Are spontaneous earthquakes stationary in California?

Qi Wang, David D. Jackson, & Jiancang Zhuang

Published 2009, SCEC Contribution #1333

Aftershocks and some main shocks are triggered, with timing controlled by preceding events. The remaining "spontaneous" earthquakes presumably respond to tectonic stresses. We consider whether triggered events can be reliably identified; whether the rest are stationary; and whether external phenomena control them. Some studies of earthquake physics and hazard assume answers to all three questions. Many suggest that stress changes from large distant earthquakes can alter the local spontaneous earthquake rate. We demonstrate significant differences in the apparent earthquake rate after declustering with different methods and present criteria for assessing the influence of distant events. The estimated spontaneous earthquake rate depends on the lower magnitude threshold of included events, whether earthquake spontaneity is treated in binary or probabilistic form, and assumptions about catalog completeness. Different statistical tests give different answers to the question of stationarity. We examine a reported rate change in southern California and the suggestion that it might result from the 1960 Chile and 1964 Alaska earthquakes. The rate change itself is questionable. If it occurred, it was probably not caused by the distant earthquakes because the rate change did not occur in northern California or in all parts of southern California.

Key Words
United States, precursors, focal mechanism, numerical models, stress, magnitude, statistical analysis, rates, California, aftershocks, Southern California, time factor, earthquake prediction, main shocks, earthquakes, Northern California

Wang, Q., Jackson, D. D., & Zhuang, J. (2009). Are spontaneous earthquakes stationary in California? . Journal of Geophysical Research,.