Continuous GPS measurements of contemporary deformation across the northern Basin and Range province

We have acquired and analyzed data from the northern Basin and Range (NEAR) continuous GPS network since July 1996. The RMS residual with respect to the best fitting lines through the individual station position estimates is 2-3 mm in the horizontal and 6-10 mm in the vertical. After the first 395 days of operation, uncertainties in horizontal velocity estimates are 1-2 mm/yr (1-sigma). Relative motion among NEAR sites located in eastern Nevada and in Utah is small, but east-west extension is significant assuming uniform strain accumulation across the whole network. The relative motion observed across the Wasatch fault zone is 2 +/- 2 mm/yr, east-west. Relative motions among stations in western Nevada and California, in contrast, are dominated by northwest, right-lateral shear. We infer an integrated grated deformation across the northern Basin and Range of 11 +/- 2 mm/yr, northwest. These rates are consistent with previous geodetic measurements. Our GPS velocity estimates, however, reveal a possibly abrupt transition from east-west extension in eastern Nevada and Utah to right-lateral shear in western Nevada. This transition is roughly coincident with the central Nevada seismic belt and is consistent with the right-oblique focal mechanisms of the 1954 Dixie Valley and Fairview Peak earthquakes. The transition also appears to correlate spatially with a transition in upper mantle structure.