2006 Fiscal Year Final Research Report Summary
A study of the survey method for 3D cavities using the high-frequency CSMT system in the transient frequency region
| Project/Area Number |
16560711
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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 |
Earth system and resources enginnering
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| Research Institution | Saga University |
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Principal Investigator |
HANDA Shun Saga University, Agriculture, Professor, 農学部, 教授 (70156529)
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| Project Period (FY) |
2004 – 2006
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| Keywords | High frequency CSMT / underground cavities / 3D finite difference method / near-field / 有限差分法 |
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| Research Abstract |
Underground cavities are one of the difficult targets to detect their positions by the electromagnetic surveys. Many unstable tunnels, of which locations are not clear, are buried in Shirasu layers in Kagosima Prefecture. In our survey using the HFCSMT system, it is found that apparent resistivities for tunnels, which are observed in the source-receiver distance of the transient frequency regions, are intensely amplified, relatively to those observed by the MT survey.
In order to confirm this, electromagnetic responses of the tunnel-shaped underground cavities buried at four depths are calculated using the three-dimensional finite difference method (3DFDM). The results of calculation are:
1 the amplification rates of apparent resistivity caused by the tunnels in the transient region are larger than those in the far-field region,
2 these values are hardly controlled by frequency and the resistivity of the Earth and are roughly proportion to an exponential of the tunnel's depth,
3 this amplifications is not caused by the vertical loop antenna but by the horizontal loop antenna by which the increase of resistivity is occurred in the transient region.
These results indicate that the amplification of apparent resistivity is advantageous to detect underground cavities in the survey.
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