| Project/Area Number |
62540583
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
地質学一般
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| Research Institution | Shimane University |
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Principal Investigator |
KOMURO Hiroaki Shimane University, 理学部, 助手 (80135897)
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| Co-Investigator(Kenkyū-buntansha) |
KOBAYASHI Yasuyuki Shimane University, 理学部, 助教授 (00033936)
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| Project Period (FY) |
1987 – 1988
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| Project Status |
Completed (Fiscal Year 1988)
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| Budget Amount *help |
¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1988: ¥200,000 (Direct Cost: ¥200,000)
Fiscal Year 1987: ¥800,000 (Direct Cost: ¥800,000)
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| Keywords | Cauldron / Caldera / Sakugi volcanic rocks / Three-dimensional finite element method / Doming / Radial fracture / 同心円状断裂 / 環状断裂 / 有限要素法 |
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| Research Abstract |
The Sakugi cauldron shows a square outline delimited with nearly vertical faults. Some of them are normal faults with wide shear zones and others are reverse faults with narrow shear zones. The reverse faults dip outward. Quartz porphyry dikes and diorite plutons intrude into these shear zones in some cases. Cauldron fills consist of andesitic tuff, andesite lava and dacitic tuff. The dacitic tuff member intercalates fine laminated alternating beds of tuffaceous sandstone and siltstone of lake origin. Namely, a caldera lake existed during eruptions.
Stress distribution was analyzed by three-dimensional finite element method. It was assumed that the earth's crust is homogeneous-compressive plastic body, and that a magma chamber with a diameter of 4 km uplifts the crust from a depth of 10 km.
The results are as follows: 1. Minimum principal tensile stress 3 is vertical near the crest of the dome. Accordingly, this zone is characterized by normal faults. They consist mainly of radial fractures or radial minor rift zones and concentric normal faults. The radial fractures are initially formed, which are followed by the concentric normal faults. These fractures produce the polygonal cauldron. 2. Another group of concentric normal faults develop from the roof of the magma chamber upward, and link with the fractures near the crest.
The normal faults along the margin of the Sakugi cauldron seem to have been formed by fracturing of initial doming. The reverse faults may have been produced by collapse of the magma chamber.
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