Abstract
Field coastal forests surveys were conducted in Miyagi Prefecture, which was inundated by the mega tsunami associated with the 2011 earthquake off the Pacific coast of Tohoku. In the field, standing and fallen trees were judged; and the tsunami depths, tree-trunk diameters, and tree heights were measured. Based on the relation between the tsunami inundation depth and the tree-trunk diameter, the tilting limit condition was determined. It was critical in determining whether the trees remained standing or fell. The tilting limit condition agrees well with the result that was obtained by a survey conducted on 184 forest trees by the Miyagi Prefecture Forestry Promotion Association. The effect of the growth of the ground soil property (sand- and gravel-based soils) of trees on the tilting limit condition was discussed. When the data for standing and fallen trees obtained from the relation between the tsunami inundation depth and tree diameter were plotted, the survey data was found to be one of the reasons for the scatter. It was also confirmed that the characteristics of the growing soil of trees had a considerable effect on the tilting limit of trees.
