Earth and Planetary Science Letters 304 (2011) 565–576 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl Spatial and temporal constancy of seismic strain release along an evolving segment of the Pacific–North America plate boundary Kurt L. Frankel a,⁎, James F. Dolan b, Lewis A. Owen c, Plamen Ganev b, Robert C. Finkel d a School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 USA b Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, USA c Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA d Department of Earth and Planetary Science, University of California-Berkeley, Berkeley, CA 94720, USA article info abstract Article history: Three new slip rates from the Death Valley–Fish Lake Valley (DVFLV) fault contribute to an exceptionally Received 10 August 2010 detailed record of lateral rate variations on this 300-km-long system. From south to north, these three new Received in revised form 15 February 2011 sites are: South Mud Canyon, Cucomongo Canyon, and Indian Creek. Slip rates were determined by combining Accepted 18 February 2011 offsets measured with 1-m-resolution airborne lidar data with 10Be cosmogenic nuclide surface exposure and optically stimulated luminescence ages from displaced alluvial fans. The offset fans date to 17.4±2.3 ka Editor: P. Shearer at South Mud Canyon, 39±3 ka at Cucomongo Canyon, and 6.3±1.8 ka at Indian Creek, yielding slip rates of Keywords: 2.1+0.5/−0.4 mm/yr, 6.1+1.3/−1.0 mm/yr and 2.2+0.8/−0.6 mm/yr, respectively. At Indian Creek, the eastern California shear zone Holocene (~6 ka) and late Quaternary (~70 ka) slip rates are the same, within uncertainty, suggesting Walker Lane temporal constancy of seismic strain release along the northern DVFLV fault zone over these time spans. lidar When combined with slip rates determined in earlier companion studies, these results show that the late cosmogenic nuclide geochronology Quaternary slip rate decreases northward and southward from the central part of the fault, as slip is optically stimulated luminescence transferred onto north-trending zones of distributed normal faulting towards the northeast and southwest of fault slip rates the central zone of rapid deformation. This complex pattern of strain accommodation may reflect structural transient strain evolution towards a straighter, structurally simpler zone of dextral shear that locally utilizes well-established strain distribution dextral faults that are linked where necessary by nascent zones of deformation. Summation of the rates of all faults major faults in the eastern California shear zone (ECSZ) at the 37°N latitude of Red Wall Canyon in northern Death Valley shows that the cumulative geologic rate of ~8.5–10 mm/yr is indistinguishable from the ~9 mm/ yr geodetic rate. Although the cumulative rate on the major faults of the ECSZ is slower to the north and south, this probably reflects more distributed deformation in these areas, rather than transient strain accumulation. These results demonstrate the importance of obtaining multiple slip rates to effectively document the behavior of any fault system, especially in studies of seismic hazard assessment and comparisons of geologic and geodetic rate data. © 2011 Elsevier B.V. All rights reserved. 1. Introduction On parts of plate boundary fault zones where both detailed geologic and geodetic rate data are available such as the central San Understanding the temporal and spatial distribution of strain along Andreas, North Anatolian, and Altyn Tagh faults and in parts of the evolving plate boundary fault systems is one of the most important eastern California shear zone (ECSZ), rates of strain release appear to topics in active tectonics. Furthermore, determining the constancy of be constant throughout the Quaternary (Argus and Gordon, 2001; strain accumulation and release on major structures is fundamental to Bennett et al., 2003; Cowgill et al., 2009; Frankel et al., 2007a; Kozaci identifying how deformation is accommodated in the lithosphere. et al., 2009; Lee et al., 2009a; McClusky et al., 2000; Sieh and Jahns, Comparisons of short-term (decadal) geodetic data and long-term 1984; Wernicke et al., 2000). Long- and short-term rates do not (103–106 years) geologic plate motion data indicate that rates of strain always agree, however, along parts of plate boundary fault systems storage and release are, to first order, constant along most plate such as the Mojave section of the ECSZ (Oskin et al., 2008), the Garlock boundaries over a wide range of timescales (e.g., Sella et al., 2002). fault (Dolan et al., 2007; McGill et al., 2009; Peltzer et al., 2001), the central Walker Lane (Frankel et al., 2007b), the Wasatch fault (Friedrich et al., 2003; Niemi et al., 2004), and parts of the Altyn Tagh fault (Cowgill, 2007). ⁎ Corresponding author. Tel.: +1 404 894 4008. These observations suggest discrepancies between long- and short- E-mail address: [email protected] (K.L. Frankel). term rates of deformation and raise basic questions about how strain is 0012-821X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2011.02.034 566 K.L. Frankel et al. / Earth and Planetary Science Letters 304 (2011) 565–576 distributed through the lithosphere along evolving plate boundaries, et al., 2009). In contrast, geodetic data suggest strain accumulation including: 1) how temporally constant are rates of strain accumulation along the central Garlock fault at rates of ≤2–3 mm/yr (McClusky and release? 2) How spatially constant are rates of strain accumulation et al., 2001; Meade and Hager, 2005; Miller et al., 2001; Peltzer et al., and release? 3) Are geologic slip rates averaged over thousands to 2001). The pronounced contrast between the short-term geodetic and millions of years compatible with short-term geodetic rates, or are longer-term (104 yr) geologic slip-rate data suggests that the Garlock secular variations in rates of deformation common? 4) If strain fault exhibits two “modes” of strain accumulation, and that the fault is transients occur, over what temporal and spatial scales do they currently in a slow strain accumulation mode (Dolan et al., 2007; operate? And 5) are strain transients localized features that charac- McGill et al., 2009; Oskin et al., 2008; Peltzer et al., 2001). terize regions of relative structural complexity or a general character- Displacement from the Mojave segment of the ECSZ is transferred istic of evolving plate boundaries (e.g., Bennett et al., 2004; Dixon et al., northward across the Garlock fault onto four main fault systems: the 2003; Dolan et al., 2007; Friedrich et al., 2003, 2004; Wernicke et al., Owens Valley, Hunter Mountain–Saline Valley, DVFLV, and Stateline 2008)? fault zones (Fig. 1). A series of down-to-the-northwest normal faults Herein, we address these issues along the Death Valley–Fish Lake are thought to transfer slip between the Owens Valley, Hunter Valley (DVFLV) fault zone by combining fault displacement measure- Mountain–Saline Valley, and DVFLV faults (Fig. 1; Dixon et al., 1995; ments determined from airborne lidar data combined with optically Lee et al., 2001a; Reheis and Dixon, 1996). Farther north, these major stimulated luminescence (OSL) and terrestrial cosmogenic nuclide fault systems act to transfer right-lateral deformation northward (TCN) geochronology of offset landforms to determine slip rates over through the major right step at the Mina Deflection and on to the faults a variety of temporal and spatial scales. Our results bear on the of the Walker Lane in western Nevada (Ganev et al., 2010; Hoeft and importance of understanding the strain distribution along structures Frankel, 2010; Lee et al., 2009b; Oldow, 2003; Wesnousky, 2005a,b). associated with this evolving segment of the Pacific–North America At the northern end of the ECSZ, dextral motion between the Sierra plate boundary. Nevada block and North America is funneled down on to two faults bounding the east and west sides of the White Mountains: the White 2. Eastern California shear zone Mountains fault zone to the west and the northern DVFLV fault zone to the east. Of these two, modeling of GPS data suggests that the Fish The ECSZ, and its northern continuation, the Walker Lane, is an Lake Valley fault system is storing ~90% (~8.4 mm/yr of right-lateral evolving segment of the Pacific–North America plate boundary shear) of the elastic strain accumulating in this region (Dixon et al., (Faulds et al., 2005; Nur et al., 1993; Wesnousky, 2005a). This 100– 2000). However, recent late Pleistocene slip rate studies on these two 300-km-wide northwest-trending transtensional zone of right-lateral faults suggest the cumulative, late Quaternary fault slip rate may be shear and extension is critical to accurately assessing the Mesozoic to much slower than the short-term geodetic rate of elastic strain Cenozoic history of the Pacific–North America plate boundary inboard accumulation; late Pleistocene slip rates on the White Mountains of the San Andreas fault (Fig. 1; Stewart, 1988). As such, numerous (b0.5 mm/yr) and northern DVFLV faults (b4 mm/yr) account for less studies have focused on this region in recent years, each with the goal than half of the region-wide 9.3±0.2 mm/yr rate of dextral shear of unraveling pieces of the spatial and temporal history of the strain determined from GPS data (Bennett et al., 2003; Frankel et al., 2007b; distribution “puzzle” (e.g., Frankel et al., 2008; 2010). Kirby et al., 2006). The ECSZ is thought to accommodate 20–25% of total relative motion between the Pacific and North American plates (Bennett et al., 2.1.