During the period from October 12 to 18, 1979, measurements of electrical resistivity and geomagnetic components were conducted in the Zyododaira area of Azumasan Volcano. The area includes fumaroles that have repeated small eruptions since a great eruption in 1893. The electrical resistivity near the surface was measured by direct current methods. A vertical sounding conducted at the center of Zyododaira indicated that the resistivity was extremely low near the surface, 2.8 Ωm at depths from 2 to 50 m and 6.5.Ωm below that (Fig. 2). This was confirmed by an electromagnetic induetion method, and the lateral extension of the low resistivity zone was examined. Elec- tromagnetic waves of frequency range from 17.4 kHz of artificial source to 8 Hz of the fundamental mode of Schumann resonance were measured at the ground surface, and the magnetotelluric techniques were applied. It has been revealed that the area of low resistivity less than 10 Ωm extends over 1 km from the fumarole sites in a SSE direction, forming a narrow belt with a width of about 500 m (Fig. 5). Geomagnetic total intensity was measured at nine repeat stations and at 38 temporary sites. Inclination and declination were observed at three of the repeat stations. The results show complex features of field distribution. Some are related to the terrain features, and others not. It should be noted that the total intensity is also low in the narrow zone of low resistivity.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
56
号
1
ページ
223 - 244
発行年
1981-08-31
ISSN
00408972
書誌レコードID
AN00162258
フォーマット
application/pdf
日本十進分類法
453
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
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吾妻山浄土平周辺の電気抵抗ならびに地磁気測定
ji0561012.pdf
(1.55MB)
