1990 Fiscal Year Final Research Report Summary
Gravity anomaly of the middle part of the Fossa Magna -- Matsumoto Bonchi Toen Fault
| Project/Area Number |
01540328
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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 |
固体地球物理学
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| Research Institution | University of Tokyo |
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Principal Investigator |
NAGASAWA Ko Earthquake Research Institute, University of Tokyo, Lecturer, 地震研究所, 講師 (40012918)
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| Co-Investigator(Kenkyū-buntansha) |
OKUBO Shuhei Earthquake Research Institute, University of Tokyo, Research Associate, 助手 (30152078)
MURATA Ichiro Earthquake Research Institute, University of Tokyo, Professor, 教授 (20012916)
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| Project Period (FY) |
1989 – 1990
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| Keywords | Gravity Anomaly / Fossa Magna / Active Fault / GPS / Dislocation Theory |
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| Research Abstract |
We measured gravity at 320 points around the Matsumoto-Bonchi Toen Fault (MBTF) which is located in the middle part of the Itoigawa-Shizuoka geotectonic line (ISGL), Honshu, Japan. Combining data published by the other institutes, we established homogeneous and dense distribution of gravity points. The total number of gravity points in this area exceeds 600. We would like to emphasize that our result is the first-class geophysical data essential to discuss the underground structure of the ISGL.
The steep horizontal gravity gradient there clearly indicates the existence of a dipping slab along the MBTF. The density perturbation due to repeated faulting there successfully explains the observed gravity low. We conclude that the gravity data reflect the thrusting fault motion along the MBTF.
We succeeded in using GPS (Global Positioning System) to determine 3-dimensional coordinates of gravity points. For the first time in Japan, we verified that the translocation GPS technique enables us to determine position of gravity points in less than 10 minutes with accuracy better than 1 meter. Our work leads a way to realize more homogeneous and denser distribution of gravity points in mountainous areas where conventional surveying technique was of little help to determine their positions.
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