2000 Fiscal Year Final Research Report Summary
Slip-partitioning on the Itoigawa-Shizuoka Tectonic Line, central Japan
| Project/Area Number |
11480019
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
自然地理学
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| Research Institution | University of Tokyo |
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Principal Investigator |
IKEDA Yasutaka Univ.Tokyo, Grad.School of Sci., Assoc.Prof., 大学院・理学系研究科, 助教授 (70134442)
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| Co-Investigator(Kenkyū-buntansha) |
IMAIZUMI Toshifumi Yamanashi Univ., Dept.Edu.Sci., Prof., 教育人間科学部, 教授 (50117694)
TOGO Masami Hosei Univ., Dept.Social Sci., Prof., 社会学部, 教授 (70061231)
SATO Hiroshi Univ.Tokyo, Earthq.Res.Inst., Assoc.Prof., 地震研究所, 助教授 (00183385)
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| Project Period (FY) |
1999 – 2000
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| Keywords | active fault / Itoigawa-Shizuoka Tectonic Line / seismic reflection profiling / slip partitioning |
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| Research Abstract |
The overall objective of this study is to clarify the partitioning of slip on low-angle, oblique-slip faults. The test field is the central and northern part of the Itoigawa-Shizuoka Tectonic Line(ISTL), central Japan. The following results are obtained :
(1)High resolution S-wave seismic reflection profiling across the Kamishiro fault(northern part of ISTL)revealed that the fault sprays up-dip into several fault planes, the lowest of which is a blind thrust at a depth of 50-60 meters.
Radiocarbon dating of deformed sediments indicates that the rate of net slip on the Kamishiro fault is about 6 mm/yr, which value is significantly larger than previous estimates without considering fault spraying
(2)P-wave and S-wave seismic reflection profiling was carried out across the central part of ISTL at Fujimi. The P-wave profile revealed that a high-angle, East-dipping fault is developed on the hanging-wall side of a low-angle, west-dipping fault. Late Quaternary surface deformation indicates that the former is dominantly strike-slip, whereas the latter is dominantly thrust. Bouguer gravity anomalies suggest that the low-angle thrust is the material boundary between Quaternary-Pliocene sediments on the east and Miocene and older rocks of Akaishi range on the west. These lines of evidence indicates that oblique slip(thrust+left slip)on the deeper part of ISTL is partitioned at shallow depths into two fault planes ; the strike-slip component is accommodated on the high angle fault that develops in the low-angle thrust sheet.
(3)Similar phenomenon is observed in the northern part of ISTL at Matumoto and Shiojiri, although the master fault(material boundary)here is not west-dipping but east-dipping.
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