caliifornia geology magazine jan-feb 1993

8/7/2019 Caliifornia Geology Magazine Jan-Feb 1993

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. 27. 28

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THE LANDERS-BIG BEAR EARTHQUAKE SEQUENCEAND ITS FELT EFFECTS .SURFACE FAULTING ASSOCIATED WITH THE JUNE 1992LANDERS EARTHQUAKE. CALIFORNIA 10ROCKFALLS AND SURFACE EFFECTS OTHERTHAN FAULTING .SURFACE RUPTURE ALONG A PORTION OFTHE EMERSON FAULT .DMG CLEARINGHOUSE FOR THE JUNE 28. 1992LANDERS AND BIG BEAR EARTHQUAKES .TEACHER FEATURE .CALIFORNIA GEOLOGY SUBSCRIPTION AND CHANGE OFADDRESS FORM 29OMG PUBLICATIONS REQUEST FORM . 30DMG OPEN-FILE REPQRT RELEASES 31

In This Issue I

0Ms00n 01 """ ' " '" Geology JAMES F DAVISStare GeoIogISI

CALIFORNIAGEOLOGY

A PUBLICATION OF THEDEPARTMENT OF CONSERVATIONDIVISION OF MINES AND GEOLOGY$W e 01 c.wom.r. PETE WILSON

GovernorThe Resourcu AoencY DOUGLAS P WHEELER

Sllaelary for RelWu/'CfIsD.\)anmenlol eons-aeoon eDWARDG. HEIDIG

Drrector

CALIFORNIA GEOlOGY

Bay A I . RegoonIII 0Il0ce 1145 Miotke! SI/"'"San Frarcsco. CA jMl031!>13415S571SOO

801 K Street 12th Floor loiS 1:l30s.:ramento. CA 958'.3531916-"51825

JANUARY/FEBRUARY 1993Volume 461Number \CGEOA46(1) 132 (\993)

COlier photo: View 10 Ille southeast. A complex zone 01 Sl..II1ace rupturealong the Emerson Fault e.lends from bottom center 01 photo to just beyondsmall playa (sag pond) al cenler 01 photo. The uplifted older alluvial fandeposits Immediately east and north 01 the small playa appear to be offsetright-Ialerally about 1.000 leel (300m). South 01 the playa, the rupture zoneextends soullleastward Into the mountain range. Emerson Lake playa is Inupper left quadrant of photo. Johnson Valley and Means lake are viSIble Inupper right corner. west 01 mountain range. light-colored, narrow lines aredirt bike and Jeep trails Photo by I.K. CurtiS SeflliCes. Inc.. July 3. 1992.

AMERICAN SOCIElY FOR SURFACE MININGAND REClAMAnON10th Annual Meeting and TTade Show

May 16-19. 1993Spokane. Washing/onPrograms: Revegetation. soils and overburden. AMD coal and metal. surfacehydrology. subsurface hydrology. landscape architecture, gold mining reclamation. wetlands. tailings reclamation. policy and regulations. philosophies of reclamation. innovative waste disposal. analytic and mensurationaltechniques andstandards.Symposium: Ecological restoration of disturbed lands.Workshops: Wetlarxl design for treatment of add rock drainage. Applicationsof computer aided design/engineering to storm-water managemenl and sediment conlrol systems. Geochemical modeling.Tours: Mine and superfund site tours will be conducted.Sponsored by: Washington State University. Bureau of Mines. Office of Surface Mining. Bureau 01 Land Management. Forest Service. Bureau of IndianAffairs. and the Northwest: Mining Association.For more infonnation. contad:

Cathy DoerrShoWorks. Inc.

702 S. WashingtonSpokane. WA 99204-2524'Zl' (509) 838-8755. FAX (509) 838-2838

Elise MallisonLena TabllioPeggy WalkerJell Tambert

CALlFQFlNIA GEOlOGY (ISSN 0026 "5SS) IS pv!:IlishemonINVby1he Oep.anmenlo le -nPOtl , o! M,nes'rodGeoIogv T1Ie RecorDsOlla 1& II 1059 V Stree1. SI.ole103 SIoatnenlO. CA 9581. Second daM po$la;e "'l1li"' IIsaa_. CA Poslrnasler- Sendacldr'" \0 CALIFQANIAGEOlOGYjUSPS350840). 80 . 29&0,s .c r - .CA 95812-2980Reports OrvISlOfl or Mones and Geology Plo,ects,and ar\Ide$ ana __ nellIS related 10 \h e ..... _ ..CaLIon'oI, arelllCl\lOed on OM Con I r _ ar\ICln.l lN*9'aphs, news ,t...... and gec:*lgoCaI_ .. ewelcomeTHE CONCLUSlOt"S AND oPlNlOt"S EXPRESSED IN ARTICLES ....RE SOLELVTHOSEOF THE ....UTHORS ND ....RENOT NECESSARilY ENOOJISEO BY THE DEP RTMENTOF CONSERV....TlOt"

C o r ~ """ 'k l be aGdreued 10 EOoIOrCALIFORNIA GEOLOGV. 801 K S1rHl. MS 1_ 33s . : r _ . CA9581_.J532Suc l s c f_ S8QOlyr (61tS) S 1 5 5 ( 1 " ' 2 ~ ( 1 2 _ l .S 2 3 . Q O ; 3 ~ 11,,_> Slcl__ OtOe


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THE lANDERS-BIG BEAR EARTHQUAKESEQUENCEAND ITS FELT EFFECTSTOUSSON A. TOPPOZADA, SeismologistDivision 01 Mines and Geology

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Photo 1. Unusual ruptures in sand dunes along northern segment of Homestead Valley Fault had about 10feet (3 m) of nghHaleraldisplacement. Nole the lehsteppmg panern and narrowness of the fault zone. Photo by W.A. Btyant.

INTRODUCTION

Last year a remarkable sequence ofmoderate to major earthquakesoccurred in the Mojave Desert. 30 to50 miles (50 to 80 km) east of San Bernardino (Photo 1). This area is north andeast of the historically active San AndreasFault and south of the Holocene-activeGarlock Fault (Hart. 1992).The table on page 4 lists the earth

quakes of magnitude (M) ~ tnal occurredbefore June 28. 1992 in the area sur-rounding Landers. Locations and magnitudes of the 1935-1986 earthquakes aretaken from the California Institute ofTechnok:.gy (ell) catalogs. Locations andmagnitudes of the pre-1935 earthquakeswere estimated from intensity data byToppozada and Parke (1982) andToppozada and others (1981). For theSee page 16 lor e.planabOfl 01 magnItude

1923 earthquake. Sanders (1986) showedthat the sparse instrumental data wereapproximately consistent I.Vith the intensitydata. The record of M ~ earthquakes inthiS area may be incomplete before 1930and probably is incomplete belore 1900.Figure 1 sho.vs the locations 01 eventsin the table. Most of the pre-1975 activityappears to be related 10 the San AndreasFault Zone. Surface faulting occurred inthe 1975 and 1979 earthquakes and was

reactivated as part of the 1992 Landersfaulling. TIle most recent earthquake ofM ~ related 10 the San Andreas Faultoccurred near Palm Springs in 1986.

EARTHQUAKE SEQUENCEJoshua Tree Earthquake

On April 22. 1992.2 months beforethe Landers and Big Bear earthquakes. anearthquake of M ~ 6 . 3 occurred 11 miles

(18 km) east of Desert Hot Springs.Subsurface faulting Irom this event propagated northward 12 mites (19 km) to theloum of Joshua Tree. where it causedthe most damage. Seismographic firstmotions indicate right-lateral strike slip ona north-nor!hwesttrending vertical faull(Hauksson and others. 1992). Aftershocksextended northward across the Holoceneactive Pinto Mountain Fault (Hart. 1992)as shown in Figure 1. No primary surfacefaulting was observed. Minor triggered slip(0.24 inches [6 mm] right lateral. 0.16inches [4 mml vertical, east side up) wasobserved 3.5 miles (5.6 km) west-northwest 01 the main shock on a less lhan1mile long. discontinuous segment of anorth-trending. west-dipping fault (Rymer.19921.Landers EarthquakeOn June 28 at 4:57 a.m. the largestearthquake ( M 7.5) in Califomia since the

CALIfORNIA GEOLOGY JANUARY/FEBRUARY 1993 3


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M:?5 earthquakes (mamshocks only) m the area of FJ9Ure I1992 June 281992June 281992 April 221986 July 81979March 151975 May311948 December 41947July 241947 April 101946July 181944 June 121940 May 171935October241923 July 231907 September 191899 July 221889 February 6

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81g BearLandersJoshua TreeNorth Palm SpnngsHomestead Valtey (Hili and others. 1980: Hullonand others, 1980: Sberman and others, 1980)Galway Lake (Beeby and HIli. 1975)Desert Hot SPl'lngs (RIChter and others. 1958)Mofongo ValleyManlxLudlow-BagdadSan Gorgonlo PassMorongo ValleySan GorgonlOMountainSan Bernardlno-Loma LindaEastern San Bernardino Mountainslytle Creek-san BernardinoMountainsMofongo Valley

19 miles (30 km) apart. with the secondevent, to the north. being twice as largeas the first (Kanamori an d others. 1992).Inversion of teleseismic P and S wavesrevealed tw o strike-slip subevents of G-

and 8'second duration and about 10 seconds apart. Th e strike of th e first event isI degree west of north. an d of the secondevent 27 degrees west of north (Kanamoriand others. 1992). TIle change in strikefrom the first 10 the second event is con


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Figure 2. Aftershocks of M ~ 3 . S for the June 28.1992 Landers and BI9 Bear earthquakesthrough september 10. 1992 Blue shading has been added to shOw surface lautbngCourtesyof CITand USGS.

AftershocksThe ahershock zones of the tw o June1992 earthquakes form a triangle about

43 miles (70 km) on a side. with theLanders zone on the east. the B'9 Bearzone on the west. and the San AndreasFault Zone (Mission Creek and Banningstrands) on the south (Figure 2).

USGS (NElC-USGS). DMG staff assignedaddillonal intensities by interpreting newspaper reports for severaltOWTls that v.>erenot listed by NEIC-USGS. The highestpredominant intensity valueswere plaitedon a map and contoured to show theareas shaken at MMl"s VI. VII. and VIll(Figure 4). This is a preliminary map.and may differ in detail from the NBCUSGS map to be published in 1993 usingmore complete intensity infonnation.It is possible that the preliminary mapincludes the effects of the Big Bear earthquake. which would result in higher intensities. particularly in the Big Bear to SanBernardino area.

CASUALTIES AND DAMAGEThe California Office of EmergencyServices (DES) reported one death. 25serious injuries. and 372 other injuriesas a result of the eartl-Kjuake series. [nSan Bernardino County. 77 homes v,rere

destroyed and 4.369 were damaged.with losses estimated to be $47.5 millionTwenty-seven buSInesses were destroyedor had major damage. and 139 otherssustained lesser damage. resuhir)g inlosses estimated to be $17 million. Publicsector damage (water. SCVJeT. and publicbuildings) was estimated al $26,6 million,Damage estimates for Riwrsidc Countyincluded 24 residences and sevenbusinesses. totaling slightly less than

The MMI VII and VIII ZOrlCS are poorlydefined because of the sparsity of population around the fault area. A[so the MMIVII zone possibly includes some effects ofthe Big Bear earthquake. The MM[ VIzone. where mllch of the damage was tocontents of buildings. appears to be moderately \.Ilell defined and extends from theLos Angeles Basin to the eastern MojaveDesert (Figure 4). It covers about 18.100square miles (47.000 kmlj. This is smallerthan the 27.000 square miles (70.000km") for the MM[ VI and greater area ofthe 1952 Kern County earthquake ofM 7.7. but larger than the land area of7.300 square miles 09.000 kmlj for theM ~ 7 _ 1 Lorna Prieta earthquake. Figure 5shows the MMI VI area for each of theseearthquakes. and for the M Il Imperialearthquake of 1941 Of these four important M> 7 earthquakes. Lorna Prieta wasthe most destructive. because the VII zoneincluded much of the metropolitan SanFrancisco Bay area.

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PRELIMINARY ISOSEISMAL MAPOF LANDERS EARTHOUAKEModified Mercalli Intensity {MMOvalues VJeTe obtained mainly from theNational Earthquake Information Center-

Aftershocks follow the trend of thesurface faulting. as seen in Figure 2_ Theepicenters of the Landers aftershocksform a continuous north- to northwesttrending zone from the San AndreasFault to the Camp Rock Fault. TIley haveextended across the Holocene-activePinto Mountain Fault and south of thesurface fault rupture as far as the SanAndreas Fault. The aftershocks of the BigBear earthquake have extended southwestas far as the San Andreas Fault. ">here aM4 earthquake occurred near Yucaipa.with mechanism parallel to the SanAndreas Fault

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Aftershocks M3.5 thaI occurredfrom June 28 to September 10 areshown in FIgure 2. and have a distribution similar to the M>3.0 aftershocksthat occurred from June 28 to July 27(Toppozada and Wilson. 1992). BothafteTShock maps show that surface faulting on the Camp Rock Fault extends 3to 6 miles (5 to 10 km) farther northwestthan the main aftershock zone. This suggests that the northwest end of the surface faulting is shalloo' and may notextend to seismogenic (earthquake-gencrating) depth. Also. both maps showa persistent cluster of earthquakes ncar

CALIFORNIA GEOLOGY JANUARYIFEBRUARY 1993 5


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FIQure 3. Sl ip distr ibution along the lau1l estimated Irom TERRAscope broadbandrecords (solid line). Surface displacements observed in the field are shown by thedashed line. From Kanamori and others. 7992.

10 20 30 40 50 60Distance (north trom the 8pIC8l1Ier). km

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observed at surfaceS8'SmologlCaily esllmated

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No significant damage to the underground natural gas distribution system wasobserved in Yucca Valley or Joshua Tree.Houses in Landers use propane gasfrom ab0ve-9round tanks. Some of these

tanks slid and fell off their concrete pads.rupturing the attached piping. Unbracednot water tanks toppled. breaking propane line connections in some cases.Rres resulted in several instances.The natural gas system in Big Beardid not suffer any breaks in its main lines.although many gas connectionswerebroken because houses shifted from theirfoundations. Some areas around Big Bearrely on propane tanks for fuel. Damageto unancnored tanks was similar to thatin the Landers area.

$1 million (Earthquake EngineeringResearch Institute. 1992).IMPACT ON LIFELINES

Damage to water and gas systemsand highways was limited 10 the epk:en'lral region because faulting occurred in adesert area. The following lifeline information is mostly from the August 1992Earthquake Engineering Research Institutereport.Water and Waste Water

Water distribution systems suffereddamage to pipelines and storage tanks.Ground-water wells and storage tankssupply all the water in Ih Landers epicenlral area. Wafer customers \.VeTe withoutwater for several hours to 2 IAleeks. Hundreds of water-line breaks were reportedIn the Landers area. Much of the pipelinedamage OCCUlTed in the fault zone. wherethere were large displacements.Damage to water systems was lesssevere in the Big Bear area. According

to the director of Big Bear Lake PublicWorks. there were approximately 50water pipe repairs made in 2 days. Waterstorage tanks appeared to be undamaged.Waste water disposal in the YuccaValley area is handled by private individual

sewage disposal facilities. Concern aboutcontamination from waste water led tothe boiling of drinking water for 2 weeks.until both systems were inspected andrepaired.

Power1lle major electric pou,ter agency inand around Landers lost service to550.000 customers due to localized dam

age within the distribution system. Most ofthe service was restored within 24 hours.Localized failures caused loss of

poy..oer for several hours 10 5.000 customers in lhe Big Bear Lake area. In the LosAngeles area 51.000 customers lostpower. again due to distribution systemfailures. Nearly all service was restoredwithin 24 hours.

The high voltage poy..oer transmissionand switching system perlonned wellbecau5C 01 the distance between the faulttrace and vulnerable swilchyards. TheCamp Rock-Emerson surface fault ruptured under a bolted steel frame 220 kVtransmission tower. moving two of thelegs approximately 9 feet (3 m) relative tothe other two (Photo 2). This resulted insubstantial deformation of the steel towerand lailure of several braces. but no damage was sustained by the transmissionlines or ceramic insulators.Fuel

ll1ere was no damage to two highpressure gas transmission lines passingthrough the area. one a 6inch (l5-cm)hne south of the primary rupture zone andthe other a 30'inch {76-cm) line north ofthe primary rupture zone_There wassome nonstructural damage to a compressor station on the 3Q..inch (76-cm) line.

Transpor1ation and CommunICationsState Highway 247 (Old WomanSprings Road) was disrupted in ten locations and not fully restored until 8 dayslater. Other county and gravel roads inthe area were Similarly disrupted. butremained open to tramc as repairs weremade. State Highway 38 10 Big BearLake remained closed for 2 weeksbecause of rock slides. Restrictions totravel on Highway 247 south of LucerneValley were imposed to reduce conges

tion in the Big Bear area.Operations at one military and threesmall civilian airports in the Yucca Valleyarea \A1CTC not adversely affected by theearthquakes. despite minor cracking ofrunways and taxiways and some loss ofpoweLTelephone systems perfonned well.ahhough service was affected by the usualpost-earthquake high volume congestion.Reported damage included a downedoverhead cable and a few tension failures

in buried cable. Although there were sometemporary disruptions immediately follow-ing the event. telephones were generallyworking throughout the epicentral regionwithin a few hours. Sporadic local outagesVJre reported lor approximately 3 daysfollowing the earthquakes.FM radio station KROR in YuccaValley. which had emergency backuppower. continued operations after theearthquakes. providing valuable Oocal

, CALIFORNIAGEOlOGY JANUARY fEBRUARY 1993


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Figure4 Prehmlnary MOdlhed Mercalh lnlensily map ollhe Landers earthquake, based largelyon Inlormatlon Irom NEIC-USGS


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FIQure 5. The areas shaken atModihed Mercalll IntenSity(MMI) VI and greater for the1992 Landers. 1989 LornaPrieta (Stover and others.1990). 1952 Kern County(Slover and Collman. 1993).and 1940 Imperial County(Neumann. 1942) earthquakes.The corresponding laull seg-ments are IndICated schematlCally by thICk III'les.

emergency) public information. Theradio station In Big Bear also remainedin service.

TRIGGERED ORSTIMULATED SEISMICITYWithin minutes after the Landersearthquake. hundreds of small earthquakes

(M


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Pnolo 2. Powerline tower severely damaged by rupture on Emerson Faull where \1 leel(3.4 m) of nght-Iateral slip was measured. Rupture lorms a relatively narrow mole trackhere but splays Inlo a complex zone nearly 1.000 feet Wide (300 mj 1mile (1.6 km) to lhenorthwest Photo by A.G. Barrows.

REFERENCES

Beeby. OJ. and HIli. RL.. 1975. Galway LakeFault, a pr9YlOOsty unmapped active faullIn lhe Mojave Desert. san BernardinoCounly, California CALIFORNIA GEOLOGY, v. 28, no. 10. p. 219221.

Earthquake Englneenng Research Inslltute.1992, special report on Landers andBig Bear earthquakes. AuguSI 1992NewsletterHart. E.W, 1992, Fault-fUplure hazard zones InCalifornia. DiVISIOn of Mines and Geology,Sp9Clal PubilCatJOfl 42. 32 p.

Hauksson. Egil. HUllon. Kale. and Jones. Lucy.1992, Prelimmary report on the 1992Landers earlhquake sequence m SOIJlhernCalifornia In Ebersold. DB . OO110r. FieldTnp Guidebook. Soulhern Calilornla SeclIOn of the ASSOClal,on of EngmoonngGeologlSISHili. RL. Pechman. J,C. Trelman. J,A..McMillan. JR Grven, J W. and EOOl.J.E.. 1980. GeologIC Sludy of lhe Homestead Valley eaflhquake swarm of Malch15. 1979 CALIFORNIA GEOlOGY. v 33.no 3. p. 6067.HUllon. LX. Johnson. CE .. Pechmann. J.C,Ebel. JE Given. J W. Cole. 0 M. and

German. PT., 1980, Epteentral 1oca110f1$for the Homeslead Valley earthquakesequence. March 15. 1979 CALIFORNIAGEOlOGY. V 33. no, 5. p. 110-114

Kanamon. Hlroo, ThIO, Hong K,e; Dreger.Doug, Hauksson. Eglll; and Healon.Tom. 1992. IMlal Invest'9atlOn Of lheLanders. California. earthquake 01 28June 1992 us'ng TERRAsoope Geophysical Research Lelle.s. v 19. no 22.P 2267-2270.

Neuman. Frank. 1942. Untled Stales earthquakes 1940: Coasl and GeodetICSurvey. S9f1al rtO 647RlChler. CF. Allen, C A, and NordqUist J M1958. The Desert HOI Spflngs earthquakes and lhelr tectOI'llC enVironment,Bullelin of the seismologICal SocI8!y ofAme.ica, v. 48. p. 315-337Rymer. M J.. 1992. The 1922 Joshua Tree.CalJfornla earlhquake: tectOniC sewngand tnggered slip (abslracl] AmencanGeophysocal UnIOn Transactions,November 1992Sande.s. C 0 .. 1986. selSmolectOnlCS of lheSan JaCinto Faull Zone and the Anzaseismic gap Ph,D dISSertatIOn, CaliforniaInsutUle 01 Teennology, Pasadena. 143 pSlIerman. OJ .. Lee, lien-Chang. Zappe.5.0. Seamount Dan, 1980. Alle.shocksollha Homestead Valley earthquake 01March 15, 1979: CALIFORNA GEOLOGY.

v 32. no 1.p.14-17Slover. C W. and Coffman. J.L., 1993. SeiSmICity of the Unrted Slales 1968-1989:U.S. GeologICal Survey ProfessIOnalPaper 1527. In pressStovef, C.W.. Reagof. BG. Baldwin. F Wand Brewer, L.R., 1990. PreliminaryISOS9lsmal map lor the Sanla Cruz (LornaPrlela). California. earlhquake of OCIober17. \989 UTC U.S. GeologJcal SurveyOpen FIle Report 90-18. 24 p.T o p p o ~ a d a , T.R and Parke. DL .. 1982.Aleas damaged by Cahfornla earthquakes. 1900-1949. AnnualleenmcaJrepon 10 lhe U.S. GeologICal SurveyCalifornia DiviSion 01 Mines and GeologyOpenFlle Report 82-17 SAC, 65 PToppo13da, fR .. Real. CA.. and Parke.O.L. 1981. PreparatIOn 01 IS05elsmalmaps and summanes of reported effectsfor po-e-l900 Cahfornla e a r t h q u a k ~ sCahfo.ma D,VISIOn of Mines and GeologyOpenFile Report 81-11 SAC. 181 PT o p p o ~ a d a . TA. and Wilson. RI., 1992,Apfll 22 Joshua Tree. and June 28Landers and Big Baal earthquakes.1992. CALIFORNIA GEOLOGY, v. 45.no 4. p. 118-120,

CALIFORNIA GEOLOGY JANUARYFEBRUARY 1993 9


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Surface Faulting Associated with theJune 1992 Landers Earthquake, California

EARL W. HART, WILLIAM A. BAYANT, AND JEROME A. TAEIMAN, GeologistsDivision of Mines and Geology

Photo 1. Geologists measuring 9.5 feel (2.9 m) 01 nghHateral olfset ot chainlink lence along Encanlado Road west ofLanders. Photo courresy of Geomalnx Consunants.

INTRODUCTIONSurface fault rupture associated withthe June 28. 1992 Landers e a r t h ~quake occurred in San BernardinoCounty. from Ihe vicinity of Yucca Valleyto the Rodman Mountains. a distance of53 miles (85 km). This was the largestfault-rupture event in California since the1906 earthquake on the San AndreasFault which had as much as 250 miles(400 km) of rupture and 15 to 20 feet(4,6106.1 m) of right-lateral slip. Ruptured duEing the Lmders event werethe Johnson Valley. Homestead Valley.Emerson. and Camp Rock faults. all ofwhich \AleTe active and previously mapped(Photo I and Figure 1). Also. several pre-viously unknown faults ruptured, includingthe Eureka Peak and Burnt Mountainfaults in Yucca Valley and the KickapooFault' in Homestead Valley. Also relerred to as the Landers FauM

These ruptures came as a big surpriseto the earth scientists who had studiedthese faults because: I) faults previouslyconsidered to be separate structureswere found to connect (Figure 1): 2} theamount of surface displacement wastwo or three times as large as generallyanticipated; 3} the magnitude" of theeanhquake was much larger than envi-sioned by seismologislS for individualfaults: and 4) seismicity was continuousacross the active Pimo Mountain Fault.

RESPONSEThe Landers eanhquake was felt bymany in soulhem California. includingauthor JeromeTreiman. He and olhereanh scientists checked for fault ruptureas soon as the epicenter was located.

"See 16 lor eXplanatIon 01 rT\iIogMude

Other geologists from the Division 01Mines and Geology (DMG), the U.S.Geological Survey (USGS}. the CaliforniaInstitute of Technology (CIl). universities.consulting finns. and other organizationsarrived during the next few days.Initially. the extent. magnitude. andsense 01 rupture were detennined. Muchof this information was channeled throughDMGs clearinghouse (see Toppozada andothers. this issue). By July 1or 2. mostof the main ruptures had been identifiedand. to some extent. measured. but thedesert terrain and its limited features didnot pennit most rupture traces to be pk>t-led accurately on topographic base maps.Aerial photographs (scale of 1:6.000,or I inch _ 500 feet). taken by IX Curtis

for USGS on June 30 and availableJuly 3. greatly facilitated the mapping of

CALIFORNIA GEOLOGY JANUARY FEBRUARY 1993


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Most of the rupture .....as right-lateralstrike-slip along nonh to northVJeSt-trending faults. with maximum slip of 15to 20feet (4.6 to 6.1 m) on the Emerson Fault(Figure 2 and Photo 2). TItere was morethan 3 feet ( l m) of right-lateral slip over38 miles (61 km) of rupture. Left-lateralslip also occurred locally along northeasl-

Johnson Valley Fault died out southwardjust north of Yucca Valley. but ruptureappeared again 10 the south of the PintoMountain Fault. 1ne zone of aftershocks iscontinuous and shows the Johnson ValleyFault to connect in the subsurface with theBumt Mountain and Eureka Peak faults.

DESCRIPTION OF SURFACERUPTURESThe epicenter was located south ofLanders on the Johnson Valley Fault andruptured mainly northward to the Homestead Valley. Emerson. and Camp Rockfaults (F"Igure 2). Rupture along the

Figure 1. Quaternary tautts of the south'centralMojave Desen shoWing Holocene faults zoned \ under lhe AIQUlst,Prlolo Special Studies Zones Act \(rust lines) and olher late Ouaternary faults (green hnes).Surface rupture zones associated wilh the Landers eanhquakeare Identltied by gray lines: triggered slip on other faults is shown bytriangles. Hell:agons mark eplC8nters. letters ldentlly ClIleS: B Barstow: BBC. Big BearCity; DHS Desen Hot Springs; JT Joshua Tree; L Landers: NS Newberry Spnngs;TP. Twentymne Palms. YV. Yucca Valley.year (Hart and others. 1988). Surfacerupture in the central Mojave Desertprior to the Lanclers event was m i n o r ~it occurred on the Manix Fault in 1947(Richter. 19581. the Galway Lake Faullin 1975 (Hill and Beeby. 1977). and theHomestead Valley and Johnson Valleyfaults in 1979 (Hill and others. 1980).

~

The principal faults and general structure of the Mojave Desert region havebeen summarized and discussed byDibblee (1980). According 10 Dokka(I 983). the principal northwest-trendingfaults of the south-central Mojave Deserthave haci 0.9 to 9.0 miles(I.5 to 14.5km) of right-lateral displacement in lateCenozoic time. Recently-active traces ofthese faults have been mapped by Bull(19781. Morton and others (1980). andHart and others (1988) using teclonicgeomorphology. Geodetic measurementsbetween 1934 and 1982 suggest cumulative right-lateral slip (strain) of 0.26 0.05 inch (6.6:t 1.3 mm) per year alongthe northVJeSHrending faults of thisregion (Sauber and others. 1986). Basedon the development of tectonic geomorphic features and offset Iale Quaternarygeologic units. the Pisgah-Bullion. Calico.and related faults to the west eachappears to have a late Quaternary sliprate approaching 0.04 inch ( l mm) per

1ne authors would like 10 acknowledge the dozens of geologists from DMG.lhe USGS. and other organizations formaking their preliminary data availablefor this report.

fault ruptures. Although many of the faultscould be seen on the air photos. it wasnecessary to examine them in the field 10measure magnitlKle of slip and to providecontinuity. Because of the large numberof ruptures and because fractures degraderapidly in soft alluvium. DMG joined theUSGS and others to map the manystrands of faults. The results presented inthis article are preliminary and generalized. More detailed and complete resultswill be published jointlywith the USGS.Other preliminary reports on the Landersearthquake have been prepared by Earthquake Engineering Research Institute(1992) and Geomatrix Consultants(1992).

TECTONIC SETTINGThe Landers earthquake occurredalong part of a group of right-lateral.northwest-trending late Quaternary faultsin the central Mojave Desert (Figure 1).Near its southern end. the rupture zone istTaversed by the east-VJeSt-trending PintoMountain Fault. The region is bounded onthe southwest by the San Andreas FaultZone and on the north by the GarlockFault.

CALIFORNIAGEOlOGY JANUARY/FEBRUARY 1993 "


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Figure 2. Surface faulting associaled with lhe 1992 Landers eanhquake. For details 01 shaded area. see Irvine and HIlI, lhls Issue

" CALIFORNIAGEOLOGY JANUARY/FEBRUARY 1993


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Photo 2. Surface rupture along the Emerson Fault offsets road 151020 teet (4.6 to 6.1 m)right-laterally. which IS lhe nearmaxlmum tault displacement measured 'or lhe Landersearlhquake. Main rupture is a broad. fissured mole track or warp aboul 50 'eet (15 m) widelIanked by subsidiary fissures extending 50 to 100 feel (15 10 30 m) on each side. Photo byW.A. Bryant.

Johnson Valley FaultRuplure that caused the Landersearthquake was initialed at the southern

end of the Johnson Valley Faull. at adepth of 5.6 miles (9 \un). Only til!! southem half 01 the Johnson Valley Faull niP'"lured (Photo 3) with the minor exceptionof triggered (?) slip near its northwesternend (PIgure 1). ITJiggered slip occurswhen strain stored along a fault at a shalIovJ depth is released by shaking.) Thefault was previously known and most ofIt was considered to be Holocene activeMaximum righI-lateral displacement wasabout 10 feet (3 m) and mOSl of the faultdisplayed more than 6 feet (2 m) of slip.

The surface ruptures splayed complexly at the south end and died-out northof Yucca Valley. The fault segment connected complexly to the north with theHomestead Valley Fault. again along aconlinuous aftershock zone. Near its junclion with the Kickapoo Fault. the JohnsonValley Fault previously had very minor.discontinuous surface rupture associatedwith lhe Homestead Valley earthquakesof 1979 (Hill and others. 1980).

to east-trending faults. but mostly wasminor. Maximum leftlateral slip measuredwas about 1.5 feet (0.5 mI. VJeSt ofGalway lllke. A vertical component ofrupture was also common and locallyattained 3 feet (J m) or more.

Zones of closely associated rupturescommonly were 33 1066 feet (10 toZO m) UJide. In some cases there weretwo or three main breaks and. together\Vith subsidiary faults. fanned complexrupture zones at least 650 feet {ZOO m)wide. TIlere were so many ruptures thatmany were obscured by reconstruction.traffic. and weather before they could befield mapped. Fortunately. most of theruptures were recorded on aerial photographs shortly after the earthquake. Theseveral segments of faults that ruptured(Figure 2) are discussed below. from southto north.Eurella Peak and BurntMountain Faults

1hese faults were not known prior totheir rupture on June 28. 1992. There isno geomorphic evidence suggesting previ-

ous Holocene activity. but there is subtleevidence of the faults in older alluviumand bedrock IT reiman. 1992). An exploratory trench across the northern part ofthe Eureka Peak Fault revealed calichefilled fraclures in alluvium. Both faults areright-lateral faults with minor down-to-thewest vertical components. Maximumright-slip on the Eureka Peak Fault was8.3 inches (21 em). There was nearly 1.6inches (4 cm) of afterslip on this fault andabout half of it occurred during the first 2weeks after Ihe earthquake (Art Sylvester.University of California. Santa Barbara.Ofal communication. December 9. 1992).Uttle if any afterslip was recorded onother faults in the epicentral area.

Although these faults align with thelllnders earthquake aftershock pattern.they do not extend continuously to thenorth or south as do the aftershocks.TIlefaults also align with minor Quaternaryfaults to the south that are apparentlyrelated to the April 22. 1992 Joshua Treeearthquake of M ~ 6 . 3 . One of lhese faultsshO\l.'ed minor right-lateral and dovm-tothewest vertical slip (Rymer. 1992).

t.-" . # I : { OJ"'J ' I" ., ~ ~ . : -V'..,..;, . . . . . ~ , .. .-.... J-1:!:...... . ..._IIr. ~ ~

Photo 3. Exposure 0' Johnson Valley Fault Inhillside CUI. had 4.6 toot (1.4 m) ot nght-lateraland 1.0 'oot (0.3 m) ot verllCal ollsel (scarplelallower right). Vertical resistent teature IScalcite-cemented rault breccia il'ldicallngprevIOus faulting in Pleistocene allUVium. NOlenew fissures In breccia. Photo by E.W. Hart.

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Photo 4. Newly dIscovered Kickapoo Fault near Charles Road shows relatIvely narrowzone 01 rupture along scarp up to Jleet (1 m) high WIth nearly J 'eet (1 m) 01 rightlateralonset. Fault seemIngly passes between house and outbul!dIl'IQ (see Photo 5). Photo byWA Bryant.

Kickapoo and Related Faultslhese newly discovered faults constitute a major connection between theJohnson Valley and Homestead Valleyfaults. 1he main element is the KickapooFaull. which had a maximum of 9.5 feet

(2.90'1) of right-lateral slip. 1he north endof the fault has a large vertical componentfanning an east-facing scarp about 3 feel(1 m) high (Photo 4). Only subtle anddiscontinuous evidence for this fault canbe seen on air photos and in okler Plalluvium in the field. This stepovr areais the approximate location of the 1979M5.3 Homestead Valley earthquake (Hilland others, 1980).Homestead Valley Fault

Virtually this entire IS-mile- (29 km-)long fault ruptured in 1992, developingmaximum right-lateral displacement of11 feel (3.35 m), It has multiple strandsfanning a wide zone. and connects complexly with the Emerson Fault. 1he southernmost segment. which had minor rupture in 1979. is separated from thecentral part of the fault by a complexlyfaulted hill. The eastern side of that hill(west-southwest of the Los Padres Mine)is bounded by a west-dipping thrust faultwith a 3-fool- (l-m-) high scarp (Hgure 2),The Homestead Valley Fault rupturesdiminish to the southeast and zones ofdiscontinuous ruptures connect it with theJohnson Valley Fault.Emerson and Galway Lake Faults

Maximum rupture associated withthe Landers earthquake occurred alongthe Emerson Fault near Bessemer MineRoad. There was 16.7 feet (5.1 m) ofrighHateral slip just north of that road.Measurements of right-lateral displacement of a road just south of the BessemerMine Road range from 15 to 20 feet (4.6to 6.1 m) (Photo 2). Only the northwestern half of the Emerson Fault ruptured inthis event. although the southeastern halfis considered active (FIgure 1). To thenorthwest the fault connects complexlywith the Camp Rock Fault. paralleling itlor Smiles (13 km). The Galway LakeFault. at the southeast end of the Emerson ruptures. also ruptured with nearly3.5 inches (9 em) of right-lateral slip (thismay have been triggered slip). 1he samesegment had minor rupture in 1975 (Hilland Beeby, 1977). Except lor some short

segments. the Emerson Fault was previ-ously recognized as a recently active fault.Camp Rock Fault

Most of the central and southeasternpans of this fault ruptured with maximumright-lateral displacement of about 6 feet(2 m). 1he rupture. ha.vever. was discontinuous where the Camp Rock Fault parallels the Emerson Fault. and the northwestern part of the fault did nOl rupture(Figures 1 and 2). 1he magnitude of surface fault rupture diminished substantiaUyto the northwest. Some ruptures splayednortheast (with as much as 9 inches[23 cml of left-lateral slip) around thesoutheast side of the R


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November verified cracks in at least threeplaces in zones at least 32 feet (10m)w'ide (Ken Lajoie. USGS. oral communication. January 1993).Lenwood Fault-o.6to 1.2-mile-

(I -2-km-) long zone of left-stepping crackssouth of Soggy Lake.

Old Womon Fault-questionableminor extensional cracking: northwesttrend.Pinto Mounlain Fault-local minorcracking VJith up to 0.8 inch (2 em) ofextension: right-stepping cracks suggestleft-lateral displacement.Other triggered slip was reported inImperial Valley on the Superstition HillsFault. the East Branch of the Bmore

Ranch Fault. and the Coyote Creek Fault(Sharp. 1992) and in Coachella Valleyalong the Indio Hills. Mecca Hills. andDurmid Hills segments of the SanAooreas Fault (Mike Rymer. USGS. oralcommunication. 1992). Maximum rightlateral slip on the San Andreas Fault was0.83 inch (2 em).

1988. Based on preliminary data.approximately 55 percent of the faultrupture associated w'ith the Landers earthquake occurred within the establishedSSZs. About 31 percent of the rupturewas outside the SSZS along previouslyunrecognized faults. including branchand subsidiary faults and interconnectingfaults. lhe remaining 14 percent 01 therupture outside the SSZS occurred onpreviously mapped faults that did notappear to meet zoning criteria. An estimated one-third of the rupture outsidethe SSZS was relatively minor. with fewerthan 4 inches (10 em) of displacementBy way of contrast. only 38 percent ofthe fault rupture from the November1987 Superstition Hills and ElmoreRanch earthquakes was within establishedSSZs. Again. part of that rupture occurredon previously unmapped faults and muchof it was relatively minor.

Another method 01 measuring theeffectiveness of zoning is to evaluate thepercentage of zone length within whichrupture occurred For the Landers earthquake. betv.


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On January 1. 1993. PreliminaryReview Maps of new and revised SSZswere issued for !he Yucca Valley andLanders areas VJhere development isunderway. These maps will become official July 1. 1993 following a 90-dayrev'ew period. The mapswil l show thefaults that ruptured during the Landersearthquake. Revised SSZs for undeveloped areas that ruptured to the north wil lbe issued In 1994 or 1995 when mapping of the recent ruptures is completed.Although no comprehensive studies

v..rere made. it is apparent that manyhouses were damaged by the Landersfault ruptures-some extensively (Photo5). A survey of air photos and limitedfiek! checking indicate 29 houses weredamaged and an additional 50 housesmay have been damaged by fault rupturein the Landers and Yucca Valley areas.There were no reports of structural collapse of houses or loss of life that resulteddirectly from fault rupture (Johnson andothers. 1992). However. an interiorstone fireplace wall did collapse in oneresidence on a minor branch fault. It isclear that houses placed astride majoractive faults may sustain severe damage.

In places where ground defonnatlonis distributive and displacements arenot large. ackIitional protection may beafforded by the use of reinforced foundations. It was noted that fault rupture. insome cases. was diverted around slabfoundations and presumably reduced~ i n t e m a r damage to the structures.

Magnitude is the measure of thestrength of an earthquake. or thestrain energy released by It. usuallyexpressed by the Richter magnuudescale. Each ....hoIe number $lep ofmagrunne on the scale represents atenlokIlOcrease in the amplitude 01the waves on a seismogram andabout a 31fold increase in energyrelease Magnitudes detenninedwithin about 400 miles (600 ken) ofan epicenter are local magnitudes(Mil. S u r f a c ~ v e and body-Wdve( M ~ . M,J magnltudes are measuredfrom s e i ~ m o g r a m s recorded fartheraway. Moment magnitudes are determIned from fault dimensions anddisplacetnent

REFERENCESBull. WB, 1978. TectonIC geomorphologyot the MOjave Desert. Calilornla:Unpublished Techmcal Report lorlhe U.S Geological Survey. Contractno. 14-080oo1G-394. 188 p.Dlbblee. TW .. Jr.. 1980. GeologlcaJ struclure of the MOjave Desert in File. D.Land Brown, A.R" Geology and mineraiwealth 01 the Cahforma desert: SouthCoast Geological Society. p. 69-100DIVISion 0' Mines and Geology. 1988. OffICialMaps of Special Sludles Zones of lheCamp Rock Mine. Silver Belt Mine. FryMountains, Iron Ridge, Galway Lake.Melville Lake. Emerson Lake. Landers.Yucca ValleyNorth and Yucca ValleySoulh quadrangles. scale 1:24.000.Dokka. AK., t983. Displacements 01 lateCenozoic slrlke-sllp faults ollhe centralMojave Desert. Califorma:Geology.

v. 11. p 305-308.Earthquake Engineering Research Institute.1992. Landers and Big Bear earthquakes of June 28 8. 29, 1992: EERISpeclaJ Earthquake Report 12 p.Geomatnx Consultanls. 1992. 1992 Landersand Big Bear earthquakes - someprehmlnary assessmenlS. Unpublishedreport of Geomatnx Consultants. SanFranciSCO. Callforma, 4 pHart. EW . 1992. Faull-ruplure hazardzones In Cahfornla DIVISion of Minesand Geology Special Report 42, 32 PHart, E.W" Bryant. WA.. Kahle, JE..

Manson. MW.. and. Bortugno. E.J.,1988. Summary report: Faull Evaluatlon Program. 19861987. MOjaveDesert and other areas: DIVISion 01Mines and Geology Open-File Report88-1.40p,.1 plale.HilI. RL.. and Beeby. D,J" 1977, Surfacefaulting aSSOClated with the 5.2 magnitude Galway Lake earthquake ot May31. t975. MOjave Desert. San Bernardino County. California GeologicalSociety 01 Ameoca Bulletin, v 88,no 10. p. 1378-1384.Hill. RL., Pechmann. J.C .. Trelman, JA .McMillan. J.R.. Given, JW., and Ebel.

J.E,. 1980. GeologIC study of lheHomestead Valley earthquake swarmof March 14. 1979: CALIFORNIAGEOLOGY, v, 33. no. 3, p 6Q..67.Johnson. Jell, Siosson. Jim, and Gray. CIlt!.1992. Modify !he A I q U l s l P n o ~ ActEarthquake Engineering ResearchInSlitule Newslelter, v 26. n. 9. p. 7,Morton. OM" Miller. FK. and Smith. CC.1980, Photoreconnalssance mapsshOWing younglooklng fault features Inthe southern Mojave Desert. Callforma'

U.S. Geological Survey MiscellaneousField Studies Map MF-l051, 7 sheets,scales 1:24.000 and 1:62.500.Richter. C.F" 1958. Elementary seismology:W.H. Freeman and Company. SanFrancisco, California, 768 p.Rymer. M.J., 1992, The 1992 Joshua Tree.

Calt!omia. earthquake: Tectomc setlll'IQand InggereO' slip: EOS. Transactionsof the Ameocan Geophysical UnlQl1.v. 73, no. 43,p. 363.

Sauber. Jeanne, Thatcher. Wayne. andSolomon, S.C .. 1986, Geodetic measurement of delorma\lon in the centralMojave Desert, California: Journal ofGeophYSICal Research. v. 91. no. B12.p.12.683-12.693.Sharp. A.V., 1992, Surtace faulting in lheImperial Valley tnggered by the 1992Landers. CaMomia. earthquake:EOS. Transactions o! the AmericanGeophysical Union, v. 73. p. 380.Trelman. JA. t992. Eureka Peak andBurnt Mountain faults. two "new" faultsin Yucca Valley San BernardinoCounty. Cahfornia In Ebersold, D.B .editor, Landers earthquake of June 28,1992 San Bernardino County. Cahlornia Field Tnp Guidebook: SouthernCall!ornla Section of the Association

01 Engineering GeologiStS. p. 1922.

SMIP 93 SEMINARON SEISMOLOGICALAND ENGINEERlNGIMPUCATIONS OF RECENTSTRONG MOnON DATA

Sacramenro. California - May 20. 1993The Division of Mines andGeoIogy's California Strong Motion

Instrumentation Program tCSMIP') willhold its lihh annual seminar on seismological and engineering implications ofrecent Strong-molion data. The findingswill be furnished 10 practicing seismicdesign professionals and earth scien'tists. For more infonTlation. contact,Strong MOhon Instf\lmentatlon Program801 I( St.eet, MS 1335Saclamento. CA 958t4-3531916322-3105

" CALIFORNIAGEOLOGY JANUARY FEBRUARY 1993


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Rockfalls and Surface Effects Other Than FaultingLanders and Big Bear Earthquakes

ALLAN G. BARROWS, GeologIstDivision of Mines and Geology

Photo'. Vehicle-size block shaken loose dUTU'IQ Big Bear ear thquake 5 miles (8 km) east 01 Barton Flats Campground onHighway 38. Allhough very close to epicenter. thiS was the only debris on road Note hole in pavement to left ot block. Photoby Jeff Knoll, CAL TRANS. laken 31 , 1:00am, June 28.1992.

INTRODUCTION

For much of the day following the earlymorning M7.5 Landers and M6.6Big Bear earthquakes. dense. white cloudsof dust. resulting from nearly continuousrockfaUs. concealed the deep canyons andrugged mountain peaks in the eastern SanBernardino Mountains. E1seo.vhere inthese mountains. widespread rockfallsfrom roadculs and steep slopes madesome roads impassable or dangerous forseveral days following Ihe earthquakes.c.eologists found evidence of rockfall andstreambank sloughing in relatively fewlocalities in the 2.700sqlJilre-mile (7.000km2) area (Photo 1 and map on page 18).

Oddly enough. in spite of forcefuland prolonged shaking. the Landers andBig Bear earthquakes neither triggered

massive landslides nor remobilized existing slumps or block glides in the SanBernardino Mountains. Consequently.the effects of the June 28. 1992 eanhqlJilkes contrast dramalically with theextensive landsliding triggered by theM64 San Fernando earthquake of February 9. 1971 (Morton. 1975) or the M7 1Lorna Prieta earthqlJilke of October 17,1989 (Spittler and others. 1990),

M7.5 LANDERS EARTHQUAKEReglOrlal selling

lhe region subtected to the strongestshaking associated with the Landersearthquake is typical Mojave Desert terrain. It is characterized by rugged. nearlybarren. faultboullded mountain rangesthat border broad valleys comprised of

coalescing alluvial fans and. locally. scattered playas, Exposed in lhe mountainsand dispersed hills are older. graniticand metamorphic ''basemen( rocksand younger vokanic rocks. Sedimentaryrocks are nearly absent in this regionThe drainage syslem consists of sandy.gravelly vrclshes incised by steep tovertical-walled channels.Rockfalls

Rockfalls were triggered near surfacefault rupture. particularly 21 miles (35 km)north of Yucca Valley (15 miles or 25 kmnorth of the epicenter) in the mounfainsbetween the Homestead Valley and Emerson faults. Large blocks thaI had weathered out of the typical jointed bedrock onthe slopes rolled. slid. and even bouncedfo fhe base of the slopes (Photo 2).

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Limits of area aHected by surlace faulting. rockfalts. and other surlace geologic etfects otlheLanders and Big Bear earthquak.es. June 28. 1992. Numbers in squares are localities ofphotos in this artICle.Fissures. ExfensionaJ Cracks,and settlement Features

Acouple miles east of the abovedescribed cracks. in the Silver Bell Minequadrangle. a zone of righl-stepping fissures could be followed across the desertfor more than 2 miles (3 km). The zoneranges from a single crack to a 200loot(60-m-) wide belt containing dozens offissures. Most of the cracks appearedto be purely extensional features withcollapsed walls that. locally. were open todepths exceeding 3 feet (I mI. At severalplaces. however, left-lateral displacementsof up to 9 inches (23 cm) were measured. This particular zone 01 fissuresstrikes tOVJard a knoll known as Ford'sKnob, upon vmich sits a microwave relaytower. The road to the tower along thewest side of the hill was blocked by abundant rockfalls and seriously damaged forabout 1.600 feet (500 m) by settlementof the downslope (west-lacing) part ofthe roadway embankment.

The exceplionalleatures in this vicinity. nearly 31 miles (SO km) from theepicenter, teslify to the strength of theearthquake shaking. The simplest explanation for such pronounced manifestalions of strong shaking relates to a peculiarity of the Landers earthquake event.According to seismologists (Haukssonand others. 1992), during the Landersearthquake M energy was released in twosubevenls. with the first subevent startingat the epicenter and the second subeventat approximately 40 kilometers 125 mileslto the north-northwest and starting about10 seconds after the beginning of therupture. M The second subevent. whichreleased more energy than the firsl.began along the Emerson Fault onlyabout 6 miles (10 km) from the featuresdescribed above.

place. This suggests they are not randomshaking features but reflect an underlyingtectonic paltern. perhaps as part of aconjugate set with the bounding CampRock and Calico faults.

Earthquake shaking was unusuallyforceful at the small desert community ofNevJberry Springs, 17 miles (27 km) eastof Barstow (Richard Willette. Hector MinegeologiSt. oral communication. 1992).The California StrongMotion Instrumentation Program slation at Yenno.52 miles (84 km) from the Landers earthquake epicenter recorded a peak acceleration of 0.25g (Shakal and others. 1992).

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Prominent earthquake shaking effectsVJere widespread in the area between theCamp Rock and Calico faults. 28 to 31miles (45 to 50 km) north 01 the epicenter. Many northeast-trending fissuresdeveloped across the aUuviated areabetween the Rcxlman Mountains and IronRidge. There is a series of short, rightstepping cracks. striking NSO" to 60 0Ewhere the road paralleling the steeltowerpoweHransmissK>n line crosses a rockyprojection of the Rcxlman Mountains,1.25 mile (2 km) east of the CampRock Fault. Lateral displacement wasnot seen on these cracks. which typicallywere open only about 1/2 10 1 inch(lor 2 em). The cracks coincided withcaliche-filled zones in the rocks, indicatingthat cracks developed earlier in the same

"'1""

Bank. CollapseNorth of Yucca Valley where OldWoman Springs Road crosses PipesWash. 1 to 2 miles (2 to 3 km) south 01the epicenter, roadcut failures occurredonly v.mere there was surface faulting(along the Johnson Valley Fault) within afew hurxlred yards (meters) of the highway. The north-facing bank of PipesWash, VJest of the highway, exhibitedvery shallow landslides within 1,600 feet(500 m) of the road.Triggered slip on the Calico Fault,34 miles (55 km) north of the epicenter,was marked b,llocalized sloughingof thevertical bank of Box Canyon Wash inthe Rcxlman Mountains. It is noteworthythat bank sloughing was seen only within600 leet (200 m) of the area ofminorsurface rupture.

" CALIFORNIA GEOlOGY JANUARYrFEBRUARY 1993


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The strength of the earthquake in thisvicinity can be attributed to the secondsubevent that started on the EmersonFault. about 22 miles (35 km) south ofNewberry Springs. and the northwardpropagation of the faulting.[n Newberry Springs. north of Interstate Highway 40. several northeasttrending fissures ruptured streets on theeast side of Mojave Valley, Three promi

nent extensional cracks. striking N30"to 35"E. crossed Valley Center Road.The crack 0.8 mile {1.3 kml east of New-berry Road had a west-facing scarp with2 inches (5 em) of relief. Cracks 1.1 miles(1.8 km) and 1.25 miles (2.0 kml eastof Newberry Road had 2.3-inch (6-cm)scarps facing each other where theycrossed Valley Center Road. Thesecracks. which could be traced mostly asopen. extensional fissures for more than980 feet (300 m). bounded a downdropped block or swale-Iike depressionalong Valley Center Road. The relief onthis down-dropped block between the twocracks is 5 to 6 feet (1.5 to 2 ml, Accordingly. the earthquake cracks fonnedwhere a pre-existing trough-like channeloccurs in the lakebed deposits of MojaveValley. A L2-inch- (3-cm-) high. eastfacing crack developed across SilverValley Road. 0.56 mile (0.9 km) east ofNewberry Road. that also mimicked theexisting gentle topography. An explanation for the development of the series offissures in Mojave Valley may lie in therapid decrease in the water table. due topumping. in this area (Wes Reeder. SanBernardino County geologist. oral communication. 1992). Prominent fissureshave developed. mostly aseismically. inmany places in the arid southwest wherethere has been rapid withdrawal ofground water.Additional Shaking Features

A concentration of surface effects wasalso seen along a 3-mile (5-km) stretch ofthe Pisgah Fault near the Hector Mine.some 38 miles (60 km) from the epicenter. One soilfall occurred in a prospectpit. However, cracked or shattered crustsaligned with the fault trace were morecommon. The shattered crusts were onpiles of prospect pit debris rich in dry.brittle clay. In addition. a broad zone ofcracks developed over an area of abouthalf a square mile ( l or 2 km2j. east of the

trace of the Pisgah Fault north of theHector Mine. Due to prolonged. eastward-directed shaking. pebbles fell fromthe western surface into many of thenorthwesHrending cracks (Photo 3).

. \Photo 2. large boulder (shaken looseduring landers earthquake) that rolleddown this windblown. sand-covered slopeon the east side ot mountains north 01Homestead Valley. Boulder came to restwithin 3 teet (\ m) otthe HomesteadValley Faull. which crosses sandimmediately behind bouldel. Pharo byA.G. Barrows.

BIG BEAR EARTHQUAKERegional Setting

The region where the strongest shaking was concentrated during the Big Bearearthquake lies in the eastern and centralSan Bernardino Mountains. Here. maximum variation in elevation exceeds 2.000feet (610 m) over a horizontal distance of1 mile (1.6 km). The rocks are predominantly igneous and metamorphic withminor sandstone and conglomerate units.

A combination of several factors contributed to the severity of the slope-failurefeatures triggered by the Big Bear event

including steep slopes. shattered rocks ina complex tectonic environment of mul-tiple major fault strands. frost-wedging athigher elevations. and lack of a continuous ground cover to protect the surface.In such places rockfalls are common. evenwithout powerful earthquake shaking.

In the vicinity of the Big Bear earthquake epicenter many very large ancientlandslide masses have been mapped(Bortugno and Spittler. 1986). In fact. theepicenter is on a very large landslide onthe slopes of Sugarloaf Mountain. 5 miles(8 km) southeast of Big Bear Lake. Else-where in the San Bernardino Mountains.a number of recently active or troublesome landslides have been mapped [fan.1989. 1990). Directly after the earthquake. several geologists checked theknown large landslide masses and theyoung problematic ones and did not findclear evidence of remobilization.Rocktalls

Nearly continuous rockfall activity inthe deeply dissected wildemess terrainsouth of 11.499-foot (3.500-m) SanGorgonio Mountain was triggered by theLanders and Big Bear earthquakes andtheir abundant aftershocks. The easternSan Bernardino Mountains were obscuredby the dense gray clouds of dust rising likesmoke all day on June 28. l1le very steepto vertical. nearly barren walls of theI.800-foot- (550-m-) deep amphitheaterat the head of Mill Creek and the 2.000foot- (6IO-m-) deep amphitheater at thehead of the Middle Fork of WhitewaterRiver were the sources of much of thebroken rock and dust that tumbled. rolled,and fell down chutelike ravines duringand for several days after the earthquakes.

Fresh rockfalls were obsetved onthe slopes of the Utile San BernardinoMountains eastward into the JoshuaTree National Monument and on bothsides of Morongo Valley as well as in thedeeply dissected canyons of the SanGorgonio Wilderness. State Highway 38.which is the only paved road across theepicentral area olthe Big Bear earthquake. was closed between June 28and July 3 to allow for road cleanup andrepair. Very near the epicenter of the BigBear earthquake. 5 miles (8 km) east ofBarton Rats. a single large rock tumbledonto Highway 38 (Photo 1).

CALIFORNIA GEOLOGY JANUARY/FEBRUARY 1993 "


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An unusual phenomenon in Mil lCreek Canyon was described by TomWellman. Rre Chief of Forest Falls (oralcommunication. 1992). There were three"fraction" f ires near Mountain HomeVillage. ignited by sparks generated byfalling rocks striking others.Blocklalls

About two dozen granodiorite blocks.each weighing between 50 and 300 tons(45 and 270 metric tons) and measuringas much as 18 feet (6 m) long. wereshaken from jointed. ledgelike outcropsclose to the trace of a branch of the Mil lCreek Fault (Dibblee. 1964). Theytumbled 600 t o 800 feet (180 to 250 m)dO\VTl the south wall of Mill Creek Canyon. breaking mature trees and landing30 to 100 feet (10 to 30 m) from variousstructures (PhOIOS 4 and 5). The blockfallsOCCUlTed in an area 9. 3 miles (15 km)southwest of the epicenter. on a hnethat coincides with the N45E orientationof the fault that generated the Big Bearearthquake. Although there were noinjuries or structural damage from theblockfalls of June 28. many of the

southernmost structures in the community of Forest Falls are in a rockfallhazard zone.Additional Shaking Features

For the Big Bear earthquake. thegreatest ground acceleration recordedby a California Strong Motion Instrumentation Program ground-responsestation was 0.57 g at the Civic Centerin Big Bear Lake. 7 miles (11 km)from the epicenter (Huang and others.1992). Damage was restricted to communit ies in the San Bernardino MQWl'tains. Liquefaction-induced lateralspreading fissures damaged structuresin the Pan Hot Springs area. east ofthe intersection of Highway 18 andParadise Way in Big BearmmMcCrink and Mark DeUsle. Divisionof Mines and Geology lDMG]. writtencommunication. 1992). At the hotsprings facility there were arcuatecracks striking N20oE. with O.5-to2-inch (1- to 5-cm). dO\VTl-to-the-east.vertical displacements. Numerouscracks also developed in the meadowto the southeast. McCrink and DeUsie

concluded that shallow ground water fromthe artesian spring and the location of thefacil ity on a sandy alluvial fan made thesHe susceptible to liquefaction.

On the south bank of the Santa AnaRiver. about 0.8 mile (1.3 km) along RiverRoad. west of its junction with Highway38 near South Fork Campground. an800-foot (250'm) zone of curved cracksdeveloped in a wooded area at the baseof the slope and disrupted unpaved RiverRoad. The cracks were as much as 4inches (10 em) wide and. locally. exhibiteddown-to-the-north displacements of asmuch as 12 inches (30 em) (photo 6).Apparently. they fonned in response tostrong shaking and were locally accompanied by sand boils (Doug Morton. U.s.Geological Survey [USGS] oral communication. 1992). Surface fault rupture wasnot found in this area.

McCrink and DeUsle (DMG. writtencommunication. 1992) observed a setof linear cracks trending N700E thatcut across a stream terrace deposit onPatterson Road along the north side 01the Santa Ana River about 0. 5 mile

Photo 3. Small. N15 W-trending extensional cracks within a broad zone of such features along the Pisgah Fault north 01the HectorMine. Prolonged shaking cleared the surlace 01 pebbles on the west side (pebbles lell into crack) resulting inlightcolored bands along each crack. Photo by A.G. Barrows

20 CALIFORNIA GEOLOGY JANUARY FEBRUARY 1993


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Photo 4. Looking southwest t ram the north side 01 Mill Creek Canyon overthe roottops at the Forest Home community across MIl! Creek toward the3.000 foot- (900 m-) high slope 01 Birch Mountain. The irregular. lightcolored streaks are debris lIow scars and creek ravines. The thin line left01 center is the track through the trees cut by the large block pictured InPhoto S. Photo by A.G. Barrows,

(800 m) southwest of the Converse Rats FireStation. The cracks probably resulted from minorlateral spreading of the terrace malerial. towardthe Santa Ana River.

ACKNOWLEDGMENTSI am indebted to rnany DMG colleagues whoshared data and obsClvallons about the effects of

the Landers and Big Bear earthquakes. Specialthanks go to Pam Irvine and Steve Bezore. withwhom I VJOrked in the field. Siang Tan contributed valuable infonnation on the Foresl Fallsrockfalls and other effects in the San BernardinoMountains.Tim McCrink and Mark DeUsie also contributed infonnation from their field investigationsin the San Bernardino Mountains. J am verygrateful to Dave Keefer of the USGS for 9ra'ciously sharing data about the extent of rockfallacllvity and. along with Randy Jibson, also of theUSGS. for the invitation to participate in a helicopter reconnaissance of the region affected byrockfalls, California Department of Transportation (CALTRANS) geologist Jeff Knott suppliedsome excellent photos of rockfall features. HectorMine geologist Richard Wj]]ette cordially guidedme on a tour of the earthquake effects along thePisgah Fault in the Heclor Mine and providedinfonnation about the effects in NewberrySprings. Wes Reeder. San Bernardino Countygeologist. shared obselVations about the fissuresin Newberry Springs and the rockfalls in theSan Bernardino Mountains.

PhotoS. The 20)( 12)(12-loot (6.1)( 3.7)( 3.7m)block came to rest 100leet (30 m) Irom the shedwith the gable rool and150 teet (46 m) from thedeck anached 10 thehouse on the right. Photoby Siang Tan.

CALIFORNIAG EOLOGY JANUARY/FEBRUARY 1993


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::;.' , . ' ' - f f

Photo 6. Down'lo-Ihe-north, curving tissure. related to lateral spreading. 11 is traceable for 820 feel (250 m) across unpaved RiverRoad 0.8 mile (1.3 km) west 01 i lsJunction with Highway 38 near South Fork Campground (along the south side of the canyon ofthe Santa Ana River, close to the epicenter of the Big Bear earthquake). Photo by Siang Tan.

REFERENCESBortugno. E.J .. and Spinier, T.E., compilers.1986, Geologic map 01 the San Bernardino quadrangle: Division of Mines andGeology Regional Geologic Map 3A,

scale 1:250,000.Dibblee, rw " Jr . 1964. Geologic map of theSan Gor90nio Mountain quadrangle,San Bernardino and Riverside counties.California: U.S. Geological Survey Miscellaneous Geologic Investigations Map1-431, scale 1:62,500.Hauksson. Egill: Jones, Lucy; Heaton. Tom:

Hutton. Kale: Mori. J im: Hough, Sue:Kanamori, Hiroo: and Thio. Hong Kie,1992, The Landers and Big Bear earthquakes in eastern San BernardinoCounty. June 28. 1992: Preliminaryupdate report wril len at 10:30 am 30June 1992: California tnstitute of Technology and U.S. Geological Survey. 5 p.

Huang. M.J.. Shakal. A.F.. Cao. T.O.. Fung.P.F., Sherburne, R.W.. Sydnor, R.H ..Malhotra. P.K .. Cramer, C.H.. Suo Feng.Darragh. R.B., and Wampole, K.G.,1992. CSMIP strongmotion recordsfrom the Big Bear. California earthquakeof 28 June 1992: Division of Mines andGeology Report No. OSMS 92-10.236 p.

Morton, D.M" t975, Seismically triggeredlandslides in lhe area above the SanFernando Valley in Oakeshott. G. B..editor, San Fernando, California, earthquake of 9 February 1971: CalitorniaDiVision of Mlfles and Geology Bulletin196. p. 145154.

Shakal, A.F., Huang. M.J.. Cao, T.O..Sherburne, R,W" Sydnor. R.H., Fung.P.F" Malhotra. PK, Cramer, C.H.. Su,Feng. Darragh, R.B.. and Wampole,K.G., 1992. CSMIP strongmolionrecords from the Landers. Californiaearthquake of 28 June 1992: Divis ion ofMines and Geology Report No. OSMS9209, 330 p.

Spittler, T.E., Harp, EL. Keefer. OK, Wilson. R.C" and Sydnor. R.H .. 1990.Landslide features and other coseismicfissures triggered by the Lorna Prietaearthquake. cenlral Santa Cruz Moun,tains, California in McNutt, S,R.. andSydnor, R.H.. editors, The Lorna Prieta(Santa Cruz Mountains). California.earthquake of 17 OCtober 1989: Divis)on of Mines and Geology SpecialPublication 104. p. 5966.

Tan. S.S., 1989, Landslide hazards In theLake Arrowhead and Big Bear Lake

region. San Bernardino Counly. California: Division of Mines and GeologyOpenFile Report 89-7, 3 plales, scale1:24.000.

Tan, S.S., 1990. Landslide hazards in theYucaipa and Forest Falls quadrangles.San Bernardino County, California:Division of Mines and Geology OpenFile Report 90-5, 2 plates, scale1:24,000,

UMTY IN 93 . CAUFORNIAMINING ASSOCIATION

Annual MeetingMarch 9-12.1993MOnlerey Ploza HolelMonlerey. California

For infonnation, contact:California Mining Association1121 L Slreet, Suite 909Sacramento, CA 95814'B' (916) 447,1977FAX (916) 4470348

22 CALIFORNIA GEOLOGY JANUARY/FEBRUARY 1993


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/

-- 3

HO HonlontalVO VertlC:il l otIWlNS Net slipAt _ , ; . , . , . , . . ~ -VO v'"""

-"'EU Easl side upIrelallVe l ID_ I-,SU Soultlllde up' ~ J V I I O nontl....WU Wasts up / ' "( re la llve to as!-, a;;;nttu wnside ollaull

1

EXPlANATION

//,,

~

'7 HO 4.S>-mIItiJ.(14.8 'Mil) RL Iva 1.3 meters(4.3 feel)EU 1NS 4.7 mete",(15.4 f8e,',I.:.P;;',:;;" . .;: 18.5,~ 3 7 " W

, / + - : - - ., 'T ' " . . . 1: f r . ' r Surface Rupture ,Along a Portion of the Emerson FaUlt

Landers E a r t h q u a ~ 01 JU(le 28. 1992 IPAME J. IRVINE and FPBERT L. HJ!..L ~ t S t s

DMSK)n of MI and aeofogy


24/32

Photo 1. View toward f1OI1heast at offset south slope 01 ridge. GeologJStlS holdmg Bruntoncompass to striatIOns {small. parallel grooves and (Idges not VISible In thIS photo) on faultwrface, SlnallOOS IndICate directIOn 01 slip (actual rather than "apparent" movement) alonga faull Line In upper nght quadrant of photo IS onented parallel to the striations. (Photo 2is a closeup of striatIOns at another locality,) Largerscale undulalJons called mullions arecommonly observed on fault surfaces. Indicating dlrec\lOn of Slip, Mullions are VISible m thiSphoto and are onented With their long alles parallel to the stflallons Photo by RL HIli,

Surface rupture along this part of theEmerson Fault was mapped on July 8.9. and 11. 1992. by geologists with theDivision of Mines and Geology (DMG) aspart of a cooperative field investigationinitiated by DMG and the U.S. GeologicalSurvey (USGS) shortly after the Ulndersearthquake. The purpose of the fieklinvestigation was to document the location and nature of the surface ruptureand to measure the displacement alongthe fault zone.

The part of the Emerson Faultlnvolved in this study is a 3.4-mile(5.5-kml segment extending from GalwayLake Road (SE comer of Sec. 4. T. 5 N..R. 4 E.) southeast to a small playa in theNE comer of Sec. 23. T. 5 N.. R. 4 E.of the Iron Ridge USGS 7.5-minutequadrangle (see map), Fault-rupturefeatures were mapped on vertical aerialphotographs at a scale of approximately1:6.000 (1 inch - SOD feet) and datawere transferred onto the USGS 7.5minute quadrangle map at a scale of1:24.000 (l inch - 2.000 feet).

GEOLOGIC SETTINGThe regional geology is summarizedby Dibblee (1964) and Bortugno andSpinier (1987). The study area is in thewestern Mojave Desert geomorphic province. an area characterizro by northVJeSttrending mountains and valleys bounded

by Quaternary (1ess-than-2-million-yearoki) faults. The oldest rocks exposed inthe study area are hornblende diorite andquartz monzonite of Jurassic and JurassicCretaceous (?) age {between 66 and 208million years oIdJ, These granitic rocksform the rugged mountains and hills onthe east side of Upper Johnson Valley(cover photo).Younger rocks in the study areainclude nonmarine sandstone and siltstone of possible Pliocene age (between1.6 and 5,3 million years old). which are

mantled by younger gravels and form lowhills with badlands topography east of thebedrock ridge (back cover photo. center).Also included are Quaternary-age olderalluvium composed of semi


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..

Photo 2. Close-up of slickenside striae (small, parallel grooves andridges) on fautt surface in Photo 3. View IS to nonheast, perpendicularto the fault. Striations indicate the block east of fault has moved diagonally upward and to the southeast ( to the viewer's right). Striationsplunge 2 3 f rom the horizontal. They are on gouge (or fault gouge)whIch conSists of finely crushed and pulverized rock and mmeraltragments and clay. The thickness of the gouge at this location andelsewhere along the faull indicates that movement has occurredintermittently. probably many times over a period ot perhaps severalhundred thousand years or more. Photo by RL Hill.

than 1.2 miles (2 km) east of the main rupture zone. Someof these features are shown on the map but they. along withthe more subtle fractures observed along the main rupture frace,are too numerous to discuss in this article. Therefore. the following descriptions win be l imited fo major fault-rupture featuresobselVed along the main rupture zone of the Emerson FaultIrom Galway lake Road south to the small playa (front andback cover photos). Localities A through J are shown onthe map.

Maximum right-lateral displacement resulting from theLanders earthquake occurs where the main trace of theEmerson Fault crosses Galway Lake Road (Locality A). Thefault rupture zone at this location consists of three or morefault traces producing a cumulative right-lateral offset (of theroad) of approximately 20 feet (6 mI.

Surface rupture along the fault between Galway Lake Roadand the ridge 0.5 mile (BOO m) to the south (between localitiesA and B: and back cover photo. bottom half) is characterizedby left-stepping en echelon fault scarps trending N32Q-37'W.which form elongate compressional ridges (mole tracks) in theyounger alluvium. The main rupture zone is approximately50 feet (IS m) wide with minor cracks extending more than82 feet t2S m) beyond the main zone. Fault rupture does notconsistently follow older fault scarps but. in some areas. doesoccur at the base of previously uplifted older alluvium.

CALIFORNIAGEOLOGY

The most dramatic fault-rupture features occur on theridge 0.5 mile (800 m) south of Galway Lake Road (betweenlocalities B and C: back cover photo. cenler) where the faultpasses through the okler. more consolidated Pliocene (?)sandstone and siltstone fanning the ridge. Fault rupture inthe northem part of the ridge is characterized by a distinctfault scarp trending N35QW and dipping 79 - B 9 ~ S W withthe east side up. and several smaller. subparallel fault scarpssplaying to the east and west f rom the main trace. Rightlateral-oblique movement along this segment of the fault hasoffset stream channels about 15 feet (4.5 m) and created faultscarps 4.3 feet (1.3 m) high. Numerous shaking cracks andsome seismically-induced gravity slides occur near the top ofthe ridge east of the main rupture zone

The northern portion of the ridge appears to have beendisplaced northward as a seismically-induced. large. incipientlandslide bounded by an arcuate zone of surface rupture. Onthe east flank of the ridge. the rupture zone consists of northtrending cracks and fissures that displace the ground surfaceas much as 13 inches (33 em). north side down. [n the alluvium near the base of the ridge. these features become discrete cracks or narrow zones of cracks with a more northwesterly trend. lhese discrete cracks offset drainage channelsas much as 7.9 inches {20 em) right-laterally. and displacethe ground surface as much as 3 inches (7.6 em) vertically.v..rest side up The cracks and fissures on the ridge are extensional features interpreted to be the break-away zone at thehead of the landslide. The discrete cracks in the alluvium are

PhOfO 3. View looking nonheast along fault scarp. Photo by B.M."Um;;le Ben" Irvine.

JANUARY/FEBRUARY 1993 25


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compressional fealUres interpreted to bethe lateral margin and toe of the slide.

REFERENCES

Photo 4 Northeast-trending tault splay. The ground surlace on whrch the geologlsf isstanding. southeast o! the splay. has been uplifted 14.2 Inches (36 em). V,ew 10 the east.Phoro by P J Irvine

In the central and southern part ofthe ridge. the main trace of fault rupturechanges orientation. trending N68Wanddipping 83NE as it crosses over the ridgetoward the southeast. This fault scarp provides excellent eXl'XlSUres of fault gougeand striations (Photos I. 2. and 3). Themain fault scarp splays into numeroussmall scarps at the south end of the ridge.These smaller scarps display the samerightlateraL east-side-up displacement asthe main discrete fault scarp. Several arcuate zones of shaking cracks occur on topof the ridge west of the main rupture zone.

South of the ridge. the fault crossesgently sloping hiUs made of Pliocene (?)sandstone and siltstone and older alluvium(between localities C and Dj. The rupturezone consists of three ormore Ieft-stepping. east-sk!e-up. en echelon faults.

The main fault-rupture trace becomesless distinct farther to the south as itcrosses younger alluvium in the activedrainages (between localities D and E).The fault-rupture zone in this area consistsof a main scarp. east side up. with manysmall-scale. en echelon fractures. Olderalluvium east of the recent fault ruptureforms older. \.\leSt-facing scarps.

Between localities Eand F. the mainrupture trace steps to the tight. forminga graben (fault-bounded. down.


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DMG Clearinghouse for the June 28, 1992 Landers and Big Bear EarthquakesTOUSSON A. TOPPQZADA, RICK I. WILSON, and CLAUDIA L HALLSTROMDivision of Mines and Geology

W ithin 24 hours of the Landers andBig Bear earthquakes. the Divisionof Mines and Geology (DMG) establishedan earthquake infolTllalian clearinghouse(CH). The CH was established near theepkentral area on Twentynine PalmsHighway in Yucca VaDey. 5 miles (8 km)south of Lmders 1he CH: 1) coordinate:! DMG field aetMIJeS; 2) collectedinformation from geosdentislS in publicand priVate sectors; 3) prclI.ided a locationfor discussion and coordination amongscientists concerning the dai}I; field work;and 4) disseIlllnated infonnation to scientific inYeStigators, government agencies.and the public.

The CH. with the support of theOffice of Emergency Services (DES).arranged for a National Guard heliCOpterto transport four geologists on a reconnaissance flight of the extensive area offaulung. The helicoptermade severalLandings enabling the geoklgists to checkfeatures on variolts fauhs. This recoonaissaoce helped identify which of the 1UTIef 'ous faults were irl\.oOh.oed In the complexfaulttng process. and helped plan and

focus the fiekl mapping during the follow-ing weeks.

The CH was In operation from June291oJu/y 15. It was staffed from 8 a.m.to 6 p.rn to receive and record data,relay messages between field personneland DMG heaciqudrters in Sacramento.and discuss f i n d ~ With SCientific mvesti-gators. re.ponse groups. andthe pub6c. The CH staff kept the publicapprised of aftershocks arv:l other U1for-mation usmg FAX updates from the Cabfomia Institute of TechncMogy (ern. compilations of fault-ruptures and groundfailures from field geologists. and detailedaerial photographs taken several daysafter the earthquakes by commercialoperators and U.S, Air Force U-2 reconnaissance aircraft Infonnalion from localnewspaperswas later used to supplementNational Earthquake Information Center( Elq ~ m a i r e s in compiling theisoseismal map ofgeographical distribution of ground shaking of varying intetlSlties from the earthquake (seeToppozada.this issue),

Every night. the CH was the meetingplace for DMG scientists. the U.s. Ge0logical Survey (USGS). universities' staff.and consulting filTT'ls, These meetingsprovided an atmosphere of scientificdiscussion and debate and were effectivein coordinating INOI'k plans among thedifferent groups

Many resdents \l.no had sustainedearthquake damage 10 their homes vbitedthe CH and wanled to speak With geosci-entists about the earthquakes and thefaults. Il"qliries from the pubtic and themedia often diverted the scientific staffsattention from coordinating field activitiesand updating and disseminating earthquake and fault lnfonnation. On July 10.Ed Heidig. Director of the Department ofConservation and Jim Davis. State Ge0lo-gist held a press conference al the CH

TIle clearinghouse was successfulthanks 10 the enthusiasllC support of SanBernardino County officials generously provided the Environmental HealthServX:e Office, support staff. and communications facililie!.

GeologISts tram DMG. USGS. and other organlZa\lOflS met at the cleannghouse each everwng to dISCUSS observa\lOflsand to coordinate fault ruplure mapping and other hekt aet'VllJe$, Photo by Claudla Hallstrom,

CALIFORNIA GEOLOGY JANUARY 'FEBRUARY 1993 "


28/32

Field Guide: Santa Catalina Islarxl By5. ROlNklnd. 5 Sorenson. C. Savrda. OJBolljer. and 0 Gorsline; Geoklgy ofSanta Catalina Island and Nearby BaSIns.By BW Pipkin and R. Lebow; Geologyof San Pedro Basin. L.A. Harbor to SantaCatalina - A Deep-Sea Field Trip. By RGivens: Nearshore Marine Biota. 5 C.Island, Pipkin. B W.. compiler 198476p $900

Geology and Landslides of the PamVerdes Hills. Cabfornia By BW Pipkin.ME. Bryant. and E.J, Baldu.in 198677 p $600

Quarternary Strcmgraphy. Soil Ge0morphology. QlI'Of"ICl6ogy and TectonICSof the Ventura. O)ai. and Sarlla Paulaareas. Western Transverse Ranges. Cabfornia E.A KeIer. editor 1981159p $SOOThe San Andreas Faull Sysr:emWhere East MeetsWest A TeachmgModule By A R Ko. By Betty HlIl"IlIlleI1. 1977,39 P $4 00Geologic Adventures in NorthernBaja. CA Gary Jacobson. editOf. 1991

50 p 10.00Geology of Northeast California_By

Terrance Kato. David MIlIer.0nn BykerkKauffman. Howard Stensnii. and VICtorAsher 1990.56 p L.. ,$8,00

Suspect Terrane Exercises 1971 p. $6,00; and Suspect Terrane. 36slides of di.agrams in exercises. By AnnBykerk-Kauffman. 19 $20.00Geok>gtc Exa.O"sions in the GreaterLos I\ngele> ,",,,, By t.aw.eoce CoDiru;.1989; FJekI Guide to St Franci!. DamArea By H Adams; Field Guide to SanGabriel Mts. By A. Barth. P Ehlig. andP Weigand. Field Guide to SubmarineFans in Santa Monica MIS Yorba LindaArea & San Clemente State Beach ByP Ascher. D. Schwartz. D. I Colburn.and V Cherven. 85 p .... $8.00

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Robert Wallace Webb Memorial Sym-posium: Quaternary Slip Rates and Earthquake Hazards; Accretion Along CoastalOregon and Washington; BoreholeRemote Sensing and MicrocomputerSoftware; Arc Magmatism; Seismic Hazard Analysis; and Strelched Pebble Con-glomerates in the Caledonian Paradox.Dorothy L. Steller, coordinator. 1985.51 p $4.00

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The names of theLesley Ann and Oro BeUepits were inadvertentlyomined from the map onpage 182, The correctedmap is shovm at right.

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Slout. M.L.. editor. 1992. Associ-ation of Engineering Geologists. Proceedings for the 35th Annual Meeting.October 2-9. 1992. Los Angeles,California $40.00

Bulletin of the Association of Engi-neering Geology Volume XX. Number 1.Conlains MGeo\ogy of Long Beach.California. Umited supply $5.00

Make checks payable to AEG South-ern California Section. Add 8.25 percentsales lax and $2.50 for the first book and50 cents for each additional book forpostage and handling. Send 10:

AEGBOOKSAlE

Shuirman, G. and James SIosson.1992. Forensic Engineering. Envi-ronmental Case Histories for CivilEngineers and Geologists. AcademicPress, Inc $49.95

Ebersold, D.B.. editor, October 10.1992. Landers Earthquake of June 28.1992, San Bernardino County,California Field Trip Guide. Umiledsupply ,$8.00$500

$12,00

$5.00$500

.$5.00$500

..... FI86

..$18,00$2200

,.$16.00.... $9.00

,....$5.00

, ... $16.00$16.00

List ot AvaIlable PublicatIons

SPGO

Number 01 COplfISSPECIAL REPORTS__ SR52 Index to geologIC maps of Cali forn ia to December 31.1956. 1958 ..SA52A Index to geologIC maps of California 19571960. 1962.SR52B Index to geologIC maps of Cahtornl8 1961-1964. 1968..SR102 Index to geologIC maps of California 1965-1968. 1972SR106 GeologIC features 01 Death Valley I l n ~ o and San Bernardinocounties]. Cahlorfll8. 1976 . . .SPECIAL PUBLICATIONS__SP57 Proposed earthquake safelyprograms and aetlYllJeS of the

Department 01 Conservation, fiscal years 1982 through 1986. 1980Earthquake planning scenario fOf a magnitude 83 earthquakeon the San Andreas Fault in soolhem California. 1982 ._ _.5Pl08 An analySIS of the seismic hazard informatiQn needs of the InsuranceIndUstry, local gov8!'nment, and property owners in Ca!l1ornl3 1990 _$7.00

REGIONAL GEOLOGIC MAP SERIES (scale: 1:250.000)__RGM1A GeologiCmap 0' the SacramenlO quadrangle(set at 'our sheets). 1982 ,__RGM2A Geologic map 0' the Santa Rosa quadrangle(set ot 'ive sheets). 1982..........RGM3A GeologIC map 01 the San BernardlOO quadrangle(set of love sheels). 1987 .RGM4A GeologiC map at the Weed quadrangle (set a! loor sheets). 1988 ...RGM5A GeologiC map at the San Francisco-San Jose quadrangle(set of tive sheets). 1991 .RGM7A GeologIC map altha Chico quadrangle (sal at ' ive sheets) 1992OTHER

Sponsored byTHE CALIFORNIA DEPARTMENT OF CONSERVATION

DIVISION OF MINES AND GEOLOGV AND THE U.S. BUREAU Of MINESApril 25-30. 1993

Sheraton Long Beach Hotel- Long Beach. CaliforniaFor 28 years. the annual Forum on the Geology of Industrial Minerals has been hostedby state and provincial geologtcal agencies throughout North America. 1be Forumprovides the opportunity to learn more about the nature and distribution of industrialmineral deposits and advances in research. exploration. mine development, procklC-lion. and marketing. The 29th FOl\lJlllAlill emphasize industrial mineral deposits of thesouthern California region and will include 2 days of technical sessions and 3 days offield trips. Anticipated registratkm fee is $125.00: field trips are additionalFor more information. contact:

- - - - - - - - - - - - - - - - - - - IDIVISION OFMINES AND GEOLOGY IPublications Request Fonn IIIII

CAUFQflNIA GEOLOGY JANUARY/FEBRUARY 1993


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STATE OF CALIFORNIATHE RESOURCES AGENCY

OEPARTMENT OF CONSERVATIONCALIFORNIA GEOLOGYOIVISION OF

MINES AND GEOLOGYPO , BOX 2980SACRAMENTO CALIfORNIA 95812-2980USPS 350 840

ADDRESS CORRECTION REOUESTED

SECOND CLASS POSTAGEPAID AT SACAMENTO, CALIFORNIA

Sunace rupture along Emerson Fault south 01 unpaved Galway lake Road Galway l ake playa IS vIsible near the upper left corner althaphoto Zone 01 sunace rupture is the dark ~ n extending trom the lower left corner to the upper fight corner. The IranI cover photo showS

caliifornia geology magazine jan-feb 1993

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