抄録
The Atera fault zone is a left-lateral active fault zone in central Japan which is about 70 km in length and strikes NW-SE and NNW-SSE. The Kashimo area which is located in the central part of the Atera fault zone indicates the most complicated fault geometries. In this area at least two active faults, the Atera and the Owachi faults, are aligned parallel in a narrow range. In order to understand the developmental process of this fault zone, it is important to clarify the activities and the histories of each active fault in this zone. In this study, we have identified some faulting events in a newly found outcrop at Nagahora site in Kashimo area. The occurrence of the undoubted faulting event was about 3,500-4,800 years ago (Event 3). The occurrences of uncertain faulting events were about 2,800-4,800 years ago (Event 2), and after about 3,200 years ago (Event 1), although the possibilities that these two events had occurred at the same time with Event 3 have remained. It was considered that the faulting events have repeated at least 50,000 years at this site, because the occurrence of another event was identified during the deposition of sediment of M2 terraces.
