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 re spect to the best fitting lines through the individual station positio n estimates is 2-3 mm in the horizontal and 6-10 mm in the vertical. A fter the first 395 days of operation, uncertainties in horizontal velo city estimates are 1-2 mm/yr (1-sigma). Relative motion among NEAR sit es located in eastern Nevada and in Utah is small, but east-west exten sion is significant assuming uniform strain accumulation across the wh ole network. The relative motion observed across the Wasatch fault zon e is 2 +/- 2 mm/yr, east-west. Relative motions among stations in west ern Nevada and California, in contrast, are dominated by northwest, ri ght-lateral shear. We infer an integrated grated deformation across th e northern Basin and Range of 11 +/- 2 mm/yr, northwest. These rates a re consistent with previous geodetic measurements. Our GPS velocity es timates, however, reveal a possibly abrupt transition from east-west e xtension 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 transitio n also appears to correlate spatially with a transition in upper mantl e structure.