Tsunami sediments

• Project/Area Number: 23540498
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Solid earth and planetary physics
• Research Institution: University of the Ryukyus
• Principal Investigator: ANDO Masataka 琉球大学, 理学部, 客員教授 (80027292)
• Co-Investigator(Kenkyū-buntansha): NAKAMURA Mamoru 琉球大学, 理学部, 准教授 (60295293) ; SHISHIKURA Masanobu 独立行政法人産業技術総合研究所, その他部局等, 研究員 (00357188)
• Project Period (FY): 2011 – 2013
• Project Status: Completed (Fiscal Year 2013)
• Budget Amount: ¥5,070,000 (Direct Cost: ¥3,900,000、Indirect Cost: ¥1,170,000); Fiscal Year 2013: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000); Fiscal Year 2012: ¥1,690,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥390,000); Fiscal Year 2011: ¥2,340,000 (Direct Cost: ¥1,800,000、Indirect Cost: ¥540,000)
• Keywords: 津波 / 琉球海溝 / 沈み込み帯 / 1771年八重山津波 / 石垣島 / 津波堆積物 / 有孔虫 / 年代測定 / 海溝系地震 / C１４年代測定 / カップリング率 / 掘削調査 / 1771年津波 / C14年代測定 / 石垣宮古島 / 明和の津波 / 津波石 / ジオスライサー / 津波発生間隔

Research Abstract

Some subduction zones are associated with large earthquakes but others are not or infrequent The Ryukyu subduction zone is grouped into the extensional group, having the fastest convergence rate (12.5cm/y). In this subduction zone, we obtained a complete set of tsunami layers which were found to be buried in a gentle slope hill. The most recent event corresponds to the 1771 documented in several records. The height documented is 20 m while the highest tsunami layer reaches to 8 m, which are very consistent with historical documents since tsunami sediments below the run-up heights of sea water. The 1771 event was estimated to have occurred near the trench with a fault slip of 20 m. This slip can be accumulated in 160 years if 100% of its relative plate motion is accumulated. However, the intervals we found are 500 and possibly 100 years, significantly longer that this slip. This suggests that the extensional subduction zone has an ineffective accumulation of slip on its interface.

Research Products

• [Presentation] (2014)
  • Author(s): Tu Y. and M. Ando
  • Organizer: JpGU Meeting
  • Place of Presentation: Yokohama
• [Presentation] Aspire Resort (2013)
  • Author(s): Ando, M. and T. Yoko
  • Organizer: Taiwan Geoscience Assembly
  • Place of Presentation: Taiwan
• [Presentation] (2013)
  • Author(s): Ando, M, Y. Tu and C.H. Lin
  • Organizer: IASPEI
  • Place of Presentation: Gotherng Sweden
• [Presentation] The distribution of benthonic foraminifera in paleo-tsunamis sediments on Ishigaki islands (2013)
  • Author(s): Tu Yoko and Msataka Ando
  • Organizer: Japan Geos
  • Place of Presentation: 千葉県幕張メッセ国際会議場
• [Presentation] Large earthquakes and tsunamis along the Ryukyu trench (2013)
  • Author(s): Masataka Ando and Yoko Tu
  • Organizer: 2013 Taiwan Geosciences Assembly
  • Place of Presentation: Aspire Resort, Taiwan
• [Presentation] A possible tsunamTsunami folklore and potential tsunami risk on the eastern coast of Taiwani source based on tsunami folklore and interview with local residents on the eastern coast of Taiwan (2013)
  • Author(s): Masataka Ando, Mamoru Nakamura and Cheng-Horng Lin
  • Organizer: IASPEI. IUGG Joint Assembly Gothenburg 2013 - IAPSO
  • Place of Presentation: Gothenburg, Sweden
• [Presentation] Tsunami recurrence from Holocene deposits on Ishigaki island along the Ryukyu suduction zone (2012)
  • Author(s): Masataka Ando, Masanobu Shishikura, Yoko Tu and Mamoru Nakamura
  • Organizer: Interbnational Geological Congress
  • Place of Presentation: Brisben
• [Presentation] The identification of paleo-tsunamis based on foraminifera distribution on Ishigaki and Miyako islands (2012)
  • Author(s): Tu Yoko、Masataka Ando, Masanobu Shishikura, and Mamoru Nakamura
  • Organizer: 日本地震学会
  • Place of Presentation: 函館
• [Presentation] Distinguish between very low frequency earthquakes and landslides signal. (2012)
  • Author(s): Tu Yoko, Masataka Ando, Masanobu Shishikura, and Mamoru Nakamura
  • Organizer: 日本地球惑星関連学会
  • Place of Presentation: 函館
• [Presentation] Tsunami recurrence inferred from soil deposits on Ishigaki island along the Ryukyu (2012)
  • Author(s): Masataka Ando, Masanobu Shishikura, Yoko Tu and Mamoru Nakamura
  • Organizer: American Geophysical Union
  • Place of Presentation: San Francisco