Submarine Topography and Geological Structure West of Kyusyu, Japan

Abstract

The surveys of submarine topography, geology, geomagnetism and gravity were conducted off the coast of Kyusyu by the Hydrographic Department, Maritime Safety Agency, Japan in 1973 and 1974.
On the basis of these surveys, the authors described the general features of the submarine topography and the geological structure, and discussed the geological history of Goto Submarine Valley and Danjo Basin, being remarkable topographies in the studied area.
General trends of geological structures are as follows.
1. The faults and folds of basement in Tokai Continetal Shelf have NNE-SSW trend.
2. Trains of banks and islands, such as Goto Islands, Danjo Islands and Kosiki Islands, and also strikes of fold axes of the sedimentary layer in Okinawa Trough shows NE-SW trend.
3. The faults which are parellel to elongation axis of Danjo Basin in Okinawa Trough have ENE-WSW trend.
4. Faults which transverse the trends mentioned above show NW-SE trend and this trend is remarkably in Goto Submarine Valley area.
Trends of NW-SE, NNW-SSE, NE-SW and ENE-WSW had been formed in the Late Miocene. In this time, the original shapes of Nisi-Goto Shelf Channels and Fukue Basin were formed at the outer ridge and its surroundings of Tokai Continental Shelf, developing in parallel with the tectonic lines of NW-SE trend. And also, Goto Submarine Valley initially incised the sea bottom between Danjo and Goto Islands in the Late Miocene, and developed during the Pleistocene age.
The framework of Danjo Basin was cotorolled with the trends of NW-SE, NE-SW and ENE-WSW, and the basin was formed by the synclinal subsidence in the Plio-Pleistocene.