HR: 0830h
AN: S21D-0326    [PDF]
TI: Comprehensive waveform cross-correlation of southern California seismograms: Part 2. Event locations obtained using cluster analysis
AU: * Shearer, P
EM: pshearer@ucsd.edu
AF: Scripps Institution of Oceanography, U.C. San Diego, La Jolla, CA 92093-0225 United States
AU: Hauksson, E
EM: hauksson@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125 United States
AU: Lin, G
EM: glin@igpp.ucsd.edu
AF: Scripps Institution of Oceanography, U.C. San Diego, La Jolla, CA 92093-0225 United States
AU: Kilb, D
EM: dkilb@epicenter.ucsd.edu
AF: Scripps Institution of Oceanography, U.C. San Diego, La Jolla, CA 92093-0225 United States
AB: We obtain precise relative locations for over 340,000 southern California earthquakes between 1984 and 2002 by applying the source-specific station term (SSST) method to existing P and S phase picks and a differential location method to about 100,000 events within similar event clusters identified using waveform cross-correlation. To simplify the computation, we first divide southern California into five polygons, such that there are $\sim$100,000 events or less in each region. Polygon boundaries are chosen to lie in regions of sparse seismicity. The entire catalog is first relocated using existing phase picks and the SSST method of Richards-Dinger and Shearer (2000). Next, we apply cluster analysis to the waveform cross-correlation output (see accompanying Hauksson et al.~abstract for details) in order to identify similar event clusters. Because we do not compute cross-correlation between all possible event pairs, some modifications to standard cluster analysis algorithms were necessary to achieve a suitable method. We relocate earthquakes within each similar event cluster using the differential times alone, keeping the cluster centroid fixed to its initial SSST location. We estimate standard errors for the relative locations from the internal consistency of differential locations between individual event pairs; these errors are often as small as tens of meters. In many cases the relocated events within each similar event cluster align in planar features suggestive of faults. We observe a surprising number of conjugate faults at small scales that strike nearly perpendicular to the main seismicity trends. In general, the fine-scale details of the seismicity reveal a great deal of structural complexity in southern California fault systems.
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting