1987 Fiscal Year Final Research Report Summary
A study on the formative processes of tectonic landforms
| Project/Area Number |
61460247
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
自然地理学
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| Research Institution | Department of Geography, Faculty of Science, University of Tokyo |
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Principal Investigator |
NONEKURA Nobuyuki Associate Professor, Dept. Geography, Univ. Tokyo, 理学部, 助教授 (30011563)
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| Co-Investigator(Kenkyū-buntansha) |
IKEDA Yasutaka Research Associate, Dept. Geography, Univ. Tokyo, 理学部, 助手 (70134442)
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| Project Period (FY) |
1986 – 1987
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| Keywords | Active fault / Intraplate thrust / Horizontal shortening / Ina Valley / Shonai basin / 庄内平野 / 駿河トラフ |
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| Research Abstract |
Overall objective of this project is to reveal the formative processes of surface deformation due to thrust faulting. The following results were obtained:
1. Geomorphological analyses of offset landforms and gravity prospecting of subsurface structure have revealed that low-angle thrust faulting and resultant horizontal shortening at an extremely high rate have occurred on the Ina Valley Fault Zone, Central Japan. This result has an important implication for the evaluation of long-term activity of intraplate thrusts.
2. Observation of an exploratory trench at the eastern margin of the Shonai basin, Northeast Japan, has disclosed low-angle thrusts that have cut late Holocene sediments. This, coupled with the above result, indicates that low-angle faulting prevails for intraplate thrusts at shalow depths, although the Shonai thrust has a striking contrast with the Ina Valley fault zone in respect of its association with large-scale folding.
3. Shallow drilling was carried out at Yaizu about 20 km west of the Suruga trough axis, at which the philippine Sea plate is subducted northwestward beneath the Honshu. It was revealed that subsidence has occurred through the Holocene, despite that the drilling site was located near, and on the upthrown side of, the megathrusts associated with subduction. This result implies that deformation due to subduction is highly complex, and would place a constraint on dislocation fault models for the past and future destractive earthquakes along the Suruga trough.
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