Submarine topography and geology in the source region of the 1983 Nihonkai- Chubu Earthquake.
This paper describes the results of sea bottom survey in the source region of the Nihonkai-Chubu Earthquake. The earthquake, of magnitude 7. 7, occurred in the eastern Japan Sea on 26 May 1983. Topographical, geological and geophysical surveys by the survey vessel "Shoyo” in 1983 and the ”Takuyo”in 1984, were carried out for the purpose of revealing the regional features. Survey items are submarine topographical survey by echo sounder and multi-beam sonar ( Seabeam), geological survey by sub-bottom profiler ( 3. 5 KHz) and seismic profiler (single and 12 channels), geomagnetic and gravity survey, and bottom sampling. The survey area is the eastern border of the Japan Sea and it covers the continental margin of Northeast Japan including the Okusiri and Sado Ridges elongating from north to south. There are many faults along the slope foot between these ridges and the Japan Basin, and the hook-shaped distribution of these faults corresponds with the area of aftershocks. A well undulated acoustic basement was recognized beneath the Japan Basin, and a small, linear hill chain was revealed on the flat floor of the Japan Basin. It is estimated that the basement high and the hills were formed by intrusive igneous rocks. In addition, fragments of manganese concretion were dredged from a small mount of 80 meters height, being one of the hill chain in the Japan Basin. The chemical and mineral composition of the samples are similar to those of hydrothermal manganese oxides reported in the lzu-Ogasawara area. Thus, there is a possibility that the samples dredged from a small hill in the Japan Basin are also hydrothermal manganese oxides.
| Main Authors: | , , , |
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| Format: | Journal Contribution biblioteca |
| Language: | Japanese |
| Published: |
1986
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| Online Access: | http://hdl.handle.net/1834/16159 |
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