Are spontaneous earthquakes stationary in California

[1] 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. To all three questions, some studies of earthquake physics and hazard assume answers. 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 by different methods, and we present criteria for assessing the influence of such distant events. The estimated spontaneous earthquake rate depends on the lower magnitude threshold of included events, whether spontaneity is treated in binary or probabilistic form, as well as 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 have resulted from the 1960 Chile and 1964 Alaska earthquakes. The rate change itself is questionable. If it has occurred, it was probably not caused by those distant events, because the rate change is not present in northern California or in all parts of southern California.