2026-05-28 九州大学
臨界度を通して見たM6クラス地震とその後 説明）詳細な地震観測によってモニターすると、M6クラス地震が起こったのちも臨界度が高いとM7クラス地震が起こる場合があることがわかりました。
＜関連情報＞
- https://www.kyushu-u.ac.jp/ja/researches/view/1464
- https://www.nature.com/articles/s41598-026-47198-y
地震モーメント効率は、マグニチュード6クラスの地震後にさらに大きな地震が発生する可能性を示唆している Seismic moment efficiency reveals the potential for larger earthquakes after M6-class events
Satoshi Matsumoto,Koki Aizawa & Takeshi Matsushima
Scientific Reports Published:28 April 2026
DOI:https://doi.org/10.1038/s41598-026-47198-y Unedited version
Abstract
Understanding how stress and strength conditions evolve before and after large earthquakes remains a fundamental challenge in seismology. Here, we introduce an observationally grounded metric—the ratio of the summed moment tensor to scalar seismic moment (Mstk/M₀)—to track temporal changes in deformation behavior surrounding earthquake faults. Using high-resolution focal mechanism datasets, we analyze two well-instrumented sequences with M6-class foreshocks followed by M7-class mainshocks: the 2016 Kumamoto and 2019 Ridgecrest events. We find that Mstk/M₀ remains elevated after M6-class foreshocks but decreases sharply after M7-class mainshocks, indicating a transition toward a more heterogeneous deformation state. To evaluate broader applicability, we examined nine inland M6–M7 earthquake sequences in Japan (2000–2020). Among ten events that exhibited high Mstk/M₀ during foreshock activity, five maintained high values after the M6-class event, and three of these were subsequently followed by even larger earthquakes. In contrast, all other sequences not followed by larger events showed clear decreases in Mstk/M₀ after the initial large earthquake. These observations suggest that sustained high Mstk/M₀ after an M6-class earthquake may indicate conditions favorable for continued rupture growth, whereas decreases may reflect reduced likelihood of further large rupture. Relationships between Mstk/M₀ and inelastic strain rate further support a physical interpretation linking deformation consistency with the ambient stress field to the potential for large earthquake occurrence. Monitoring Mstk/M₀ in the immediate aftermath of large earthquakes may therefore provide useful information for assessing whether an even larger event is likely to follow.
