Abstract
Did intra-arc deformations in SW Japan occur associated with the opening of the Japan Sea back-arc basin? To answer this question, we studied the Lower Miocene Kuma Group, central SW Japan. The Group is shown to be alluvial fan deposits. The sedimentary basin of the Kuma Group may have been formed as half grabens. The multiple inverse method was applied to mesoscale faults of the Kuma Group and detected six stresses from in situ and from tilt corrected fault-slip data. One stress state determined from the tilt corrected data is consistent with the paleostress that formed the E-W trending half grabens in the Kuma Group. One other stress is consistent with that inferred from 15 m.y. old dike swarm in this area. Accordingly, this area was subject to extensional tectonics in the Early to early Middle Miocene.
