Identification of Repeating Earthquakes: Controversy and Rectification

Repeating earthquakes (repeaters) are events that recurrently rupture the same fault patch with nearly identical magnitudes. Although repeaters have been widely studied and utilized in many fields over the last four decades, there are no standard criteria for reliably identifying such events. The current criteria adopted in the geophysical research community are inconsistent and difficult to justify. Different criteria may inescapably incur inadequate hypotheses and lead to controversial interpretations, highlighting the urgent need for seeking a uniform approach to reliably identify repeaters. In this study, we address this long-standing issue by deriving the most logical criteria on the basis of theoretical calculation with simple yet reasonable assumptions. Quantitatively, we define a repeating pair if their interevent distance is <= 80% of the rupture area of the larger event and their magnitude difference is <= 0.3. We demonstrate the superiority of our proposed approach with challenging cases in California, and our results shed new insight into the hierarchical fault structures in the source areas. Although this study focuses on defining repeating earthquakes, the application to repeating seismic events in other planetary bodies such as moonquakes and marsquakes is straightforward, potentially help avoid misinterpretations of the physical processes in both Earth and planetary interiors.

Automated summary

This study addresses the issue of identifying repeaters by deriving logical criteria based on theoretical calculations. The proposed approach is demonstrated to be superior in identifying repeating earthquakes in challenging cases in California, providing new insights into hierarchical fault structures. The findings are also applicable to repeating seismic events on other planetary bodies, potentially avoiding misinterpretations of physical processes in Earth and planetary interiors.