Surface wave tomography of the western United States from ambient seismic noise: Rayleigh wave group velocity maps

We have applied ambient noise surface wave tomography to data that have emerged continuously from the EarthScope USArray Transportable Array ( TA) between October 2004 and January 2007. Estimated Green's functions result by cross- correlating noise records between every station- pair in the network. The 340 stations yield a total of more than 55,000 interstation paths. Within the 5- to 50- s period band, we measure the dispersion characteristics of Rayleigh waves using frequency- time analysis. High- resolution group velocity maps at 8-, 16-, 24-, 30-, and 40- s periods are presented for the western United States. The footprint of the TA encloses a region with a resolution of about the average interstation spacing (similar to 70 km). Velocity anomalies in the group velocity maps correlate well with the dominant geological features of the western United States. Coherent velocity anomalies are associated with the Sierra Nevada, Peninsular, and Cascade Ranges, Great Valley, Salton Trough, and Columbia basins, the Columbia River flood basalts, the Snake River Plain and Yellowstone, and mantle wedge features associated with the subducting Juan de Fuca plate.