Sediment resuspension, transportation and redeposition by tsunami: Example from the 2011 Tohoku-oki tsunami on Sendai and Sanriku shelves
Abstract
Although it is accepted that large tsunami waves impact the sea floor, the response of surface sediments to tsunami is not yet fully understood. Tsunami by the 2011 off the Pacific coast of Tohoku earthquake caused considerable damage to Northeast Japan. Large friction velocity at sea floor by the tsunami waves might agitate and resuspend the surface sediments especially on the shallow shelf. Therefore, formation of event deposits is expected at the wide area off Sanriku region. To understand the phenomena by the 2011 Tohoku-oki tsunami at sea floor, we conducted several surveys on Sendai and Sanriku shelf to forearc area. Large resuspension, transportation and redeposition of shelf mud and sand by the 2011 tsunami was recognized on mid-inner shelf in Sendai Bay. Resuspension of shelf mud made highly turbid water on the shelf. Settling of the suspended mud formed upward-fining graded (sometimes parallel-laminated) mud on the inner-mid shelf. Collapse of such high turbid water mass generated the turbidity currents, and formed turbidite on the outer shelf. Sediment resuspension and turbidity current generation also occurred on Sanriku shelf. Benthic foraminifera assemblage of the uppermost layer of event deposit occurred on the forearc basin floor contained shelf to upper slope species. This also indicates transportation of tsunami-induced gravity flow from shelf to forearc basin. Low gradient of shelf suggests that tsunami is most possible origin of sediment resuspension and turbidity current generation. Therefore, the tsunami-related sediment resuspension occurred at least on shelf to upper slope area, and turbidity currents generated with relation to such sediment resuspension is an important process to transport sediment from shelf to offshore basins.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMNH51D..04I
- Keywords:
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- 4302 NATURAL HAZARDS Geological;
- 3022 MARINE GEOLOGY AND GEOPHYSICS Marine sediments: processes and transport;
- 7221 SEISMOLOGY Paleoseismology;
- 4558 OCEANOGRAPHY: PHYSICAL Sediment transport