High-Resolution Seismic Reflection Imaging of the Low-Angle Panamint Valley Normal Fault System, Eastern California

Date: 4/24/2019

Time: 11:00 AM

Room: Vashon

A fundamental question in seismic hazard analysis is whether <30º-dipping low-angle normal faults (LANFs) slip seismogenically. In comparison to more steeply dipping (50-60º) normal faults, LANFs have the potential to produce stronger shaking given increased potential rupture area in the seismogenic crust and increased proximity to manmade structures built on the hanging wall. The western margin of the Panamint Range in eastern California is defined by an exhumed, archetype LANF. In addition, high-angle normal faults displace mid-to-late Quaternary alluvial fans near the range front. To observe shallow (<1 km depth), crosscutting relationships between the low- and high-angle normal faults along the range front, we acquired two high-resolution P-wave seismic reflection profiles. The northern 4.7-km profile crosses the 2-km-wide Wildrose Graben and the southern 1.1-km profile extends onto the Panamint Valley playa, ~7.5 km S of Ballarat, CA. We used a minivib trailer-mounted vibrator source, which swept through 20 to 180 Hz with 5 m source and receiver spacings. The profile across the Wildrose Graben reveals a robust, low-angle reflector that likely represents the LANF separating Plio-Pleistocene alluvial fan conglomerate and pre-Cambrian meta-sedimentary deposits. High-angle faults interpreted in the seismic profile correspond to fault scarps on Quaternary alluvial fan surfaces. Preliminary interpretation of the reflection data suggests that the high-angle faults displace the LANF within the Wildrose Graben. Similarly, the profile south of Ballarat reveals a low-angle reflector, which also appears displaced by high-angle faults. These preliminary results suggest that near the Panamint range front, the high-angle faults are the dominant late Quaternary structures. We speculate that, at least at shallow (<1 km) depths, the LANF is not seismogenically active today.

Presenting Author: Ryan D. Gold

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