Summer earthquakes in southern California related to pressure patterns at sea level and aloft

Abstract

This paper attempts to confirm with an expanded data set the author's earlier conjecture that pressure and wind patterns over a large portion of the northern hemisphere play a role in triggering moderate size earthquakes in southern California. Various indices of atmospheric pressure and geostrophic wind over the eastern North Pacific, western North America, and eastern North America suggest a connection between seasonal anomalous pressure patterns and moderate size quakes (or their absence) over southern California in summer. Composite charts of seasonal pressure anomalies indicate that summer quakes are more likely when the North Pacific high, the western North American low‐pressure, and the continental upper level anticyclone over eastern United States are well developed, and conversely, quakes are inhibited when these centers of action are poorly developed. A low‐frequency signal shows up in both the summer earthquake and pressure anomaly data. The above conclusions are statistically significant at the 90% confidence level or above. These empirical findings appear significant enough to warrant further testing and the development of a physical hypothesis. Some speculations are offered.