A New Method for Event Detection and Location — Matched Field Processing Application to the Salton Sea Geothermal Field

We present a new method for microearthquake event detection and location. We have adapted the Matched Field Processing (MFP) technique, originally developed to locate continuous underwater acoustic sources, to detect transient microearthquake signals. We create templates derived from previously identified earthquake signals and compare these master templates to the continuous seismic data stream to detect previously unidentified events. We call this method the empirical MFP method.

We propose that empirical MFP can complement existing earthquake catalogs and techniques by significantly increasing the number of earthquakes that can be detected on existing seismic networks. For example, in the Southern California Earthquake Data Center (SCEDC) earthquake catalog, 333 events are listed as occurring in the Salton Sea Geothermal Field (SSGF) during January 2011. By examining all events in the SSGF between 2008 and 2010 we identified 231 master template events. We compare these master templates to the continuous seismic data and successfully identify 1526 events as occurring in the SSGF during January 2011. This is over a 450% increase in the number of events detected. We investigate the optimal frequency bands and threshold levels for which the empirical MFP method works best in our study area.

We also apply Coulomb stress modeling to understand earthquake interaction and fault orientation in the SSGF. We calculate Coulomb stress change using focal mechanism information and compare it with the locations of seismic events to investigate the effectiveness of Coulomb stress modeling to reflect possible fault opening or shearing.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California