Fig. 9

Depth-domain RFs. The locations of each section are defined as in Fig. 4. Red represents positive RF amplitudes, indicating a velocity increase downwards, while blue represents negative RF amplitudes, indicating a velocity decrease downward. The brown line indicates the depths of the upper boundaries of the PAC (Nakajima et al. 2009). The RF sections in a–c were made from OBSs that were in the area where the PHS is not present (Uchida et al. 2009), and the sections in panels f–h show the major emphatic phases. The RF sections in d and e were made from OBSs only north or south of 35°N, respectively, in the area where the PHS is subducted. The section in panel i shows the major emphatic phases in d. The RF section in j was made from the same OBSs as that in d, but its RF amplitudes are shown as absolute values. Interpretations of the interfaces are as follows: (1) Conrad in the NA, (2) Moho in the NA, (3) the plate boundary between the NA and the PAC, (4) the oceanic Moho in the PAC, (5) the bottom of the low-velocity anomaly in the NA, and (6) the plate boundary between the NA and the PHS