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| | Abstract | | 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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