抄録
A self-potential (SP) survey was carried out in Aogashima volcano in Izu-Ogasawara arc, which erupted about 200 years ago from the center of Ikenosawa crater. A terrain related SP distribution of about -1.2 mV per meter of elevation was observed. In the crater, positive SP anomalies were detected over western half of Maruyama pyroclastic cone and along the inner side of the crater rim. Negative SP anomalies were found over the eastern half of the cone and in the central area north of the cone. A post-processor to calculate electrokinetic potentials from histories of underground conditions (temperature, pressure, salinity, flow rate etc.) computed by geothermal reservoir simulation was applied to two-dimensional models of the volcano. The main features of the SP distribution were reasonably well reproduced in the models. The terrain related SP distribution is reproduced as caused by downflows of meteoric water. If impermeable structure beneath the crater rim interrupts the meteoric water downflow, a positive SP is produced along the inner side of the crater rim. Beneath the western half of the cone, continuous heat supply from the deep magma is required to keep the high temperature upflows at present, which also produce positive SP anomalies.
