An active fault line likely runs directly beneath Mount Fuji, one of Japan’s most iconic landmarks, according to studies by a science ministry investigative team.
An earthquake striking along a fault line close to a volcano, such as Mount Fuji, could cause large-scale landslides called "sector collapse." Detailed investigations are necessary to evaluate the risks of such disasters, a scientist in the team said.
The team engaged in a three-year research project, from fiscal 2009, to investigate the Kannawa-Kozu-Matsuda fault zone near the border of Shizuoka and Kanagawa prefectures.
In fiscal 2011, the scientists studied seismic waves and other clues to estimate underground structures beneath a region that spreads to the west of the fault zone and around Mount Fuji, the highest peak in Japan, at 3,776 meters above sea level.
As a result, they confirmed the presence of a fault-like structure stretching from beneath the eastern foot of Mount Fuji to directly beneath the volcanic mountain. The fault, about 30 kilometers long, extends from just beneath the surface to a depth of about 5 km.
The fault is likely to have been active during the past million years and has the potential to generate magnitude-7 class earthquakes, the scientists said.
At least five sector collapse events have taken place on Mount Fuji during the last 100,000 years or so. The latest occurred between 2,500 and 2,900 years ago.
"No activity records or the precise scale of the fault are available at the current stage," said team member Hiroshi Sato, a professor of structural geology at the Earthquake Research Institute of the University of Tokyo. "Excavation and other surveys are necessary."
The research results will be presented during an annual meeting of the Japan Geoscience Union to be held in Chiba from May 20.
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