A tsunami is a wave provoked by a rapid movement of a large volume of water (ocean or sea). This movement is generally due to an earthquake, to a explosive submarine volcanic eruption or to a large-scale submarine landslide. A meteorite impact can also be the cause, as well as a submarine atomic explosion. Thus a tsunami is not created by the wind. To avoid false association with tides and to overcome the vagueness of the term of tidal wave, scientists prefer the word tsunami, officialized in 1963 to describe such phenomena. The term is also used in everyday language.
Degree 1 : Very light. Wave so weak as to be perceptible only on tide-gauge records
Degree 2 : Light. Wave noticed by those living along the shore and familiar with the sea. On very flat shores generally noticed
Degree 3 : Rather strong. Generally noticed. Flooding of gently sloping coasts. Light sailing vessels or small boats carried away on shore. Slight damage to light structures situated near the coast. In estuaries reversal of the river flow some distance upstream
Degree 4 : Strong. Flooding of the shore to some depth. Light scouring on man-made ground. Embankments and dikes damaged. Light structures near the coasts damaged. Solid structures on the coast injured. Big sailing vessels and small ships carried inland or out to sea. Coasts littered with floating debris
Degree 5 : Very strong. General flooding of the shore to some depth. Breakwater walls and solid structures near the sea damaged. Light structures destroyed. Severe scouring of cultivated land and littering of the coast with floating items and sea animals. With the exception of big ships all other type of vessels carried inland or out to sea. Big bores in estuary rivers. Harbour works damaged. People drowned. Wave accompanied by strong roar
Degree 6 : Disastrous. Partial or complete destruction of man-made structures for some distance from the shore. Flooding of coasts to great depths. Big ships severely damaged. Trees uprooted or broken. Many casualties
Degree Not specified : (when codes A, B and C are alone, without value. That means that the tsunami is just noticed in a town. No other precision)
This site is subject to written documentation detailing the effects of historical tsunamis.
If the provision of relevant literature is achieved by an annual State of the update, the site also in agreement with the Archives of France a number of documents scanned and available online subject to duties reproduction.
Source : BRGM / tsunamis.brgm.fr
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