SECULAR CRUSTAL DEFORMATION OF THE WESTERNMOST BASIN AND RANGE AS INFERRED FROM MAGNET AND OTHER GPS NETWORKS

In the westernmost Basin and Range the relative motion of the Sierra Nevada with respect to the central Great Basin is accommodated in a focused zone of transtension 150-200 km wide. South of 39°N latitude, in the central Walker Lane Belt, this deformation is contained in a single zone of transtension. North of 39°N latitude, however, the pattern of geodetically observed crustal deformation changes dramatically, separating into two distinct zones. The first zone lies to the west, adjacent to the rigid Sierra Nevada, and experiences northwest-directed shear, while the second lies ~150 km further east and experiences roughly NW/SE extension. While this picture of eastward deferral of extension and westward focusing of shear is kinematically self-consistent, it may not represent secular deformation since post-seismic effects of large 20th century earthquakes in the Central Nevada Seismic Belt (CNSB) may give the impression of the strain segregation. Modeling of the historic earthquakes suggests that at least a large proportion of CNSB contemporary geodetic extension results from viscoelastic relaxation of the lower crust and upper mantle. Thus geodetic velocities need to be adjusted before secular strain rates, or slip rates on faults, can be inferred.

We will present the latest results from the MAGNET (Mobile Array of GPS for Nevada Transtension) GPS network, which will have 1.5 years of data collected semi-continuously. This network has 60 sites east of Reno, NV and west of Austin, NV that traverse the most rapidly deforming portion of the western Basin and Range. The network is two-dimensional and is well-configured to address the transition of strain style across the Northern Walker Lane. Using velocities inferred from MAGNET and combining them with results from other regional GPS networks, we will infer the spatial distribution and style of deformation with and without a correction for CNSB postseismic effects. We will show the effect that this correction has on three scales, 1) the microplate level, with particular emphasis on the motions of the Sierra Nevada with respect to the central Great Basin, 2) deformation domain level, i.e. how the deformation has organized itself into separate domains that have distinct styles, 3) the crustal block level associated with individual ranges and particular fault systems.