Contemporary Fault Slip Rates in the Southern Walker Lane from Block Modeling of GPS Data

The southern Walker Lane is a right-lateral shear zone in western Nevada and eastern California that accommodates ~25% (9.3 ± 0.2 mm/yr) of the relative motion between the Pacific and North American plates. The region is characterized by discontinuous NNW-trending right-lateral strike-slip faults, and NE-trending, down-to-the-NW normal faults. The late Quaternary cumulative slip across the southern Walker Lane is only 1/2 the observed regional current geodetic rate of right-lateral shear. In order to better understand the modern distribution of strain accumulation and release across this region, we established a dense network of 50 new and existing campaign GPS monuments (from MAGNET and other networks). GPS data were processed using GIPSY-OASIS software to obtain sub-cm precision locations. To determine a new regional crustal velocity field we combine data from surveys of entirely new monuments only instrumented in 2010 and 2011 with existing monuments that were first instrumented as early as 1994, and reoccupied in 2010/11. We will report on initial velocity results for campaigns through 2011. As well, we will report on our successes with using the determined velocities in a modern regional block model (Meade and Loveless, BSSA 2009) to determine slip rates on individual faults in the southern Walker Lane. Elucidating slip on individual structures allows for a better accounting of slip across the region, and helps reveal distributed deformation that may not be preserved in the geologic record. These new results have important implications for the temporal and spatial distribution of strain accumulation and release along this portion of an evolving plate boundary.