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CONTENTS Introduction I – Formation & propagation of a tsunami II – Dangers related to tsunamis and Prevention III – Physical characteristics Conclusion

Introduction

I – Formation & propagation of a tsunami

II – Dangers related to tsunamis and Prevention

III – Physical characteristics

Conclusion

Introduction A tsunami is a series of waves Causes: Earthquakes, landslides, meteorite impacts, underwater explosions, … Not created by the wind

A tsunami is a series of waves

Causes: Earthquakes, landslides, meteorite impacts, underwater explosions, …

Not created by the wind

I – a) Definition Comes from the Japanese words meaning harbor (“tsu”) and wave (“nami”) small amplitude but very long wavelength generally pass unnoticed in open water

Comes from the Japanese words meaning harbor (“tsu”) and wave (“nami”)

small amplitude but very long wavelength

generally pass unnoticed in open water

BEFORE AFTER These images make it possible to realize the power of the Tsunami. The violence of the wave has totally destroyed a whole part of the shore which sheltered the port.

BEFORE

AFTER

I – b) Generation of Tsunamis mainly by seisms sometimes by underwater landslides more rarely by volcanic eruptions exceptionally by the impact of a meteorite The seisms with not very deep hearth located along the subduction zones generated destroying tsunamis

mainly by seisms

sometimes by underwater landslides

more rarely by volcanic eruptions

exceptionally by the impact of a meteorite

The seisms with not very deep hearth located along the subduction zones generated destroying tsunamis

I – c) Propagation tsunami reaches a few tens of centimetres height in open water but increases quikly nearing the coast the energy of the tsunami goes always from surface to the sea-bed exceptional withdrawal of the sea must be taken as a warning of the waves of tsunami which will succeed

tsunami reaches a few tens of centimetres height in open water but increases quikly nearing the coast

the energy of the tsunami goes always from surface to the sea-bed

exceptional withdrawal of the sea must be taken as a warning of the waves of tsunami which will succeed

This picture shows the Kalutra’s beach in an ordinary situation

← + 300 m -> Between the various waves, the sea is withdrawn on more than three hundred meters by carrying all on its passage.

The wave caused by the Tsunami is withdrawn by training violent one swirls of water.

II – a) Damage can destroy dwellings, infrastructures and the vegatation penetrate in the grounds and destroys the fields and harvests can destroy installations which contain toxic products (pollution) risk of epidemic (cholera, diphteria,…)

can destroy dwellings, infrastructures and the vegatation

penetrate in the grounds and destroys the fields and harvests

can destroy installations which contain toxic products (pollution)

risk of epidemic (cholera, diphteria,…)

All the dwellings on the coast were destroyed

The scale of Soloviev Intensity Characteristics of the wave 1 very light, the wave is weak, perceptible only on the marigraphs 2 light, the wave is noticed by the familliers of the sea on the very flat shores 3 enough strong, the wave floods the soft inclined coasts, the light boats are failed 4 strong, the shore is flooded, constructions on the coast are degraded 5 very strong, general flood, destruction of the buildings, losses human 6 disastrous, destruction of the structures, general flood, many victims, damage with the ships

The Scale of Imamura & Iida Magnitude Height of the waves Height of the strongest waves Damage - 1 - 10 cm - 1 m None 0 ~ 10 cm 1 m No prejudice 1 25 cm 2 m Damage to houses & ships 2 50 cm 4-6 m Destruction of ships and losses human 3 ~ 1 m 10-20m destruction of the coasts on approximately 200 km 4 ~ 2 m + 50 m destruction of the coasts on approximately 500 km

BEFORE AFTER At Banda Aceh, most of the residentials district was devastated by the Tsunami.

BEFORE

AFTER

II – b) Human loses victims carried by a tsunami can be projected violently victims can also be trapped under the destroyed dwellings After tidal wave than the wave itself can be mortal ( putrefaction of corpses, contamination of drinking water, the time limitation of food )

victims carried by a tsunami can be projected violently

victims can also be trapped under the destroyed dwellings

After tidal wave than the wave itself can be mortal ( putrefaction of corpses, contamination of drinking water, the time limitation of food )

Provisional assessment after the Tsunami 178 132 dead including at least 3 049 foreigners 43 914 disappeared including 37 066 considered dead 15 428 wounded 1 003 200 moved people

178 132 dead including at least 3 049 foreigners

43 914 disappeared including 37 066 considered dead

15 428 wounded

1 003 200 moved people

II – c) Prevention alarm system allowing to alert the population sensibilisation to the risks and the gestures of survival security of the habitat two clues : - fast and unexpected withdrawal of the sea - earthquakes

alarm system allowing to alert the population

sensibilisation to the risks and the gestures of survival

security of the habitat

two clues : - fast and unexpected withdrawal of the sea

- earthquakes

To Prevent To alert

III – a) Wavelength higher than the hundred kilometers depends on the period T and depth on water h according to the relation : λ = T*sqrt(g*h) where g = 9,81 m.s-2 (gravity) can reach 870 km (tectonic origins)

higher than the hundred kilometers

depends on the period T and depth on water h according to the relation :

λ = T*sqrt(g*h)

where g = 9,81 m.s-2 (gravity)

can reach 870 km (tectonic origins)

III – a) Propagation velocity For the tsunamis of sufficiently long period, typically ten minutes, the speed ν of displacement of a tsunami is a function only depth of water h : v = sqrt(g*h)

For the tsunamis of sufficiently long period, typically ten minutes, the speed ν of displacement of a tsunami is a function only depth of water h :

v = sqrt(g*h)

Velocity propagation of the Tsunami

III – b) Amplitude A ~ E^(1/2)*r^(-1/2)*h^(-1/4) where E > energy r > distance Stockes’ current : u = [A²/(2h²)]*v

A ~ E^(1/2)*r^(-1/2)*h^(-1/4)

where E > energy

r > distance

Stockes’ current :

u = [A²/(2h²)]*v

Some Videos

Conclusion and … Tsunamis are mainly generated by earthquakes Small amplitude in open water but very long wavelength Characterized by an exceptional withdrawal of the sea

Tsunamis are mainly generated by earthquakes

Small amplitude in open water but very long wavelength

Characterized by an exceptional withdrawal of the sea

… the most important points Great velocity and amplitude nearing the coast Speak about natural disaster but also about ecological catastrophe ( lots of damages & victims) Sensibilisation & alarm system can reduce the number of victim

Great velocity and amplitude nearing the coast

Speak about natural disaster but also about ecological catastrophe ( lots of damages & victims)

Sensibilisation & alarm system can reduce the number of victim

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http://www.clg-caillols.ac-aix-marseille.fr/sismo/seismes/20041226/anim/anim.htm