Japanese study reveals cause of unusual destructive power of 2011 tsunami
Five years after a devastating tsunami struck northwestern Japan, a study has revealed its unusual destructive power was due to its first waves which swept the beaches and the seabed, facilitating the subsequent rush.
A team of researchers from the International Research Institute of Disaster Science of Tohoku University, led by Prof. Fumihiko Imamura, has simulated the tsunami’s impact on the geographical features of the area using a supercomputer.
In the computergenerated images given to EFE Wednesday by the institution, a counter running at full speed shows the secondbysecond evolution of the arrival of the waves and simulates how the powerful torrent of water inundates the coasts at a greater speed than usual.
In Iwate prefecture’s Rikuzentakata city, the first onslaught by the tsunami swept massive amounts of sand from the beaches, which reduced coastal resistance and friction and allowed subsequent waves to rapidly engulf the coast, the team told public broadcaster NHK.
The simulation shows that the giant waves caused by the powerful 9magnitude earthquake which rocked the country on Mar. 11, 2011, reached the center of the city 30 seconds faster than it would have under normal circumstances.
The city registered waves of up to 13 meters (43 feet) high, one meter (3 feet) higher than what would have been expected if the sand and the mud had blocked the tsunami, according to the study.
In the simulation one can also see the second wave advancing at a speed twice that of a conventional wave, dragging buildings and cars into the sea.
In the city of Kesennuma of Miyagi prefecture, the first waves swept massive amounts of underground mud from a narrow gulf, lowering the sea level and allowing successive waves to hit the banks more quickly.
The study indicates it is likely that, because of this, subsequent tsunamis pushed large fishing vessels docked at the port into inland areas and the debris floating in the water helped trigger large fires.