Tsunami run-up and topography change by the 2011 off the Pacific coast of Tohoku earthquake tsunami in the Hazaki coast

Abstract

The tsunami traces and the topography survey in the Hazaki coast in southern part of Ibaraki Prefecture facing the Pacific Ocean were carried out after the tsunami caused by the 2011 off the Pacific coast of Tohoku earthquake. The tsunami run-up characteristic and topography change before and after tsunami raid on the sandy open coast were examined. In the survey area, the highest tsunami run-up reaches D.L.+10.10 meters, where the beach slopes of sand dune front and surfzone are both steep. The topography change by the tsunami is small because of two factors that the tsunami run-ups do not cross the top of dune and that the beach is not saturated with seawater by only ten times tsunami run-ups.