Postseismic relaxation across the Central Nevada Seismic Belt

Two GPS geodetic surveys across the Basin and Range (BR) province of western North America have detected an anomalous compression east of the Central Nevada Seismic Belt (CNSB). The first network, installed by the U. S. Geological Survey along an east-west trending transect across the BR at approximately 40degreesN, consisted of 63 monuments observed campaign style in 1992, 1996, and 1998. The second network, installed by the California Institute of Technology, consisted of 50 continuously operating GPS receivers, 18 of which were roughly along the same transect as the campaign survey. We have used a viscoelastic postseismic relaxation model of the four largest earthquakes in the CNSB (on the Pleasant Valley fault in 1915, the Cedar Mountain fault in 1932, and on the Fairview Peak and Dixie Valley faults in 1954) to interpret the geodetic velocities observed across the CNSB. A model of postseismic relaxation with a lower crustal Maxwell viscosity of 5-50 x 10(18) Pa s can explain the apparent compression regardless of the assumed mantle viscosity. The geodetic velocities that we determined after removing the postseismic contribution indicate that within current GPS detection limits the BR is stable east of the CNSB and is undergoing rapid right-lateral shear west of the CNSB.