Detailed Regional Resource Mapping in Nevada Using Natural and Mining Seismic Sources

Our objective is to contribute to geothermal resource assessment in Nevada and the Great Basin by providing uniform, high-resolution, regional maps of seismic velocity in the crust and shallow mantle. We analyze earthquakes and mining explosions of local magnitude greater than 2.5 recorded from 2005 to 2008 by the Earthscope Transportable Array (TA) seismic network, by the Nevada Seismic Network, and by the Southern Great Basin Digital Seismic Network. We use two complementary tomographic methods: 1) P- and S-body-wave arrival times image the mid- to- deep crust and shallow mantle with a block size of 10 km or smaller; 2) surface waves image the shallow to deep crust, with depth sensitivity depending on wave frequency. To identify surface waves, we use improved Rayleigh-wave detection algorithms based on wavelet transforms. Surface-wave detector improvements include solving for Love-Rayleigh interference and the capability to identify and analyze higher-mode Rayleigh waves. Once a Rayleigh phase is identified, group-velocity dispersion curves are determined using a multiple-filter analysis technique. With the advent of the TA station deployment, group-velocity dispersion for the path between two stations in line with the source may be estimated from the dispersion between the two stations. This technique eliminates the need to correct for earthquake source phase. The results of our study will be integrated with previous seismic data compilations and interpreted in terms of parameters of interest to the geothermal community, such as crustal thickness and seismic velocities.