著者

和田 博夫 伊藤 潔 梅田 康弘 角野 由夫

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B (ISSN:0386412X)

巻号頁・発行日

vol.36, no.B-1, pp.291-303, 1993-04-01

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Earthquake swarm activities have been occurring since January 1990 in the vicinity of Mount Yake-dake volcano in central Honshu, Japan.The volcano erupted frequently but it has been 30years since the last eruption in 1962.Temporary observation of microerarthquakes was conducted -near the volcano to survey the seismic activity.A station was set at about 1.5 km away from the summit crater in September, 1990 and five temporary stations were installed in the surrounding area of the volcano during the period from July to September, 1992. After that, three stations have been maintained to monitor the seismic activity.Although only a few events were located in the volcano during the period from July to September, 1992, the focal depths of the events were found to be very shallow as less than 3 km.In October and December, earthquake swarms occurred right beneath Yake-dake volcano.Earthquake swarms were also found in northeast, north and southeast of the volcano.Reviews of the studies on the volcano activity and earthquake swarms near the volcano are also given in this paper.

著者

角野 由夫 青木 知世 寺谷 尚子 梅村 宗太郎 片山 泰三 五十嵐 麻咲美 関口 玲奈 菊地 悠一郎 鈴木 友里 上本 季更 小林 雅裕 村上 英貴 澤崎 絵理子 土田 恭子 南谷 太一 西口 知久

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.87, no.1, pp.7-17, 2012

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Since 1992, geodetic measurements with GPS have been taken in the southern area of the Matsumoto basin, Nagano Prefecture, central Japan. The Matsumoto basin is located on the Itoigawa-Shizuoka Tectonic Line, which has recently been regarded as a plate boundary between the Eurasian plate and the North American plate. The GPS network of Shinshu University, established along the Itoigawa-Shizuoka Tectonic Line, consists of four observation stations: Shinshu University, Muroyama, Nakayama, and Matsumoto City Hall. The observed data were analyzed using broadcast ephemeris and default meteorological values with the double-difference technique. From the present GPS measurements, it was found that, during the period from 1992 to 2010, the distance between Muroyama and Shinshu University̶about 12km in the east-west direction̶contracted 4 cm (4 ppm). Subsequently, during the three years from 2010 to 2012, the temporal change of the baseline length between Muroyama and Shinshu University showed an extension of 4 cm (4 ppm). In particular, the steep change of the baseline length between them showed an extension of 1.5 cm following the massive Tohoku Earthquake, with a magnitude of 9.0 on March 11, 2011. The distance between Nakayama and Shinshu University̶about 6 km in the north-south direction̶extended 1 cm (2 ppm) during the period from 1992 to 2010. Subsequently, in 2011, it contracted 1.5 cm following the Naganoken Chubu Earthquakes, with magnitudes of 5.4 and 5.1, on June 30, 2011, which struck Matsumoto city. Crustal deformation in the southern area of the Matsumoto basin, Nagano Prefecture during the last twenty years, 1992-2012, is reported and discussed in the present study.