1988 Fiscal Year Final Research Report Summary
Study of the Electric and Magnetic Structure of the Japan Islands
| Project/Area Number |
62302017
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| Research Category |
Grant-in-Aid for Co-operative Research (A)
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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 |
YUKUTAKE Takesi Earthquake Research Institute, University of Tokyo, Prof., 地震研究所, 教授 (90012898)
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| Co-Investigator(Kenkyū-buntansha) |
HONKURA Yoshimori Department of Applied Physics, Tokyo Institute of Technology, Ass. Prof., 理学部, 助教授 (00114637)
HAMANO Yozo Earthquake Research Institute, University of Tokyo, Ass. Prof., 地震研究所, 助教授 (90011709)
YASKAWA Katsumi Dept. Earth Sciences, Faculty of Science, Kobe University, Prof., 理学部, 教授 (20020084)
SUMITOMO Norihiko Dept. Earth Sciences, College Liberal Arts, Kyoto University, Prof., 教養部, 教授 (30026687)
MIYAKOSHI Jun'ichiro Institute of Earth Sciences, Tottori University, Prof., 教養部, 教授 (60032116)
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| Project Period (FY) |
1987 – 1988
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| Keywords | Electrical Resistivity / Low Resistivity Layer / Electrical Conductivity / Lower Crust / Conductivity Anomaly / Induction Vector / 誘導ベクトル / 地磁気変換関数 |
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| Research Abstract |
During the past decade, electrical resistivity structures of the Northeast Japan and the Central Japan have been investigated by cooperative projects of universities and government organizations. One of the results obtained in the projects is existence of low resistivity region in the lower crust. In order to obtain the overall structure of the electrical resistivity of the Japan Islands, the experiments have been extended to the western part of Japan in this study.
In 1987, observations of geomagnetic variations and telluric currents were conducted for longer periods, from 5 minutes to several hours, at 14 sites on land from Tru^^ goku to Sikoku area, and at 3 sites on the floor of the Sikoku Basin. In 1988, additional observations were made. For shorter period variations, with a frequency range of VLF to ULF, magnetotelluric measurements were carried out.
As expected, the observations of shorter periods suggest that low resistivity regions extend in the lower crust in Sikoku-Ty^^ goku district too. Corresponding to complex surface geology, the resistivity structure near the surface has been found to be complicated. The low resistivity is supposedly caused by groundwater contained in rocks. Tentative analyses suggest existemce of correlation between the resistivity structure and seismicity. seismic activity in the southern half of Sikoku is seen in the high resistivity regions.
Magnetic variations over Japan islands are usually under strong influence of the ocean. The induction vectors derived from magnetic transfer functions mormally point oceanwards. However, in the present study area the vectors for long periods as 120 min. point rather westwards, i.e. in parallel with the coast and the strike of the tectonic structure. This implies that a highly anomalous region exists in the western part of the Japan Islands.
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