Evidence for erosion and deposition by the 2011 Tohoku-oki tsunami on the nearshore shelf of Sendai Bay,Japan |
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| Authors: | Email author" target="_blank">Shuro?YoshikawaEmail author Toshiya?Kanamatsu Kazuhisa?Goto Izumi?Sakamoto Masatoshi?Yagi Mikio?Fujimaki Riichirou?Imura Kenji?Nemoto Hide?Sakaguchi |
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| Institution: | 1.Department of Mathematical Science and Advanced Technology,Japan Agency for Marine-Earth Science and Technology,Yokohama,Japan;2.Research and Development Center for Earthquake and Tsunami,Japan Agency for Marine-Earth Science and Technology,Yokosuka,Japan;3.International Research Institute of Disaster Science (IRIDeS),Tohoku University,Sendai,Japan;4.School of Marine Science and Technology,Tokai University,Shizuoka,Japan;5.Graduate School of Science and Engineering,Tokai University,Shizuoka,Japan;6.Coastal Ocean Research Co., Ltd.,Tokyo,Japan;7.Fuyo Ocean Development & Engineering Co., Ltd.,Tokyo,Japan |
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| Abstract: | Ongoing geological research into processes operating on the nearshore continental shelf and beyond is vital to our understanding of modern tsunami-generated sediment transport and deposition. This paper investigates the southern part of Sendai Bay, Japan, by means of high-resolution seismic surveys, vibracoring, bathymetric data assimilation, and radioisotope analysis of a core. For the first time, it was possible to identify an erosional surface in the shallow subsurface, formed by both seafloor erosion and associated offshore-directed sediment transport caused by the 2011 Tohoku-oki tsunami. The area of erosion and deposition extends at least 1,100 m offshore from the shoreline down to water depths of 16.7 m. The tsunami-generated sedimentological signature reaches up to 1.2 m below the present seafloor, whereas bathymetric changes due to storm-related reworking over a period of 3 years following the tsunami event have been limited to the upper ~0.3 m, despite the fact that the study area is located on an open shelf facing the Pacific Ocean. Tsunami-generated erosion surfaces may thus be preserved for extended periods of time, and may even enter the rock record, because the depth of tsunami erosion can exceed the depth of storm erosion. This finding is also important for interpretation of modern submarine strata, since erosion surfaces in shallow (depths less than ~1 m) seismic records from open coast shelves have generally been interpreted as storm-generated surfaces or transgressive ravinement surfaces. |
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