| 講演要旨(和文) | | 伊豆大島は活動的な火山であり,度々噴火災害を引き起こしていることから,火山活動を適切にモニタリングし,将来の噴火の時期および場所を正確に予測していくことが必要とされている.噴火予知の精度を高めていくためには,マグマ貫入に伴う熱水系の変動を把握し,そのメカニズムを解明することが重要と考えられる.我々はその目的のため,自然電位の繰り返し測定や連続観測を継続している。観測されたデータを解釈するためには,自然電位発生にかかわる地下の水理的,電気的特性を明らかにする必要がある.そこで,火山を北東-南西に横切る2本の測線に沿って,AMT法電磁探査を実施した.また,連続観測データには年周変化や日変化のほか,観測点によって異なる降雨による変化が不定期に現れていた.これは地表付近の透水性の違いによるものと考えられたので,我々は代表的な観測点の近傍において,降雨の前後で浅部電気探査を実施した. |
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| | 講演要旨(英文) | | Izu-Oshima volcano is one of the most active volcanoes in Japan and caused much serious eruption disaster frequently. During the latest eruption in 1986 - 87, various phenomena indicating interaction between magma and ground water were observed as magma ascended and descended. Therefore, we have sometimes carried out the repeated SP surveys to reveal the subsurface fluid flows beneath Izu-Oshima volcano. In order to estimate the hydrothermal system of the volcano and interpret the SP data, we conducted AMT measurements at 18 sites along two NE-SW profiles traversing the volcano in 2006 and 2007. We have also carried out the continuous SP measurement since 2006 on the south foot to monitor the change of subsurface hydrothermal system accompanying volcanic activity. Although annual and diurnal SP changes have been recognized, they change with places. Especially after rain, those differences appear clearly. Since we think it is due to the difference of the permeability near the surface, we carried out precise electric surveys before and after rain near the SP observation points. This paper mainly reports the result of AMT and electric surveys. |
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