Observations of Dynamic Triggering in the Coso Geothermal Field 2004-2013

Over a ten-year period (2004-2013), we search for remotely triggered seismicity utilizing data from EarthScope's USArray Transportable Array (TA) and the Southern California Seismic Network. In particular, we apply an STA/LTA approach for 154 M ≥ 7 earthquakes and use local earthquake catalogs (magnitude of completeness 0.8) to investigate triggered seismicity in the Coso Geothermal Field (CGF). Of 154 remote mainshocks, we find 34 mainshocks (22%) show triggered seismicity based on the increase in the magnitude and frequency (rate) from pre-mainshock to post-mainshock auto-detection rates and cataloged seismicity. We observe both instantaneous (16) and delayed (18) triggering within ± 5 hours of the mainshock. We also find that remote triggering in the CGF region is enhanced by the orientation (back-azimuth) of the passing seismic (mostly surface) waves in relation to the local stress field (NNE-SSW trending faults), and there appears little correlation between the peak dynamic stress and event triggering. Our results suggest that remote dynamic triggering strongly depends on the regional stress orientation, and for the CGF region the stress threshold for remote M ≥ 7 earthquakes is not critically important for dynamic triggering.