Self-potential Measurements on Shinmoe-Dake, Kirishima Volcanic Group
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概要
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We conducted self-potential(SP) surveys on Shinmoe-Dake, one of the active volcanoes in Kirishima volcanic group. The surveys cover an area of 1km × 1km including the crater. One of the prominent features is a negative anomaly on the crater basin. The streaming potential caused by drainage of water from the crater basin is a promising candidate for a cause of the negative anomaly. We quantitatively verified the plausibility of the mechanism using seepage of the lake water and the permeability of the ground, which were estimated from the water balance of the crater lake. Another prominent feature is positive SP anomalies on the eastern and southern slopes of Shiiimoe-Dake. These positive anomalies lie over relatively low resistive regions revealed by a magnetotelluric survey. This fact suggests that the present positive anomalies are generated by the streaming potential accompanied by hydrothermal upflows, although there still remains uncertainty because we have no information on the ground temperature. We also found positive patches of SP which were located at the fumaroles in the crater basin. However, they turned out to be rather small both in size and intensity after correcting for topographic effects. This suggests that hydrothermal activity just under the crater of Shinmoe-Dake is weak at present.霧島火山群に属する成層火山新燃岳において,火口を含む約1km四方の自然電位分布を調査した.新燃岳火口底の自然電位は,過去に調べられたいくつかの活火山の例に反して負の異常を示すことがわかった.この負異常の原因についていくつかの可能性を定量的に検証した結果,火口湖からの漏水に伴う流動電位がその主要な原因であるとの結論を得た.山体東斜面と南斜面には正の電位異常が見られる.MT法による比抵抗測定によって得られている低比抵抗層の分布と,この正の電位異常の分布は良い一致を示すことから,地下での熱水の上昇が示唆される.しかしながら,地中温度のデータがないためこれは確証的ではない.
- 1995-03-31
論文 | ランダム
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