Research press release


Nature Geoscience

Earth science: Supershear earthquakes more common than previously estimated

2000〜2020年に起きた横ずれ大地震の少なくとも14%は超剪断地震であったことを報告する論文がNature Geoscienceに掲載される。この発見は、そのような破壊的な地震が、これまで考えられていたよりも50%以上多いことを示唆している。


今回、Lingsen Mengたちは、過去20年間に起きた全ての大きなマグニチュード(Mw)の横ずれ断層地震(Mw 6.7以上)の地震データを解析し、これまで報告されていなかった4つの超剪断事象を特定した。評価した地震のうちの14%が超剪断と決定され、これはこれまで確定された値より50%大きい。この新たに認識された地震は全て海洋下で起きており、超剪断地震は陸上と同様に海洋でも一般的であることを示唆している。これらの地震が起きた断層の観測結果から、断層領域が大きいと超剪断地震を増長させる可能性があることが分かった。海洋と大陸の境界における断層のように、断層をまたぐ物質が対照的であることも要因になり得る。


At least 14% of all large, strike-slip earthquakes between 2000 and 2020 were supershear, according to a study published in Nature Geoscience. These findings suggest that such potentially destructive events are 50% more common than previously thought.

Supershear earthquakes occur when the speed at which the fault ruptures is greater than the travel speed of the seismic waves produced. These earthquakes, which are generally observed on land, can be highly destructive as the fast rupture speeds can generate stronger ground motion. They are considered rare; only a few large magnitude earthquakes generated by strike-slip faults — faults in which two blocks of the Earth’s crust slide past each other — have been categorised as supershear.

Lingsen Meng and colleagues analysed seismic data from all large magnitude (Mw) (Mw = 6.7 or greater), strike-slip earthquakes over the last 20 years and identified four previously unreported supershear events. Of all the earthquakes evaluated, 14% were determined to be supershear, 50% more than previously confirmed. These newly recognised events all occurred beneath the ocean, suggesting that supershear earthquakes are just as common under the ocean as they are on land. Observations from faults where these earthquakes occurred indicate that wider fault zones may promote supershear events.Contrasting material across the fault, for example in faults at an oceanic-continental boundary, may also be a factor.

These newly identified supershear earthquakes suggest they are not as rare as previously thought, and help us to understand what conditions may generate such fast rupture speeds, the authors conclude.

doi: 10.1038/s41561-022-01055-5


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