Project Abstract
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We investigate the characteristics of both induced and tectonic seismicity in the Salton Sea region with a focus on their response to large remote earthquakes and their stress orientations and variations. We first developed a relocation catalog for all the events between 1981 and 2016 in our study area by applying the 3-D ray-tracing and waveform cross-correlation relocation methods. The relocation catalog is then used to calculate seismicity rate change in the study area corresponding to several remote earthquakes, including the 1992 Landers, 1999 Hector Mine, 2002 Denali and 2010 Baja California earthquakes. We also solved for focal solutions for all the relocated events by using the HASH program, which were then used to calculate the average stress orientation based on the SATSI package. Our results show that although the Salton Sea Geothermal Field shares similar average stress orientations, it is not as responsive as the surrounding fault areas following each remote mainshock. We also estimated the Vp/Vs ratios for similar earthquake clusters using waveform cross-correlation data. These ratios show correlations with the heat flow and well production data, indicating that the near-source Vp/Vs ratios strongly depend on the subsurface natural properties, but are influenced by the amount of injection volume throughout the production period. Our systematic comparison between inside and outside of the SSGF enables a better understanding of induced and tectonic seismicity, which will help constrain future seismic hazard assessments in the area. |
