付加体中の低角逆断層沿いに発生した豪雨に伴う深層崩壊について

Abstract

2011 Typhoon Talas induced a large numbers of rain-induced rock avalanches in the Kii Peninsula, where is underlain by Jurassic-lower Miocene accretion complexes. We performed geological investigation in the Akatani area, where two huge rock avalanches with volumes of 2 million and 8 million m3 occurred, and we found that these two rock avalanches had their sliding surfaces along a large-scale low-angle thrust-fault extending more than 5 km. This fault had been exposed at riversides by long-term river incision and overlying dip slopes had started to deform and finally failed catastrophically, being triggered by the heavy rainstorm. This finding suggests that locating a large-scale low-angle thrust fault is essentially important to predict potential sites of rock avalanche as well as finding a gravitational slope deformation using high-resolution DEMs.