Mechanical Models of Fault Slip Rates in the Imperial Valley, CA

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

Published August 14, 2017, SCEC Contribution #7609, 2017 SCEC Annual Meeting Poster #218

The Imperial Valley, located in southern California and northern Mexico, is composed of a seismically active network of dominantly strike-slip faults, which together act to accommodate the majority of Pacific-North American plate motion. While many geologic studies have been conducted in the region, some faults have poorly-constrained slip rates, and there is still disagreement about the presence of various linking faults. To better constrain slip rates and distributions, we have created a series of Boundary Element Method (BEM) models based on the SCEC Community Fault Model version 5.0. Modeled deformation is driven by a far-field plate rate of 50 mm/yr at an azimuth of 320 degrees. To evaluate these models, we compare the model-calculated slip rates to both UCERF3 average slip rate ranges as well as numerous published geologic point estimates of slip rate. Models of the raw CFM geometry fit 4/19 total slip rate point estimates and 8/12 UCERF3 average slip rate estimates. Two key issues are that the CFM model predicts only 4.6 mm/yr on the Imperial fault (UCERF3 estimates 15-40 mm/yr), and 0.4 mm/yr on the Elmore Ranch fault (UCERF3 estimates 0.5-1.5 mm/yr). To test whether several proposed connecting faults improve the model fit to slip rate data, we have created a suite of additional models with various proposed connections between the Imperial fault and the Coachella segment of the San Andreas fault (SAF) to the north and the Cerro Prieto fault to the south. The best-fitting model utilizes connecting faults directly between the Imperial, SAF, and Cerro Prieto faults with the Cerro Prieto fault being terminated just south of the Cerro Prieto Volcano. In this model, the average slip of Elmore Ranch increases to 1.5 mm/yr, fitting both the point (1.2 mm/yr) and UCERF3 estimates. Additionally, the average slip rate of the Imperial fault increases to 14.6 mm/yr, coming the closest out of our suite to fitting the UCERF3 estimate while also being the only model to fit the point estimate (15.2 mm/yr). In the end, the best-fitting model fits 10/19 slip rate point estimates and 10/12 UCERF3 estimates and suggests that the Imperial fault may be hard linked with the SAF fault to the north and the Cerro Prieto fault to the south.

Key Words
fault slip rate, Imperial Valley, model, geodesy, deformation

Citation
Dorsett, J. H., Marshall, S. T., Madden, E. H., & Cooke, M. L. (2017, 08). Mechanical Models of Fault Slip Rates in the Imperial Valley, CA. Poster Presentation at 2017 SCEC Annual Meeting.

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