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1990 Fiscal Year Final Research Report Summary

Gravity anomaly of the middle part of the Fossa Magna -- Matsumoto Bonchi Toen Fault

Research Project

Project/Area Number 01540328
Research Category

Grant-in-Aid for General Scientific Research (C)

Allocation TypeSingle-year Grants
Research Field 固体地球物理学
Research InstitutionUniversity of Tokyo

Principal Investigator

NAGASAWA Ko  Earthquake Research Institute, University of Tokyo, Lecturer, 地震研究所, 講師 (40012918)

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)
Project Period (FY) 1989 – 1990
KeywordsGravity Anomaly / Fossa Magna / Active Fault / GPS / Dislocation Theory
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.

  • Research Products

    (4 results)

All Other

All Publications (4 results)

  • [Publications] 大久保 修平: "糸魚川ー静岡構造線の重力調査(III)ー松本盆地東縁断層北側延長部の追跡ー" 東京大学地震研究所彙報. 65. 649-663 (1990)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 大久保 修平: "糸魚川ー静岡構造線の重力調査(IV)ーGPS支援下で松本盆地東縁断層延長部の重力測定" 東京大学地震研究所彙報.

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] S. Okubo, K. Nagasawa, I. Murata and Hwa-Chu Sheu: "Gravity Observations along the Itoigawa-Shizuoka Geotectonic Line (III) -- Bouguer Anomaly around the Northern Part of Matsumoto Bonchi Toen Fault --" Bull. Earthq. Res. Inst., Univ. of Tokyo. 65. 649-663 (1990)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] S. Okubo, K. Nagasawa, I. Murata and Jun Ando: "Gravity Observations along the Itoigawa-Shizuoka Geotectonic Line (IV) -- Determination of Bouguer Anomaly around the Matsumoto Bonchi Toen Fault with the aid of GPS translocation technique --" Bull. Earthq. Res. Inst., Univ. of Tokyo.

    • Description
      「研究成果報告書概要(欧文)」より

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Published: 1993-08-12  

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