Science of Tsunami Hazards (Apr 2023)
TSUNAMI DESTRUCTION IN JAPAN CANNOT BE PREVENTED WITH USE OF EXISTING SEAWALLS – Case Study: The Great Tsunami of 11 March 2011
Abstract
A megathurst magnitude 9.0–9.1 (Mw),underseaearthquake on 11 March 2011 off Japan’s Tohoku region on the Pacific coast, generated massive tsunami waves. Extremely high waves and the resultant debris flow overtopped and destroyed the existing seawalls which offered little or no protection, thus resulting in thousands of deaths and causing extensive destruction of coastal facilities, including the Fukushima Daiichi nuclear plant. The tsunami destroyed easily the tidal gates on the roads connecting the port to the town, and since there was no seawall protection on the tsunami’s path on rivers, there was also extensive inland damage upstream, as the waves striking over river banks reverted river flows, thus causing the water to rise and form even higher waves with greater inland inundation. Even weak tsunamis striking a river outlet on a coast can generate a high- volume river water flow reversal and potentially cause substantial damage upstream. The present government tsunami countermeasures in Japan for such river areas are unable to prevent such enhancement of tsunami damage and to provide adequate protection for inland areas.
