1998 Fiscal Year Final Research Report Summary
Electromagnetic Research on Structure of Graben and its implication to Volcanism
| Project/Area Number |
09640504
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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 | The University of Tokyo |
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Principal Investigator |
KAGIYAMA Tsuneomi Earthqnake Research Institute, The Univ.of Tokyo, Associate Proffesor, 地震研究所, 助教授 (50126025)
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| Co-Investigator(Kenkyū-buntansha) |
UTUDA Hisashi Eartq.Res.Inst., The Univ.of Tokyo Associate Proffesor, 地震研究所, 助教授 (70134632)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Graben / Resistivity Structure / Kyushu / Volcanism |
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| Research Abstract |
We carried out magnetotelluric survey at 26 sites along East-West lines across the southern Kyushu in 1997, and 13 sites in the northern part of Miyazaki Prefecture in 1998. Simultaneous magnetic and electric field variations were measured in the ULF, ELF and VLF band. The experiment found some anomalous regions suggesting magmatic activity. Volcanic area is characterized by a simple four-layer structure ; relatively resistive overburden, very conducting second layer at the depth of a few hundred meters, resistive basement, and deep conductor. On the other hand, a rather resistive second layer and lack of deep conductor characterize non-volcanic region. The low-resistivity second layer (Shallow Low Resistivity Region) is distributed around Kirishima volcanic region and other volcanoes, which have gold mines or geothermal areas. This evidence indicates that SLRR is a water-saturated porous layer or altered layer. The deep conductor (Deep Low Resistivity Region) appears about a few tens km below the surface in average, but shallower beneath the presently active volcanoes. These SLRR and DLRR mainly distribute from Kushikino to Kirishima volcanic region via Miyanojo and Okuchi Basins, which have volcanic activity within several million years, but partly elongates to the non-volcanic such as Hitoyoshi Basin in the NE direction. This direction may correspond to the direction of the trend of the depression region or old graven.
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