Late Holocene Slip History Recorded in Alluvial Fan Sequences, Panamint Valley, Eastern California

Late Holocene rupture history of the Ash Hill fault, Eastern California Shear Zone, and the potential for seismogenic strain transfer between nearby faults

“…The first is an age estimate based on soil and surface development. The Qf8 surface and soil characteristics at Site 1 are nearly identical to those of a deposit on the east side of the Panamint Valley that has an age of ~0.5–0.8 ka (Tables 1, 2, S5, and S6) (Hoffman, 2009; Kirby & McDonald, 2016; Sethanant, 2019). An ~0.5–0.8 ka age estimate for Qf8 is consistent with relative age constraints for Qf8 placed by the IRSL ages of the next oldest and next youngest‐dated deposits along the Ash Hill fault.…”

“…We define six generations of Holocene alluvial deposits (Qf8, Qf7a–b,Qf6a–c) and three generations of Pleistocene deposits (Qf5, Qf2, Qf1; Table 1) with surface morphologies that correlate with mapped and dated Late Holocene surfaces elsewhere in the Panamint Valley and Mojave region (e.g. Bacon et al, 2010; Hoffman, 2009; Mahan et al, 2007; McDonald et al, 2003; McGill et al, 2009; Rittase et al, 2014; Sethanant, 2019). We find that in the mid‐distal fans of the western Panamint Valley, the surface morphological parameters that best track with surface age are modification of bar and swale morphology, pavement development, varnish strength on indicator clasts, and Av horizon thickness and ped size.…”

“…Units that bracket the timing of the three most recent earthquakes along the Ash Hill fault, IRSL ages for dated units (bold text and purple stars), and correlated estimated ages for units without geochronologic ages (italic text and orange stars). A = Hoffman (2009) and Sethanant (2019); B = this study; C = Rittase et al (2014). See Figures 4 and 5 and Tables 2 and 3 for sample locations and data [Color figure can be viewed at wileyonlinelibrary.com]…”

“…At the latitude of the Ash Hill fault, GPS and InSAR data indicate that ~10–11 mm/yr of oblique transtensional deformation is accommodated across the Death Valley–Panamint Valley–Owens Valley system, and one‐third to one‐half of that slip (~4–6 mm/yr) is accommodated across the Panamint Valley (Bennett et al, 2003; Miller et al, 2001). Previous estimates of geologic slip rates along the central and southern portions of the Panamint Valley fault, based on offset Holocene and Pleistocene geomorphic markers, range from ~2–6 mm/yr (Choi, 2016; Hoffman, 2009; Zhang et al, 1990), with a dip‐slip to strike‐slip ratio of ~2:1 and a northwest‐directed dextral oblique‐slip vector (Hoffman, 2009; Sethanant, 2019). Slip rates for the Ash Hill fault, determined from an offset Miocene basalt flow (~4 Ma) and deformed Pleistocene shorelines (~70–100 ka), yield total slip‐rate estimates of 0.3–0.5 mm/yr, with a strike‐slip to dip‐slip ratio of ~4:1 and a slip vector towards ~330° (Densmore & Anderson, 1997).…”

“…While the timing of Late Holocene earthquakes has been documented along the Panamint Valley fault, little is known about the Holocene rupture history of the Ash Hill fault. Four Holocene earthquakes have been identified from a trench on the southern Panamint Valley fault, with events bracketed to 0.33–0.48 ka, 0.9–3.0 ka, 3.3–3.6 ka, and >4.1 ka (McAuliffe et al, 2013), and tectono‐geomorphic mapping along the central Panamint Valley fault suggests these Late Holocene ruptures extend ~45 km north of the trench site (Figure 1; Hoffman, 2009; Sethanant, 2019; Smith, 1976; Zhang et al, 1990). In comparison, previous geologic mapping of surface ruptures along the Ash Hill fault concluded only that the latest slip on the Ash Hill fault is Holocene in age, based on the observation that all but the youngest generations of alluvium are offset (Densmore & Anderson, 1997; Smith, 1976).…”