Regional P-Wave Tomographic Imaging with Geothermal Application

Abstract

We present progress on body- and surface-wave tomographic inversion results for seismic velocity in Nevada. The goal of the study is to develop indicators relevant for regional geothermal assessment. The inversions use joint station coverage of the permanent Nevada seismic networks, plus the temporary state-wide network deployed by the NSF-funded Earthscope Transportable Array project. Current inversions use over 130,000 arrival times from this joint station coverage. These data provide unprecedented coverage and resolution compared to previous work using surface waves or the more limited Nevada network data. The combined coverage allowed us to reduce model block size to 10x10x5 km. We present results from P-wave resolution analyses and comparison of the velocity models to mapped geology. Vs correlates with Vp in most cases, with some interesting differences that appear associated with regional fracturing and faulting. Vp and Vs-wave images identify the Carson Sink as being anomalously low velocity to at least mid-crustal depths, as expected for a structurally controlled low. P-wave velocities are relatively slow in the western part of the state where faults bounding the White-Inyo range meet and join NE-trending faults at the north end of the range. The area on the east end of this trend is associated with shallow thermal anomalies, so together they suggest a deep and perhaps widespread common explanation. Other major fault systems and geologic blocks are indicated as well at mid-crustal depths.