Fig. 4

S anisotropy within marine sediments in the northwestern Pacific. a Yellow bars represent the degree of anisotropy and the fast polarization direction at each ocean-bottom seismometer (OBS) site. Mechanism solutions, which were determined by F-net centroid moment tensor (CMT) with M > 4 and depths shallower than 60 km (Fukuyama et al. 1998; Okada et al. 2004), are displayed by red beach balls. Red triangles and orange bars indicate locations of three OBS sites and the results of S anisotropy at the sites in Tonegawa et al. (2013). b Definition of the regions for areas A, B, and C from the abyssal plain to the trench. c A rose diagram created using the anisotropic parameters inside box 1 in Fig. 4a. The degree of anisotropy was averaged at each azimuth range of 10°. Red arrows represent the fast polarization direction parallel to the trench axis. Orange arrows indicate a N 30° E-trending fast axis. d Same as Fig. 4c but for box 2. Red arrows represent the fast polarization direction parallel to the trench axis. Blue, pale blue, and orange arrows indicate other directions than that parallel to the trench axis (see text in details). e A magnified inset map image in box 2 in Fig. 4a. A dashed line is the boundary between the northern and southern parts in box 2. Colored arrows indicate OBS sites in which a relatively large degree of S anisotropy was observed