Three-dimensional seismic velocity structure of the northwestern United States

Abstract

We present a high-resolution, three dimensional, P-wave tomography model for the northwestern United States. Major features of the model include clear, well-resolved images of the Juan de Fuca-Gorda slab to depths of at least 500 km, reduced velocities beneath Newberry volcano and north-central Oregon, increased velocities beneath the Idaho batholith, and a deep, slab-like, eastward-dipping feature of increased velocities beneath Nevada. We find no evidence for a mantle plume in this region, and demonstrate that suggested disruption of the Juan de Fuca slab beneath Oregon in the vicinity of Newberry volcano is an inversion artifact. We interpret the primary features of this new model within the framework of post-Laramide tectonomagmatism and the continuing tectonic evolution of the Cascadia Subduction Zone. A model explaining the regional tectonomagmatic history consistent with the imaged seismic velocity structure is one driven by mantle flow responding to the evolving subduction system. Copyright 2008 by the American Geophysical Union.