Tohoku's Earthquake & Tsunami

Tohoku’s Earthquake & Tsunami

I. Presentation of Tohoku’s disaster

On the 11th of March 2011, within a few hours, Japan faced a triple disaster: an earthquake, followed by a tsunami which caused a nuclear disaster.

This earthquake is however responsible only for few victims and damages thanks to the quality of the Japanese earthquake-resistant constructions. The scale of this disaster results essentially from the tsunami which followed and which is at the origin of more deaths and missing persons, destructions and wounded persons. This tsunami also pulled the nuclear accident of Fukushima, the highest on the international scale of the nuclear events of the nuclear and radiological accidents.

II. Tohoku’s tragedy

a) What is : - an Earthquake ?

An earthquake is translated on surface by vibrations of the ground. It comes from the fracturing of the in-depth rocks; this one is due to the accumulation of a big energy which releases itself, creating weaknesses, as the threshold of mechanical break of rocks is affected. The damages observed on surface are a function of the amplitude, the frequency and the duration of the vibrations. We distinguish earthquakes: of tectonic origin, the most devastating, volcanic origin and human origin (explosions in quarries)

- a Tsunami ?

Marine disaster in which a sudden, enormous and devastating wave is caused by a seismic action, a cyclone, even nuclear weapons, particularly in the Pacific.

In a general way tsunamis are usually generated by big submarine earthquakes (magnitude > 7) little deep (depth 50 km). The intensity of the tsunami will depend at the same time on the magnitude and on the depth of the earthquake: the more the latter is superficial, the more he has a chance to generate an important tsunami.

b) What’s happenned ?

An earthquake of magnitude 9 took place off the coast the of Honshu island at 2:46 pm local time. Its epicenter was situated in 130 kilometers off the city of Sendai and in 32 kilometers deep, in the region of Tohoku, city situated in approximately 300 km in the northeast of Tokyo.

It engendered a tsunami waves of which reached a height estimated at more than 30 m by places. These browsed up to 10 km inside lands, ravaging about 600 km of coast and destroying partially or totally about numerous cities and harbour zones.

This earthquake of magnitude 9 is however responsible only for few victims and damages thanks to the quality of the Japanese earthquake-resistant constructions. The scale of this disaster results essentially from the tsunami which followed and which is at the origin of more than 90 % of 18 079 deaths and missing persons, destructions