21 août 2007 · The study examines the resolution and group velocity maps produced for the western United States from a data set obtained from October 2004 through January 2007. During this period, the TA expanded to cover California, Oregon, Washington, most of Nevada and Idaho, and western Utah, Montana, and Arizona. We present the results of Rayleigh wave and Love wave phase velocity tomography in the western United States using ambient seismic noise observed at over 250 broad-band stations from.