Fig. 1. Location of the study sites (KMV#5) and seismic profiles of the Kumano forearc basin.

(A) Bathymetric map showing the location of KMV#5 in the Kumano forearc basin and IODP Sites C0002 and C0009. (B) Transect seismic cross-section in the middle part of the Kumano Basin based on the data from Morita et al. (17). (C) P-wave velocity predicted by three-dimensional (3D) tomography inversion during 3D prestack depth migration based on the data from Tsuji et al. (18). The overpressure zone (fluid or gas accumulation zone) is identified as a low-amplitude and low-velocity zone at 400 to 700 mbsf in the forearc basin sequence. The low-velocity zone, which is located above the ridge because of the megasplay fault displacement, suggests that the overpressured fluids are moving upward along the interpreted ancient megasplay faults. The mud volcanoes are located along the northern extension of the megasplay faults.