A block-fault model for deformation of the Japanese Islands derived from continuous GPS observation

We interpret the continuous GPS data for the Japanese islands from 1996 to 1999 using the model of Hashimoto and Jackson (1993). In this model crustal deformation is represented by a combination of rigid block motions and def ormation due to slip deficits along the fault-bounding blocks. Hashimoto an d Jackson used 19 blocks, 104 faults, and geodetic data spanning 100 years. In the present work we assume the same fault and block geometry, and we us e only the continuous GPS data. Compared to the previous study, the motions of the major blocks are a bit larger: 107 +/- 8 mm/yr for the Pacific plat e, 47 +/- 2 mm/yr for the Philippine Sea plate, and 24 +/- 2 mm/yr for the Izu block, all relative to the Amurian plate. The estimated slip directions on active inland faults are now more consistent with geological estimates. Slip deficit rates exceed 10 mm/yr along the Itoigawa-Shizuoka Tectonic Li ne, Shinanogawa Seismic Zone, Atotsugawa fault, Hanaori fault, Arima-Takats uki Tectonic Line, Rokko faults, Median Tectonic Line, and southern boundar y of the Beppu-Shimabara graben. Some interplate faults along the Japan and Kurile trenches have slip deficit rates larger than 100 mm/yr, although po stseismic deformation from the 1994 Far Off Sanriku earthquake may contamin ate these estimates. An interplate fault off Kyushu has a negative slip def icit, possibly due to post-seismic movements from the 1996 events in Hyugan ada.