Spatial variations in the onset times of active faultings in Japan

Yasue, Kenichi; Doke, Ryosuke; Niwa, Masakazu   ; Tanikawa, Shinichi; Nakayasu, Akio; Niizato, Tadafumi  ; Asamori, Koichi; Ishimaru, Tsuneari ; Umeda, Koji

A started age of present faulting pattern is meaningful to suggest the beginning of neotectonic regime such as evolution stages of mountains. The onset times of faulting in the Japanese Islands are estimated using previous study data. We used a calculation method which is the total displacement subdivided by the slip rate. We also used information of the strata indicating the appearance of the faulting. The main results are shown as follows : (1) In northeast Japan, reverse faulting in the N-S direction started since about 3 million years ago. (2) In southwest Japan, the onset times of faulting are estimated in the Kinki district and the northern part of the Izu peninsula, which are younger than those in other regions. (3) There appear to be many active faults in the Niigata-Kobe Tectonic Zone which started since about 1 million years ago.