日本地球惑星科学連合2018年大会

講演情報

[EJ] ポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG59] 日本列島の構造と進化: 島弧の形成から巨大地震サイクルまで

2018年5月22日(火) 13:45 〜 15:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:佐藤 比呂志(東京大学地震研究所地震予知研究センター)、篠原 雅尚(東京大学地震研究所)、石川 正弘(横浜国立大学大学院環境情報研究院、共同)、松原 誠(防災科学技術研究所)

[SCG59-P08] Subduction structure around the Amami Plateau in the northern Ryukyu island-arc trench system

*仲西 理子1新井 隆太1高橋 努1山本 揚二朗1三浦 誠一1小平 秀一1金田 義行2 (1.海洋研究開発機構、2.香川大学)

In the Ryukyu (Nansei-Shoto) island arc-trench system, seismic activity is high around its back arc basin, the Okinawa Trough, island arc, and the subduction zone where the Philippine Sea plate is subducting towards the island arc. Although great (M>8) interplate earthquakes have not occurred for few hundred years, various type s of slow earthquake have been detected by recent seismic studies in this region. In particular, slow earthquake activity is high around the Hyuga-nada off Kyushu and the Amami Island where the Kyushu-Palau ridge and the Amami Plateau are subducting beneath the overriding plate.
To reveal he relation between the structural variation and seismic activity, we performed active source seismic surveys around the Amami Island last year just south of previous survey [Arai et al., 2017a]. We conducted a ~305km long seismic refraction profile across the northern Ryukyu Trench passing through just south of the Amami Island. 30 OBSs were deployed along the profile with interval of ~6km. A tuned airgun array of R/V Kaimei shot with a total volume of 7950 cu. in. every 100m. Multichannel seismic (MCS) reflection surveys using the 1.5km-long, 480-channel hydrophone streamer were also performed along the same line although its length is ~250km shorter for its northwestern part. Another ~135km long MCS reflection profile is set just north of the refraction profile, east off of the Amami Island.
In the both two time-migrated reflected section, the plate interface steepens very rapidly as it approaches the seafloor of the seamount/plateau, which is also reported based on the previous survey just north of this region [Arai et al., 2017a].
Based on the reflection phases from the plate interface and Moho interpreted from the OBS data, thick subducting slab recognized at just north of this region [Arai et al., 2017a] may also exist in this region.
We will show a preliminary result of first-arrival tomography based on the OBS data. Structural characteristics in the northern Okinawa Trough will be able to be compared with those of the southern Okinawa Trough shown by Arai et al. [2017b]
This study was supported by Research project for compound disaster mitigation on the great earthquakes and tsunamis around the Nankai Trough region of Japanese Ministry of Education, Culture, Sports, Science and Technology.