JpGU-AGU Joint Meeting 2017

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[JJ] Poster

H (Human Geosciences) » H-QR Quaternary research

[H-QR05] [JJ] Diachronic dynamics of human-environment interactions

Thu. May 25, 2017 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall HALL7)

convener:Toshihiko Sugai(Department of Natural Environmental Studies, Institute of Environmental Studies, Graduate School of Frontier Science, The University of Tokyo), Mamoru Koarai(Earth Science course, College of Science, Ibaraki University), Kiyohide Mizuno(Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology), Minoru YONEDA(The University Museum, The University of Tokyo)

[HQR05-P01] Consideration for marine alluvium in Bisan-Seto, Seto Inland Sea. –by re-examination of seismic profiles-

*Ryo Ohira1, Yoshio Inouchi2 (1.ocean engineering corporation, 2.Waseda Univ.)

Keywords:alluvium, Seto Inland Sea, seismic profiles

Re-examination of stratigraphy of so called alluvium all over Japan has been in progress. Investigations at alluvial plains are mainly based on analysis of drilled samples. On the other hand, so called marine alluvium has not yet been re-examined up to the present. Marine alluvial stratigraphy around Bisan-Seto at the central part of Seto Inland Sea is focused this time. As a result of re-examinations based on seismic profiles acquired by Bubble Pulser (Boomer) system, a new acoustic reflector is identified in marine stratum of upper portion of alluvium. This reflector divides upper sandy layer that forms sand bank in present marine sedimentary condition and lower muddy layer, and it reflects environmental change caused by the formation of strait between eastern Bisan-Seto and western Bisan-Seto (or the formation of straits lying between islands). This is the largest environmental change of Bisan-Seto caused by sea level rise after the end of last glacial period. Bay muds are distributed beneath the reflector, and sandy sediments which deposit under the influence of tidal current are distributed above the reflector.