著者

鍵山 恒臣 筒井 智樹 三ヶ田 均 森田 裕一 松島 健 井口 正人 及川 純 山岡 耕春 熊谷 博之 西村 裕一 宮町 宏樹 渡辺 了 西村 太志 高木 朗充 山本 圭吾 浜口 博之 岡田 弘 前川 徳光 大島 弘光 植木 貞人 橋本 恵一 仁田 交一 茂原 諭 中道 治久 汐見 勝彦 中原 恒 青木 重樹 青地 秀雄 井田 喜明

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.70, no.2/4, pp.33-60, 1996-03-15

---

In recent years, investigations on the structures of volcanoes have been noteworthy for further understanding volcanic processes, including locations of magma reservoirs, magma rising process before eruptions and causes of related phenomena. In 1994, a joint experiment was conducted on Kirishima Volcanoes, Southern Kyushu, to reveal the structure and the magma supply system by a group of scientists from national universities under the National Research Project for the Prediction of Volcanic Eruptions. The experiment was carried out by seismological, electromagnetic and other geophysical methods. The following seven papers including this one present some results of the experiments. This paper outlines a seismic explosion experiment in Kirishima, and presents all data on the first motion. An extensive explosion seismic experiment was conducted on December 1, 1994. Observations were made along a 30-km major line lying in the NNW-SSE direction and other sub-lines which cross the major line in and around the Kirishima Volcanoes. Along these lines, 6 shots with a charge size of 200-250 kg, and 163 temporary observations were arranged by many universities and institutes. A newly developed data logger was used for these temporal observations, and the position of each site was determined by GPS. All 6 shots were successfully fired, and clear onset and significant phases were observed at most observation sites. A travel time diagram suggests that a high velocity layer crops out south of the Kirishima Volcanoes, while in the Kirishima Volcanoes, this layer is covered with a lower velocity layer, which is thick at the northern part. It is also suggested that a structural discontinuity exists between S3 and S4.

著者

松本 浩幸 三ヶ田 均 大町 達夫 井上 修作

出版者

公益社団法人 土木学会

雑誌

海岸工学論文集 (ISSN:09167897)

巻号頁・発行日

vol.51, pp.281-285, 2004-10-08 (Released:2010-06-04)

参考文献数

13

被引用文献数

1 1

---

本研究では, 津波地震の発生原因が「断層面上のゆっくりとした断層破壊」と仮定して, それに伴う「ゆっくりとした海底面変動」が津波を引き起こす過程および伝播の特性を数値計算によって検討した.ライズタイムが100s程度であれば断層破壊の影響は無視でき, 静的変位から予想される津波と同程度の津波が発生する. また, ライズタイムが500sのゆっくりとした海底面変動でも水塊移動を引き起こし津波が発生することを示した. ただし, 津波の波高が小さくなり, 周期が長くなる点は従来の予測とは大きく異なる.本研究は, ゆっくりとした断層破壊による地震津波に対しても, 沖合観測によって早期に津波を検知できることを示唆している.

著者

酒井 慎一 山田 知朗 井出 哲 望月 将志 塩原 肇 卜部 卓 平田 直 篠原 雅尚 金沢 敏彦 西澤 あずさ 藤江 剛 三ヶ田 均

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.110, no.2, pp.145-155, 2001-04-25 (Released:2009-11-12)

参考文献数

6

被引用文献数

38 54

---

From June 26, 2000, an intensive earthquake swarm started under Miyake-jima Island, 180 km south off Japan. This swarm was closely related to the eruption of Miyake-jima Island, probably dominated by underground magmatic activity. The swarm spread toward the northwestern ocean region from Miyake-jima Island, in which a huge number of earthquakes (over 100, 000) including five large events of M>6.0 were detected over about two months. This earthquake swarm was the most active since we started seismic observations in the 1970's.Although there are some telemetered observation stations on the Izu volcanic islands, no offshore instruments were operated in the area of this earthquake swarm. To understand both the spatial and temporal changes of this activity, we conducted a series of ocean bottom seismometer observations. According to the variation in the seismic activity with time, we changed the array configuration of OBSs six times. Furthermore, real-time seismic observations were undertaken using a buoy-telemetering OBS system.Combining the OBS data with those of the island stations, very precise earthquake locations were determined. The epicenter distribution obtained strongly indicates a northwest-southeastern lineament. The vertical cross-section of the events shows two characteristic trends. Deeper (7- 13km) events are forming a very thin (2-km thick) plane, while shallower ones (< 7 km) show a much thicker distribution. These distribution patterns will provide important constraints on the physical mechanism for understaning magma migration.