Relationships between seismic intensities and damages to earth dams for irrigation during the 2011 Offshore Pacific Coast Tohoku Earthquake

摘要

The 2011 Offshore Pacific Coast Tohoku Earthquake, with a moment magnitude (M) of 9.0, damaged a large number of agriculture facilities in Tohoku and Kanto areas. In this study, in order to clarify factors related to the damages of facilities, especially earth dams, which are one of the most important facilities in the irrigation of Japan, we analyzed relationships between damage costs, relative locations to the epicenter and seismic intensities. In the process, we introduced some indexes: damage density, mean and 1 km mesh seismic intensities, and damage ratio for earth dams and angle of dam axis with respect to the epicenter. It was found from the analysis that damages by the Tsunami and by earthquake motions were clearly identified by the damage density; the damages by Tsunami were approximately 40 times higher than for earthquake motions; the damage densities in earth dams increased with an increase in seismic intensities; and when the dam axes were normal to the epicenter, the damages of dams were likely to be large.