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Active 200-km Fault Found off Honshu’s Kii Peninsula

Previous shifts caused magnitude 8.6 quake, huge tsunami: scientists

An active fault around 200 km long that is believed to have been a source of huge quakes in the past has been found off Honshu’s Kii Peninsula, according to researchers at the University of Tokyo. If the fault on the Nankai Trough moves, it could trigger a magnitude 8.0 earthquake, the researchers said, adding they have found a seabed cliff several hundred meters high that was created by the fault’s past movements. “There is a high probability that fault shifts have caused great tsunami,” said Park Jin Oh, associate professor of marine geology. “We need to reformulate disaster countermeasures by taking into account an active fault on the seabed 200 km or longer.”

Park analyzed sonar 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 in an area west of the southern tip of the Kii Peninsula in Wakayama Prefecture. The fault was found to be connected to a similar fault to the east of the peninsula and to extend at least 200 km, the researchers said.

While it remains unclear exactly when or how many times the fault has moved, the eastern and western parts are believed to have shifted often and at the same time, judging from the geographical characteristics of the area. Such movements may have caused the 8.6-magnitude Hoei earthquake in 1707, Park said.

The eastern part of the fault is  believed to have caused a magnitude 7.9 and tsunami that struck in 1944.

In addition, an extended area of the newly discovered western part overlaps the area where a magnitude 8.0 quake struck in 1946. It is therefore possible that the western part moved two years after the eastern part did, Park said.

…(Japan Times)

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January 31, 2012 - Posted by | Seismic | , , , ,

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