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

Abstract

Understanding how fault systems interact and transfer strain over seismogenic timescales (seconds to ka) requires temporal records of past ruptures along adjacent and intersecting fault networks. Here we document the record of Late Holocene ruptures as recorded in the geomorphology of alluvial deposits along the Ash Hill fault, in the Eastern California Shear Zone (ECSZ). We leverage a multi-faceted approach to evaluate the relative timing of Ash Hill fault ruptures to those of nearby faults in the ECSZ. We determine the number and timing of Late Holocene earthquakes on the Ash Hill fault using high-resolution tectono-geomorphic mapping, a locally calibrated alluvial fan stratigraphy, feldspar luminescence dating, and fault offset analysis from field observations, LiDAR, and drone-based digital surface elevation models. We find evidence for three surface-rupturing earthquakes that have occurred since ~4 ka, each with ~1.0 ± 0.2 m of oblique slip per event (Mw ~ 6.9–7.0), and we constrain the timing of these earthquakes by dating deposits that bracket each event. The timing of these three ruptures is similar to the paleoseismic record along the adjacent range-bounding fault in southern Panamint Valley. Specifically, the two adjacent faults exhibit similar numbers of earthquakes during the Late Holocene, with similar recurrence intervals and rupture timing. These data suggest that it is possible that these two faults have ruptured in the same or closely temporally related events throughout the Late Holocene. Similar spatio-temporal clustered earthquakes have been recognized in both historic and paleoseismic records in the region, and such behaviour may be common in complexly interlinked fault networks, like those that exist in the ECSZ.