静岡県函南町畑地区に新設された丹那断層地下観察室

抄録

The Tanna fault in the northern part of Izu Peninsular, central Japan, is a principal strand of the Kita-Izu active fault system, a conjugate system of faults for about 35 km that consists of left-lateral faults of N-S or NNE-SSW in trend and right-lateral faults of E-W or WNW-ESE in trend. During the Kita-Izu earthquake of 1930 (Magnitude 7.3), the Tanna fault that extends N-S, moved in a leftlateral sense. In 1997, one trench as its underground observation room, was excavated across this surface rupture line wih the maximum horizontal offset of 2.6m, at Hata, Kannami, Shizuoka prefecture. In this trench, the sharp and fresh fault plane with thin fault clay and some tracks of leftlateral displacement in landslide and debris flow deposits, is exposed. It is estimated that the surface rupture in 1930, make an arrangement of a left echelon type near this site because the fault plane in the trench, is obviously in a direction of southwest to northeast.