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Three-dimensional resistivity structure of Asama Volcano revealed by data-space magnetotelluric inversion using unstructured tetrahedral elements

Geophys. J. Int.208-3_1359-1372.pdf10.75 MBPDF見る/開く

タイトル: Three-dimensional resistivity structure of Asama Volcano revealed by data-space magnetotelluric inversion using unstructured tetrahedral elements
著者: Usui, Yoshiya 著作を一覧する
Ogawa, Yasuo 著作を一覧する
Aizawa, Koki 著作を一覧する
Kanda, Wataru 著作を一覧する
Hashimoto, Takeshi 著作を一覧する
Koyama, Takao 著作を一覧する
Yamaya, Yusuke 著作を一覧する
Kagiyama, Tsuneomi 著作を一覧する
キーワード: Inverse theory
Electrical properties
Volcanic arc processes
発行日: 2017年 3月
誌名: Geophysical Journal International
巻: 208
号: 3
開始ページ: 1359
終了ページ: 1372
出版社 DOI: 10.1093/gji/ggw459
抄録: Asama Volcano is an andesitic composite volcano and one of the most active volcanoes in Japan. In order to reveal electrical resistivity structure beneath the volcano accurately, we performed a 3-D inversion of dense magnetotelluric survey data. In order to prevent misinterpretation of the subsurface resistivity due to the steep topography around Asama Volcano, we used an unstructured tetrahedral mesh to represent the topography. Furthermore, we reduced the calculation time by transforming the inverse problem from the model space into the data space. Comparison of the new data-space method to the original model-space method showed that the calculation time required to update the model parameterswas reduced as a result of the transformation, whereas the resistivity structure obtained remained unchanged. In the subsurface resistivity structure around Asama Volcano that was estimated from the inversion, resistive bodies were discovered to be located under the old eruption centres. In particular, under the 24 ka collapse caldera to the west of the presently active crater, a spherical resistive body was found to exist in isolation. In addition, there was a widespread conductive layer below the resistive surface layer. By comparison with previous hydrological and geochemical studies, the conductive layer was interpreted as being a high-water-content layer and an overlying layer rich in altered clay minerals. Because the western part of the volcanic conduit was considered to be the resistive area, which is inferred to consist of unfractured rocks with lower permeability than their surroundings, it would appear that the area obstructs the westward flow of the hydrothermal fluid beneath the summit, thereby contributing to higher concentrations of SO4 2− and Cl− in the spring water at the northern and eastern feet as well as the uneven location of a diffuse CO2 anomaly.
Rights: This article has been accepted for publication in Geophysical Journal International ©:2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
資料タイプ: article
出現コレクション:雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

提供者: 橋本 武志


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