Characteristics of Seismicity inside and outside the Salton Sea Geothermal Field

Yifang Cheng, & Xiaowei Chen

Published May 22, 2018, SCEC Contribution #8025

The number of “man-made” earthquakes is on the rise in recent years and has led to increasing attention on the associated hazards. At the Salton Sea Geothermal field (SSGF), one of the largest geothermal field in Southern California, a local borehole seismic network has improved monitoring of small earthquakes and allow us to better understand the seismogenic response to injection operations and corresponding earthquake hazard. We analyze the spatial distribution of seismicity and b-value for both inside and outside of geothermal operation field from 2008 to 2014. Comparing with areas outside the geothermal production field, there are 5 times more small earthquakes (M<2) inside the production field at 2 to 5 km depth range with high b-value. But the seismic rate and depth range of large earthquakes (M>3) do not have obvious relationship with injection activities and most of them are located at low b-value area. Then we investigate the characteristics of 48 spatiotemporal isolated earthquake clusters. The analysis reveals the wide distribution of swarms and aftershock sequences across the whole region. Meanwhile, there is a concentration of small-magnitude-mainshock swarms and mixtures (small mainshock, short-duration bursts with high aftershock productivity) in high b-value geothermal operation area. The differences suggest that fluid injection has clear influence on event quantity and cluster properties. The difference in cluster characteristics suggests the possibility to recognize energy operation induced seismicity versus natural tectonic earthquakes.

Citation
Cheng, Y., & Chen, X. (2018). Characteristics of Seismicity inside and outside the Salton Sea Geothermal Field. Bulletin of the Seismological Society of America, 108(4), 1877-1888. doi: 10.1785/0120170311.