地殻変動から推定される2004年浅間山噴火前後の浅部マグマ供給系

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(3) ! " # $ % & ',**/ ( . ) +3 *+,- ,**/ ( 2 ) ,+ *+῏.. Magma Supply System of the ,**. Eruption at Asama Volcano Estimated by Crustal Deformation Data Akimichi TAKAGI῍, Keiichi FUKUI῍, Kenji FUJIWARA῍, Yoshihiro UEDA῍῍, Sei IIJIMA῍῍, Tetsuya YAMAMOTO῍, Takayuki SAKAI῍, Tomoyuki KANNO῍῍῍ and Hiroaki KATAYAMA῍῍῍ A geodetic observation network with GPS and EDM at Asama volcano detected pre- and co-eruptive crustal deformation. Observed horizontal displacements by GPS before the ,**. eruption indicated radial pattern outward from the active summit crater. An east-west baseline indicated secular extension with 1 mm/yr from ,**, to the occurrence of the ,**. eruption. Rapid extension of +* mm was detected at the baseline near the summit, which may suggest magma discharge into the shallower chamber. We estimated the magma supply system from the observed geodetic data assuming buried two pressure sources. One is at a height of ,,** m above sea level beneath the summit crater (Source A) and another is +./ km east of the summit at sea level (Source B). Our data indicated that before the first eruption discharged magma from the deeper to source B was ,**/+*- m-, and from source B to source A was +./+*- m-. Total amount of increase in volume of source A was estimated to be more than /*/+*- m- by EDM and GPS data by the end of the eruptive activity. These small but significant signals could be observed only in our network near the crater. Our results indicated that dense geodetic observation near the active crater or vent could give important and interesting data to clarify and monitor the active volcano. Key words : Asama volcano, magma supply system, GPS, EDM. +ῌ ῐ ῎ ῑ ῏. @om3- 01ApZYhiqrstu5Bvwx. 01234- ,**. ( 3 ) + *567892:;<=. iyzy{|}A\]4- ~ (+33*) _54. >? @A925BC- 2ῑ4DE3FGHIJῌ 0. onin? À῏῍492A012. km AKL5MN=- 9OPQ>2R4ῌ / STU3. :- E '- ,**, . 'Y. VW> 'JXEYZ[\]^- ,**/a.? 01A678. \]^ Z῏- ,**. . ABihk:. 92A;<4 +32- (_῎3VW>? Àa- - bA67. 3Vv234inn@- m>- Da5;. 892cdefghi92jk:l( +, )m3gn>?. <=>678924 ,+ ( A@3- GPS ABi¡. ¢-*/ῌ**/, £¤¥¦§¨©ª« +ῌ+ ¬\]^Z[2\]® Seismology and Volcanology Research Department, Meteorological Research Institute, +ῌ+, Nagamine, Tsukuba, Ibaraki -*/ῌ**/,, Japan. ¢-23ῌ*++/ ª!¥I¯°±² ³´µ¶ ++/+ῌ, Karuizawa Weather Station, ++/+ῌ,, Oiwake, Karuizawa, Nagano -23ῌ*++/, Japan.. ¢+**ῌ2+,, JX·¸¹ºE»´ +ῌ-ῌ. ¬¼Z[2® Seismological and Volcanological Department, Japan Meteorological Agency, +ῌ-ῌ., Otemachi, Chiyodaku, Tokyo +**ῌ2+,,, Japan. Corresponding author : Akimichi Takagi e-mail : [email protected].

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