Recent and historical tsunami deposits from Lake Tokotan, eastern Hokkaido, Japan, inferred from nondestructive, grain size, and radioactive cesium analyses
Tetsuya Shinozaki (),
Yuki Sawai,
Kazumi Ito,
Junko Hara,
Dan Matsumoto,
Koichiro Tanigawa and
Jessica E. Pilarczyk
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Tetsuya Shinozaki: University of Tsukuba
Yuki Sawai: National Institute of Advanced Industrial Science and Technology (AIST)
Kazumi Ito: National Institute of Advanced Industrial Science and Technology (AIST)
Junko Hara: National Institute of Advanced Industrial Science and Technology (AIST)
Dan Matsumoto: National Institute of Advanced Industrial Science and Technology (AIST)
Koichiro Tanigawa: National Institute of Advanced Industrial Science and Technology (AIST)
Jessica E. Pilarczyk: Simon Fraser University
Natural Hazards: Journal of the International Society for the Prevention and Mitigation of Natural Hazards, 2020, vol. 103, issue 1, No 33, 713-730
Abstract:
Abstract Geological evidence of recent tsunamis from sediment samples collected from Lake Tokotan, a coastal lagoon in eastern Hokkaido, northern Japan, was detected using computed tomography (CT) and soft X-ray images, grain size, and radionuclide profiles. Initial field observations revealed that sediments had no discernable sedimentary structures at the top of the core. However, results of CT imaging, soft X-ray, and grain size analyses show evidence for three invisible sand layers that are intercalated with mud layers. These sand layers exhibit trends of landward fining and thinning. Furthermore, the distribution of sand layers was limited to the center and seaward parts of the lake. Vertical profiles of cesium and lead concentrations in combination with recent eyewitness accounts indicated that these sand layers are correlated with the 1973 Nemuro-oki, 1960 Chilean, and 1952 Tokachi-oki tsunami events. The deeper part of the sediment cores includes three volcanic ash layers and three prehistoric coarse sand layers. The prehistoric layers are correlated with unusually large tsunamis that were geologically identified in previous studies from eastern Hokkaido. These findings suggest that nondestructive techniques, in combination with radionuclide analysis, allow for detection of frequent but faint tsunami deposits. This technique allows for an improved understanding of the history of tsunami inundation in Lake Tokotan and of other locations for which stratigraphic evidence for faint tsunamis layers is not readily apparent from field assessments.
Keywords: Tsunami deposit; Computed tomography; Radioactive cesium and lead; Hokkaido (search for similar items in EconPapers)
Date: 2020
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DOI: 10.1007/s11069-020-04007-7
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