Anomalous Seismicity and Accelerating Moment Release Preceding the 2001 and 2002 Earthquakes in Northern Baja California, Mexico

An algorithm recently developed by RUNDLE et al. (2002) to find regions of anomalous seismic activity associated with large earthquakes identified the location of an Mw = 5.6 earthquake near Calexico, Mexico. In this paper we analyze the regional seismicity before this event, and a nearby Mw = 5.7 event, using time-to-failure algorithms developed by BOWMAN et al. (1998) and BOWMAN and KING (2001a,b). The former finds the radius of a circular region surrounding the epicenter that optimizes the time-to-failure acceleration of seismic release. The latter optimizes acceleration based on the expected stress accumulation pattern for a dislocation source. Both methods found a period of accelerating seismicity in an optimal region, the size of which agrees with previously proposed scaling relations. This positive result suggests that the Rundle algorithm may provide a useful technique to identify regions of accelerating seismicity, which can then be analyzed using signal optimization time-to-failure techniques.