| 講演要旨(和文) | | 産業技術総合研究所とオーストリア地質調査所は, 2002年と2004年にイタリア・エオリア諸島のストロンボリ火山とその周辺海域において,当該地域の地下構造を推定するため,ヘリコプターを用いた空中磁気探査を実施した.データ処理を施し両観測データを編集して,観測面の下方に等価異常を仮定する手法により,滑らかな曲面上での磁気異常を求めた.上面が地形,下面が一定深度の地形モデルを仮定して,観測磁気異常と合成磁気異常とを比較して地形効果を計算したところ,山体の平均的な磁化強度は,2.2A/mと推定された.この際,一様磁化を仮定した合成磁気異常で説明できない部分は,山体の磁化構造の不均質性を示すものであり,これを解析することにより当該火山の内部構造を明らかにすることができると考えられる.そこで,今回当該の磁気異常について2次元の磁化強度マッピングと3次元イメージングを行った結果について報告する. |
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| | 講演要旨(英文) | | Helicopter-borne magnetic surveys were conducted over Stromboli Volcano and its surrounding areas in 2002 and 2004. Observed data from those surveys were merged and aeromagnetic anomalies for Stromboli Island and its vicinity were reduced onto a smoothed surface. The average magnetization intensity was calculated to be 2.2 A/m for the edifice of Stromboli shallower than 1,200 m below sea level by comparing the observed and synthetic data. Next, apparent magnetization intensity mapping was applied to the observed anomalies using a uniform magnetization of 2.2 A/m as the initial value. A magnetization low occupies the center of the island where the summit craters reside, suggesting demagnetization caused by the heat of conduits and/or hydrothermal activity in addition to the thick accumulation of less magnetic pyroclastic rocks. 3-D magnetic imaging was preliminarily applied to the same magnetic anomalies as well as for the magnetization intensity mapping. A distinctive regional magnetization high is distributed on a saddle area between Stromboli and Basiluzzo islands and extends to the two submarine eruptive centers on the southwestern submarine edifice of Stromboli. A careful examination on the results of the 2-D and 3-D magnetic imaging implies that the saddle area is occupied by volcanic rocks from these eruptive centers and is also underlain by partially and/or completely concealed volcanic structures formed along a NW-SE direction conjugate to the main axis of regional tectonic trend in this area. |
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