Seabottom survey of Tatibana and Simabara Bays urged by the eruption of Uuzen volcano northwestern part of Kyusyu.
Mt. Unzen, which is located northwestern part of Kyusyu, erupted in November 1990 after about 200-years silence. The volcanic activity gradually became active. On June 3, 1991, apyroclastic flow ran down the flank of the Unzen mountain, to burn out houses, farms and automobiles, and more than 40 lives were lost at that time. In order to reveal the detailed geophysical and geological characteristics at Tatibana and Simabara Bays located right off Unzen volcano, Japan Hydrographic Department conducted seabottom survey, including echo sounding, 1000 joule sparker reflection profiling, geomagnetic survey and sea surface gravity survey, with Survey Vessle Meiyo June 1991. Seaward elongation of the Futsu Fault, which is the southern margin of the Unzen-Simabara graben, was recognized in Simabara Bay which is located east of Unzen volcano. On the other hand, a negative free air gravity anomaly, which supports existence of a buried caldera, was observed in Tatibana Bay which is located west of Unzen volcano. Complex geomagnetic anomalies were also observed in the bay.The depth of the magnetic basement, which is estimated by spectrum analysis of magnetic anomaly in Tatibana Bay, becomes about 560 meters below sealevel.
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| Format: | Journal Contribution biblioteca |
| Language: | Japanese |
| Published: |
1992
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| Online Access: | http://hdl.handle.net/1834/16002 |
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