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

We report a "slow thrust slip event" that occurred beneath the Bungo Channe l region, southwestern Japan. On Oct. and Dec., 1996, two Hyuganada earthqu akes (both M-w = 6.7), followed by afterslips, occurred. In addition, a cru stal movement characterized by an extremely slow rise was observed around t he 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 estima te its duration and surface displacements front GPS time series data by cur ve-fitting, and then, determine the fault slip distribution. We found that a slow slip without ally earthquakes continued for neatly one year and rele ased the seismic moment comparable to that of the Hyuganada earthquakes. Oc currence 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 inter plate coupling.