WALKER LANE AND WESTERN BASIN AND RANGE TRANSTENSION AND ROTATION RATES FROM GPS OBSERVATIONS, CONTINUUM AND BLOCK MODELS

The Walker Lane is a ~100 km wide zone of active intracontinental transtension that absorbs roughly 20% of Pacific/North America plate boundary relative motion in the western U.S. Lying west of the Sierra Nevada/Great Valley microplate and adjoining the Basin and Range Province to the east, deformation is predominantly shear strain overprinted with a minor component of extension. The system responds through a combination of faulting, block rotations, and structural step-overs, with distinct and varying partitioned domains of shear and extension.

Over the past decade the expanding scope, duration, and improvement in data processing techniques have contributed to a rapid increase in our understanding of Walker Lane crustal deformation. The University of Nevada, Reno operates the 373 station (and growing) Mobile Array of GPS for Nevada transtension (MAGNET) that with its ~20 km spacing densifies coverage by continuous networks such as the EarthScope Plate Boundary Observatory. Together these networks provide thousands of stations to map the velocity field with detail and scope that is not matched in any other of the world's active rifts.

We model the velocity field with complementary approaches of province-scale continuum and block models that reveal new aspects of the interseismic velocity field. The continuum approach provides a visualization of the geographic variation of seismic loading rate, shows higher strain rates in the western Walker Lane, little sensitivity to major structural stepovers, and a northward widening of the deformation zone. Our new block model estimates rotations of individual blocks and block bounding fault slip rates for the entire Walker Lane, from the Mojave desert to northern Nevada. This model has block dimensions derived from known Quaternary faults, allowing for more accurate estimates of slip rates, and better comparison between contemporary deformation and geologic slip rates. GPS-derived block rotation rates are somewhat dependent on model regularization, but are generally within 1˚ per million years, and tend to be slower than published paleomagnetic rotations rates. GPS data, together with neotectonic and rock paleomagnetism studies provide evidence that the relative importance of Walker Lane block rotations and fault slip continues to evolve.