Active Faulting In The Walker Lane

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TECTONICS, VOL. 24, TC3009, doi:10.1029/2004TC001645, 2005Active faulting in the Walker LaneSteven G. WesnouskyCenter for Neotectonic Studies, University of Nevada, Reno, Nevada, USAReceived 2 March 2004; revised 15 December 2004; accepted 3 February 2005; published 16 June 2005.[1] Deformation across the San Andreas and WalkerLane fault systems accounts for most relativePacific–North American transform plate motion.The Walker Lane is composed of discontinuous setsof right-slip faults that are located to the east andstrike approximately parallel to the San Andreas faultsystem. Mapping of active faults in the centralWalker Lane shows that right-lateral shear is locallyaccommodated by rotation of crustal blocks boundedby steep-dipping east striking left-slip faults. The leftslip and clockwise rotation of crustal blocks boundedby the east striking faults has produced major basinsin the area, including Rattlesnake and Garfield flats;Teels, Columbus and Rhodes salt marshes; andQueen Valley. The Benton Springs and PetrifiedSprings faults are the major northwest strikingstructures currently accommodating transform motionin the central Walker Lane. Right-lateral offsets oflate Pleistocene surfaces along the two faults pointto slip rates of at least 1 mm/yr. The northern limit ofnorthwest trending strike-slip faults in the centralWalker Lane is abrupt and reflects transfer of strike-slipto dip-slip deformation in the western Basin and Rangeand transformation of right slip into rotation of crustalblocks to the north. The transfer of strike slip in thecentral Walker Lane to dip slip in the western Basin andRange correlates to a northward broadening of themodern strain field suggested by geodesy and appearsto be a long-lived feature of the deformation field. Thecomplexity of faulting and apparent rotation of crustalblocks within the Walker Lane is consistent with theconcept of a partially detached and elastic-brittle crustthat is being transported on a continuously deforminglayer below. The regional pattern of faulting withinthe Walker Lane is more complex than observedalong the San Andreas fault system to the west.The difference is attributed to the relatively lesscumulative slip that has occurred across the WalkerLane and that oblique components of displacement areof opposite sense along the Walker Lane (extension)and San Andreas (contraction), respectively. Despitethe gross differences in fault pattern, the WalkerLane and San Andreas also share similarities indeformation style, including clockwise rotations ofCopyright 2005 by the American Geophysical Union.0278-7407/05/2004TC001645 12.00crustal blocks leading to development of structuralbasins and the partitioning of oblique components ofslip onto subparallel strike-slip and dip-slip faults.Citation: Wesnousky, S. G. (2005), Active faulting in theWalker Lane, Tectonics, 24, TC3009, doi:10.1029/2004TC001645.1. Introduction[2] Pacific –North American relative plate motion at thelatitude of the San Andreas fault system is 50 mm/yr(Figure 1) [DeMets and Dixon, 1999]. The transformmotion is taken up largely along the San Andreas faultsystem. Up to one fourth of the strike-slip motion isdistributed on faults east of the San Andreas fault systemwithin the Eastern California Shear Zone and the WalkerLane [Bennett et al., 1998, 2003; Dixon et al., 1995; Dokkaand Travis, 1990a, 1990b; Minster and Jordan, 1987;Oldow et al., 1994; Reheis and Dixon, 1996; Sauber,1994; Sauber et al., 1986; Thatcher et al., 1999]. I presenthere the results of a field study of a set of active faults in thecentral Walker Lane (Figure 1). The area encompasses aright step in the northwest trending system of strike-slipfaults. The purpose of the study is to lend clarity to the style,recency of displacement, and slip rate of active faults in thearea. The resulting observations provide the underpinningsof discussion bearing on the role of active faulting in thestructural and physiographic development of the region,mechanisms of displacement transfer along the discontinuous set of faults defining the Walker Lane, the relationshipof active faults to variations in measures of geodetic strainalong the Walker Lane, and reasons for similarities anddifferences in styles of faulting between the Walker Laneand San Andreas fault systems. For context, I first reviewavailable observations describing strain accumulation andthe history of slip on faults within the Eastern CaliforniaShear Zone and Walker Lane. The results of the field studyare provided in the subsequent observations section.2. The Eastern California Shear Zone andWalker Lane: Displacement History and StrainAccumulation2.1. Overview[3] The term Eastern California Shear Zone (ECSZ) wasfirst used by Dokka and Travis [1990b] for the set ofnorthwest striking right-lateral faults that cut the MojaveDesert (Figure 1). The earliest accounts of strike-slipfaulting east of the Sierra Nevada include Gianella andTC30091 of 35

TC3009WESNOUSKY: ACTIVE FAULTING IN THE WALKER LANETC3009Figure 1. (left) Regional fault map. The Walker Lane and Eastern California Shear Zone are outlined bylarge box. (right) Larger scale map. Small box on left bounds faults mapped in this study. Fault names areannotated and regions subdivided for convenience of discussion. Locations of 26 March 1872 M7.6Owens Valley, 28 June 1992 M7.3 Landers, and 16 October 1999 M7.1 Hector surface ruptures aredenoted by thicker lines. Area enveloping 1932 Ms7.2 Cedar Mountain earthquake ground ruptures isshaded gray. Mount Shasta (MS) and Lassen Peak are shown by stars. Pacific – North American relativeplate motion vector is from the work of DeMets and Dixon [1999].Callaghan’s [1934] description of the 1932 Cedar Mountain earthquake and the mapping of Ferguson and Muller[1949] and Nielsen [1965]. The zone of strike-slip faultsand associated disrupted topography, all or in part, hasbeen referred to as the Walker Lane [Locke et al., 1940],the Walker Line [Billingsley and Locke, 1941], the WalkerBelt [Stewart, 1980], and the Walker Lane Belt [Carr,1984]. For convenience, I use the term Walker Lane toencompass the zone of right-lateral faults that extendsnorthward from the Garlock fault. Stewart [1980] broughtto attention that the pattern of faulting in the WalkerLane is structurally complex and does not consist of asingle throughgoing system of right-lateral faults. Hedivided the Walker Lane into 9 discrete ‘‘structuralblocks.’’ The grouping and labeling of Walker Lanefault domains in Figure 1 is modified from his work.2.2. The Eastern California Shear Zone of theMojave Desert[4] The San Andreas fault bends sharply westward at thelatitude of San Bernardino where it forms the southwest2 of 35

TC3009WESNOUSKY: ACTIVE FAULTING IN THE WALKER LANETC3009Figure 2. (left) Map of active faults in and around central Walker Lane. (right) Map of northwesterntrending faults of central Walker Lane and dextrally offset Tertiary and older rocks. Location is shown bysmall box at left (simplified from work of Ekren and Byers [1984]). Half-sided arrows show sense ofstrike slip.margin of the Mojave Desert (Figure 1). There the rightlateral shear deformation associated with the Pacific – NorthAmerican plate boundary is partially transferred from theSan Andreas to a broadly distributed and complex shearzone that extends northwestward through the Mojave andthen further northward through the Walker Lane. TheEastern California Shear Zone consists of at least sevenmajor faults, each of which shows a steep dip, right slip, andanastomosing and en echelon fault segments. Dokka [1983]and Dokka and Travis [1990a] report 65– 80 km of rightlateral offset of Miocene terrain across the faults. Theyfurther interpret that displacement commenced between 10and 6 Ma (perhaps as recently as 1.5 to 0.7 Ma) and that thecumulative slip represents at least 9 – 14% of Pacific – NorthAmerican plate motion during that time. The 28 June 1992Landers (Mw 7.3) and 16 October 1999 Hector Mine (Mw7.1) earthquakes occurred on faults within this zone. Sauber[1994] analyzed a geodetic network spanning the EasternCalifornia Shear Zone and the northern portion of theLanders earthquake rupture. The analysis shows the equivalent of 12 mm/yr of right-lateral slip across the region,approximately 25% of the total North American – Pacificplate motion budget. The east striking left-lateral Garlockfault does not now appear to be accumulating left-lateralsimple shear strain due to slip at depth [Savage et al., 2001],despite geologic evidence for both long-term and Holoceneleft-lateral slip [Davis and Burchfiel, 1973; McGill andRockwell, 1998; Smith, 1962]. Geodetic measurementsshow right-lateral strain accumulation within the EasternCalifornia Shear Zone is continuous across the Garlock faultinto the southern Walker Lane [Peltzer et al., 2001; Savageet al., 2001]. The curvature of the Garlock fault may be theresult of the accumulation of strain within the Mojave[Dokka and Travis, 1990a]. The bending may provide amechanism to transmit strain, and thus stress, northward.2.3. The Southern Walker Lane[5] The southern Walker Lane extends northward fromthe Garlock fault. Major northwest striking right-lateralstrike-slip fault systems include the Owens Valley fault,the Panamint Valley– Hunter Mountain – Saline Valley faultsystem, and the Death Valley – Furnace Creek – Fish LakeValley fault system.[6] Estimates of total right slip on the Furnace Creek–Fish Lake Valley fault zone range from 40 –100 km basedon offsets of various stratigraphic and geochemical markersand isopach trends [Stewart, 1988]. Reheis and Sawyer[1997] favor a value of 40– 50 km arising from McKee’s[1968] observation of an offset Jurassic quartz monzonite in3 of 35

WESNOUSKY: ACTIVE FAULTING IN THE WALKER LANETC3009TC3009Table 1. Radiocarbon SamplesSampleLab Numbers 0058014C Ageb 2sd13CcCalendar Age,d years B.P. 2s1415 452940 35780 353960 35 25 20.5 22.1 22.11335 703088 122709 494407 115aCenter for Accelerator Mass Spectrometry (CAMS) at Lawrence Livermore National Laboratory.Uses Libby’s half-life 5568 years.cThe d13C values without decimal places are the assumed values according to Stuiver and Polach [1977]. Values with a single decimal place aremeasured for the material itself.dDendrochronologically calibrated ages calculated with Web-based University of Washington Calibration Program [Stuiver and Reimer, 1993].bnorthern Death Valley. Displacement initiated between 12and 8 Ma [Reheis and McKee, 1991; Reheis and Sawyer,1997; Stewart, 1988]. Paleozoic rocks are right laterallyoffset 16 –19 km along the State Line fault to the east[Stewart, 1988]. Right-lateral displacement on the HunterMountain fault is on the order of 8 – 10 km in the last4 Myr [Burchfiel et al., 1987]. Net right slip on theOwens Valley Fault has been considered to be no morethan a few kilometers [Moore and Hopson, 1961; Ross,1962] though Beanland and Clark [1994] suggest that10 –20 km of right slip is permissive. Kylander-Clark etal. [2005] and J. M. Bartley et al. (Large dextral offsetacross Owens Valley, California, and its possible relationto tectonic uproofing of the southern Sierra Nevada,submitted to Special Paper of the Geological Society ofAmerica, 2005) recognize 65 5 km of right slip acrossOwens Valley since 83.5 Ma, but also point to regionalrelationships to interpret that most of the displacementtook place in latest Cretaceous– early Tertiary, prior todevelopment of the San Andreas transform fault system.Thus net right slip across the region since inception of theSan Andreas transform is no more than 150 km and byfavored estimates less than 100 km. Within attendantuncertainties, the timing and cumulative amount of rightslip registered across the southern Walker Lane is similarto or slightly greater than observed across the EasternCalifornia Shear Zone.[7] Slip rates based on geology have been reported forthe major strike-slip faults. Dextral slip along the northernDeath Valley fault zone is 3 – 9 mm/yr near Red WallCanyon [Klinger, 2001]. Reheis and Dixon [1996] observethe slip rate to increase northward by 3 – 5 mm/yr on thenorthern Furnace Creek and Fish Lake Valley fault zones,respectively, though average rates along the Fish LakeValley fault zone are dependent on the location and thetime spanned by the measurement [Reheis and Sawyer,1997]. The suggested increase corresponds to the faultintersection with northeastern trending normal faults ofEureka Valley and Deep Springs Valley, and probablyrelates to a transfer of slip eastward from the HunterMountain – Saline and White – Inyo fault systems alongnortheast striking normal faults in Deep Springs andEureka Valleys [Lee et al., 2001a; Oswald and Wesnousky,2002; Reheis and Dixon, 1996]. Zhang et al. [1990]interpret Holocene dextral slip at 2.4 0.8 mm/yr onthe southern Panamint Valley fault zone. Geomorphic andTable 2. Tephra SamplesSampleLab 5184/T508-35185/T508-4Agea14 1 – 2 C ka 2.56 to 2.81 Ma 3.5 4.2 Ma 2.56 – 2.81 Ma.9 – 1.0 14C ka.9 – 1.0 14C ka3.4 Ma0.8 – 1.2 14C ka3.3 – 3.9 14C ka0.8 – 1.2 14C kaNamebMonolower tuffs of the Badlands at Willow Washcor Tuff of Curry CanyoncLower tuffs of the Badlands at Willow WashcMonobMonobPutah TuffcMonobMonobMonobaCorrelation and age estimates were provided by A. M. Sarna-Wojcicki (Head), E. Wan (Lab Supervisor), J. Walker (electronmicroprobe analyst), and M. Dodge and K. Hepper (Physical Science Technicians) at the Tephrochronology Laboratory at USGS inMenlo Park using a JEOL 8900 Superprobe. The method of analysis is described by Sarna-Wojcicki and Davis [1991].bCorresponding ages of Mono ashes are based on best correlation to tephra layers previously dated by 14C but do not exclude thepossibility that the tephra may be as young as 600 or as old as 6700 years, a period over which numerous compositionally verysimilar tephras were ejected from the Mono Craters area.cRefer to Sarna-Wojcicki et al. [2005] for type localities.dCorrelation by author is based on proximity and identical stratigraphic setting to sample SGW-H21.4 of 35

TC3009WESNOUSKY: ACTIVE FAULTING IN THE WALKER LANETC3009Figure 3. Rattlesnake fault trace and distribution of Quaternary deposits. Scarp heights and featuresindicative of sense of offset and ongoing fault activity are annotated. Units Qy, Qi, and Qo are Quaternarydeposits of relatively increasing age (see text for discussion). Unit Rx is undifferentiated bedrock. Faults(bold lines) are dashed and dotted where approximately located or inferred, respectively. Direction ofview for photos in Figure 4 is indicated by open end of solid bold rotated V shapes. Topographic map isprovided in Figure 5 of site marked by star.climatic considerations suggest a 3.3– 4.0 mm/yr rightlateral slip rate along the Hunter Mountain fault zone overthe last 15 thousand years [Oswald and Wesnousky,2002]. Right lateral slip during the Holocene has averagedbetween 1 and 4 mm/yr along the Owens Valley fault[Beanland and Clark, 1994; Lee et al., 2001b; Lubetkin,1988]. The 1872 Mw 7.6 Owens Valley earthquakeproduced dextral offsets averaging about 6 m along the 100 km fault length [Beanland and Clark, 1994].Normal and right-slip components of slip on the WhiteMountains frontal fault has averaged 0.1 mm/yr[dePolo, 1989] and 0.3 0.2 mm/yr, respectively [Reheisand Dixon, 1996]. Estimates of the normal displacementrate of the Sierra Nevada frontal fault adjacent to theOwens Valley fault range between 0.1 and 0.2 mm/yr[Gillespie, 1982; Reheis and Dixon, 1996].[8] Space geodetic data show 10 mm/yr of northnorthwest directed right-lateral shear is being accommodated across the southern Walker Lane [Dixon et al., 1995;Gan et al., 2000]. The value is similar to the ratesobserved to the south in the Eastern California ShearZone. Reheis and Dixon [1996] reproduce the observedstrain field across the area with a fault model that assumesright-lateral slip at depth on the individual fault systems:Owens Valley fault zone, 3.9 1.1 mm/yr; Death Valley –Furnace Creek fault zone, 3.3 2.2 mm/yr; White Mountains fault zone in northern Owens Valley, 3.4 1.2 mm/yr;and Fish Lake Valley fault zone, 6.2 2.3 mm/yr. Analysisof a linear array of monuments across the region by Gan etal. [2000] yields slightly different results: Owens Valleyfault, 6.9 1.6 mm/yr; Death Valley Furnace Creek, 3.2 0.9 mm/yr; and Hunter Mountain– Panamint Valley fault,3.3 1.6 mm/yr. Both models show some inconsistencywith available geologic observations. For example, themodel of Reheis and Dixon [1996] requires a higher sliprate than is observed on the White Mountains fault zone.The Gan et al. [2000] model requires more slip be placedon the Owens Valley fault than is observed. It is not clearwhether the inconsistencies are a reflection of the differenttime periods measured, viscoelastic response of the crustand upper mantle to historical earthquakes, or inadequaciesof the geologic data.2.4. The Central Walker Lane[9] The region includes faults of Stewart’s [1988]Excelsior-Coaldale and Walker Lake blocks (Figures 1and 2). Faults of the Excelsior-Coaldale Block generallystrike east-northeast and display evidence of late Quaternary displacement [dePolo, 1993; Oldow et al., 1994;Stewart, 1988; Wetterauer, 1977]. The east-northeaststriking faults include the Candelaria, Excelsior Mountain,Huntoon Valley, Anchorite Hills, North Mono Basin, andRattlesnake fault zones (Figure 2). The faults generally sitwithin a right step between northwest striking strike-slipfaults of the southern Walker Lane and the Walker LaneBlock to the north. The main strike-slip faults of theWalker Lane Block are, from east to west, the PetrifiedSprings, Benton Springs, Gumdrop Hills, and Indian HeadPeak fault zones. The Walker Lane Block is bounded onthe west by the east dipping active normal fault thatbounds the east flank of the Wassuk Mountains. OffsetTertiary tuffs and lavas and older granites and volcaniclastic rocks are interpreted to indicate that the northweststriking strike-slip faults of the Walker Lane Block havetaken up 48– 60 km of right-lateral strike slip during thelast 10– 15 Myr [Ekren and Byers, 1984, 1985a, 1985b,1986a, 1986b; Ferguson and Muller, 1949; Hardyman,1980, 1984; Hardyman and Oldow, 1991; Nielsen, 1965].The observations are consistent with the idea that slipfrom the southern Walker Lane is transferred to theWalker Lake Block via the Excelsior-Coaldale Block5 of 35

TC3009WESNOUSKY: ACTIVE FAULTING IN THE WALKER LANETC3009Figure 4. Rattlesnake fault. (a) View northwestward showing linear valleys and ridges, side hillbenches, closed depressions, and uphill-facing scarps, which define the strike of Rattlesnake fault (alongstrike between arrows). View is to the northeast. (b) View westward along strike shows tracecharacterized by side hill bench and enclosed depression in foreground characteristic of strike-slipdisplacement. Trace bends sharply to south in distance and exhibits oversteepening of the range front andtriangular facets indicating primarily normal fault displacement. Perspective of photos is shown on mapin Figure 3.[Oldow, 1992]. Geodetic observations indicate that theamount of right-lateral shear strain currently being accommodated within the central Walker Lane is about 10 mm/yr[Bennett et al., 2003; Oldow et al., 2001], similar to thatobserved to the south in the Eastern California ShearZone and southern Walker Lane. Quaternary expressionof faults within this region and the manner in whichstrain is accommodated by faults within the centralWalker Lane is examined in detail later as a main focusof this paper.[10] The Mw 7.2 Cedar Mountain earthquake of 1932occurred immediately east of the Benton and PetrifiedSprings faults (Fi

the Walker Line [Billingsley and Locke, 1941], the Walker Belt [Stewart,1980],andtheWalkerLaneBelt[Carr, 1984]. For convenience, I use the term Walker Lane to encompass the zone of right-lateral faults that extends northward from the Garlock fault. Stewart [1980] brought to attention that the pattern of faulting in the Walker

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