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

We present the first detailed geodetic image of the entire western United S tates south of lat 42 degrees N, merging both campaign and continuous Globa l Positioning System (GPS) and very long baseline interferometry (VLBI) dat a sets in a combined solution for station velocities having a single, unifo rm reference frame. The results are consistent with a number of features pr eviously observed through local geodetic studies and very sparse space geod etic studies, including a dominant pattern of right-lateral shear associate d with the San Andreas fault, rates of the westernmost sites (along the Cal ifornia 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 degr ees N, the solution also shows that the southernmost San Andreas fault syst em accommodates effectively all interplate motion and that the southern Bas in and Range is not deforming significantly. At lat 37 degrees N, the easte rn California shear zone appears to exhibit simple shear oriented between s imilar to N20 degrees W and similar to N40 degrees W relative to North Amer ica, with a fairly well defined transition zone from localized shear to dif fuse spreading in the Basin and Range. Enigmatically, this transition invol ves 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 m m/yr toward sites within the eastern California shear zone. To the north, i n contrast, there appears to be a relatively smooth transition from east-we st spreading within the eastern Great Basin to northwest-southeast shear ac ross the westernmost Basin and Range.