Full waveform earthquake location: Application to seismic streaks on the Calaveras Fault, California

Abstract

We use a novel technique based upon source array analysis to locate three moderate earthquakes that occur at the edge of previously identified streaks of seismicity on the Calaveras Fault, California. Our method determines centroid locations for earthquakes, in addition to the hypocenters previously determined using first-break picks. Application of the method to smaller earthquakes indicates that the errors associated with the locations are on the order of 100 m, much less than the rupture dimensions of the M > 4.5 events that we have analyzed. We treat high-precision locations of microearthquakes near the earthquakes that we want to locate as source arrays and compute the slowness of waves leaving these source arrays. We then use the slowness parameters to locate the earthquakes of interest. We find that the medium-magnitude events nucleate on the streaks and rupture into a zone devoid of seismicity. On this basis, we argue that streaks represent the boundary between creeping and locked sections of a fault. Our location technique has the potential for wide application, including circumstances where it may be necessary or desirable to locate earthquakes without using direct arrivals. Copyright 2007 by the American Geophysical Union.