Submarine topography of the eastern Sagami Trough to the triple junction.

Abstract

This report summarizes the results of a sea-bottom survey in the eastern Sagami Trough to the triple junction of plates by the survey vessel "TAKUYO" on May and June, 1984. The survey, using a multi narrow beam echo sounder (SEA BEAM), revealed that a meandering deep canyon, the Boso Canyon (BOC), exists along the north border of the Sagami Trough. Up to this time, the canyon had been thought to be composed of echelon depressions. The BOC is a part of a long canyon with a length of more than 300 kilometers (from Sagami Bay to the Izu-Ogasawara Trench). As the longitudinal profile of the bottom of the BOC shows no undulation, it suggests that the BOC is a transporting route of sediments gathered from a wide back area. Another submarine canyon, the Awa Canyon (AWC), runs along the southern border of the Sagami Trough, parallel to the BOC. Its topography is in great contrast to the BOC. For instance, the AWC is a shallow valley with a gentle slope and is shallower than 4,500 meters (a singular canyon making small depressions of greater than 4,500 meters). It is worth noting that the bottom of the Sagami Trough is the AWC in the shallower part, and it transfers to the BOC in the deeper parts. Considering the topographical features and the seismic profiles, the material boundary of plates in the eastern Sagami Trough seems to be along the bottom of trough (as mentioned). At the triple junction, three topographic belts parallel to the direction of the Izu-Ogasawara Trench, (wide trench floors, inner highs and small basins) are recognized.