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