GPS Modeling of Fault Slip-Rates within San Gorgonio Pass

Event Center BC

GPS data collected by CSUSB students from benchmarks within a transect across the Pacific-North America plate boundary passing through San Gorgonio Pass were combined with published velocities for other sites within the transect to conduct elastic modeling to obtain fault slip rates using a MatLab computer routine. The best-fitting model had a deep creep rate of 22 ± 2 mm/yr for the San Jacinto Fault, 15.2 ± 1.2 mm/yr for the Johnson Valley Fault and 2.8 ± 0.6 mm/yr for the PisgahBullion fault. Surprisingly, the Mission Creek strand of the San Andreas fault has a deep creep rate of only 0.1 ± 1.8 mm/yr, and the San Gorgonio Pass strand of the San Andreas Fault, the Elsinore fault and the NewportInglewood fault all had slip rates of zero. Another model with a slip rate of 4 mm/yr for the San Gorgonio Pass strand fits the GPS velocities almost as well, and is more consistent with geologic slip rate estimates. The maximum amount of slip that can be placed on the SAF, while still fitting the GPS velocities reasonably well is 8 mm/yr on the San Gorgonio Pass strand and 3 mm/yr on the Mission Creek strand.