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Geophysics seminar: Kenneth Hudnut (USGS) "Cross-Fault Interaction in the July 2019 Ridgecrest Earthquake Sequence, Southern California"

03/03/2020 - 12:00pm
Munk Conference Room
Event Description: 

Talk Abstract:

The July 2019 Ridgecrest earthquake sequence in southern California marked the intersection of two antithetic regional Holocene active fault systems, the northeast-striking, left-lateral boundary between the Sierra Nevada and Mojave blocks, and the northwest-striking, right-lateral eastern boundary of the Sierra Nevada block. Two large strike-slip ruptures 34.3 hours apart occurred on intersecting, nearly orthogonal, vertical faults during the Ridgecrest sequence. The first significant event (M 6.4) in the 2019 sequence ruptured a northeast-southwest oriented left-lateral “cross-fault” and the second event (M 7.1) initiated its rupture 13 km northwest of its soon-to-be intersection with the cross-fault, then ruptured bi-laterally, towards both the northwest (for 18 km) and southeast (for 30 km) with predominantly right-lateral slip. We previously advanced an hypothesis called “cross-fault triggering” to explain the sequence of events, and especially the inter-event delay and stress triggering effect, associated with the Elmore Ranch – Superstition Hills earthquake sequence of November 1987. Here, we explore whether that mechanism, or a variant, may potentially also be applied to understanding the 2019 Ridgecrest earthquake sequence. Strong similarities are evident between the 1987 and 2019 sequences; both seemed to involve cross-fault interaction, but not in identical ways. The 2019 sequence appears be inherently more complex than the 1987 sequence. New data on the sequence of surface faulting, first in the M 6.4 and then in the M 7.1, serve to improve our understanding of earthquake source physics and short & long-term fault interactions and hazards, not only in southern California, but in general.

For more information on this event, contact: 
Michael Murphy
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