Abstract

The number of human‐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 allows 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 the geothermal operation field from 2008 to 2014. Comparing with areas outside the geothermal production field, there are five 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 an obvious relationship with injection activities, and most of them are located within low b‐value area. Then we investigate the characteristics of 48 spatiotemporal isolated earthquake clusters. The analysis reveals a wide distribution of swarms and aftershock sequences across the whole region. Meanwhile, there is a concentration of small‐magnitude‐mainshock swarms and mixture‐type clusters (small mainshock, short‐duration bursts with high aftershock productivity) within the high b‐value geothermal operation area. The differences suggest that geothermal operation has clear influence on seismicity characteristics, indicating a possibility of distinguishing induced seismicity from natural seismicity.

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