Abstract

We present the first detailed geodetic image of the entire western United States south of lat 42°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°N. South of 36°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°N, the eastern California shear zone appears to exhibit simple shear oriented between ∼N20°W and ∼N40°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 ∼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.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.