Estimation of 2011 tohoku-oki tsunami deposit origins by cluster analysis using metal composition

Abstract

A tsunami generated by The Great East Japan Earthquake inundated 3.1 - 5.4 km inland of the lowlying coastal areas of the Tohoku district, Japan, leaving sand and silt deposits over parts of the inundated areas. Applying cluster analysis to the deposits to ascertain their heavy metal compositions, we tried to estimate the tsunami deposit origin and attempted to ascertain their characteristics and distribution based on the shoreline topography and the land use of the backland. Cluster analysis results revealed that most tsunami deposits have similar metal compositions to those of marine sediments. The results suggest dominant marine sediment origin. The tsunami deposits showing soil origin of a unique location were subjected to strong tsunami waves because of the topography of surrounding areas. Moreover, a unique location around a building that disturbed the tsunami wave water currents showed soil origin. The silt contents in tsunami deposits were influenced by differences in tsunami wave water currents attributable to differences in shoreline topography. The metal compositions of tsunami deposits reflected both the mineralogical characteristics of the sediment and pollution profiles of the backland land use.