Sedimentary diversity of the 2011 Tohoku-oki tsunami deposits on the Sendai coastal plain and the northern coast of Fukushima Prefecture, Japan

Abstract

This paper documents the sedimentary characteristics of the widespread deposits associated with the 2011 Tohoku-oki tsunami on the lowlands along the Pacific coast of the Sendai and Fukushima regions, northern Japan, and observed tsunami inundation depths. In eight areas of the region, field observation was carried out at a total of 123 locations and sampling at a total of 49 locations. Grain-size analysis and soft X-ray imaging reveal that the tsunami deposits are usually composed of sheetlike sandy beds and generally show landward-thinning and landward-fining trends and a landward increase in mud content, although site-specific distributional patterns are apparent along each transect. These thickness and grain-size patterns indicate a landward decrease in flow capacity. This information on the sedimentology of tsunami deposits and observed inundation depths will assist with the identification of paleo-tsunami deposits in the geological record and provide valuable constraints for mathematical analyses of tsunami hydraulic conditions related to sedimentary characteristics.[Figure not available: see fulltext.]