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Mechanical Models Suggest Fault Linkage through the Imperial Valley, California, U.S.A.

Jacob H. Dorsett, Elizabeth H. Madden, Scott T. Marshall, & Michele L. Cooke

Published June 11, 2019, SCEC Contribution #9010

The Imperial Valley hosts a network of active strike-slip faults that comprise the southern San Andreas and San Jacinto fault systems and together accommodate the majority of relative Pacific-North American plate motion in southern California. In order to understand how these faults partition slip, we model the long-term mechanics of four alternative active fault networks with different degrees of connectivity through the Imperial Valley using faults from the Southern California Earthquake Center Community Fault Model version 5.0. We evaluate model results against average fault slip rates from the Uniform California Earthquake Rupture Model version 3 (UCERF3) and geologic slip rate estimates from specific locations. The model results support continuous linkage from the San Andreas fault through the Brawley Seismic Zone to the Imperial fault and to the Cerro Prieto fault. Linked models decrease surface strain rates throughout the region and match more slip rate data. Only one linked model matches the UCERF3 rate on the Imperial fault, reaching the lower bound of 15 mm/yr. None of the tested models match the preferred rate of 35 mm/yr. In addition, high strain energy density around the Cerro Prieto fault in all models suggests that the UCERF3 preferred rate of 35 mm/yr may require revision. The Elmore Ranch fault slip rate matches the UCERF3 rate only in models with continuous linkage. No long-term slip rate data is available for the El Centro and Dixieland faults, but all models return less than 2 mm/yr on the El Centro fault and 3.5-9.6 mm/yr on the Dixieland fault. This suggests that the Dixieland fault may accommodate a significant portion of plate-boundary motion.

Key Words
Faults, mechanical model, BEM, slip rate, imperial

Dorsett, J. H., Madden, E. H., Marshall, S. T., & Cooke, M. L. (2019). Mechanical Models Suggest Fault Linkage through the Imperial Valley, California, U.S.A.. Bulletin of the Seismological Society of America, 109(4), 1217-1234. doi: 10.1785/0120180303. https://www.seismosoc.org/publications/bssa/