Examination of relation with tsunami behavior reconstructed from on-site sequence photographs, topography, and sedimentary deposits from the 2011 Tohoku-oki tsunami on the Kamikita Plain, Japan

This report presents an examination of tsunami behavior for the Misawa coast of northeastern Japan based on interpretations of sequential digital photographs of the 2011 Tohoku-oki tsunami, spatial distribution of tsunami deposits, and topographical conditions reconstructed using the Digital Elevation Model (DEM). In the study area, run-up flow and then backwash flow occurred only once. Run-up flow reached maximum inundation height several minutes after tsunami flooding started. Topographic features such as terraces, dissected valleys, coastal lowlands, and artificial seawall constrained the tsunami flow. The sandy tsunami deposit distribution is limited to several hundred meters from the shoreline. Deposits show inland thinning and fining. They also indicate thinning and fining in the direction of higher surfaces. Thick deposits, which are distributed locally in the basin area between the beach ridge and the seawall, exhibited multiple layers of inverse and normal grading formed by repeated acceleration and deceleration for several minutes during the run-up flow. In the area with concentrated backwash flow after the tsunami struck, the sedimentation for tsunami deposits was affected not only by the run-up flow, but also by the backwash flow.