Seismicity prior to the 2016 Kumamoto earthquakes

TL;DR

This study analyzes precursory seismic patterns before the 2016 Kumamoto earthquakes using multiple methods, revealing diverse signals at different scales and highlighting the potential for improved earthquake forecasting and hazard reduction.

Contribution

It demonstrates that combining various seismic analysis methods can detect different precursory signals, enhancing earthquake prediction capabilities.

Findings

Multiple methods detected different precursory signals.

Regional seismic quiescence was a common precursor.

Precursory anomalies lasted from 1.5 to over 3 years.

Abstract

We report precursory seismic patterns prior to the 2016 Kumamoto earthquakes, as measured by four different methods based on changes in seismicity that can be used for earthquake forecasting: the b-value method, two methods of seismic quiescence evaluation, and an analysis of seismicity density in space and time. The spatial extent of precursory patterns differs from one method to the other and ranges from local scales (typically, asperity size) to regional scales (e.g., 2 degree x 3 degree around the source zone). The earthquakes were preceded by periods of pronounced anomalies, which lasted in yearly scales (1.5 years), or longer (> 3 years). We demonstrate that a combination of multiple methods detected different signals prior to the Kumamoto earthquakes. This indicates great potential to reduce the hazard at possible future sites of earthquakes relative to long-term seismic hazard assessment. We also found that the seismic quiescence in a regional scale area, detected by using the two methods of seismic quiescence evaluation, was a common precursor to the 2016 Kumamoto earthquakes and 2015 Off Satsuma Peninsula earthquake. The result allows us to interpret both events as the onset that occurred at a section along the tectonic line from the Okinawa Trough through the Beppu-Shimabara graben.