Non-randomness of Japan megaquakes implied by stress recovery and accumulation

TL;DR

This study analyzes stress recovery patterns and earthquake precursors to understand the non-random timing of Japan's megaquakes, revealing that their recurrence intervals are more predictable than previously thought.

Contribution

It introduces a comparative analysis of stress indicators and seismic phenomena to demonstrate the non-random recurrence of major earthquakes in Japan.

Findings

High b-values indicate low stress in Tohoku quake zone

Low b-values indicate high stress in Hokkaido quake zone

Seismic quiescence and plate coupling are observed before megaquakes

Abstract

Monitoring stress recovery and accumulation associated with megaquakes helps to assess their recurrence. Previous studies proposed a high likelihood of imminent recurrence for the 2011 Tohoku and the 17th-century Hokkaido megaquakes belonging to the magnitude-9 class, although their current stress state remains uncertain. Here we compare the occurrence of small earthquakes relative to larger ones, using b-values, showing high b-values in the source area of the Tohoku earthquake, indicating low stresses. In contrast, low b-values occurred in the source area of the 17th-century earthquake, indicating high stresses as seen before the Tohoku event. Around the low-b-value zone, phenomena that provide insight into subsequent large earthquakes are observed, and which were reported for worldwide earthquakes: seismic quiescence, a seismic gap, strong plate coupling, and slow earthquake activity avoiding megaquakes' rupture zones. Results imply that the Hokkaido and Tohoku megaquakes occur nonrandomly in time, rather their recurrence intervals are more characteristic.