iPlex Lunch fall-2012

Earthquakes strongly cluster in space and time. Different clustering styles represent different triggering processes. For example, aftershock sequences represent stress triggering from mainshocks; while earthquake swarms likely reflect triggering by some underlying physical processes, such as aseismic transients or fluid. Here, we studies isolated earthquake clusters in space and time across southern California. We developed a weighted least-square method to model the spatial migration of seismicity onset, and obtained statistical significance of migration based on a bootstrap resampling method. The results show that the swarm-like clusters mostly show significant migration compared with aftershock-like clusters. The migration parameters are compared with focal mechanism dataset to examine their relationship with tectonic stress orientation. For clusters in geothermal sites, we studied the possibility of triggering from geothermal activities, through comparing seismicity pattern with injection location and time, modeling diffusive migration behavior and examining earthquake stress drop relative to injection data. A strong relationship with injection activities at the Salton Sea geothermal field is suggested.