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The San Andreas Fault Paleoseismic Record at Elizabeth Lake: Why are There Fewer Surface-Rupturing Earthquakes on the Mojave Section?

Sean P. Bemis, Kate Scharer, & James F. Dolan

Published April 27, 2021, SCEC Contribution #10887

The structural complexity of active faults and the stress release history along the fault system may exert control on the locus and extent of individual earthquake ruptures. Fault bends, in particular, are often invoked as a possible mechanism for terminating earthquake ruptures. However, there are few records available to examine how these factors may influence the along-fault recurrence of earthquakes. We present a new paleoearthquake chronology for the southern San Andreas fault at Elizabeth Lake and integrate this record with existing paleoearthquake records to examine how the timing and frequency of earthquakes vary through a major restraining bend. This restraining bend features a mature, through-going right-lateral strike-slip fault, two major fault intersections, proposed subsurface fault dip changes, and a > 200 km-long section of fault misaligned with the regional plate motion. The Frazier Mountain, Elizabeth Lake, Pallett Creek, Wrightwood, and Pitman Canyon paleoseismic sites are located on this relatively linear surface trace of the San Andreas fault between fault bends. Our paleoseismic investigations at Elizabeth Lake document 4-5 earthquakes since ~1100 CE, similar to the number of earthquakes recorded at Pallett Creek. In contrast, the Frazier Mountain and Wrightwood sites each record 8-9 earthquakes during this same time period. Differences in earthquake frequency demonstrate that fewer earthquakes rupture the central portion of the restraining bend than occur near the fault bends and intersections. Furthermore, the similarity of earthquake records from the Bidart Fan and Frazier Mountain paleoseismic sites suggests that the broad, 30° curve of the Big Bend section of the San Andreas fault exerts less influence on fault rupture behavior than the fault geometry of the Mojave sections.

Bemis, S. P., Scharer, K., & Dolan, J. F. (2021). The San Andreas Fault Paleoseismic Record at Elizabeth Lake: Why are There Fewer Surface-Rupturing Earthquakes on the Mojave Section?. Bulletin of the Seismological Society of America, 111(3), 1590-1613. doi: 10.1785/0120200218. https://pubs.geoscienceworld.org/ssa/bssa/article/doi/10.1785/0120200218/596452/The-San-Andreas-Fault-Paleoseismic-Record-at