Kinematic modeling of fault slip rates using new geodetic velocities from a transect across the Pacific-North America plate boundary through the San Bernardino Mountains, California

Sally F. McGill, Joshua C. Spinler, John D. McGill, Richard A. Bennett, Michael Floyd, Joan E. Fryxell, & Gareth J. Funning

Published 2015, SCEC Contribution #2063

Campaign GPS data collected from 2002-2014 result in 41 new site velocities from the San Bernardino Mountains and vicinity. We combined these velocities with 93 continuous GPS velocities and 216 published velocities to obtain a velocity profile across the Pacific-North America plate boundary through the San Bernardino Mountains. We modeled the plate-boundary-parallel, horizontal deformation with 5-14 parallel and one obliquely oriented screw dislocations within an elastic half-space. Our rate for the San Bernardino strand of the San Andreas fault (6.5 ± 3.6 mm/yr) is consistent with recently published latest Quaternary rates at the 95% confidence level, and is slower than our rate for the San Jacinto fault (14.1 ± 2.9 mm/yr). Our modeled rate for all faults of the Eastern California Shear Zone (ECSZ) combined (15.7 ± 2.9 mm/yr) is faster than the summed latest Quaternary rates for these faults, even when an estimate of permanent, off-fault deformation is included. The rate discrepancy is concentrated on faults near the 1992 Landers and 1999 Hector Mine earthquakes; the geodetic and geologic rates agree within uncertainties for other faults within the ECSZ. Coupled with the observation that post-earthquake deformation is faster than the pre-1992 deformation, this suggests that the ECSZ geodetic-geologic rate discrepancy is directly related to the timing and location of these earthquakes and is likely the result of viscoelastic deformation in the mantle that varies over the time scale of an earthquake cycle, rather than a redistribution of plate boundary slip at a time-scale of multiple earthquake cycles or longer.

Citation
McGill, S. F., Spinler, J. C., McGill, J. D., Bennett, R. A., Floyd, M., Fryxell, J. E., & Funning, G. J. (2015). Kinematic modeling of fault slip rates using new geodetic velocities from a transect across the Pacific-North America plate boundary through the San Bernardino Mountains, California. Journal of Geophysical Research: Solid Earth, 120(4), 2772-2793. doi: 10.1002/2014JB011459.