Saturday, January 28, 2012

200 km-long active fault found on seabed off Kii Peninsula

TOKYO (Kyodo) -- An active fault around 200 kilometers in length, which is believed to have caused massive earthquakes in the past, has been found on the seabed off the Kii Peninsula on the country's main island of Honshu, researchers at the University of Tokyo said Friday.

Once the fault, which lies on the Nankai Trough, moves, it could cause a magnitude-8-level earthquake, they said, adding they have found a cliff several hundred meters high on the seabed that was created as a result of the fault's movement in the past.

"There is a high probability that fault shifts have caused great tsunami," said Park Jin-Oh, associate professor of marine geology at the university. "We need to reformulate disaster countermeasures by taking into account an active fault on the seabed 200 km or longer."

Park analyzed sound wave data on the seabed collected by the Japan Agency for Marine-Earth Science and Technology, and found a fault branching off from a boundary between two tectonic plates on the seabed west of the southern tip of the Kii Peninsula.

The fault was found to connect to a similar fault east of the peninsula's southern tip, stretching over at least 200 km, according to the researchers.

While it remains unclear exactly when or how many times the fault has moved, the eastern and western parts are believed to have moved often at the same time, judging from the geographical characteristics of the area.

Such a fault movement may have caused a magnitude 8.6 earthquake in 1707 known as the Hoei Earthquake, Park said, adding, the eastern part of the fault is believed to have caused a magnitude 7.9 quake and tsunami in 1944. Read More