Research press release




今回、Dan Bassettたちは、地形データと重力データを用いて、東北沖地震が発生した地域の地質構造の絞り込みを行った。Bassettたちは、太平洋プレートが本州の下に潜り込んでいる沈み込み帯を研究対象として、この沈み込み帯の上のくさび形物質を調べた。Bassettたちが得たデータからは、覆いかぶさっているプレート(上部プレート)に境界線が突然生じていることが明らかになった。この境界線について、Bassettたちは、陸上で観測できるいわゆる中央構造線の海上での延長線上にあり、さまざまな起源と密度の岩石が併置されているという解釈を示している。Bassettたちは、上部プレートの地質構造が地震挙動を制御する上で重要であり、地質的構造が類似した地球上の他の地域での地震の危険を解明するために今回の研究結果を利用できると考えている。


A detailed study of the geological structure of the region where the March 2011 Tohoku-oki earthquake took place, in northeast Japan, helps to elucidate earthquake behaviour in the area and possibly elsewhere. The findings are reported in this week’s Nature.

Only the second giant earthquake (with a moment magnitude of at least 9) to have occurred in the last 50 years, the 2011 Tohoku-oki earthquake is one of the most widely known disasters of the last decade. Although high-resolution data describing the kinematics of the earthquake rupture - the sudden release of energy associated with fault movement - are available, the physical or structural characteristics that contributed to the rupture were not previously clear.

Dan Bassett and colleagues used topographical and gravity data to constrain the geological structure of the area where the earthquake occurred. They focus regionally on the wedge of material above the subduction zone, where the Pacific plate is diving beneath Honshu. Their data reveal the existence of an abrupt boundary in this overthrusting plate, which the authors interpret to be an offshore continuation of the so-called Median Tectonic Line that can be observed onshore, juxtaposing rocks of different origins and densities. They propose that the geological structure of the overthrusting plate is important in controlling earthquake behaviour and that these results may be used to understand seismic hazards in other areas of the globe with a similar geological make-up.

In a Comment piece published in the same issue of Nature, Masahiro Sugiyama and colleagues reflect on the five years since the events of March 2011, distilling the lessons learned in energy, policy and beyond. Japan needs to take to make its scholarship more international and more interdisciplinary, they conclude: “Going global is the key, and will pay dividends”.

doi: 10.1038/nature16945

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