Body and Surface Wave Seismic Tomography for Regional Geothermal Assessment of the Western Great Basin

Abstract

We present P-wave tomographic images of the shallow crust and discuss correlations of notable velocity anomalies with tectonic and structural elements of the Western Great Basin. Low velocities are identified in a closed contour on the south edge of the Carson Sink. This anomaly is interpreted to reflect the tectonic complexity in this area. Northwest dipping normal faults of the southern Stillwater Range intersect with NW-trending strike-slip faults of the eastern Walker Lane. We infer that at depth this mechanical incompatibility creates space, reflected at the surface in basin formation, and at depth by wide-spread fracturing that reduces body-wave velocity. Fracturing is probably responsible for a subtle NE-trending velocity reduction beneath the Mina Deflection. The value of the inversions will be their application to areas where the geology and tectonics are not as well understood. We also present new tomographic inversions of surface wave dispersion curves developed from earthquake and ambient noise sources. Model layers at 5.5 and 7 second periods are shown. At 5.5 seconds lower Raleigh wave group velocities in several cases parallel larger sedimentary basins. This effect is less pronounced for 7 second period waves. At this period waves are averaging over approximately the upper 7 km or so, and reflect to a greater degree the wave speed of basement rock beneath the basins. Integration of these complimentary sources of information has only just begun, but results seem likely to provide meaningful constraints and background information for use in regional geothermal assessment