Modern California Earthquake Catalogs and Their Comparison

Abstract

Earthquake catalogs are primary data sources for inferring earthquake behavior, testing earthquake pattern hypotheses, and estimating seismic hazards. As in any quantitative science, understanding uncertainties is crucial to proper interpretation. Examining catalog properties will also help guide future improvements in seismic observation and catalog reporting. In an effort to create a combined earthquake catalog for southern California, I analyze several earthquake catalogs compiled in California since the 1970's to determine the accuracy of their magnitude determinations and earthquake focal mechanisms. California local earthquake catalogs were among the first to be compiled in the instrumental era (Hileman et al. , 1973; Bolt and Miller, 1975). Many catalogs are now available in California: Some earthquake lists can be extracted from instrumental global catalogs (Kagan, 2002), and several catalogs of historical events exist (Toppozada et al. , 2000, and references therein), as do a few local and regional catalogs. Many catalog compilations from original data sets and different publications have also been published. Focal mechanisms are now used for various investigations, among which studies of earthquake stress triggering ( cf . Ziv and Rubin, 2000) and stress inversion (Abers and Gephart, 2001; Hardebeck and Hauksson, 2001; Provost and Houston, 2001) are some of the most important. Moreover, catalogs with focal mechanisms are primary data sets with complete first-order information about the earthquake process; low-frequency seismograms, static displacements, and strain patterns can be computed using these data. Although global and regional focal mechanism catalogs have been compiled since the 1960's, catalogs based on compilations from individual earthquake studies have rather low and highly nonuniform accuracy of earthquake focal mechanisms (Kagan and Knopoff, 1985). Only in relatively recent catalogs of focal mechanisms does the solutions' quality allow us to analyze their routine statistical uncertainty quantitatively. Extensive and reliable earthquake catalogs with focal …