GPS観測による2000年7月14日三宅島噴火に伴う地殻変動

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(4) , ! " # $ % & . * ( + , ' ( ) - .,**- / 1 0 ,- 1234 ,**/ / . 0 ,2 1256. Crustal Deformation Associated with the July +., ,*** Eruption of Miyakejima Volcano Detected by GPS Measurements Nobuto BANDO῍, Shinichi KARIYA῍, Fumiaki KIMATA῍, Shigeru NAKAO῍῍,῍῍῍, Jun OIKAWA῍῍, ῍῍, Eisuke FUJITA῍῍῍῍, Koji KAWAI῍῍῍῍῍, Hidefumi WATANABE῍῍, Motoo UKAWA῍῍ Takeshi MATSUSHIMA῍῍῍῍῍῍, Rikio MIYAJIMA῍ and Takashi OKUDA῍ Based on GPS data at adjacent +/ stations, a process of the ,*** eruption at Miyakejima volcano is analyzed for the period before the first phreatic eruption on July +.. Consequently the following results are obtained : +) Deflation was remarkable up to around a caldera collapse with a small eruption on July 2. The observed data are explained by a deflation source of 7+.,8+*2 m- in volume, which was located - km south west of the center of the summit (i.e, the formerly highest peak of Oyama) at 0 km in depth. The location was close to the first deflation source detected by the kinematic GPS data on June ,1, suggesting that the deflation started on June ,1 at around 0 km in depth (Meilano et al., ,**-). ,) After then the volcano inflated slightly at a shallower depth, and resulted in a phreatic eruption on July +.. In this period, however, the deflation at 0 km in depth is assumed to have continued with a rate suggested by an exponential curve fitted to the data during June ,3 and July 2. The inflation during July 2 and +, was considered to be +.-8+*1 m- in volume, which was located , km south-southwest of the center of the summit at -./ km in depth. The shallow inflation source was just below the source of low frequency tremors (Kikuchi et al., ,**+). It suggests a close correlation between the inflation source and occurrence of the tremors. Key words : ,*** Miyakejima Volcano eruption, spherical source, deflation, eruption process, magma intrusion, GPS measurements +ῌ ῐ ῎ ῑ ῏. BC ,* /@DE<FG;HIJKLMN +32- /OPQ. 9:(;<=>? 0* /@A +3.* /4 +30, /4 +32- /. R4 SOG;TUHVWTUXYZ[A\]^_E4 `. a.0.ῌ20*, bc

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(6) hihijklimno Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya .0.ῌ20*,, Japan. a++-ῌ**-, pqpg phirsmnt Earthquake Research Institute, University of Tokyo, Bunkyo, Tokyo ++-ῌ**-,, Japan. uv : a23*ῌ**0/ wx(dyz^ ,+ { -/ wx(hi5i| Present : Faculty of Science, Kagoshima University, +ῌ,+ῌ-/, Korimoto, Kagoshima 23*ῌ**0/, Japan. a-*/ῌ***0 }~d oimnt. National Research Institute for Earth Science and Disaster Prevention, Tsukuba -*/ῌ***0, Japan. a+*.ῌ**./ pqg | Hydrographic and Oceanographic Department, Japan Coast Guard, Chuo, Tokyo +*.ῌ**./, Japan. a2//ῌ*2.- (d hihij5imno Graduate School of Science, Kyusyu University, Shimabara 2//ῌ*2.-, Japan. Corresponding author : Fumiaki Kimata e-mail : [email protected].

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(22) / <2 +331. 5 (,**-) 2678 1. +333 ²D GPS ;"xt%;". Fig. +. Time series of the ground deformation detected by GPS measurements and ground tilt in Miyakejima in the period of June-August, ,***. Remarkable eruptions are shown by arrows. (A) Baseline coordinates and line length between the GPS sites of 3-*/3 and 3-*0* (Kaidzu et al., ,***), (B) ground tilt at MKE, same as the GPS site of *,00 (Ukawa et al., ,***)..

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(162) 182. º;{_@ Jx-LM|-N[»(¼N. (,**+) . 3/ +,+ῌ+,2. Ito, T. and Yoshioka, S. (,**,) A dike intrusion model in and around Miyakejima, Niijima and Kozushima in ,***. Tectonophysics, -/3,+1+ῌ+21. Kaidzu, M., Nishimura, T., Murakami, M., Ozawa, S., Sagiya, T., Yarai, H. and Imakiire, T. (,***) Crustal deformation associated with crustal activities in the northern Izu-islands area during the summer, ,***. Earth Planets Space, /,, ix-xviii.

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(164) (,**+) ,*** !" #$ ++* ,*.ῌ,+0. %&'()* + (+332) GPS ,-./0123456789: ;<9<= , /+ +1+ῌ+2*. Kumagai, H., Ohminato, T., Nakano, M., Ooi, M., Kubo, A., Inoue, H. and Oikawa, J. (,**+) Very-long-period seismic signals and caldera formation at Miyake Island, Japan. Science, ,3-, 021ῌ03*. Meilano, I., Kimata, F., Fujii, N., Nakao, S., Watanabe, H., Sakai, S., Ukawa, M., Fujita, E. and Kawai, K. (,**-) Rapid ground deformation of the Miyakejima volcano on ,0ῌ,1 June ,*** detected by kinematic GPS analysis. Earth Planets Space, //, e+-ῌe+0. Miyasaka, M., Nakagawa, M. and Nakada, S. (,**/) Magma plumbing system of the ,*** eruption of Miyakejima volcano, Japan. Bull. Volcanol., 01, ,/.ῌ,01. Mogi, K. (+3/2) Relation between the eruption of various volcanoes and the deformations of the ground surface around them. Bull. Earthq. Res. Inst., Univ. Tokyo, -0, 33ῌ+-.. > ?@ ABCDE F!G"H (#$ I%& "JK L'*( )* +,-.K (,***) /M ,*** 0 1 23 +, 4N#OP56QROP3S TU V/M ,*** 7WXYZ8[9,O P\ 30ῌ+*,. Murase, M., Nakao, S., Kato, T., Tabei, T., Kimata, F. and Fujii, N. (,**-) Dike intrusion process of ,*** Miyakejima ] Kozujima event estimated from GPS measurements in Kozujima ] Niijima Islands, central Japan. ,**- AGU Fall Meeting. :^_"#"# #OPN;`"#OPab c"#"# #OPN (,***) GPS ,dZ e1,],*** f<g=hiZ e1 (+33/. 3ῌ+333. 2) > 23 j?@ABkl C :^_"##D;`"#OPabc"## D (+332) GPS ,dZhiZem21. n+33/ῌ+331 o ?@ABkk 1+ 2.ῌ 2/. EpFq-FG (+333) e1!Hrs6tuv MICAP-G wI , /, +*+ῌ+*-. J Kx- yLMz {_+@ A |-}$N~O P QR S[ (,***) hiZe1]"# 7WN#OPa T mUD GPS 8V !H #k? ,*** 4"k A+/. NW(DN *XYFG "YZR[D\ (,**+) ,*** ]]E^_` ] #$ ++* +02ῌ+2*. Nishimura, T., Ozawa, S., Murakami, M., Saiya, T., Tada, T., Kaidzu, M. and Ukawa, M. (,**+) Crustal deformation caused by magma migration in the northern Izu Islands, Japan. Geophys. Res. Lett., ,2, -1./ῌ-1.2. Ra( R S %b& c d efghN i5j k|-}$ (,**,) ,*** ,e11 l OPam 11 //ῌ0/. ¡no (,**,) ¢£8¤ -D pq ¥¦§ +.2 p. Ueda, H., Fujita, E., Ukawa, M., Meilano, I. and Kimata F. (,**/) Magma intrusion and discharge process at the initial stage of the ,*** Miyakejima activity inferred from tilt and GPS data. Geophys. J. Int. (in press). Ukawa, M., Fujita, E., Yamamoto, E., Okada, Y., and Kikuchi, M. (,***) The ,*** Miyakejima eruption : crustal deformation and earthquakes observed by the NIED Miyakejima observation network. Earth Planets Space, /,, xix-xxvi. ~r |-}$ N~O ¨N©K

(165) sª« (,**+) ,*** hiZ¤v 3I+¬=;®6¯°±1 #$ ++* +2+ῌ+3*. Yamaoka, K., Kudo, M., Kawamura, M., Kimata, F. and Fujii, N. (,**/) Long-lasting dike intrusion in the ,*** eruption of Miyake-jima Volcano ] Where did the magma come from ? ] J. Volcanol. Geotherm. Res., 01, ,-,ῌ,.,. N²& (,**-) ,*** ? ³´]tuµv¶/·´¸w .2 -/ῌ.,. Wessel, P. and Smith, W. H. F. (+33+) Free software helps map and display data. EOS Trans. Amer. Geophys. Union, 1,, ..+, ../ῌ..0. nxyz "{¹po.

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