相模トラフ・駿河トラフ周辺の海底地形

抄録

Tectonic elements of submarine landforms and geologic structures are studied with thereference to the neotectonics concerning to the convergence of the Philippine Sea (PHS) plate with Honshu on the Eurasian (EUR). The northern tip of Izu Arc is morphologicallycharacterized by upwarping with an axis in the direction of 323°, the Niijima-shinkuroseUplift zone, which is oblique to the axis of Izu-Ogasawara volcanic arc. Intersectionand capture of consequent canyons on the northeastern slope of Izu Arc are well observed. This indicates the downbending of PHS associated with subduction along SagamiTrough. The sense of convergence between PHS and the overriding plates might havechanged from northward to northwestward (323°) at about 0.5Ma B. P. This can be evidencedby the following features on the accretionary wedge along Sagami Trough:(1) the graben-like structure in a trend of 325° was filled with the undeformed middle Pleistocenestrata on the accretionary wedge;(2) segmentation of the mechanical plate boundarydue to a forearc tectonics related to APC plate and to the strike-slip motion along the outerridge. However, no significant feature necessary to infer such a change in direction ofrelative motion between EUR and PHS plates is found along the Suruga Trough.