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Research reveals cause of huge 2011 Japan tsunami, may improve forecasting


OSAKA -- Research results released by Osaka University on April 29 have attributed the massive plate-boundary fault slip and tsunami of the March 2011 Great East Japan Earthquake to increased pressure due to frictional heat between plates.

Researchers said friction between the plates created temperatures of at least 500 degrees Celsius, causing water trapped underneath to expand and push open faults between plates, making huge slips more likely. The team says their work will help predict the size of tsunamis and the characteristics of earthquakes in the Nankai Trough, inland and other regions.

On the same day, the group's research results were published in the English online journal Scientific Reports.

The March 2011 earthquake was caused when a shallow area close to the Japan Trench slipped 50 to 80 meters, raising the seabed and generating a huge tsunami. Before the disaster, shallow areas were considered safe from major slips. To determine the cause of such a massive slip, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) deployed the Deep-sea Scientific Drilling Vessel "Chikyu" in 2012 to collect pieces of the fault for analysis.

Tetsuro Hirono, associate professor at the Department of Earth and Space Science at Osaka University, and his team analyzed material recovered by Chikyu. They studied the level of pressure, permeability, heat and other conditions near the plate boundary required for the rock to slip or break. While some believed that slippery clay composites in the fault were to blame for the slip, it became evident that had it not been for the expansion of water caused by friction-generated heat, there would not have been a major fault slip.

Historical and other data are currently used to predict the chances of a large earthquake and its intensity. Following the Osaka team's results, it is possible that analysis of fault lines will improve the ability to forecast the size or intensity of tsunamis and earthquakes, reducing the effects of natural disasters.

Hirono said, "The Heisei era was affected by several large earthquakes, but researchers were only reactive to events. I want earthquake research to proactively reduce disasters as we advance into the new Reiwa era."

(Japanese original by Takeshi Nemoto, Osaka Science and Environment News Department)

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