Fig. 2

a Vertical cross sections of the spatial distribution of the residual (Eq. 1) for EV2003 obtained by the spatial grid search performed with the best (0 s) origin time correction. The cross section through the best (FAMT) source position (middle), the cross section shifted from the middle one in the positive X direction by 9.6 km (top), and the cross section shifted from the middle one in the negative X direction by 9.6 km (bottom) are shown. Red corresponds to the small (good) residuals, and the best point is indicated by the white cross on the middle figure. Gray curves denote the interfaces of the 3D structure model. The plate interface (Plate Int.), layer 2 (OC-L2), and layer 3 (OC-L3) of the oceanic crust are indicated. b Same as a but for EV2007. c Various results of source position estimations for EV2003. The JMA hypocenter (JMA) and the positions of the F-net MT (best depth of a point moment tensor), the GCMT and the JMA-CMT (best locations of the centroids), and the FAMT (this study) are projected on the best cross section displayed in a. The “LPMT” (long-period MT) determined in this study is also projected (see text). d Same as c but for EV2007