Potential of the Ridgecrest Earthquake Sequence to Enhance Earthquake Activity along Low-Angle Detachment Faults in Panamint and Searles Valley, California

The location and style of the Ridgecrest earthquake sequence imply it occurred as a consequence of distributed shear along the Pacific-North America plate boundary system through California. At this latitude, the Eastern California Shear Zone (ECSZ) overlaps with the western edge of the Basin and Range extensional province. How these two deformational systems interact - does activity on one trigger or dampen activity on the other - remains an open question. The Ridgecrest sequence is an opportunity to evaluate this interaction along the ECSZ. In the SW Basin and Range of North America, large magnitude extension during Miocene - Pliocene time was accommodated on a system of low-angle detachment faults. In Panamint Valley, the active range-front fault system exploits a low-angle (15-30°), curviplanar detachment fault that is linked to strike-slip faults at its southern and northern ends. Analyses of geomorphic and stratigraphic records of recent faulting, along with a detailed event chronology allow assessment of surface displacement during past ruptures. These data suggest that 3-4 surface ruptures occurred during the past ~4-5 ka. The most recent event occurred ~330-485 cal yr BP and was characterized by 2-3 meters of displacement along >40-50 km of the southern and central fault system. Structural and kinematic relationships imply that Late Holocene earthquakes occurred along this low-angle detachment system.

We have assessed the impact of the Ridgecrest sequence on the stress conditions on these low-angle fault systems (some of which may extend to or beneath the shallow strike-slip system that ruptured during the Ridgecrest events). Models of Coulomb stress change indicate that the effects of the Mw 7.1 main shock would increase the potential for normal faulting activity on west-dipping low-angle structures in the Panamint, Searles, and western Death Valley region, consistent with the occurrence of aftershocks in that region. These results imply that stress changes associated with moderate-to-large earthquakes in the ECSZ can potentially trigger activity in the westernmost Basin and Range along low-angle structures. Additionally the timing of seismic activity along this N-S corridor of the ECSZ may induce sympathetic activity along the low-angle structures of the adjacent extensional domains.