TECTONOGEOMORPHIC MAPPING REVEALS THE LATE HOLOCENE RUPTURE HISTORY OF THE ASH HILL FAULT (ECSZ) AND POTENTIAL FOR SEISMOGENIC STRAIN TRANSFER (Invited Presentation)

The eastern California Shear Zone (ECSZ) is a network of active faults extending from Baja California to west-central Nevada that accommodate dextral shear. Strain is transferred among geometrically complex fault systems, and large magnitude earthquakes appear able to rupture across adjacent fault systems. However, confidently correlating paleoseismic ruptures across these complex fault systems is challenging as coarse alluvial deposits are not readily amenable to high-precision chronology. Here we document the record of late Holocene ruptures along the Ash Hill fault, located in western Panamint Valley, leveraging a multifaceted approach that combines tectono-geomorphic mapping using a locally-calibrated, high-resolution, alluvial fan stratigraphy, feldspar luminescence dating, and fault offset analysis from field observations, lidar, and drone based digital surface elevation models. These data yield evidence for three surface rupturing earthquakes since ~4 ka, with the most recent event occurring the past 300-600 years. Each event accommodated ~1.0 +/- 0.2 m of right lateral oblique slip, and likely occurred during earthquakes of magnitude ~6.9-7.0. Our data show that the timing of the last three ruptures on the Ash Hill fault are similar to the paleoseismic record along the adjacent range-bounding fault in southern Panamint Valley. Specifically, the two adjacent faults have similar numbers of earthquakes during the Late Holocene, similar recurrence intervals, and similar rupture timing. These data suggest that it is possible that these two faults have ruptured in the same or closely temporally related events over multiple seismic cycles throughout the Late Holocene. Similar spatio-temporal clusters and multi-fault earthquakes have been recognized in both historic and paleoseismic records in the ECSZ, and such behavior may be common in complexly interlinked fault networks, like those that exist in evolving transtensional systems in the western US.