Abstract
The Nishiyama fault zone in North Kyushu runs from Tsuyazaki to Iizuka. We have carried out three trench excavations across this fault at Anzunosato, Nuyama and Myoujyouji, where we had detected terrace deposits displaced vertically in aerial photographs. Trench excavations revealed the following.
The faults, observed in these trenching studies, strike from NW to SE. They ap p eared as high angle faults. The south-western side of the fault apparently uplifted relatively. The latest event of the fault occurred after 11,000 y. B. P. at Anzunosato. At Nuyama, the latest event occurred between 1 1,000 y. B. P. and the 5th cent ury. At Myoujyouji, the latest event is confirmed to occur before 2,100 y. B. P. Therefore the latest event of the Nishiyma fault zone probably occurred between 11,000 y. B. P. and 2,100 y. B. P. The apparent vertical displacement of the latest event is 25cm at Nuyama trench. The exploratory drilling at Myoujyouji revealed that the apparent vertical fault displacement amounts to 38m after middle Pleistocene.
