The applicability of frictional reactivation theory to active faults in Japan based on slip tendency analysis

To investigate the applicability of frictional reactivation theory to active faults, we evaluated the slip tendency of active faults in Japan. Slip tendency is defined as the ratio of shear stress to the frictional resistance acting on a fault plane. To estimate the stress field near active faults, we determined focal mechanisms for numerous shallow earthquakes in the intraplate region of Japan, using data from dense seismic observation networks. The stress fields were estimated by applying the stress inversion method to the focal mechanisms. We found that most active faults are well oriented with respect to the stress field, having slip tendencies of ≥0.6, which indicates that fault reactivation theory is applicable to active faults, and that the present day tectonic stress field has contributed substantially to the development of active faults. Conversely, several steeply dipping active faults in northeast Japan, as well as the source faults of the 1995 Hyogoken–Nanbu earthquake, are mis-oriented, with slip tendencies of