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Case 25 Application of the Concentration Parameter of Seismoactive Faults to Southern California

Alexey Zavyalov, Ray E. Habermann, Paul Reasenberg, & Chen Yong

Published 1997, SCEC Contribution #183

In this paper we evaluate the present state of the seismic regime in Southern California using the concentration parameter of seismogenic faults (K sf ,Sobolev andZavyalov, 1981). The purpose of this work is to identify potential sites for large earthquakes during the next five or ten years. The data for this study derived from the California Institute of Technology''s catalog of southern California earthquakes, and spanned the period between 1932 to June 1982. We examined events as small asM L ge1.8 but used a magnitude cutoff atM L =3.3 for a detailed analysis. The size of the target earthquakes (M M ) was chosen as 5.3 and 5.8.
The algorithm for calculating Ksf used here was improved over the algorithm described by Sobolev and Zavyalov (1981) in that it considered the seismic history of each elementary seismoactive volume. The dimensions of the elementary seismoactive volumes were 50 km×50 km and 20 km deep. We found that the mean value of Ksf within 6 months prior to the target events was 6.1±2.0 for target events with ML >=5.3 and 5.4>=1.8 for targets with ML>=5.8. Seventy-three percent of the targets with ML>=5.8 occurred in areas where Ksf was less than 6.1. The variance of the time between the appearance of areas with low Ksf values and the following main shocks was quite large (from a few months to ten years) so this parameter cannot be used here for accurate predictions of occurrence time.
Regions where the value of Ksf was below 6.1 at the end of our data set (June, 1982) are proposed as the sites of target earthquakes during the next five to ten years. The most dangerous area is the area east of San Bernardino where Ksf values are presently between 2.9 and 3.7 and where there has been no earthquake with ML>=5.3 since 1948.

Zavyalov, A., Habermann, R. E., Reasenberg, P., & Yong, C. (1997). Case 25 Application of the Concentration Parameter of Seismoactive Faults to Southern California. Pure and Applied Geophysics, 149(1), 129-146. doi: 10.1007/BF00945164.