Modern California Earthquake Catalogs and Their Comparison

Yan Y. Kagan

Published 2002, SCEC Contribution #693

The Caltech, Harvard CMT, and USGS moment tensor (MT) catalogs, two catalogs (northern and southern California) of first-motion (FM) focal mechanism solutions, based on the HYPO71 program, as well as two regional catalogs of moment tensor inversion (from UC Berkeley and Caltech) are compared. I investigate the differences in magnitude estimates in these catalogs and focal mechanism orientation uncertainty for earthquakes with magnitude 4.7 and higher. I define the focal mechanism discrepancy by determining the smallest 3-D rotation angle needed to transform one double-couple mechanism into another. Only several tens of earthquakes can usually be matched in different catalogs; thus the statistical analysis reliability is relatively low. However, using pairwise differences between the catalogs I evaluate the magnitude uncertainties (standard deviations) as about 0.08 for MT catalogs, and 0.23 for conventional catalogs. The average rotation angle accuracy is approximately 19 degrees for MT catalogs and 34 degrees for FM catalogs. I note that the focal mechanism accuracy for the first-motion observations (HYPO71 solutions) is low, since the quoted angle is only by about a factor of two smaller than the average angle obtained for the random rotation of a double-couple source (75.2 +/- 20.8 degrees).

Citation
Kagan, Y. Y. (2002). Modern California Earthquake Catalogs and Their Comparison. Seismological Research Letters, 73, 921-929.