TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 65 (No. 6), pp. 505-515, 2013

Volume change of the magma reservoir relating to the 2011 Kirishima Shinmoe-dake eruption—Charging, discharging and recharging process inferred from GPS measurements

Shigeru Nakao1, Yuichi Morita2, Hiroshi Yakiwara3, Jun Oikawa2, Hideki Ueda4, Hiroaki Takahashi5, Yusaku Ohta6, Takeshi Matsushima7, and Masato Iguchi8

1Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan
2Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
3Nansei-Toko Observatory of Earthquake and Volcano, Kagoshima University, 10861 Yoshinocho, Kagoshima 892-0871, Japan
4National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenoudai, Tsukuba 305-006, Japan
5Graduate School of Science, Hokkaido University, Kita-10-jyo Nishi-8-chome, Kitaku, Sapporo 060-0810, Japan
6Graduate School of Science, Tohoku University, 6-6 Aramaki aza Aoba, Aobaku, Sendai 980-8578, Japan
7Faculty of Sciences, Kyushu University, 2-5643-29 Shinyama, Shimabara 855-0843, Japan
8Disaster Prevention Research Institute, Kyoto University, 1722-19 Sakurajima, Yokoyamacho, Kagoshima 891-1419, Japan

(Received November 20, 2012; Revised May 28, 2013; Accepted May 29, 2013; Online published July 8, 2013)

Abstract: Using GPS data, we evaluate the volume change of the magma reservoir associated with the eruption of Kirishima Shinmoe-dake volcano, southern Kyushu, Japan, in 2011. Because ground deformation around Shinmoe-dake volcano is strongly affected not only by regional tectonic movement but also by inflation of Sakurajima volcano located approximately 30-40 km to the southwest, we first eliminate these unwanted contributions from the observed data to extract the signals from Shinmoe-dake volcano. Then, we estimate the source locations and volume change before, during, and after the highest eruptive activity occurring between January 26 and 31. Our model shows that the magma began to accumulate about one year prior to the sub-Plinian eruption, with approximately 65% of the accumulated magma being discharged during the peak of the eruptive activity, and that magma accumulation continued until the end of November 2011. An error analysis shows that the sources during the three periods indicated above are located in almost the same position: 5 km to the northwest of the summit at a depth of 8 km. The 95% confidence interval of the estimated source depth is from 7.5 to 13.7 km.
Key words: Magma reservoir, GPS observation, ground deformation, the 2011 Kirishima Shinmoe-dake eruption.

Corresponding author E-mail: nakao@sci.kagoshima-u.ac.jp

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