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Published April 10, 1995 | Published
Journal Article Open

Patterns of seismic release in the southern California region

Abstract

Southern California experiences earthquakes on the San Andreas system of vertical right-lateral predominantly strike-slip faults and on a second system of faults that includes thrusts, oblique-slip, left-lateral, and other faults. Pattern recognition and cluster analysis are used to analyze the catalog of earthquakes with magnitudes ≥5.5 from 1915 to 1994. We use pattern recognition to find a suite of traits that would characterize each of these two systems and distinguish them from each other. Both pattern recognition and cluster analysis show that epochs of seismic release occur in which one or the other system is the predominant form of earthquake activity. For the past 2 decades the second system has been the active one. Small changes in the direction of plate movements could account for this phenomenon. Seismic release on the San Andreas system is preceded by episodes of activity in the Great Basin or in the Gulf of California. Presumably, these episodes would represent extension in the former region and spreading and slip on transform faults in the latter.

Additional Information

© 1995 by the American Geophysical Union. Paper number 95JB00316. Received August 5, 1994; revised December 20, 1994; accepted January 26, 1995. We thank Bernard Minster, Mark Zoback, V. I. Keilis-Borok, Barbara Romanowicz, and Selwyn Sacks for their helpful advice. Reviewers Albert Hsui, Lucy Jones, and an anonymous reviewer made valuable suggestions which helped us improve the paper. Lucy Jones provided us with the aftershock free catalog of southern California earthquakes. F.P. is grateful for support as a Fairchild Scholar at Caltech. Contribution 5511 Division of Geological and Planetary Sciences, California Institute of Technology.

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August 20, 2023
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