Fault linkage through the Imperial Valley, California is required to match current slip rate estimates

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

Published August 14, 2018, SCEC Contribution #8564, 2018 SCEC Annual Meeting Poster #166

The Imperial Valley hosts a seismically active network of 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 better understand how these faults link and accommodate plate motions, we use a suite of mechanical models to simulate the long-term fault mechanics of four fault networks with different degrees of connectivity through the Imperial Valley. The full three-dimensional distribution of fault slip rates is solved for based on a far-field Pacific-North American plate rate of 45-50 mm/yr at an azimuth of 320-325 degrees. We evaluate model results against average fault slip rates from the Uniform California Earthquake Rupture Model version 3 (UCERF3) and geologic slip rate estimates made at individual points along the regional faults. A model incorporating faults from the SCEC Community Fault Model version 5.0 (CFM5.0) fits 8 of 12 UCERF3 slip rates and 5 of 19 geologic estimates and the Imperial fault has a modeled average slip rate of 3.5-6.6 mm/yr, in disagreement with the minimum UCERF3 estimate of 15.0 mm/yr and far below the UCERF3 preferred rate of 35 mm/yr. A model with continuous linkage from the Coachella segment of the southern San Andreas fault to the Imperial fault through the western Brawley Seismic Zone to the Cerro Prieto fault matches 11 of 12 average slip rates and 8 of 19 geologic slip rates. With a modeled rate of 13.6-15.1 mm/yr, this is the only model that matches the UCERF3 rate on the Imperial Fault. The Elmore Ranch fault slips left-laterally at geologically compatible rates only in models with continuous linkage. The El Centro fault slips less than 1 mm/yr in all models. Analysis of model-calculated strain energy density patterns suggests that models with continuous linkage produce less off-fault strain compared to the raw and less connected CFM5.0 geometry.

Key Words
Imperial Valley, Southern San Andreas fault, Mechanical Model, Slip Rate

Citation
Marshall, S. T., Madden, E. H., Dorsett, J. H., & Cooke, M. L. (2018, 08). Fault linkage through the Imperial Valley, California is required to match current slip rate estimates. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)