Interplate coupling along the Nankai Trough off southwest Japan derived from GPS measurements

We investigate interplate coupling between the Philippine Sea and the Euras ian plates at the Nankai Trough off southwest Japan during the interseismic period. Plate coupling is modeled by imaginary backward normal slip superp osed on the steady-state subduction. We divide the plate interface into sev eral segments, and estimate coupling on each segment from GPS horizontal ve locity data. Estimated coupling is in general agreement with the rate of st eady-state subduction predicted from a plate motion model. This implies tha t current coupling at the Nankai Trough is so strong that much of the relat ive plate motion is taken up by shortening of the leading edge of the overr iding plate. It seems that stronger interseismic coupling is realized on th e segment where larger coseismic dislocation occurred, and vice versa. Time fluctuation of plate coupling from 1995 to 1996 is found on a small segmen t.