There May Be an Active Fault Right Underneath Mt. Fuji, Tokyo University Geologist Says

The result of the research by Professor Hiroshi Sato and his group at Tokyo University Earthquake Research Institute will be presented at the Japan Geoscience Union conference that will be held in Chiba on May 20, 2012.

If an earthquake of Magnitude 7 or larger occurs on that fault, Professor Sato's group says, it may cause "sector collapse" of Mt. Fuji.

It that should ever happen, it will be not just the collapse of Mt. Fuji but the collapse of the 2,000-year Japanese culture... All through Japan's history (and pre-history, for that matter), Mt. Fuji has retained its shape, and has been revered for the shape.

From Yomiuri Shinbun (5/10/2012):

富士山直下に活断層か、Ｍ７級地震で山体崩壊も

Active Fault directly below Mt. Fuji? Sector collapse possible with M.7 class earthquake

富士山東麓の地下に長さ約３０キロ・メートルの活断層がある可能性が高いことが、東京大学地震研究所の佐藤比呂志教授（構造地質学）らによる調査でわかった。

It has been revealed by the research by Professor Hiroshi Sato (structural geology) and his group at Tokyo University Earthquake Research Institute that it is highly possible that there is a 30-kilometer long active fault underneath the eastern foot of Mt. Fuji.

この断層が動けばマグニチュード７級の地震を起こす恐れがあり、山の一部が崩れる「山体崩壊」の引き金となる可能性も否定できないという。千葉市で２０日から始まる日本地球惑星科学連合大会で発表する。

If this fault moves, it could cause a Magnitude 7-class earthquake which could trigger "sector collapse", a collapse of part of the mountain. The result of the research will be presented at the Japan Geoscience Union conference that will start in Chiba City on May 20.

活断層が見つかったのは、富士山東麓の静岡県御殿場市付近。陸側のプレート（地球を覆う岩板）に、伊豆半島を乗せたフィリピン海プレートが南側からぶつかる境界とみられる場所で、これまでに確認された活断層「神縄・国府津―松田断層帯」の西側に続いている。

The active fault was discovered on the eastern foot of Mt. Fuji, near Gotenba City in Shizuoka Prefecture. The location is considered to be where the continental plate is hit by the Philippine Sea Plate from the south. Izu Peninsula is on the Philippine Sea Plate. The fault is on the west side of the active fault already confirmed.

地面を震動させて地下構造を調べた結果、長さは北東―南西に約３０キロ・メートルで、断層の両側から押し合う力が働く「逆断層」タイプ。富士山頂の方向に深くなっており、山頂直下では深さ十数キロ・メートルに達しているとみられる。最近１００万年の間に動いた形跡がみられるが、動いた時期や周期はわかっていない。

The group studied the subsurface structure by vibrating the ground. The length of the fault is about 30 kilometers in the northeast-southwest direction, and it is a reverse fault. The fault deepens toward the direction of the mountain top of Mt. Fuji, and it is considered that it is over 10 kilometers deep right beneath the mountain top. There is evidence of the fault having moved in the most recent 1 million years, but it is not known when it moved or at what cycle.

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