| 초록 |
We conducted an air-photo interpretation, an investigation of fault outcrops, a trench survey, and/or an array drilling survey for the northeastern part of the Tokusa-Jifuku fault (T-JF) and the central part of Sakota-Ikumo fault (S-IF) in central-eastern Yamaguchi Prefecture, in order to clarify their characteristics and activity. By the trench survey for the northeastern T-JF at Tokusa-naka, Ato Town, the age of the latest movement is estimated to range from 10,800 to 3,400 yrBP. Review of previous 14 C dating data obtained from former trench survey of the southwestern T-JF suggests that the entire region of the fault being approximately 35 km long moved at one time in a period between 6,300 and 5,200 yrBP. On the other hand, by trench surveying of the central part of S-IF at Ikumo-naka, Ato Town, located approximately 10 km southwest of the epicenter of the 1997 Mj (Japan Meteorological Agency Scale) = 6.6 earthquake which occurred in northern Yamaguchi Prefecture, it was judged that a movement of the fault occurred between 14,400 and 8,500 yrBP. These data of the latest fault movement, combined with those from previous studies, suggest that the fault movement tends to migrate southwestward from the S-IF to the northeast, through the T-JF, to the W. Kidoyama fault to the southwest, which constitutes the Lake Ohara - W. Yauneyama fault system. |
