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Seismic reflection imaging of the low-angle Panamint normal fault system, eastern California, 2018

August 19, 2020

A fundamental question in seismic hazard analysis is whether <30?-dipping low-angle normal faults (LANFs) slip seismogenically. In comparison to more steeply dipping (45-60?) normal faults, LANFs have the potential to produce stronger shaking because of their increased possible rupture area in the seismogenic crust. While LANFs have been documented globally, examples of seismogenically active LANFs are limited. The western margin of the Panamint Range in eastern California is defined by an archetypal LANF that dips west beneath Panamint Valley. In addition, high-angle dextral-oblique normal faults displace mid-to-late Quaternary alluvial fans near the range front. To image shallow (<1 km depth), crosscutting relationships between the low- and high-angle faults along the range front, we acquired two high-resolution P-wave seismic reflection profiles. The northern 4.6-km-long profile crosses the 2-km-wide Wildrose Graben and the southern 0.8-km-long profile extends onto the Panamint Valley playa. The profile across the Wildrose Graben reveals a robust, low-angle reflector interpreted to represent the LANF. High-angle faults interpreted in the seismic profile correspond to fault scarps on Quaternary alluvial fan surfaces. Interpretation of the reflection data suggests that the high-angle faults vertically displace the LANF up to 81 m within the Wildrose Graben. Similarly, the southern profile reveals a low-angle reflector, which appears both rotated and displaced up to 260 m by high-angle faults. These results suggest that near the Panamint rangefront, the highangle faults are the dominant late Quaternary structures. We conclude that, at least at shallow (<1km) depths, the LANF imaged is not seismogenically active today.