| Project/Area Number |
07640542
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体地球物理学
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| Research Institution | Tohoku University |
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Principal Investigator |
YAMAMOTO Kiyohiko Tohoku Univ., Science, Assoc.Professor, 理学部, 助教授 (90004390)
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| Co-Investigator(Kenkyū-buntansha) |
KATO Naoyuki Tohoku Univ., Science, Research Assoc., 理学部, 助手 (60224523)
MISHINA Masaaki Tohoku Univ., Science, Assoc.Professor, 理学部, 助教授 (70004421)
HIRASAWA Tomowo Tohoku Univ., Science, Professor, 理学部, 教授 (80011568)
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| Project Period (FY) |
1995 – 1996
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| Project Status |
Completed (Fiscal Year 1996)
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| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1996: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1995: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | in-situ stress / seismogenic stress / stress uniformity / deformation rate analysis / plate boundary / coupling coefficient / プレート間相互作用 / 地殼応力 / 地殼水平歪 / 内陸の応力場 / 変形率変化法 / 応力記憶 / 非弾性歪 / 弾性定数 |
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| Research Abstract |
In the Kitakami area in northeast Honshu, Japan, seismic activity is known tobe low. The comparison of the stress field in this area with the area of high seismic activity is expected to reveal the conditions on the stress field to generate earthquakes. The northeast Honshu is considered to be placed on the north American plate under which the Pacific ocean plate subducts toward the west. In the Kitakami area, the coseismic change in crustal strain with a large earthquake at or near the plate boundary is predominantly observed in the east-west component. Nevertheeless, geodetic measurements have shown that the extension in the north-south or the northeast-southwest direction dominates during a long term of about 75 years. These appear to be inconsistent each other. What this inconsistency states is still unknown. The relation of the stress field to the crustal strain is expected to yield a solution about this problem and to present a knowledge about the role of the plate boundary on th
… More
e stress field in the intraplate crust.
For the above expectation, in-situ stresses are measured at four sites in the Kitakami area by deformation rate analysis (DRA). The sites are located within about 40 km at most apart from the coast facing the Pacific ocean. This measurement reveals as follows : 1) The largest horizontal stress is nearly equal to or slightly smaller than the vertical stress in magnitudes at all sites. 2) The smallest horizontal stress axis lays along the north-south or the northeast-southwest direction at every site. 3) The ratio r of the maximum shear stress to the normal stress on the maximum shear plane ranges from 0.17 to 0.35. The results of (1) and (2) are consistent with the horizontal strain change of long term. This suggests that the stress field in the Kitakami area and thus that in the northeast Japan is not mechanically formed directly by the collision of the Pacific ocean plate to the north American plate. Comparing the result (3) with the stresses in the focal area of the 1984 Western Nagano Prefecture earthquake of M=6.8, for both the areas seismic activity seems to be active around the sites where r is larger than about 0.3. Further, the comparison shows that the maximum shear stress in the Kitakami area is not smaller on an average and the variation of the tress is smaller than the focal area. This may suggest that the non-uniformity of stress field plays an important role on generating earthquakes. Less
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