Erosional Subduction Zone in the Northern Japan Trench: Review of Submersible Dive Reports - Accretionary Prisms and Convergent Margin Tectonics in the Northwest Pacific Basin - page 46

Fig. 6 Slopes and cliffs with cobbles on the landward slope from the video of dive 6K#274
(Adapted from Ogawa et al. 1996 ) ( top ). Sketch of the Sanriku escarpment. Ages (Ma) of sampled
diatom fossils correspond to those in Fig. 5 (Modified from Ogawa et al. 1996 ) ( bottom )
to Pliocene sedimentary rocks (Satoshi Hirano, personal communication 2005).
It can thus be speculated that methane venting along thrust faults is the original
cause of both the brecciation and the calcite cementation. During the Miocene, the
Japan trench landward slope may have been part of an accretionary prism zone
extending from the south Boso area northward to the area off Miyako. At present,
this accretionary prism of Miocene age is being removed by subduction (tectonic)
erosion.