Poster #070, Earthquake Geology

Tectonogeomorphic evidence for late Holocene complex rupture linking the Panamint Valley and Ash Hill faults, Eastern California Shear Zone

Aubrey LaPlante, & Christine Regalla
Poster Image: 

Poster Presentation

2021 SCEC Annual Meeting, Poster #070, SCEC Contribution #11427 VIEW PDF
The 2019 Ridgecrest sequence, 1992 Landers, and 1999 Hector Mine earthquakes reinforced the importance of understanding the timing and location of complex and multi-fault rupture as a contributor to seismic hazard in the Eastern California Shear Zone. Here we investigate geologic evidence for complex rupture in Panamint Valley, located ~50 km northeast of the Ridgecrest ruptures. Late Holocene scarps in the 10 km wide transfer zone between the Ash Hill and Panamint Valley faults display surface rupture geometries analogous to those produced during the 1992 Landers and the 1999 Hector Mine earthquakes. We generated new 1:4000 scale tectonogeomorphic mapping in a 25 kmĀ² area between the Ash Hi...ll and Panamint Valley faults using lidar DEMs and aerial imagery to identify ruptures. We mapped multiple generations of Holocene deposits using relative age alluvial fan surface morphology and weathering criteria. Preliminary results of our field and lidar mapping show that the transfer zone consists of 100+ fault strands that are ~.15-4.2 km in length, and occur in parallel and en echelon arrays with ~15-250 m spacing. Using our relative fan stratigraphy, we identified seven generations of fan units with three distinct ruptures between Qal and Qf7y, Qf7y and Qf7o, and Qf6y and Qf6o. We measured vertical and lateral offsets of bars, swales and channels from field mapping and LaDiCaoz_v2 backslipped reconstructions of newly generated high resolution (5 cm) drone-based structure from motion digital surface models. Lateral offsets of geomorphic features range between ~.5-2.5 m and vertical offsets range between ~.02-.60 m. Given fault scaling relationships, our mapped faults cannot rupture independently, and must rupture in conjunction with either the adjacent Ash Hill, Panamint Valley or Searles Valley faults. Alluvial units that bracket earthquakes in the transfer zone have similar morphologies to alluvial units that bracket earthquakes on the Ash Hill and Panamint Valley faults, suggesting this region acts as a zone for complex strain transfer over multiple earthquake cycles. Our future work will use feldspar infrared stimulated luminescence dating of offset deposits to bracket the ages of newly mapped ruptures and will quantify fault kinematics to constrain how rupture propagates through this transfer zone.