|Budget Amount *help
¥140,400,000 (Direct Cost: ¥108,000,000、Indirect Cost: ¥32,400,000)
Fiscal Year 2013: ¥16,120,000 (Direct Cost: ¥12,400,000、Indirect Cost: ¥3,720,000)
Fiscal Year 2012: ¥16,770,000 (Direct Cost: ¥12,900,000、Indirect Cost: ¥3,870,000)
Fiscal Year 2011: ¥16,770,000 (Direct Cost: ¥12,900,000、Indirect Cost: ¥3,870,000)
Fiscal Year 2010: ¥36,660,000 (Direct Cost: ¥28,200,000、Indirect Cost: ¥8,460,000)
Fiscal Year 2009: ¥54,080,000 (Direct Cost: ¥41,600,000、Indirect Cost: ¥12,480,000)
We conducted mechanical and hydrological tests on materials cored from the shallow Nankai Trough accretionary prism, the shallow plate-boundary fault along Japan Trench, and the sedimentary cover on the Cocos plate off Costa Rica. The results revealed that their mechanical and hydrological properties systematically change according to the amount of clay minerals. With increasing amount of clay minerals, frictional strength decreases and the flow component in friction sliding increases. Sediments rich in clay minerals are rather impermeable, and fail slowly.
The shallow plate-boundary fault along Japan Trench is found to be rich in clay minerals and very weak in frictional strength so that seismic slip is easy to propagate through. In addition, it is impermeable so that thermal pressurization likely occurs during seismic slips, which further weakens the fault. These well explain the large slip of the shallow plate-boundary fault during the Tohoku-oki earthquake in 2011.