P-wave velocity models for each line shown in Fig. 1. The models are only displayed for the SB region. Red vertical broken line indicates the inferred location of the extinct spreading center. White circles and black arrows on the seafloor show the positions of OBSs. Iso-velocity contours with an interval of 0.25 km/s are shown. The position of the Kinan Escarpment based on the seafloor topography is shown as KE.