Reduced seismic activity after mega earthquakes

TL;DR

This study investigates how mega-earthquakes influence subsequent seismic activity, revealing a reduction in remote earthquake rates after large events, and suggesting a global energy release mechanism not captured by existing models.

Contribution

It provides new insights into post-seismic activity by showing a reduction in remote earthquake rates after mega-earthquakes and highlights limitations of the ETAS model.

Findings

Significant decrease in earthquake rate beyond certain distances after mega-earthquakes.

Remote earthquake rate can be higher after the strongest earthquakes compared to surrogate data.

Existing models like ETAS do not fully explain the observed post-seismic activity patterns.

Abstract

Mainshocks are often followed by increased earthquake activity (aftershocks). According to the Omori-Utsu law, the rate of aftershocks decays as a power law over time. While aftershocks typically occur in the vicinity of the mainshock, previous studies have suggested that mainshocks can also trigger earthquakes in remote locations. Here we examine the earthquake rate in the days following mega-earthquakes (magnitude >= 7.5) and find that the rate is significantly lower beyond a certain distance from the epicenter compared to surrogate data. However, the remote earthquake rate after the strongest earthquakes (magnitude >= 8) can also be significantly higher than that of the rate based on surrogate data. Comparing our findings to the global ETAS model, we find that the model does not capture the earthquake rate found in the data, hinting at a potential missing mechanism. We suggest that the diminished earthquake rate is due the release of global energy/tension subsequent to substantial mainshock events. This conjecture holds the potential to enhance our comprehension of the intricacies governing post-seismic activity.