| Description |
This study combines seismic event detection and ambient noise surface wave tomography in order to investigate a producing geothermal basin in southwestern Utah. We conducted four geophone array experiments in southwestern Utah between July 2016 and October 2017 to characterize regional levels of microseismicity and perform seismic imaging. Each experiment comprised between 48 and 93 geophones and recorded continuously for ~30 days. Using a new frequency domain array-based detector and a traditional STA/LTA detector, we identified 242 earthquakes. We were able to precisely locate 203 of these earthquakes using HYPOINVERSE. During the same time period, the University of Utah Seismograph Stations (UUSS) catalog contained 68 earthquakes in the study area. Therefore, we were able to locate 135 additional events. We estimate local magnitudes for events using maximum peak-to-trough amplitude and epicentral distance. As expected, our detection threshold becomes lower with higher station density. We find sparse seismicity across the study area apart from two areas that contain clustered and more frequent activity (Dog Valley and Cove Fort), which together account for roughly 70% of the recorded seismicity. A third prominent cluster in the central Mineral Mountains contains about 15% of the recorded seismicity. The remainder of the detected seismicity is spread across the study area. Seismic imaging was performed using ambient noise surface wave tomography for a single geophone array. Noise characteristics made it challenging to obtain velocity iv measurements across a broad frequency band, but phase and group velocity measurements are obtained between 3-10 seconds, as well as -.5 to 1 seconds when for a densely spaced portion of the array. Inversion results show Rayleigh wave velocities from 2-3.5 km/s for longer periods and high velocity anomalies in the granitic Mineral Mountains. At the short periods, velocities range from 400-600 m/s and exhibit higher velocities near the Mineral Mountains as bedrock shallows. Sensitivity kernels are calculated and imaging depths range from 3-8 km for longer periods examined, and <500 m for the higher frequency signals. Mapped velocities are also comparable with results of spatial autocorrelation results for the same region. |
