Fig. 1

a Tectonic setting in and around Japan. Solid lines indicate plate boundaries. Red ellipses roughly show the areas of the Nankai and Tokai earthquakes. Red dots indicate the epicenters of low-frequency earthquakes. Blue circles schematically show the areas of the long-term slow slip events discovered along the Suruga and Nankai trough subduction zones. 1 Tokai, 2 Kii channel, 3 western to central Shikoku, 4 Bungo, 5 northern Miyazaki, 6 southern Miyazaki, 7 Boso. b Enlarged map of the Shikoku and Kyushu regions indicated by the rectangle in (a). Black broken lines indicate the iso-depth contours of the upper surface of the Philippine Sea plate with a contour interval of 20 km. The red solid polygon shows the fault patch used to estimate aseismic slip for Shikoku and Kyushu. The T-direction and S-direction are defined by black arrows (see text). Blue circles indicate the locations of the GNSS sites used in the inversion of the detrended dataset (see text). Red circles schematically show the areas of the long-term slow slip shown in (a). The position time series of sites 1126, 0437, 0090, 0466, 0713, and 0715, whose locations are denoted by open circles, are shown in Fig. 2. The epicenters of the last Hyuga-nada earthquakes on October 19 and December 3, 1996, are denoted by their focal mechanisms. Data are from Yagi et al. (1999)