Volcano-electromagnetic Survey on Hokkaido Komaga-take

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  • 北海道駒ヶ岳における地球電磁気学的調査
  • 北海道駒ケ岳における地球電磁気学的調査
  • ホッカイドウ コマガタケ ニ オケル チキュウ デンジキガクテキ チョウサ

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We made self-potential (SP) mapping, magneto-telluric sounding at 17.4 kHz and geomagnetic survey over a major part of Hokkaido Komaga-take volcano. The objectives were 1) to delineate the hydrothermal state of the volcano ; 2) to detect the intrusive rocks beneath a long fissure (1.8 km) which was formed at the time of the 1942 eruption ; 3) to clarify the origin of a hill, Akahage-yama, situated at the southern flank. The present study reveals the following results : 1) A positive SP anomaly, amounting to about 400mV, is observed along the fissure where is the high ground-temperature and the low resistive zone. These evidences indicate that the SP anomaly is mainly caused by the electrokinetic effect due to upwelling of the hot ground water through the permeable fissure. 2) We do not find any magnetic anomalies due to the intrusive rocks. The anomalies, if any, may be masked by other anomalies due to the complex surface topography. 3) Akahage-yama is composed of highly magnetized rocks (3 A/m) in comparison with the surroundings (0.6 A/m). Considering the intensity of magnetization, Akahage-yama may be a parasitic volcano.

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