2002 Fiscal Year Final Research Report Summary
Development of the ACTIVE system : an Array of Controlled Transientelectromagnetics to Image Volcanic Environment
| Project/Area Number |
12554014
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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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 |
UTADA Hisasi The University of Tokyo, Earthquake Research Institute, Professor, 地震研究所, 教授 (70134632)
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| Co-Investigator(Kenkyū-buntansha) |
SHIMIZU Hisayoshi The University of Tokyo, Earthquake Research Institute, Research Associate, 地震研究所, 助手 (70302619)
UYESHIMA Makoto The University of Tokyo, Earthquake Research Institute, Associate Professor, 地震研究所, 助教授 (70242154)
KAGIYAMA Tsuneomi The University of Tokyo, Earthquake Research Institute, Associate Professor, 地震研究所, 助教授 (50126025)
YAMAMOTO Tetsuya Japan Meteorological Agency, Meteorological Institute, Researcher, 気象研究所, 主任研究官
KANDA Wataru Kyoto University, Disaster Prevention Research Institute, Research associate, 防災研究所, 助手 (00301755)
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| Project Period (FY) |
2000 – 2002
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| Keywords | Volcanic activity / Electrical resistivity / Time change / Electromagnetic method / Controlled source / Array observation |
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| Research Abstract |
This three-year project was carried out to develop an accurate system (ACTIVE) to monitor active volcanoes by a controlled electromagnetic method.
In 2000, numerical simulation studies were made to determine the optimal array configuration to monitor the structural change due to volcanic activity of Izu-Oshima. Observation system was designed, such as transmitter circuits, sensitivity of the receiver, and record length, and then prototype instruments (one transmitter and two receivers) were manufactured.
In 2001, field test experiment was carried out twice around the Mihara-yama, the central cone of Izu-Oshima volcano. The first experiment was intended to debug the system, while the second experiment aimed to explore 3-D conductivity distribution around the central cone. In addition to these experimental efforts, we developed a scheme to image time changes in the electrical conductivity structure.
In 2002, automatic repeated measurement was started in August, 2002, using the transmitter dipole installed last year and five receivers newly installed around the central pit crater. Data acquisition have been repeated once every two days (from 2-3 AM). Time series data are recorded in a PC card that is attached in the receiver. PC cards from all instruments were retrieved once every two months and data processing were adopted to monitor the conductivity charge. Imaging program was also applied to the experimental data but so far no significant change was obtained.
Our repeated measurement indicated no significant change, because the activity of Izu-Oshima volcano still remains very low. On the other hand, we re-examined changes i n the apparent resistivity observed before the 1986 summit eruption and found that they can be explained by pre-eruptive migration of magma in the conduit. Further numerical experiments clearly showed that the ACTIVE system would be able to image the magma migration before the 1986 eruption with a high accuracy.
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