Sedimentary features of the 2011 Tohoku earthquake tsunami deposits on the central Kujukuri coast, east Japan

DOI Web Site 9 Citations 27 References
  • Fujiwara Osamu
    Active Fault and Earthquake Research Center, National Institute of Advanced Industrial Science and Technology
  • Sawai Yuki
    Active Fault and Earthquake Research Center, National Institute of Advanced Industrial Science and Technology
  • Shishikura Masanobu
    Active Fault and Earthquake Research Center, National Institute of Advanced Industrial Science and Technology
  • Namegaya Yuichi
    Active Fault and Earthquake Research Center, National Institute of Advanced Industrial Science and Technology

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Other Title
  • 2011年東北地方太平洋沖地震に伴う津波により九十九里海岸中部に形成された堆積物
  • 2011ネン トウホク チホウ タイヘイヨウオキ ジシン ニ トモナウ ツナミ ニ ヨリ キュウジュウキュウリ カイガン チュウブ ニ ケイセイ サレタ タイセキブツ
  • Sedimentary features of the Tohoku earthquake tsunami deposits on the central Kujukuri coast, east Japan
  • Sedimentary features of the 2011 Tohoku earthquake tsunami deposit, on the central Kujukuri coast, east Japan

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This article describes the characteristic bedforms of the tsunami deposit formed on the Kujukuri coast, East Japan, during the 2011 off the Pacific coast of Tohoku Earthquake (Mw9.0). Two days later, on March 13, we observed tsunami deposits showing various bedforms reflecting their formative processes before the disturbances by weather. Similar to many previous studies, the tsunami deposits show a gross landward thinning and fining trend on a hundreds-of-meters scale. Our observations suggest that the trend is principally controlled by the sequential segregation and settlements of coarser grains from the inundation flow corresponding to the decrease of flow velocity and depth. Bedforms characterizing the tsunami deposits show a wide morphological variety. Current ripples with a wavelength ranging from several cm to 10cm are the most prevalent bedform. Barchan ripples are also commonly observed on the tsunami deposit. These bedforms suggest a flow condition dominated by a uni-directional current. In the vertical section of the tsunami deposit, the fine alternation of sand sheets and mud drapes recorded the repeated arrival of tsunami waves. Each set of a sand sheet and overlying mud drape represents a tsunami flooding and subsequent slack water period. These sedimentological observations will contribute to understanding the tsunami sedimentation process, and also will improve our ability to differentiate tsunami deposits from storm deposits, which is indispensable knowledge in paleo-tsunami research.

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