New GPS Site Velocities in San Gorgonio Pass, Southern California and Preliminary Elastic Modeling

Naomi Jahan, Matthew Peterson, Sally F. McGill, & Joshua C. Spinler

Submitted August 12, 2016, SCEC Contribution #6641, 2016 SCEC Annual Meeting Poster #149

Campaign GPS observations have been collected from 23 new sites in San Gorgonio Pass 1-3 times per year since 2013. After 3 years of observations, consistent velocities are now available for these sites and are well constrained enough to support elastic modeling of fault slip rates. We conducted one-dimensional elastic modeling of right-lateral fault slip rates in two transects across the plate boundary passing through the San Gorgonio Pass and Desert Hot Springs. For the San Gorgonio Pass transect, the best-fitting model puts all of the slip on the Johnson Valley and San Jacinto faults, with a very small amount of slip on the Pisgah-Bullion fault and no slip on either strand of the San Andreas fault. Other models, which have almost as low a chi2, put 9 mm/yr on the two strands of the San Andreas fault combined. The maximum amount of slip that can be given to the two strands of the San Andreas combined while still fitting the observed GPS velocity profile reasonably well is 19 mm/yr. The models indicate that the San Andreas fault can reasonably have between 0 and 19 mm/yr of slip and the San Jacinto fault can have between 8 and 21.5 mm/yr of slip. For the Desert Hot Springs transect, the best-fitting model placed large amounts of slip on the Burnt Mountain (11.4 mm/yr) and San Jacinto faults (13.4 mm/yr), with 5.6 mm/yr of slip on the San Andreas fault (Banning strand). Other models resulted in a nearly equally good fit, with a San Andreas fault slip rate of 10 mm/yr, and slip on the Burnt Mountain fault of 9 mm/yr. The maximum slip rate of the San Andreas fault that still fits the data reasonably well is 25 mm/yr. Our results suggest that little or no elastic bending is presently occurring across the Banning or Mission Creek faults within the San Gorgonio Pass or Desert Hot Springs transects. These results support interpretations in which most of the slip on the Mojave section of the San Andreas fault transfers southward onto the San Jacinto fault and most of the slip on the southernmost San Andreas fault transfers northward into the Eastern California shear zone, leaving only a small amount of slip on the San Andreas fault between Cajon Pass and Thousand Palms.

Citation
Jahan, N., Peterson, M., McGill, S. F., & Spinler, J. C. (2016, 08). New GPS Site Velocities in San Gorgonio Pass, Southern California and Preliminary Elastic Modeling. Poster Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Tectonic Geodesy