Reactivation of map-scale faults in response to changes in crustal stress: Examples from Boso Peninsula, Japan

We have investigated the reactivation of Quaternary faults near the trench-trench-trench type triple junction off Boso Peninsula, central Japan. On the Pacific side of the Boso Peninsula (PSBP region), map-scale NNE-SSW-trending faults developed during ∼1.2-0.7 Ma, although these faults are inactive at present. We observed multiple and overlapped slickenlines on parts of map-scale fault planes in the PSBP region. These slickenlines can be classified into two different directions, which we consider to be the reactivation of the map-scale faults in response to a change in crustal stress after ∼1 Ma. Based on angular misfits between the predicted and observed slip directions, we successfully compared the older and younger slip directions to dip-slip normal faulting and oblique sinistral normal faulting, respectively. The reactivation of the map-scale faults in response to a relatively short (105 yrs) stress change has been verified based on the direct evidences on the map-scale fault planes.