Seismicity rate changes in the San Jacinto Fault Zone and the Salton Sea Geothermal Field following the 2010 Mw7.2 El Mayor-Cucapah Earthquake

Xiaofeng Meng, & Zhigang Peng

Published June 2014, SCEC Contribution #1814

Whether static or dynamic stress changes play the most important role in triggering earthquakes in the near field is still in debate. Here we examine the seismicity rate changes in southern California following the 2010 Mw7.2 El Mayor-Cucapah earthquake. We focus on the Salton Sea Geothermal Field and the San Jacinto Fault Zone because of high-sensitivity continuous borehole recordings and ample background seismicity. A significant increase in seismic activity is found in both study regions immediately following the main shock. However, near the Salton Sea Geothermal Field where the static Coulomb stress decreased, the seismicity rate dropped below the pre-main-shock rate after ~1 month. In comparison, along the San Jacinto Fault Zone with an increase in the static Coulomb stress, the seismicity rate remained higher than the pre-main-shock rate with several moderate-size earthquakes occurring in the subsequent months. While we cannot completely rule out other mechanisms, these observations are best consistent with a widespread increase in seismicity from dynamic stress changes immediately after the main shock, and longer-term seismicity rate changes from static stress changes. Our observation, together with other recent studies, suggests that both static and dynamic stress changes are important in triggering near-field earthquakes, but their affected regions and time scales are different.

Citation
Meng, X., & Peng, Z. (2014). Seismicity rate changes in the San Jacinto Fault Zone and the Salton Sea Geothermal Field following the 2010 Mw7.2 El Mayor-Cucapah Earthquake. Geophysical Journal International, 197(3), 1750-1762. doi: 10.1093/gji/ggu085.