Sensitivity of deformation to activity along the Mill Creek and Mission Creek strands of the southern San Andreas fault

Jennifer L. Hatch, Michele L. Cooke, & Scott T. Marshall

Published October 12, 2018, SCEC Contribution #7975

Assessment of seismic hazards in southern California may be improved with more accurate characterization of the active San Andreas fault strands within the San Gorgonio Pass region. On-going debate centers on the activity and geometry of the Mill Creek and Mission Creek strands. Here, we investigate crustal deformation models with five geologically plausible geometries of the Mill Creek and Mission Creek strands. Model results suggest that differences in active fault geometry along the San Andreas fault also impact slip rates along the San Jacinto fault by up to 3 mm/yr. Each model fits many but not all of the available geologic strike-slip rates. The calculated misfits to the geologic strike-slip rates reveal two best-fitting models: the Inactive Mill Creek model and the North-dipping Mission Creek model, which incorporates active portions of the Mill Creek, Mission Creek and Galena Peak strands, consistent with recent studies,. The North-dipping Mission Creek model produces ~4 mm/yr greater overall strike-slip rate than the Inactive Mill Creek model, suggesting that kinematic slip budgets should consider off-fault deformation. The two best-fitting models produce uplift patterns with significant differences in the hanging walls of dipping faults. New uplift rate data in these regions and additional geologic slip rates along the northern fault strands could give preference to one of the interpreted active fault configurations. An assessment of the seismic hazard of the region indicates the potential for a rupture through the San Gorgonio Pass region with Mw ~7.8.

Citation
Hatch, J. L., Cooke, M. L., & Marshall, S. T. (2018). Sensitivity of deformation to activity along the Mill Creek and Mission Creek strands of the southern San Andreas fault. Geosphere,. doi: 10.1130/GES01666.1.