Mechanical Analysis of Fault Slip Rate Sites within the San Gorgonio Pass Region, Southern California USA

Jennifer L. Hatch, Michele L. Cooke, & Hanna M. Elston

In Preparation 2022, SCEC Contribution #11878

Crustal deformation models show incompatibility between inferred fault geometry and geologic slip rates where model and geologic slip rates disagree. We do not know if the impact of these incompatibilities are limited to near sites or have wider effect on the fault system deformation. Here, we investigate the roles of structural position of sites and uncertainty of slip rates using one suite of mechanical models that limits the dextral slip rates to within the range of observed slip rates at the sites of geologic investigations and another suite that explores the impact of each slip rate site on each other and on the nearby fault system. The suites of models employ two viable configurations for the southern San Andreas fault: with and without an active northern slip pathway around the San Gorgonio Pass. While the Active Northern Pathway model has greater mismatch to geologic slip rates < 16ka, it produces lesser off-fault deformation than the Inactive Northern Pathway model. The impact of strike-slip rate sites on the system depends on their structural positions. Sites along segmented faults may have lesser impact than either sites along the same fault segment or sites at fault branches. Consequently, inaccuracies in the slip rates used for seismic hazard assessment may have differing impacts depending on location of the slip rates. Fault branches along strike-slip faults warrant detailed investigation because these areas have high spatial variability of slip rate and accrue nearby off-fault deformation, affecting our ability to accurately assess seismic hazard of the region.

Citation
Hatch, J. L., Cooke, M. L., & Elston, H. M. (2022). Mechanical Analysis of Fault Slip Rate Sites within the San Gorgonio Pass Region, Southern California USA. Seismica, (in preparation).