| Project/Area Number |
02402013
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体地球物理学
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| Research Institution | Faculty of Science, Chiba University |
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Principal Investigator |
ISEZAKI N. Faculty of Science, Chiba Univ. Professor, 理学部, 教授 (60107943)
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| Co-Investigator(Kenkyū-buntansha) |
ASANUMA T. Faculty of Science, Chiba Univ. Res. Assis., 理学部, 助手 (50092028)
HIRATA N. Faculty of Science, Chiba Univ. Ass. Prof., 理学部, 助教授 (90156670)
IIYAMA T. Faculty of Science, Chiba Univ. Professor, 理学部, 教授 (90107699)
藤井 直之 神戸大学, 理学部, 教授 (60011631)
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| Project Period (FY) |
1990 – 1991
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| Project Status |
Completed (Fiscal Year 1991)
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| Budget Amount *help |
¥31,700,000 (Direct Cost: ¥31,700,000)
Fiscal Year 1991: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1990: ¥31,000,000 (Direct Cost: ¥31,000,000)
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| Keywords | Okinawa Trough / CA Structure / Crusral Structure / Heat Flow / Magnetic Anomaly / 3 Component Anomaly / Seafloor Spreading / Rifting / 電気伝導構造 / 地殻熱流売 / 地下電気伝導度構造 / 地震波構造 / 地磁気三成分異常 / 海底電位磁力計 / 海底地震計 / マルチチャンネル探査 |
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| Research Abstract |
1. Between 10Ma and 4Ma, the south Ryukyu Island Arc rotated about 19' clockwisely. If at this moment the Okinawa Trough was opened, the opening mode could not be "sea floor spreading". but like "continental rifting", because there is no observed magnetic anomaly lineation in the Okinawa Trough. The central part of Ryukyu Arc is thought not to rotate but to move without rotation, however, we could not get any paleomagnetic conclusion for the northern part of Ryukyu Arc.
2. The other evidence for the "not seafloor spreading" mode is the result of of ocean bottom seismometer and air-gun research, that is, the seismological structure of the earth' crust in the south Okinawa Trough is not the oceanic type but the continental.
3. Before 2Ma, the direction of the regional stress in the Ryukyu Arc changed from east-west to north-south. This change must correspond to the change of movement of the Philippine Sea Plate subducting beneath the Ryukyu Arc.
4. The existence (size and potision) of the high electrical conductive layer or block beneath the Okinawa Trough will be soon made clear from the ocean bottom electric and magnetic research, which has been suggested from the study of mineralogical dehydration process occurring under the back arc associated with plate subduction.
5. lnferring from the magnetic anomaly, seismic data, radiometric age and heat flow, the presently tectonically active region is the Yaeyama Graben where continental rifting has been occurring since 2Ma.
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