Northwest Basin and Range tectonic deformation observed with the Global Positioning System, 1999–2003

We use geodetic velocities obtained with the Global Positioning System (GPS) to quantify tectonic deformation of the northwest Basin and Range province of the western United States. The results are based on GPS data collected in 1999 and 2003 across five new quasi‐linear networks in northern Nevada, northeast California, and southeast Oregon. The velocities show ∼3 mm/yr westward movement of northern Nevada with respect to stable North America. West of longitude 119°W the velocities increase and turn northwest, parallel to Sierra Nevada/Great Valley microplate motion, and similar to velocities previously obtained to the south. The observations are explained by a kinematic model with three domains that rotate around Euler poles in eastern Oregon and western Idaho. Northeast California experiences internal dextral shear deformation (11.2 ± 3.6 nstrain/yr) subparallel to Pacific/North America motion. Relative motions of the domains imply 2–5 mm/yr approximately east‐west extension in northwest Nevada and 1–4 mm/yr approximately north‐south contraction near the California/Oregon border. The northward decreasing approximately east‐west extension in northwest Nevada is consistent with the northern termination of Basin and Range deformation, faulting and characteristic topography. No significant extension is detected in the Oregon Basin and Range. The Oregon Cascade arc moves north at ∼3.5 mm/yr and is possibly influenced by the approximately eastward motion of the Juan de Fuca plate. These results disagree with secular northwest trenchward motion of the Oregon forearc inferred from paleomagnetic rotations. South of latitude 43°, however, trenchward motion exists and is consistent with block rotations, approximately east‐west Basin and Range extension, and northwest Sierra Nevada translation.