| 講演要旨(和文) | | 今回,岩手火山地域の空中磁気観測データについて最新のデータ処理を実施し,精緻な磁気異常図の編集を行い,空中磁気図シリーズの一環として公表した.本報告では,出版した磁気図をもとに,磁気異常分布の詳細について説明するとともに,見掛け比抵抗分布との比較を通じて,岩手火山の浅部地下構造の特徴について述べる.詳細な検討の結果,噴気活動が見られた西岩手カルデラ内・黒倉山付近と,変質帯が分布する西岩手火山南斜面の谷筋では,局所的な低見掛け比抵抗・低磁気異常が分布することが明らかとなり,これらを検出するための手法の有効性が確認された.さらに,変質帯分布域に近接して,地表兆候はないものの局所的な低磁気異常が分布する山体部分においては,過去の火山活動による変質等による岩盤の脆弱化が推定され,特に急峻な地域においては地滑りや斜面崩壊に備える必要があると考えられる. |
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| | 講演要旨(英文) | | A new aeromagnetic anomaly map of Iwate volcano has been published by the Geological Survey of Japan/AIST recently, on the basis of the compilation of aeromagnetic anomalies observed by a helicopter-borne EM and aeromagnetic survey conducted over the volcano in 2000. The observed magnetic data has been processed and total magnetic intensity anomalies and RTP anomalies have been calculated on a smoothed observed surface. Whereas, apparent resistivity maps were created for each sampling frequencies of 220, 1,100, 5,500, 27,500 and 137,500 Hz. In general, the characteristics of the distribution of RTP anomalies and apparent resistivities are similar to each other. RTP and apparent resistivity lows lie on Nishi-Iwate volcano, while RTP and apparent resistivity highs lie on Higashi-Iwate volcano. Coincidences of local lows of RTP anomalies and apparent resistivities often correspond to the geothermal alteration areas confirmed by geologic mapping. It is concluded that the airborne method is useful to map alteration areas in stratovolcanoes with rugged terrain. |
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