Block Kinematics and Slip Rates in the Southern Walker Lane Estimated From GPS Data
AdvisorHammond, William C
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The southern Walker Lane (SWL) is a part of the Eastern California Shear Zone that lies north of the Mojave region, bounded by the Garlock Fault to the south, the Sierra Nevada to the west, the Basin and Range to the east and by Mono Lake to the north. The region includes many northwest striking right-lateral strike slip and sub-parallel normal faults (e.g. Death Valley/Furnace Creek, Fish Lake Valley, Owens Valley), which together accommodate ~25% of the Pacific/North American relative motion. For many of these faults, and the system as a whole, there appears to be a discrepancy between geodetically and geologically inferred fault slip rates. Since the installation of the EarthScope Plate Boundary Observatory (PBO), and the Nevada Earthquake Response Network (NEARNET) of the University of Nevada, Reno, many recently obtained high-precision GPS data are now available to place improved constraints on the pattern and rates of crustal deformation of this region. In this study we use a block modeling methodology to estimate block motions and fault slip rates from GPS velocities of PBO, NEARNET and Basin and Range geodetic network (BARGEN) continuous sites. We solve for the motion of blocks using the GPS velocities to estimate long-term motion. In previous geologic studies, fault slip rates have been obtained from the published literature. To evaluate the consistency between the geologic and geodetic data, we compare long-term fault slip obtained from geologic studies to slip rates we infer from the geodetic results obtained over <10 years. We account for transient earthquake cycle effects by incorporating a model of the viscoelastic postseismic relaxation following major historic earthquakes in the region. GPS velocities adjusted for transient effects indicate that there is a distinct NW trend in the motions of the blocks with rates decreasing to the east. The results obtained in this study, suggest that geodetic and geologic fault slip rates in most cases agree with one another to within uncertainties. Some of the faults show lower geodetic rates, which might be due to accommodation of fault slip somewhere in the region, which has not been accounted for in the model.