DOCSLIB.ORG

Slip Rate of the Western Garlock Fault, at Clark Wash, Near Lone Tree Canyon, Mojave Desert, California

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Slip rate of the western Garlock fault, at Clark Wash, near Lone Tree Canyon, Mojave Desert, California

Sally F. McGill1†, Stephen G. Wells2, Sarah K. Fortner3*, Heidi Anderson Kuzma1**, John D. McGill4

1Department of Geological Sciences, California State University, San Bernardino, 5500 University Parkway, San Bernardino, California 92407-2397, USA 2Desert Research Institute, PO Box 60220, Reno, Nevada 89506-0220, USA 3Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W Dayton St., Madison, Wisconsin 53706, USA 4Department of Physics, California State University, San Bernardino, 5500 University Parkway, San Bernardino, California 92407-2397, USA *Now at School of Earth Sciences, The Ohio State University, 275 Mendenhall Laboratory, 125 S. Oval Mall, Columbus, Ohio 43210, USA **Now at Department of Civil and Environmental Engineering, 760 Davis Hall, University of California, Berkeley, California, 94720 - 1710, USA

  • ABSTRACT
  • than rates inferred from geodetic data. The ously published slip-rate estimates from a simi-

high rate of motion on the western Garlock lar time period along the central section of the
The precise tectonic role of the left-lateral fault is most consistent with a model in which fault (Clark and Lajoie, 1974; McGill and Sieh, Garlock fault in southern California has the western Garlock fault acts as a conju- 1993). This allows us to assess how the slip rate been controversial. Three proposed tectonic gate shear to the San Andreas fault. Other changes as a function of distance along strike. models yield significantly different predic- mechanisms, involving extension north of the Our results also fill an important temporal niche tions for the slip rate, history, orientation, Garlock fault and block rotation at the east- between slip rates estimated at geodetic time and total bedrock offset as a function of dis- ern end of the fault may be relevant to the scales (past decade or two) and fault motions tance along strike. In an effort to test these central and eastern sections of the fault, but inferred from longer term (>1 m.y.) offsets of models, we present the first slip-rate estimate they cannot explain a high rate of slip on the geologic features. for the western Garlock fault that is con- western Garlock fault.

  • strained by radiocarbon dating. A channel
  • Tectonic Models

(referred to here as Clark Wash) incised into INTRODUCTION a Latest Pleistocene alluvial fan has been left-

Hill and Dibblee (1953) viewed the left-lateral

laterally offset at least 66 6 m and no more

The tectonic role of the Garlock fault (Fig. 1) Garlock and Big Pine faults and the right-lateral than 100 m across the western Garlock fault, has been an intriguing question for several San Andreas fault as conjugate shears defining a indicating a left-lateral slip rate of 7.6 mm/ decades. Three primary models have been pro- regional strain pattern of north-south compresyr (95% confidence interval of 5.3–10.7 mm/ posed. It has been interpreted (1) as a conjugate sion and east-west extension (Fig. 2A). In this yr) using dendrochronologically calibrated shear to the SanAndreas fault (Hill and Dibblee, view the Garlock and San Andreas faults both radiocarbon dates. The timing of aggrada- 1953) that helps to accommodate convergence accommodate eastward motion of the Mojave tional events on the Clark Wash fan corre- at the major restraining bend in the San Andreas block as it extrudes from the Transverse Ranges sponds closely to what has been documented fault in southern California (Stuart, 1991), (2) as restraining bend formed between the Pacific and elsewhere in the Mojave Desert, suggesting a transform fault accommodating extension in North American plates along the San Andreas that much of this activity has been climati- the Basin and Range (Davis and Burchfiel, fault in southern California. Consistent with this

callycontrolled.Therange-frontfault,located 1973), and (3) as a structure accommodat- model, left-lateral faulting of Quaternary age in

a few hundred meters northwest of the Gar- ing block rotation in the northeastern Mojave California is largely confined to the vicinity of lock fault, has probably acted primarily as a (Humphreys and Weldon, 1994; Guest et al., this regional-scale restraining bend in the San normal fault, with a Holocene rate of dip-slip 2003). In contrast to all three geologic models, Andreas fault (Figs. 1 and 2A). Similar lateral

of 0.4–0.7 mm/yr. The record of prehistoric geodetic data suggest that the region surround- extrusion models have been proposed for strike-

earthquakes on the Garlock fault at this site, ing the Garlock fault is dominated by northwest- slip faults in other parts of the world (McKenthough quite possibly incomplete, suggests a oriented, right-lateral shear and that very little zie, 1972; Tapponnier et al., 1982), as well as for longer interseismic interval (1200–2700 yr) left-lateral strain is accumulating on the Garlock the Los Angeles basin and western Transverse for the western Garlock fault than for the fault (Savage et al., 1981, 1990, 2001; Gan et al., Ranges (Walls et al., 1998), although Argus et

central Garlock fault. The relatively high slip rate determined Peltzer et al., 2001).

here indicates that the western and central In an effort to test proposed models and to of convergence in the Los Angeles basin and segments of the Garlock fault show similar better understand the tectonic role of the Gar- western Transverse Ranges (Fig. 2A). rates of movement that are somewhat faster lock fault, we have measured the latest Pleisto- Other investigators proposed
2000; McClusky et al., 2001; Miller et al., 2001; al. (1999) argue that crustal thickening, rather than westward extrusion, is the dominant mode

  • a
  • second

cene to Holocene slip rate on the western strand model in which the Garlock fault is a transform of the Garlock fault, for comparison with previ- fault (Fig. 2B), with left slip on the Garlock

†E-mail: [email protected] GSA Bulletin; March/April 2009; v. 121; no. 3/4; p. 536–554; doi: 10.1130/B26123.1; 14 figures; 1 table; Data Repository item 2008251.

For permission to copy, contact [email protected]

536

© 2009 Geological Society of America

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/121/3-4/536/3400247/i0016-7606-121-3-536.pdf by California Inst of Technology user

Slip rate of the western Garlock fault

Holocene faults

California

GF

37°N

Quaternary faults

slip-rate and paleoseismic sites

BASIN AND RANGE

SAF

Saline Valley

Area of fig. 1

Sierra Nevada

36°N

  • SV
  • SR

SSH

  • AM
  • El Paso Peaks

EPM
Searles Lake shoreline
Christmas Canyon

SM
Mesquite Canyon

Bakersfield
Koehn Lake
SLB

Clark Wash

Oak Creek
Twin Lakes

35°N

Mojave
PM

Barstow

MOJAVE DESERT

Los Angeles

34°N

  • 100
  • 50
  • 0
  • 100 km

  • 118°W
  • 117°W
  • 120°W
  • 119°W
  • 116°W

Figure 1. Location of the Clark Wash site (large white circle) as well as other slip-rate and paleoseismic sites (small white circles) along the Garlock fault. AM—Avawatz Mountains; EPM—El Paso Mountains; GF—Garlock fault; PM—Providence Mountains; SAF—San Andreas fault; SLB—Soda Lake Basin; SM—Soda Mountains; SR—Slate Range; SSH—Salt Spring Hills; SV—Searles Valley.

  • fault accommodating differential extension in perpendicular to the northeast- to east-striking
  • The Cenozoic extension direction in the

the Basin and Range province (between the Garlock fault (Fig. 2B). Modern deformation Basin and Range province is west-northwestSierra Nevada and Death Valley) relative to in the portion of the Basin and Range province ward (Stewart, 1983; Burchfiel et al., 1987; the Mojave block (Hamilton and Myers, 1966; north of the Garlock fault is largely northwest- Jones, 1987; Wernicke et al., 1988; Snow and Troxel et al., 1972; Davis and Burchfiel, 1973). oriented dextral shear (Fig. 2D). Late Qua- Wernicke, 2000). This orientation more closely The location of the Garlock fault at the south- ternary extension north of the Garlock fault approaches the strike of the central and eastern margin of the western Basin and Range appears to be largely concentrated within pull- ern Garlock fault but is still at a 45° angle to province is consistent with the transform apart basins (Death Valley, Panamint Valley, the western Garlock fault. The transform fault model, as is the eastward termination of the and Saline Valley) between northwest-strik- model may thus be a partially viable model for Garlock fault at the eastern limit of significant ing, right-lateral faults. It is these right-lateral the initiation of left slip on the central and eastQuaternary extension in the western Basin and faults, rather than the Garlock fault, that are ern Garlock fault (if that portion of the fault has Range province (Figs. 1 and 2B). The present- parallel to the present-day extension direction not been rotated—see third model below and day extension direction in the Basin and Range and appear to be serving as transform faults discussion section), but it is unable to explain province, however, is northwestward (Minster for the Late Quaternary extension north of the the orientation of the western Garlock fault, nor

  • and Jordan, 1987; Dixon et al., 2000), nearly Garlock fault (Fig. 2B).
  • does present-day extension seem capable of

  • Geological Society of America Bulletin, March/April 2009
  • 537

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/121/3-4/536/3400247/i0016-7606-121-3-536.pdf by California Inst of Technology user

McGill et al.

  • 538
  • Geological Society of America Bulletin, March/April 2009

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/121/3-4/536/3400247/i0016-7606-121-3-536.pdf by California Inst of Technology user

Slip rate of the western Garlock fault

Figure 2. Proposed tectonic models for the Garlock fault. (A) Conjugate faulting (Hill and Dibblee, 1953). Convergence at the large restrain- ing bend in the San Andreas fault is accommodated by a combination of eastward extrusion of the Mojave Desert and westward extrusion (Walls et al., 1998) and crustal thickening (indicated by large “+” symbol) (Argus et al., 1999) of the Transverse Ranges. LA—Los Angeles; WTR—western Transverse Ranges province. (B) Transform fault model (Davis and Burchfiel, 1973). DV—Death Valley; PV—Panamint Valley; SV—Saline Valley. (C) Model in which the eastern Garlock fault accommodates clockwise block rotation in the northeastern Mojave Desert (Guest et al., 2003). KL—Koehn Lake slip-rate site (Clark and Lajoie, 1974); RS—Rand schist; RS? —schist between stands of Garlock fault zone that may correlate with Rand schist; SSH—Salt Spring Hills; SR—Slate Range. (D) Geodetic velocity vectors from the Southern California Earthquake Center’s Crustal Motion Model, version 3 (CMM3) (http://epicenter.usc.edu/cmm3/) relative to a refer- ence frame defined by 12 stations on the North American plate. Vectors shown have been arbitrarily selected from the complete data set to reduce clutter. Dashed polygons show the locations of two transects plotted in Figure 13.

driving a significant amount of left slip on any has remained an important, throughgoing fault The rotating block model (Fig. 2C) primarily

  • part of the Garlock fault (Figs. 2B and 2D).
  • that has produced several large earthquakes in explains slip on the eastern Garlock fault and

Since the recognition of the Eastern Califor- the past few thousand years (McGill and Sieh, predicts little or no slip on the western Garlock nia Shear Zone (Dokka and Travis, 1990), with 1991; McGill, 1992; Dawson et al., 2003) and is fault (Humphreys and Weldon, 1994).

  • throughgoing, northwest-oriented, right-lateral still seismically active (Astiz and Allen, 1983).
  • Our results from the Clark Wash site indicate

shear both north and south of the Garlock fault Evidence for Holocene left-lateral slip is abun- that the Holocene slip rate of the western strand (e.g., Savage et al., 1990) (see Fig. 2D), it is dant and nearly continuous along the entire of the Garlock fault is at least as fast as previno longer easy to view the Garlock fault as an ~250-km length of the fault (Clark, 1970; Clark, ously published rates along the central section accommodation structure separating two prov- 1973; McGill and Sieh, 1991), whereas the right- of the fault. Neither the transform nor rotating inces with radically different tectonic regimes. lateral faults to the north and south die out (e.g., block models are capable of explaining the oriInstead, the Garlock fault appears as an enig- Oskin and Iriondo, 2004) or exhibit possible left- entation of and rate of slip on the western Garmatic anomaly within a single large province— lateral drag folding as in the case of the southern lock fault. Some combination of the above modthe Eastern California Shear Zone. Both north Death Valley and Panamint Valley faults, as they els seems necessary to understand the tectonic and south of the Garlock fault, the Eastern Cali- approach the Garlock fault (Fig. 1). fornia Shear Zone (Fig. 1) has accommodated In light of recent understanding of dextral role of the fault as a whole. tens of kilometers of northwest-oriented, right- shear and vertical-axis block rotation in the SITE DESCRIPTION lateral shear in the late Tertiary (Stewart, 1983; Eastern California Shear Zone (Luyendyk et

  • Burchfiel et al., 1987; Dokka and Travis, 1990), al., 1985; Carter et al., 1987; Ross et al., 1989;
  • The site discussed here is informally named

at rates of 5–10 mm/yr across the zone since the Dokka and Travis, 1990; Schermer et al., 1996), the Clark Wash site because the offset chanlate Pleistocene (Lee et al., 2001; Oswald and Humphreys and Weldon (1994) and Guest et al. nel used for the slip-rate measurement was Wesnousky, 2002; Oskin et al., 2006). Geodetic (2003) have suggested a third model for the Gar- first noted by Clark (1973). The intersection of data (Fig. 2D) indicate that the Garlock region lock fault in which clockwise rotation of blocks Clark Wash with the Garlock fault is located is currently dominated by northwest-trending, in the northeastern Mojave Desert contributes near the center of section 26, T. 31 S., R. 36 right-lateral strain rather than by northeast- left slip to the eastern part of the Garlock fault E. (N35.205°, W118.087°), ~3.5 km southwest trending, left-lateral strain (Savage et al., 1981, (Fig. 2C). Guest et al. (2003) have shown that a of Lone Tree Canyon (Fig. 3), and ~18 km 1990, 2001; Gan et al., 2000; Miller et al., 2001; combination of large magnitude (~35° or more), northeast of the town of Mojave. The site is Peltzer et al., 2001). Present-day, northwest-ori- domino-style, clockwise rotation of blocks (and located ~3 km west of the western end of the ented, right-lateral shear has been documented of their left-lateral bounding faults) both south 3.5-km-wide left step in the Garlock fault that at rates of 9–11 mm/yr north of the Garlock fault and north of the Garlock fault and a moderate separates the western section of the fault from (Dixon et al., 2000; Meade and Hager, 2005) and amount of extension north of the Garlock fault the central section (Fig. 1). Koehn Lake occu~7–15 mm/yr south of the Garlock fault (Sauber between the Slate Range and the Salt Spring pies the center of a large closed depression that

  • et al., 1986, 1994; Meade and Hager, 2005).
  • Hills (Fig. 2C) can accommodate the full, has formed within this 3.5-km-wide dilational

Despite the prominence of the Eastern Cali- 48–64 km of left slip on the Garlock fault with- stepover in the fault. Within the study area the fornia Shear Zone, the Garlock fault arcs north- out requiring a search for an elusive eastward dominant strand of the Garlock fault is the segeasterly to easterly through this zone (Fig. 1), extension of the Garlock fault (e.g., Plescia and ment that enters the Koehn Lake stepover from with undeniable left-lateral bedrock offsets Henyey, 1982) that was previously thought nec- the west. However, the central segment of the

  • of 48–64 km (Smith, 1962; Smith and Ketner, essary (Davis and Burchfiel, 1973).
  • fault, which enters the Koehn Lake stepover

1970; Davis and Burchfiel, 1973; Carr et al., These three different models for the tectonic from the east, may continue westward into the 1993; Monastero et al., 1997; Jachens and Cal- role of the Garlock fault each result in different study area as a buried fault along the southern zia, 1998) and a Holocene slip rate between 4 predictions for the slip rate of the fault as a func- range front of the Sierra Nevada (Smith, 1964). and 9 mm/yr (Clark and Lajoie, 1974; McGill tion of position along strike. The conjugate fault This fault strand is referred to as the rangeand Sieh, 1993). Dextral shear in the East- model (Fig. 2A) predicts a slip rate that would front fault in this paper.

  • ern California Shear Zone may have rotated gradually decrease eastward, away from the San
  • The Clark Wash site is located on an alluvial

the central and eastern sections of the Garlock Andreas fault. The transform model predicts an fan complex that drains southeastward from the fault from an original northeastward strike to incrementally westward-increasing slip rate, as southern Sierra Nevada (Figs. 3 and 4). Clark their current east-northeast and eastward strikes each normal fault north of the Garlock fault con- Canyon, the drainage from which most of the (Fig. 2C) (Jones, 1987), but the Garlock fault tributes additional left slip to the fault (Fig. 2B). alluvialdepositsdiscussedhereemanated, drains

  • Geological Society of America Bulletin, March/April 2009
  • 539

Recommended publications
  • Tectonic Influences on the Spatial and Temporal Evolution of the Walker Lane: an Incipient Transform Fault Along the Evolving Pacific – North American Plate Boundary

    Tectonic Influences on the Spatial and Temporal Evolution of the Walker Lane: an Incipient Transform Fault Along the Evolving Pacific – North American Plate Boundary

    Arizona Geological Society Digest 22 2008 Tectonic influences on the spatial and temporal evolution of the Walker Lane: An incipient transform fault along the evolving Pacific – North American plate boundary James E. Faulds and Christopher D. Henry Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada, 89557, USA ABSTRACT Since ~30 Ma, western North America has been evolving from an Andean type mar- gin to a dextral transform boundary. Transform growth has been marked by retreat of magmatic arcs, gravitational collapse of orogenic highlands, and periodic inland steps of the San Andreas fault system. In the western Great Basin, a system of dextral faults, known as the Walker Lane (WL) in the north and eastern California shear zone (ECSZ) in the south, currently accommodates ~20% of the Pacific – North America dextral motion. In contrast to the continuous 1100-km-long San Andreas system, discontinuous dextral faults with relatively short lengths (<10-250 km) characterize the WL-ECSZ. Cumulative dextral displacement across the WL-ECSZ generally decreases northward from ≥60 km in southern and east-central California, to ~25 km in northwest Nevada, to negligible in northeast California. GPS geodetic strain rates average ~10 mm/yr across the WL-ECSZ in the western Great Basin but are much less in the eastern WL near Las Vegas (<2 mm/ yr) and along the northwest terminus in northeast California (~2.5 mm/yr). The spatial and temporal evolution of the WL-ECSZ is closely linked to major plate boundary events along the San Andreas fault system. For example, the early Miocene elimination of microplates along the southern California coast, southward steps in the Rivera triple junction at 19-16 Ma and 13 Ma, and an increase in relative plate motions ~12 Ma collectively induced the first major episode of deformation in the WL-ECSZ, which began ~13 Ma along the N60°W-trending Las Vegas Valley shear zone.
  • Kinematics of the Northern Walker Lane: an Incipient Transform Fault Along the Pacific–North American Plate Boundary

    Kinematics of the Northern Walker Lane: an Incipient Transform Fault Along the Pacific–North American Plate Boundary

    Kinematics of the northern Walker Lane: An incipient transform fault along the Paci®c±North American plate boundary James E. Faulds Christopher D. Henry Nevada Bureau of Mines and Geology, MS 178, University of Nevada, Reno, Nevada 89557, USA Nicholas H. Hinz ABSTRACT GEOLOGIC SETTING In the western Great Basin of North America, a system of dextral faults accommodates As western North America has evolved 15%±25% of the Paci®c±North American plate motion. The northern Walker Lane in from a convergent to a transform margin in northwest Nevada and northeast California occupies the northern terminus of this system. the past 30 m.y., the northern Walker Lane has This young evolving part of the plate boundary offers insight into how strike-slip fault undergone widespread volcanism and tecto- systems develop and may re¯ect the birth of a transform fault. A belt of overlapping, left- nism. Tertiary volcanic strata include 31±23 stepping dextral faults dominates the northern Walker Lane. Offset segments of a W- Ma ash-¯ow tuffs associated with the south- trending Oligocene paleovalley suggest ;20±30 km of cumulative dextral slip beginning ward-migrating ``ignimbrite ¯are up,'' 22±5 ca. 9±3 Ma. The inferred long-term slip rate of ;2±10 mm/yr is compatible with global Ma calc-alkaline intermediate-composition positioning system observations of the current strain ®eld. We interpret the left-stepping rocks related to the ancestral Cascade arc, and faults as macroscopic Riedel shears developing above a nascent lithospheric-scale trans- 13 Ma to present bimodal rocks linked to Ba- form fault.
  • Regional Tectonic Systems of the Pacific Northwest Delineated from ERTS-1 Imagery

    Regional Tectonic Systems of the Pacific Northwest Delineated from ERTS-1 Imagery

    University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1975 Regional tectonic systems of the Pacific Northwest delineated from ERTS-1 imagery Linda Kay Wackwitz The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Wackwitz, Linda Kay, "Regional tectonic systems of the Pacific Northwest delineated from ERTS-1 imagery" (1975). Graduate Student Theses, Dissertations, & Professional Papers. 7103. https://scholarworks.umt.edu/etd/7103 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. APR 1 6 1984 (iETo;,pr<i a 1384 ' r' r: ^ REGIONAL TECTONIC SYSTEMS OF THE PACIFIC NORTHWEST DELINEATED FROM ERTS-1 IMAGERY by Linda K. Wackwitz B.A. Colby College, 1972 Presented in partial fulfillment of the requirements for the degree of Master of Arts UNIVERSITY OF MONTANA 1975 Approved by Chairman, Board of Examiners / ^ f - / - - -- Dean, Graduate School I ,y. Date UMI Number: EP37904 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion.
  • Long-Term Fault Slip Rates, Distributed Deformation Rates, and Forecast Of

    Long-Term Fault Slip Rates, Distributed Deformation Rates, and Forecast Of

    1 Long-term fault slip rates, distributed deformation rates, and forecast of seismicity 2 in the western United States from joint fitting of community geologic, geodetic, 3 and stress-direction datasets 4 Peter Bird 5 Department of Earth and Space Sciences 6 University of California 7 Los Angeles, CA 90095-1567 8 [email protected] 9 Second revision of 2009.07.08 for J. Geophys. Res. (Solid Earth) 10 ABSTRACT. The long-term-average velocity field of the western United States is computed 11 with a kinematic finite-element code. Community datasets include fault traces, geologic offset 12 rates, geodetic velocities, principal stress directions, and Euler poles. There is an irreducible 13 minimum amount of distributed permanent deformation, which accommodates 1/3 of Pacific- 14 North America relative motion in California. Much of this may be due to slip on faults not 15 included in the model. All datasets are fit at a common RMS level of 1.8 datum standard 16 deviations. Experiments with alternate weights, fault sets, and Euler poles define a suite of 17 acceptable community models. In pseudo-prospective tests, fault offset rates are compared to 18 126 additional published rates not used in the computation: 44% are consistent; another 48% 19 have discrepancies under 1 mm/a, and 8% have larger discrepancies. Updated models are then 20 computed. Novel predictions include: dextral slip at 2~3 mm/a in the Brothers fault zone, two 21 alternative solutions for the Mendocino triple junction, slower slip on some trains of the San 22 Andreas fault than in recent hazard models, and clockwise rotation of some domains in the 23 Eastern California shear zone.
  • Since 1967, the Seismological Laboratory at the California Institute

    Since 1967, the Seismological Laboratory at the California Institute

    Bulletin of the Seismological Society of America, Vol. 75, No.3, pp. 811-833, June 1985 FAULT SLIP IN SOUTHERN CALIFORNIA BY JOHN N. LOUIE, CLARENCE R. ALLEN, DAVID C. JOHNSON, PAUL C. HAASE, AND STEPHEN N. COHN ABSTRACT Measurements of slip on major faults in southern California have been per­ formed over the past 18 yr using principally theodolite alignment arrays and taut­ wire extensometers. They provide geodetic control within a few hundred meters of the fault traces, which complements measurements made by other techniques at larger distances. Approximately constant slip rates of from 0.5 to 5 mmfyr over periods of several years have been found for the southwestern portion of the Garlock fault, the Banning and San Andreas faults in the Coachella Valley, the Coyote Creek fault, the Superstition Hills fault, and an unnamed fault 20 km west of El Centro. These slip rates are typically an order of magnitude below displace­ ment rates that have been geodetically measured between points at greater distances from the fault traces. Exponentially decaying postseismic slip in the horizontal and vertical directions due to the 1979 Imperial Valley earthquake has been measured. It is similar in magnitude to the coseismic displacements. Analysis of seismic activity adjacent to slipping faults has shown that accumu­ lated seismic moment is insufficient to explain either the constant or the decaying postseismic slip. Thus the mechanism of motion may differ from that of slipping faults in central California, which move at rates close to the plate motion and are accompanied by sufficient seismic moment. Seismic activity removed from the slipping faults in southern California may be driving their relatively aseismic motion.
  • Upper Neogene Stratigraphy and Tectonics of Death Valley — a Review

    Upper Neogene Stratigraphy and Tectonics of Death Valley — a Review

    Earth-Science Reviews 73 (2005) 245–270 www.elsevier.com/locate/earscirev Upper Neogene stratigraphy and tectonics of Death Valley — a review J.R. Knott a,*, A.M. Sarna-Wojcicki b, M.N. Machette c, R.E. Klinger d aDepartment of Geological Sciences, California State University Fullerton, Fullerton, CA 92834, United States bU. S. Geological Survey, MS 975, 345 Middlefield Road, Menlo Park, CA 94025, United States cU. S. Geological Survey, MS 966, Box 25046, Denver, CO 80225-0046, United States dTechnical Service Center, U. S. Bureau of Reclamation, P. O. Box 25007, D-8530, Denver, CO 80225-0007, United States Abstract New tephrochronologic, soil-stratigraphic and radiometric-dating studies over the last 10 years have generated a robust numerical stratigraphy for Upper Neogene sedimentary deposits throughout Death Valley. Critical to this improved stratigraphy are correlated or radiometrically-dated tephra beds and tuffs that range in age from N3.58 Ma to b1.1 ka. These tephra beds and tuffs establish relations among the Upper Pliocene to Middle Pleistocene sedimentary deposits at Furnace Creek basin, Nova basin, Ubehebe–Lake Rogers basin, Copper Canyon, Artists Drive, Kit Fox Hills, and Confidence Hills. New geologic formations have been described in the Confidence Hills and at Mormon Point. This new geochronology also establishes maximum and minimum ages for Quaternary alluvial fans and Lake Manly deposits. Facies associated with the tephra beds show that ~3.3 Ma the Furnace Creek basin was a northwest–southeast-trending lake flanked by alluvial fans. This paleolake extended from the Furnace Creek to Ubehebe. Based on the new stratigraphy, the Death Valley fault system can be divided into four main fault zones: the dextral, Quaternary-age Northern Death Valley fault zone; the dextral, pre-Quaternary Furnace Creek fault zone; the oblique–normal Black Mountains fault zone; and the dextral Southern Death Valley fault zone.
  • And Short-Term Stress Interaction of the 2019 Ridgecrest Sequence and Coulomb-Based Earthquake Forecasts Shinji Toda*1 and Ross S

    And Short-Term Stress Interaction of the 2019 Ridgecrest Sequence and Coulomb-Based Earthquake Forecasts Shinji Toda*1 and Ross S

    Special Section: 2019 Ridgecrest, California, Earthquake Sequence Long- and Short-Term Stress Interaction of the 2019 Ridgecrest Sequence and Coulomb-Based Earthquake Forecasts Shinji Toda*1 and Ross S. Stein2 ABSTRACT We first explore a series of retrospective earthquake interactions in southern California. M ≥ ∼ We find that the four w 7 shocks in the past 150 yr brought the Ridgecrest fault 1 bar M M closer to failure. Examining the 34 hr time span between the w 6.4 and w 7.1 events, M M we calculate that the w 6.4 event brought the hypocentral region of the w 7.1 earth- M quake 0.7 bars closer to failure, with the w 7.1 event relieving most of the surrounding M stress that was imparted by the first. We also find that the w 6.4 cross-fault aftershocks M shut down when they fell under the stress shadow of the w 7.1. Together, the Ridgecrest mainshocks brought a 120 km long portion of the Garlock fault from 0.2 to 10 bars closer to failure. These results motivate our introduction of forecasts of future seismicity. Most attempts to forecast aftershocks use statistical decay models or Coulomb stress transfer. Statistical approaches require simplifying assumptions about the spatial distribution of aftershocks and their decay; Coulomb models make simplifying assumptions about the geometry of the surrounding faults, which we seek here to remove. We perform a rate– state implementation of the Coulomb stress change on focal mechanisms to capture fault complexity. After tuning the model through a learning period to improve its forecast abil- ity, we make retrospective forecasts to assess model’s predictive ability.
  • Late Cenozoic History and Styles of Deformation Along the Southern Death Valley Fault Zone, California

    Late Cenozoic History and Styles of Deformation Along the Southern Death Valley Fault Zone, California

    Late Cenozoic history and styles of deformation along the southern Death Valley fault zone, California PAUL RAY BUTLER* j BENNIE W. TROXEL > Department of Geology, University of California, Davis, California 95616 KENNETH L. VEROSUB j ABSTRACT Late Cenozoic deposits in the southern Death Valley region have just a few kilometres north of its intersection with the Garlock fault zone. been offset -35 km by right-lateral, strike-slip faulting on the southern The determination of the age and amount of displacement provide infor- Death Valley fault zone since Miocene time. Virtually all slip took mation on the relationship of the southern Death Valley fault zone to the place prior to ~1 m.y. ago along western traces of the fault zone. formation of the pull-apart basin in central Death Valley and provide During the past 1 m.y., the eastern traces of the fault zone have been constraints on models for the intersection of this fault zone with the Gar- active and characterized by oblique slip, with a lateral component of lock fault zone. In addition, new insights are gained into the varying styles only a few hundred metres. Movement along these eastern traces has of deformation that may be associated with strike-slip faults. formed normal faults and gentle-to-isoclinal folds that have uplifted fan gravel and lacustrine sediments as much as 200 m above the modern alluvial fan surface. Surveying of the longitudinal profile of the Amargosa River, which flows within the eastern traces of the fault zone, suggests that vertical deformation continues today. The 35 km of right-lateral offset, which is based on matching offset alluvial fan gravel with its source area, refines earlier estimates of 8 to 80 km of movement for the southern Death Valley fault zone, and it is consistent with the geometry of a pull-apart basin model for central Death Valley.
  • The Tectonic Evolution of the Madrean Archipelago and Its Impact on the Geoecology of the Sky Islands

    The Tectonic Evolution of the Madrean Archipelago and Its Impact on the Geoecology of the Sky Islands

    The Tectonic Evolution of the Madrean Archipelago and Its Impact on the Geoecology of the Sky Islands David Coblentz Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM Abstract—While the unique geographic location of the Sky Islands is well recognized as a primary factor for the elevated biodiversity of the region, its unique tectonic history is often overlooked. The mixing of tectonic environments is an important supplement to the mixing of flora and faunal regimes in contributing to the biodiversity of the Madrean Archipelago. The Sky Islands region is located near the actively deforming plate margin of the Western United States that has seen active and diverse tectonics spanning more than 300 million years, many aspects of which are preserved in the present-day geology. This tectonic history has played a fundamental role in the development and nature of the topography, bedrock geology, and soil distribution through the region that in turn are important factors for understanding the biodiversity. Consideration of the geologic and tectonic history of the Sky Islands also provides important insights into the “deep time” factors contributing to present-day biodiversity that fall outside the normal realm of human perception. in the North American Cordillera between the Sierra Madre Introduction Occidental and the Colorado Plateau – Southern Rocky The “Sky Island” region of the Madrean Archipelago (lo- Mountains (figure 1). This part of the Cordillera has been cre- cated between the northern Sierra Madre Occidental in Mexico ated by the interactions between the Pacific, North American, and the Colorado Plateau/Rocky Mountains in the Southwest- Farallon (now entirely subducted under North America) and ern United States) is an area of exceptional biodiversity and has Juan de Fuca plates and is rich in geology features, including become an important study area for geoecology, biology, and major plateaus (The Colorado Plateau), large elevated areas conservation management.
  • Garlock Fault: an Intracontinental Transform Structure, Southern California

    Garlock Fault: an Intracontinental Transform Structure, Southern California

    GREGORY A. DAVIS Department of Geological Sciences, University of Southern California, Los Angeles, California 90007 B. C. BURCHFIEL Department of Geology, Rice University, Houston, Texas 77001 Garlock Fault: An Intracontinental Transform Structure, Southern California ABSTRACT Sierra Nevada. Westward shifting of the north- ern block of the Garlock has probably contrib- The northeast- to east-striking Garlock fault uted to the westward bending or deflection of of southern California is a major strike-slip the San Andreas fault where the two faults fault with a left-lateral displacement of at least meet. 48 to 64 km. It is also an important physio- Many earlier workers have considered that graphic boundary since it separates along its the left-lateral Garlock fault is conjugate to length the Tehachapi-Sierra Nevada and Basin the right-lateral San Andreas fault in a regional and Range provinces of pronounced topogra- strain pattern of north-south shortening and phy to the north from the Mojave Desert east-west extension, the latter expressed in part block of more subdued topography to the as an eastward displacement of the Mojave south. Previous authors have considered the block away from the junction of the San 260-km-long fault to be terminated at its Andreas and Garlock faults. In contrast, we western and eastern ends by the northwest- regard the origin of the Garlock fault as being striking San Andreas and Death Valley fault directly related to the extensional origin of the zones, respectively. Basin and Range province in areas north of the We interpret the Garlock fault as an intra- Garlock.
  • Cenozoic Thermal, Mechanical and Tectonic Evolution of the Rio Grande Rift

    Cenozoic Thermal, Mechanical and Tectonic Evolution of the Rio Grande Rift

    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 91, NO. B6, PAGES 6263-6276, MAY 10, 1986 Cenozoic Thermal, Mechanical and Tectonic Evolution of the Rio Grande Rift PAUL MORGAN1 Departmentof Geosciences,Purdue University,West Lafayette, Indiana WILLIAM R. SEAGER Departmentof Earth Sciences,New Mexico State University,Las Cruces MATTHEW P. GOLOMBEK Jet PropulsionLaboratory, CaliforniaInstitute of Technology,Pasadena Careful documentationof the Cenozoicgeologic history of the Rio Grande rift in New Mexico reveals a complexsequence of events.At least two phasesof extensionhave been identified.An early phase of extensionbegan in the mid-Oligocene(about 30 Ma) and may have continuedto the early Miocene (about 18 Ma). This phaseof extensionwas characterizedby local high-strainextension events (locally, 50-100%,regionally, 30-50%), low-anglefaulting, and the developmentof broad, relativelyshallow basins, all indicatingan approximatelyNE-SW •-25ø extensiondirection, consistent with the regionalstress field at that time.Extension events were not synchronousduring early phase extension and were often temporally and spatiallyassociated with major magmatism.A late phaseof extensionoccurred primarily in the late Miocene(10-5 Ma) with minor extensioncontinuing to the present.It was characterizedby apparently synchronous,high-angle faulting givinglarge verticalstrains with relativelyminor lateral strain (5-20%) whichproduced the moderuRio Granderift morphology.Extension direction was approximatelyE-W, consistentwith the contemporaryregional stress field. Late phasegraben or half-grabenbasins cut and often obscureearly phasebroad basins.Early phase extensionalstyle and basin formation indicate a ductilelithosphere, and this extensionoccurred during the climax of Paleogenemagmatic activity in this zone.Late phaseextensional style indicates a more brittle lithosphere,and this extensionfollowed a middle Miocenelull in volcanism.Regional uplift of about1 km appearsto haveaccompanied late phase extension, andrelatively minor volcanism has continued to thepresent.
  • Yellowstone Plume Trigger for Basin and Range Extension, and Coeval Emplacement of the Nevada–Columbia Basin Magmatic Belt

    Yellowstone Plume Trigger for Basin and Range Extension, and Coeval Emplacement of the Nevada–Columbia Basin Magmatic Belt

    Geosphere, published online on 17 February 2015 as doi:10.1130/GES01051.1 Cenozoic Tectonics, Magmatism, and Stratigraphy of the Snake River Plain–Yellowstone Region and AdjacentYellowstone Areas plume themed trigger issuefor Basin and Range extension Yellowstone plume trigger for Basin and Range extension, and coeval emplacement of the Nevada–Columbia Basin magmatic belt Victor E. Camp1, Kenneth L. Pierce2, and Lisa A. Morgan3 1Department of Geological Sciences, San Diego State University, San Diego, California 92182, USA 2U.S. Geological Survey, Northern Rocky Mountain Science Center, 2327 University Way, Box 2, Bozeman, Montana 59715, USA 3U.S. Geological Survey, 973 Federal Center, Box 25046, Denver, Colorado 80225-0046, USA ABSTRACT and Range. It was not the sole cause of Basin Juan de Fuca–Farallon plates, tractional forces and Range extension, but rather the catalyst applied to the base of the lithosphere, buoyancy Widespread extension began across the for extension of the Nevadaplano, which was forces associated with lithospheric density varia- northern and central Basin and Range already on the verge of regional collapse. tions, and basal normal forces associated with Province at 17–16 Ma, contemporaneous mantle upwelling and/or gravitational insta- with magmatism along the Nevada–Colum- INTRODUCTION bilities. They concluded that boundary forces bia Basin magmatic belt, a linear zone of associated with plate interaction would produce dikes and volcanic centers that extends for The Basin and Range Province is one of the neither the magnitude nor the rates of extension >1000 km, from southern Nevada to the best exposed extensional areas in the world for observed in the northern and central Basin and Columbia Basin of eastern Washington.