Present-day pattern of Cordilleran deformation in the western United States

We present the first detailed geodetic image of the entire western United States south of lat 42 degrees N, merging both campaign and continuous Global Positioning System (GPS) and very long baseline interferometry (VLBI) data sets in a combined solution for station velocities having a single, uniform reference frame. The results are consistent with a number of features previously observed through local geodetic studies and very sparse space geodetic studies, including a dominant pattern of right-lateral shear associated with the San Andreas fault, rates of the westernmost sites (along the California coast) of 46-48 mm/yr relative to a North America reference frame, and some 11-13 mm/yr of deformation accommodated east of the Sierra Nevada in the Basin and Range province north of lat 36 degrees N, South of 36 degrees N, the solution also shows that the southernmost San Andreas fault system accommodates effectively all interplate motion and that the southern Basin and Range is not deforming significantly. At lat 37 degrees N, the eastern California shear zone appears to exhibit simple shear oriented between similar to N20 degrees W and similar to N40 degrees W relative to North America, with a fairly well defined transition zone from localized shear to diffuse spreading in the Basin and Range. Enigmatically, this transition involves a significant component of contraction normal to the overall shear-zone trend; sites in the Great Basin move southwestward at up to similar to 5 mm/yr toward sites within the eastern California shear zone. To the north, in contrast, there appears to be a relatively smooth transition from east-west spreading within the eastern Great Basin to northwest-southeast shear across the westernmost Basin and Range.