault behavior on Great Basin normal faults, Proceedingsof Chronologyand ratesof faulting of Ventura River terraces,Cali- Workshop XXVIII on the Borah Peak, Idaho, Earthquake, U.S. fornia, Geol. Soc.Am. Bull., 95, 1466-1474, 1984. Geol. Surv. Open File Rep., 85-290, 153-160, 1985. Rockwell, T. K., D. L. Lamar, R. S. McElwain, and D. E. Mill- Segall, P., and D. D. Pollard, Mechanics of discontinuousfaults, J. man, Late Holocene recurrent faulting on the Glen Ivy north Geophys.Res., 85, 4337-4350, 1980. strand of the Elsinore fault, southernCalifornia, Geol. Soc. Am. Sharp, R. V., San Jacinto fault zone in the peninsular ranges of Abstr. Programs,17, 404, 1985. southernCalifornia, Geol. Soc. Am. Bull., 78, 705-730, 1967. Rogers,G. C., Juan de Fuca plate map: Seismicityanalysis, Open Sharp, R. V., Map showing recent tectonic movement on the Con- File Rep. 80-3, Seismol.Serv., Can. Earth Phys.Branch, Sidney, cord fault, Contra Costa and Solano counties, California, U.S. B.C., Canada, 1980. Geol. Surv. Misc. Field Stud. Map, MF-505, 1973. Roquemore,G. R., Active faults and associatedtectonic stressin Sharp, R. V., En echelon fault patternsof the San Jacinto fault the Coso Range, California. Rep. NWC JP 6270, 101 pp., Nav. zone, Spec.Rep. Calif. Div. Mines GeoL, 118, 147-151, 1975a. WeaponsCent., China Lake, Calif., 1981. Sharp, R. V., Displacement on tectonic ruptures, Bull. Calif. Div. Rust, D. J., Radiocarbon dates for the most recent prehistoric Mines Geol.,196, 187-194,1975b. earthquake and for late Holocene slip rates. San Andreas fault in Sharp, R. V., 1940 and prehistoric earthquake displacementson the part of the TransverseRanges north of Los Angeles(abstract), Imperial fault, Imperial and Mexicali Valleys, in Proceedings Geol. Soc.Am. Abstr. Programs,14, 229, 1982a. Symposium on Human Settlementson the San Andreas Fault, Rust, D. 3., Trenching studiesof the San Andreasfault bordering pp. 68-81, California Seismic Safety Commission, Sacramento, western Antelope Valley, southern California, in Summaries of 1980. Technical Reports, vol. XIV, U.S. Geol. Surv. Open File Rep., Sharp, R. V., Variable rates of late Quaternary strike slip on the 82-840, 89-91, 1982b. San Jacinto fault zone, southernCalifornia, J. Geophys.Res., 86, Rust, D. J., Evidencefor uniformityof largeearthquakes in the '•ig 1754-1762, 1981. bend" of the San Andreas fault, Eos Trans. AGU, 63, 1030, Sharp, R. V., Comparisonof the 1979 surfacefaulting to earlier dis- 1982c. placementsin central Imperial Valley, The Imperial Valley, Cali- Sage, O. J., Paleocene geographyof the Los Angeles region, fornia, Earthquake, October 15, 1979, U.S. Geol. Surv. Prof. Proceedingsof the Conference on Tectonic Problems of the San Pap., 1254, 213-221, 1982. Andreas Fault System, edited by R. L. Kovach, and A. Nur, Sharp, R. V., and J. J. Lienkaemper, Preearthquake and postearth- StanfordUniv. Publ. Geol. Sci., 13, 348-357, 1973. quake nearfield leveling across the Imperial fault and Brawley Saint-Amand, P., and G. R. Roquemore, Tertiary and Holocene fault zone, The Imperial Valley, California, Earthquake of developmentof the southernSierra Nevada and Coso Range, October 15, 1979, U.S. Geol. Surv. Prof. Pap., 1254, 169-182, California, Tectonophysics,52, 409-410, 1979. 1982. Salyards, S. L., Patterns of offset associatedwith the 1983 Borah Sharp, R. V., J. L. Lienkaemper, M. G. Bonilla, D. B. Burke, B. F. Peak, Idaho, earthquake and previous events, Proceedingsof Fox, D. G. Herd, D. M. Miller, D. M. Morton, D. J. Pont, M. J. Workshop XXVIII on the Borah Peak, Idaho, Earthquake, U.S. Rymer, J. C. Tinsly, J. C. Yound, J. E. Kahle, E. W. Hart and Geol. Surv. OpenFile Rep., 85-290, 59-75, 1985. K. E. Sieh, Surface faulting in the central Imperial Valley, The Sanders,C. O., and H. Kanamori, A seismotectonicanalysis of the Imperial Valley, California, Earthquake of October 15, 1979, U. Anza seismicgap, San Jacinto fault zone, southernCalifornia, J. S. Geol. Surv. Prof. Pap., 1254, 119-144, 1982. Geophys.Res., 89, 5873-5890, 1984. Shedlock, K. M., R. K. McGuire, and D. G. Herd, Earthquake Sarna-Wojcicki,A.M., and R. F. Yerkes, Comment on article by recurrencein the San FranciscoBay region, California, from fault R. S. Yeats on "Low-shake faults of the Ventura basin, slip and seismic moment, U.S. Geol. Surv. Open File Rep., 80- California," in Neotectonicsin Southern California, compiled by 999, 20 pp., 1980. J. D. Cooper, pp. 17-19, Geological Society of America, Cordil- Shimazaki, K., Nemuro-Oki earthquake of June 17, 1973: A leran Section, Anaheim, Calif., 1982. lithosphericrebound at the upper half of the interface,Phys. Sarna-Wojcicki,A.M., K. M. Williams, and R. F. Yerkes, Geology Earth Planet. Inter., 9, 314-327, 1974. of the Ventura fault, Ventura County, California, scale 1:6,000, Shimazaki, K., and P. Somerville, Static and dynamic parameters U.S. Geol. Surv. Misc. Field Stud. Map, MF-781, 1976. of the Izu-Oshima, Japan, earthquake of Jan. 14, 1978, Bull. Sarna-Wojcicki, A.M., K. R. Lajoie, S. W. Robinson, and R. F. Seismol. Soc. Am., 69, 1343-1378, 1979. Yerkes, Recurrent Holocene displacement on the Javon Canyon Sibson,R. H., Fault zone models,heat flow, and the depth distribu- fault, rates of faulting and regional uplift, western Transverse tion of earthquakesin the continentalcrust of the United States, Ranges,California, Geol.Soc. Am. Abstr. Programs,11, 125, 1979. Bull. Seismol. Soc. Am., 72, 151-163, 1982. Savage,J. C., and R. O. Burford, Geodetic determination of rela- Sibson,R. H., Rupture interactionswith fault jogs, in Earthquake tive plate motion in central California, J. Geophys.Res., 78, SourceMechanics, Geophys. Monogr., vol. 37, edited by S. Das, 832-845, 1973. J. Boatwright,and C. H. Scholz,pp. 157-167, Washington,D.C., Savage,J. C., and W. H. Prescott,Strain accumulation on the San 1986. Jacintofault near Riverside,California, Bull. Seismol. Soc. Am., Sieh, K. E., Prehistoriclarge earthquakesproduced by slip on the 66, 1749-1754, 1976. San Andreasfault at Pallett Creek, California, J. Geophys.Res., Savage,J. C., W. H. Prescott,and W. T. Kinoshita, Geodimeter 83, 3907-3939, 1978a. measurementsalong the San Andreas fault, ProceedingsConfer- Sieh, K. E., Slip along the San Andreas fault associatedwith the ence on Tectonic Problemsof the San AndreasFault System, great 1857 earthquake,Bull. Seismol. Soc. Am., 68, 1421-1448, StanfordUniv. Publ. Geol. Sci., 13, 44-53, 1973. 1978b. Savage,J. C., W. H. Prescott,M. Lisowski,and N. King, Geodetic Sieh, K. E., Central California foreshocksof the great 1857 earth- measurementsof deformation near Hollister, California, 1971- quake, Bull. Seismol.Soc. of Am., 68, 1731-1749, 1978c. 1978, J. Geophys.Res., 84, 7599-7615, 1979. Sieh, K. E., Lateral offsetsand revised dates of large prehistoric Scholz, C. H., and T. Kato, The behavior of a convergentplate earthquakesat Pallett Creek, southern California, J. Geophys. boundary: Crustal deformation in the South Kanto District, Res., 89, 7641-7670, 1984. Japan, J. Geophys.Res., 83, 783-797, 1978. Sieh, K. E., and R. H. Jahns,Holocene activity of the San Andreas Scholz,C. H., M. Wyss,and S. W. Smith, Seismicand aseismicslip at Wallace Creek, California, Geol. Soc. Am. Bull., 95, 883-896, on the San Andreasfault, J. Geophys.Res., 74, 2049-2069, 1969. 1984. Scholz, C. H., C. A. Aviles, and S. G. Wesnousky, Scaling Silver,E. A., Tectonicsof the Mendocinotriple junction, Geol. Soc. differencesbetween large intraplate and interplate earthquakes, Am. Bull., 82, 2965-2978, 1971. Bull. Seismol.Soc. Am., 76, 65-70, 1986. Silver, E. A., Structuralinterpretation from free-air gravity on the 12,630 WESNOUSKY:SEISMIC HAZARD IN CALIFORNIA
California continental margin, 35ø to 40ø N, Geol. Soc. Am. Toppozada, T. R., and D. L. Parke, Areas damaged by California Abstr. Programs,9, 524, 1974. earthquakes,1900-1949, Calif Div. Mines Geol. Open File Rep., Silver, E. A., The San Gregorio-Hosgrifault zone: An overview, 82-i7 SAC,65 pp., Sacramento,Calif., 1982. Spec.Rep. C•tlif.Div. Mines Geol.,137, 1-2, 1978 Toppozada, T. R., C. R. Real, and D. L. Parke, Preparation of Singh, S. K., L. Astiz, and J. Havskov, Seismicgaps and recl•rrence isoseismalmaps and summaries of reported effectsfor pre-1900 California earthquakes,Calif Div. Mines Geol. Open File Rep., Aperiods reexamination,oflarge earthquakesBull. Seismol.alongSoc. theAm., Mexican 71, 827-843,subdqction 198 •one: . 81-'11 SAC, 182 pp., Sacramento, Calif., 1981. Singh, S. K., M. Rodriguez,and L. Esteva,Statistics of small earth- Toppozada, T. R., C. R. Real, and D. L. Parke, Earthquake history quakes and frequency of occurrenceof large earthquakesalong of California, Calif Geol., 39, 27-33, 1986. the Mexican subduction zone, Bull. Seismol. Soc. Am., 73, Trifunac, M.D., Tectonic stressand the source mechanism of the 1779-1798, 1983. Imperial Valley, California, earthquake of 1940, Bull. Seismol. Slemmons, D. B., Geological effects of the Dixie Valley-Fairview Soc. Am., 62, 1283-1302, 1972. Peak, Nevada, earthquakesof December 16, 1954, Bull. Seismol. Troxel, B. W., and P. R. Butler, Tertiary and Quaternary fault his- Soc. Am., 47, 353-373, 1957. tory of the intersectionof the Garlock and Death Valley fault Slemmons, D. B., State of the art for assessingearthquake hazards zones, southern Death Valley, California, Summaries of Techni- in the United States: Determination of the design earthquake cal Reports, National Earthquake Hazards Reduction Program, magnitude from fault length and maximum displacementdata, U.S. Geol. Surv. Open File Rep., 80-6, 45-47, 1980. 109 pp., U.S. Army Eng. WaterwaysExp. St., Vicksburg,Miss., Tsai, Y. B., and K. Aki, Simultaneousdetermination of the seismic 1977. moment and attenuation of seismic surface waves, Bull. Seismol. Smith, G. I., Large lateral displacement on Garlock fault, Califor- Soc. Am., 59, 275-287, 1969. nia, as measured from offset dike swarms, Am. Assoc. Pet. Geol. Urhamner, R. A., Observations of the Coyote Lake, California Bull., 46, 85-104, 1962. earthquakesequence of August 6, 1979, Bull. Seismol. Soc. Am., Smith, G. I., Holocene movement on the Garlock fault, Geological 70, 559-570, 1980. Survey Research,U.S. Geol. Surv. Prof Pap., 975, 202, 1975. Urhamner, R. A., R. D. Darragh, and B. Bolt, The 1983 Coalinga Smith, G. I., Holocene offset and seismicity along the Panamint earthquakesequence: May 2 through Aug. 1, Spec. Rep. Calif Valley fault zone, western Basin and Range Province, California, Div. Mines Geol., 66, 221-232, 1983. br Tectonophysics,52, 411-415, 1979. Utsu, T., Aftershocksand earthquake statistics(III), J. Fac. Sci., Smith, G. I., B. W. Troxel, C. H. Gray, Jr., and R. Von Huene, Hokkaido Univ. Ser. 7, 3, 379-441,1971. Geologic reconnaissanceof the Slate Range, San Bernardino and von Seggern,D., A random stressmodel for seismicitystatistics and Inyo counties,California, Spec.Rep. Calif Div. Mines Geol., 96, earthquakeprediction, Geophys.Res. Lett., 7, 637-664, 1980. 33 pp., 1968. Wallace, R. E., Earthquake recurrence intervals on the San Andreas Stein, R. S., and W. Thatcher, Seismic and aseismic deformation fault, Geol. Soc. Am. Bull., 81, 2875-2890, 1970. associatedwith the 1952 Kern County, California, earthquake Wallace, R. E., Patterns of faulting and seismicgaps in the Great and relationshipto Quaternary history of the White Wolf fault, J. Basin province, Proceedingsof Conference VI, Methodology for Geophys.Res., 86, 4913-4928, 1981. Identifying Seismic Gaps, U.S. Geol. Surv. Open File Rep., 78- Sykes,L. R., Aftershockzones of great earthquakes,seismicity gaps, 943, 857-868, 1978. and earthquake prediction for Alaska and the Aleutians, J. Geo- Wallace, R. E., and R. A. Whitney, Late Quaternary history of the phys. Res., 76, 8021-8041, 1971. Stillwaterseismic gap, Nevada, Bull. Seismol. Soc. Am., 74, 301- Sykes, L. R., and S. P. Nishenko, Probabilities of occurrence of 314, 1984. large plate rupturing earthquakes for the San Andreas, San Weber, F. H., Jr., Total right lateral offset along the Elsinore fault Jacinto, and Imperial faults, California, J. Geophys.Res., 89, zone, southern California, paper presentedat 73rd Annual Meet- 5905-5927, 1984. ing, Cordilleran Sect., Geol. Soc. of Am., Sacramento, Calif., Sykes, L. R., and R. C. Quittmeyer, Repeat times of great earth- 1977. quakesalong simple plate boundaries, in Earthquake Prediction: Weber, F. H., Jr., Geological features related to character and An International Review, Maurice Ewing Ser., vol. 4, edited by recency of movement along faults, north-central Los Angeles D. W. Simpson and P. G. Richards, pp. 297-332, AGU, County, California, Earthquake Hazards Associated With the Washington,D.C., 1981. Verdugo-Eagle Rock and Benedict Canyon Fault Zones, Los Sylvester,A. G., and A. C. Darrow, Structureand neotectonicsof AngelesCounty, California, edited by F. H. Weber,Jr., J. H. the westernSanta Ynez fault systemin southernCalifornia, Tec- Bennett, R. H. Chapman, G. W. Chase,and R. B. Saul, Calif tonophysics,52, 389-405, 1979. Div. Mines Geol. Open File Rep., 80-10 LA, BI-B116, 1980. Takeo, M., K. Abe, and H. Tsuji, Mechanism of the Shizuoka Weber, G. E., Geologicinvestigation of the marine terracesof the earthquakeof July 11, 1935 (in Japanesewith English abstract), San Simeon region and Pleistoceneactivity on the San Simeon J. Seismol. Soc. Jpn., 32, 423-434, 1979. fault zone, San Luis Obispo County, California, final technical Tanimoto, T., and H. Kanamori, Linear programmingapproach to report contract, 14-08-0001-18230, 66 pp., U.S. Geol. Surv., moment tensor inversion of earthquake sourcesand some tests Menlo Park, Calif., 1981. on the three-dimensionalstructure of the upper mantle, Geophys. Weber, G. E., and W. R. Cotton, Geologic investigation of J. R. Astron. Soc., 84, 413-430, 1986. recurrenceintervals and recency of faulting along the San Gre- Taylor, G. C., and W. A. Bryant, Surfacerupture associatedwith gorio fault zone, San Mateo County, California, U.S. Geol. Surv. the Mammoth Lakes earthquakesof 25 and 27 May, 1980, Spec. OpenFile Rep., 81-263, 133 pp., 1981. Rep. Calif Div. Mines Geol., 150, 49-68, 1980. Weber, G. E., and K. R. Lajoie, Map of Quaternaryfaulting along Thatcher, W., Strain accumulation and releasemechanism of the the San Gregoriofault zone, San Mateo and SantaCruz counties, 1906 San Franciscoearthquake, J. Geophys.Res., 80, 4862-4872, California, scale 1:24,000, U.S. Geol. Surv. Open File Rep., 80- 1975. 907, 1980. Thatcher, W., J. A. Hileman, and T. C. Hanks, Seismicslip distri- Weldon, R. J., Climatic control for the formation of terracesin bution along the San Jacintofault zone, southernCalifornia, and CajonCreek, southern California (abstract), Geol. Soc. Am. Abstr. its implications,Geol. Soc.Am. Bull., 86, 1140-1146, 1975. Programs,15, 429, 1983. Thatcher, W., T. Matsuda, T. Kato, and J. B. Rundle, Lithospheric Weldon, R., and E. Humphreys, A kinematic model of California, loadingby the 1896 Rikuu earthquakein northernJapan: Impli- Tectonics,5, 33-48, 1986. cationsfor plate flexure and asthenosphericrheology, J. Geophys. Weldon, R. J., and K. E. Sieh, Holocene rate of slip along the San Res., 85, 6429-6435, 1980. Andreasfault and related tilting near Cajon Pass,southern Cali- Tocher, D., Movement on the Rainbow Mountain fault, Bull. fornia, Geol. Soc. Am. Abstr. Programs, 12, 159, 1980. Seismol. Soc. Am., 46, 10-14, 1956. Weldon, R. J., and K. E. Sieh, Holocene rate of slip and tentative Toppozada, T. R., History of earthquake damage in Santa Clara recurrence interval for large earthquakeson the San Andreas County and comparisonof the 1911 and 1984 earthquakesin the fault, Cajon Pass,southern California, Geol. Soc. Am. Bull., 96, in the Morgan Hill, California earthquake, Calif Div. Mines 793-812, 1985. Geol. Spec.Publ., 68, 237-248, 1984. Wesnousky,S. G., C. H. Scholz,and K. Shimazaki,Deformation WESNOUSKY.'SEISMIC HAZARD IN CALIFORNIA 12,631
of an island arc: Rates of moment releaseand crustal shortening Yeats, R. S., Stratigraphyand paleogeographyof the Santa Susana in intraplace Japan determined from seismicity and Quaternary fault zone, Transverse ranges, California, in Cenozoic fault data, J. Geophys.Res., 87, 6829-6852, 1982. Paleogeographyof the Western United States, Pacific Coast Wesnousky, S. G., C. H. Scholz, K. Shimazaki, and T. Matsuda, PaleogeographySymposium, edited by J. M. Armentrout, M. R. Earthquake frequency distribution and the mechanicsof faulting, Cole, H. Ferbest,Jr., pp. 191-204, Los Angeles,Califi, 1979. J. Geophys.Res., 88, 9331-9340, 1983. Yeats, R. S., Low-shakefaults of the Ventura basin, California, in Wesnousky, S. G., C. H. Scholz, K. Shimazaki, and T. Matsuda, Neotectonicsof SouthernCalifornia, compiled by J. D. Cooper, Integrationof geologicaland seismologicaldata for the analysisof pp. 3-23, Geological Society of America, Cordilleran Section, seismichazard: A case study of Japan, Bull. Seismol. Soc. Am., Anaheim, Califi, 1982. 74, 687-708, 1984. Yeats, R. S., Large-scaleQuaternary detachments in Ventura Basin, Whitney, J. D., The Owens Valley earthquake, Overland Mon., 9, southernCalifornia, J. Geophys.Res., 88, 569-583, 1983a. (2 and 3), 130-140, 226-278, 1872. Yeats, R. S., Simi: A structuralessay, in CenozoicGeology of the Willis, B., A fault map of California, Bull. Seismol. Soc. Am., 13, Simi Valley Area, SouthernCalifornia, edited by S. R. Squires 1-12, 1923. and M. V. Filewicz, pp. 233-240, PacificCoast Section,Society Wilson, J. T., Foreshocksand aftershocksof the Nevada earthquake for Economic Paleontologistsand Mineralogists,Bakersfield, of December 20, 1932, and the Parkfield earthquake of June 7, Calif., 1983b. 1934, Bull. Seismol. Soc. Am., 26, 189-194, 1936. Yeats, R. S. and and, D. J. Olson, Alternate fault model for the Witkind, I. J., Reactivated faults north of Hebgen Lake, U.S. Geol. Santa Barbara, California, earthquakeof 13 August 1978, Bull., Surv. Prof Pap., 435, 37-50, 1964. Seismol.Soc. Am., 74, 1545-1553, 1984. Wong, I. G., Reevaluation of the 1892 Winters, California, earth- Yeats, R. S., M. N. Clark, E. A. Keller, and T. K. Rockwell, Active quakes based upon comparison with the 1983 Coalinga earth- fault hazard in southern California: Ground rupture versus quake, Eos Trans. AGU, 65, 996, 1984. seismicshaking, Geol. Soc.Am. Bull., 92, 189-196, 1981. Woodward-Clyde Consultants,Earthquake evaluation studiesof the Yerkes,R. F., and C. M. Wentworth,Structure, Quaternary history, Auburn Dam area, report prepared for U.S. Bureau of Reclama- and general geology of the Corral Canyon area, Los Angeles tion, 8 vol., San Francisco,Calif., 1977. County, California, U.S. Geol. Surv., Open File Rep., 864, 215, Woodward-Clyde Consultants, Evaluation of the potential for 1965. resolvingthe geologicand seismicissues at the Humboldt Bay Yerkes, R. F., T. H. McCulloch, J. E. Schoellhamer,and J. G. Power Plant Unit No. 3, report prepared for Pacific Gas and Vedder, Geology of the Los Angeles Basin, California--An intro- Electric Co., 74 pp., San Francisco,Calif., 1980. duction, U.S. Geol. Surv. Prof Pap., 420-A, 57, 1965. Wright, L. A., and B. W. Troxel, Limitations on right-lateral, Yerkes, R. F., and W. H. K. Lee, Faults, fault activity, epicenters, strike-slip displacement, Death Valley and Furnace Creek fault focal depths, and focal mechanisms, 1970-1975 earthquakes, zones, California, Geol. Soc. Am. Bull., 78, 933-950, 1967. western Transverse Ranges, California, scale 1:250,000, U.S. Wright, R. H., D. H. Hamilton, T. D. Hunt, M. L. Traubenik, and Geol. Surv. Misc. Field Stud. Map, MF-1032, 1979. R. J. Shlemon, Character and activity of the Greenville structural Yerkes, R. F., H. G. Greene, J. C. Tinsley, and K. R. Lajoie, trend, ProceedingsConference on Earthquake Hazards in the Seismotectonicsetting of the Santa Barbara Channel area, south- Eastern San FranciscoBay Area, edited by E. W. Hart, Calif. ern California, U.S. Geol. Surv. Misc. Field Map, 1169, 1981. Div. Mines Geol. Spec.Publ., 62, 187-196, 1982. Wright, T. L., E. S. Parker, and R. C. Erickson, Stratigraphicevi- dence for timing and nature of late Cenozoic deformation in Los S. G. Wesnousky, TennesseeEarthquake Information Center, Angelesregion, California (abstract),Am. Assoc.Pet. Geol. Bull., Memphis State University, Memphis, TN 38152 57, 813, 1973. Wyss, M., Preliminary sourceparameter determination of the San Fernando earthquake, U.S. Geol. Surv. Prof Pap., 733, 38-40, 1971. (ReceivedAugust 13, 1985; Yeats, R. S., Newport-Inglewood fault zone, Los Angeles Basin, revised April 21, 1986; California, Am. Assoc.Pet. Geol. Bull., 57, 117-135, 1973. acceptedMay 29, 1986.)