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Shallow Resistivity Structure of Sakurajima Volcano Revealed by Audio-frequency Magnetotellurics

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Title: Shallow Resistivity Structure of Sakurajima Volcano Revealed by Audio-frequency Magnetotellurics
Other Titles: AMT 観測から推定される桜島火山の浅部比抵抗構造
Authors: KANDA, Wataru1 Browse this author
YAMAZAKI, Tomoya2 Browse this author
OGAWA, Yasuo3 Browse this author
HASHIMOTO, Takeshi4 Browse this author
SAKANAKA, Shinʼya5 Browse this author
AIZAWA, Koki6 Browse this author
TAKAKURA, Shinichi7 Browse this author
KOYAMA, Takao8 Browse this author
YAMADA, Kenta9 Browse this author
KOBAYASHI, Tsukasa10 Browse this author
KOMORI, Shogo11 Browse this author
Authors(alt): 神田, 径1
山崎, 友也2
小川, 康雄3
橋本, 武志4
坂中, 伸也5
相澤, 広記6
高倉, 伸一7
小山, 崇夫8
山田, 健太9
小林, 宰10
小森, 省吾11
Keywords: Sakurajima volcano
electrical resistivity structure
hydrothermal system
flank eruption
prediction of volcanic eruptions
Issue Date: 2013
Volume: 58
Issue: 1
Start Page: 251
End Page: 267
Publisher DOI: 10.18940/kazan.58.1_251
Abstract: An audio-frequency magnetotelluric (AMT) survey was conducted at the foot of Sakurajima volcano in November 2007. This survey was carried out within the framework of the 7th National Project for Prediction of Volcano Eruptions. The main objective was to clarify the shallow layers of Sakurajima volcano for better understanding of the volcanic activity. We measured electromagnetic fields at frequencies from 1 to 10400 Hz at 27 locations along only three lines set on the northern, western, and southeastern flanks of the volcano. The three profiles enclosed the summit area where access is prohibited because of frequent explosive vulcanian eruptions. The data quality was generally considered to be good at frequencies higher than 2 Hz. Two-dimensional and three-dimensional (3-D) modeling approaches were applied to the data. As a result of 3-D modeling, we obtained the following features in the resistivity model. The surface layer showed a high resistivity from several hundreds to thousands of ohm-meters and corresponded to the lava. This surface layer covered a highly conductive layer with a resistivity of less than tens of ohm-meters, interpreted as containing seawater or groundwater. However, the basement structure was not clearly detected, except for in an area of northern Sakurajima. The first lava layer was distributed thickly in northern and western parts of Sakurajima, and the boundary between the first and second layers was typically located at around sea level. The conductive second layer was found at deeper levels beneath areas such as the Haruta-yama lava dome and the Nabe-yama pumice cone. This depression of the low resistivity layer is probably caused by the fracture zone associated with previous eruptions, which is formed above the conductive layer. In the proximity of Hikino-hira lava dome and the Taisho crater, the second conductive layer was found at a depth shallower than sea level, suggesting that a hydrothermal system has developed underneath this area. In contrast, elevation of the second layer was not seen on the side of Taisho crater located nearest to the edge of Nabe-yama, implying that a heat source is not present beneath the eastern foot of Sakurajima.
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 橋本 武志

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