A slow thrust slip event following the two 1996 Hyuganada Earthquakes beneath the Bungo Channel, southwest Japan

Abstract

We report a “slow thrust slip event” that occurred beneath the Bungo Channel region, southwestern Japan. On Oct. and Dec., 1996, two Hyuganada earthquakes (both Mw = 6.7), followed by afterslips, occurred. In addition, a crustal movement characterized by an extremely slow rise was observed around the Bungo Channel, about 200 km north from the epicenters, and continued for about 300 days long. Assuming a slow slip on the plate boundary, we estimate its duration and surface displacements from GPS time series data by curve‐fitting, and then, determine the fault slip distribution. We found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the Hyuganada earthquakes. Occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling.