抄録
Chojagahara fault in southeast of Hiroshima prefecture and Yoshii fault in southwest of Okayama prefecture are both NE-SW extending right lateral strike slip faults being separated with 10km gap in Kannabe plain. Distinctive geomorphic evidence along the Chojagahara fault suggests that the fault has moved during the recent geological period. We identified young sharp lineaments forming left echelon stepping in the plain, cutting and disturbing the rectangular field pattern originated from“ Jon-lot system” on alluvial lowland, indicating their activity during the historical period.
A trench was dug across one of the lineaments to confirm the latest event of the fault, and a fault outcrop that cuts up to the base of cultivated soil appeared on the trench walls. The fault strikes N530E, and dips 700N and the northern block has been pushed up. The radiocarbon ages agrees that the latest event took place after the“ Jorilot system”.
The pattern of dip-slip distribution along these strike-slip faults, i. e. the northern side up in the east and southern side up in the west, also suggests that they continue to each other to form a long active fault system.
