Project Abstract
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In this project we use waveform-based template matching technique (WMFT) and ambient noise cross-correlation method to systematically analyze the spatial-temporal evolution of seismicity and seismic velocity in the Salton Sea Geothermal Region (SSGF). With the GPU-based WMFT, we detect earthquakes 10 days before/after some regional and teleseismic earthquakes that induced relatively high dynamic stress changes in during 2007-2014, when the Calenergy Borehole Network (EN) data are open to public. Then we search for triggered seismicity in SSGF around the target earthquakes with the statistics β-value. We find possible evidence of triggered seismicity after two regional and teleseismic earthquakes. Using empirical green’s functions (EGFs) obtained from ambient-noise cross-correlations, we find clear co-seismic reduction of seismic velocity following the 2010 M7.2 El Mayor-Cucapah earthquake, and larger co-seismic changes are associated with higher frequencies. In addition, there are clear differences in velocity changes for different station-pairs. By modeling the pore-pressure change and water flow velocity and energy during 2007-2014, we find a negative correlation between co-seismic changes and water flow velocities. We suggest that persistent fluid flow of geothermal production unclogs the fracture network, resulting in a lack of co-seismic velocity changes. This is consistent with the recent observation that remote triggering of microseismicity mostly occurred outside of geothermal regions (Zhang et al., 2017). However, we were unable to observe this pattern in Salton Sea Geothermal Field following the 2010 M7.2 El Mayor-Cucapah earthquake. |