Abstract

We used new horizontal global positioning system (GPS) velocities along with earthquakes, faults, and volcanic features to assess how strain is accommodated in the northern Basin and Range Province. We estimated horizontal velocities for 132 stations within the Snake River Plain and the surrounding Basin and Range from GPS phase data collected from 1994 to 2007. These velocities show regional-scale clockwise rotation suggestive of driving forces beyond those associated with the Yellowstone hotspot. Within the western Centennial tectonic belt, the GPS measurements indicate that the Basin and Range is extending at a rate an order of magnitude greater than the Snake River Plain, which explains its low seismicity. Between these two regions, we discern the “Centennial shear zone,” a NE-trending zone of right-lateral shear with estimated slip rates that increase northeastward from 0.9 ± 0.3 mm/yr in the SW to 1.7 ± 0.2 mm/yr in NE. We interpret the new GPS velocities to indicate: (1) right-lateral shear may be accommodated by strike-slip earthquakes on NE-trending faults in the Centennial shear zone; (2) three Basin and Range faults (Lost River, Lemhi, and Beaverhead) terminate at the Snake River Plain margin; and (3) extension in the Snake River Plain occurs at a much lower rate than the rate of normal faulting in the western Centennial tectonic belt.

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