Exposé Anglais Tsunamis

Slide 1: TSUNAMIS www.jexpoz.com

Slide 2: CONTENTS • Introduction • I – Formation & propagation of a tsunami • II – Dangers related to tsunamis and Prevention • III – Physical characteristics • Conclusion

Slide 3: Introduction • A tsunami is a series of waves • Causes: Earthquakes, landslides, meteorite impacts, underwater explosions, … • Not created by the wind

Slide 4: 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

Slide 5: 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.

Slide 6: 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

Slide 7: 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

Slide 8: This picture shows the Kalutra’s beach in an ordinary situation

Slide 9: Between the various waves, the sea is ← + 300 m → withdrawn on more than three hundred meters by carrying all on its passage.

Slide 10: The wave caused by the Tsunami is withdrawn by training violent one swirls of water.

Slide 11: 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,…)

Slide 12: All the dwellings on the coast were destroyed

Slide 13: The scale of Soloviev Intensity Characteristics of the wave 1 very light, the wave is weak, perceptible only on the marigraphs light, the wave is noticed by the familliers of the sea on 2 the very flat shores enough strong, the wave floods the soft inclined coasts, the light 3 boats are failed strong, the shore is flooded, constructions on the 4 coast are degraded very strong, general flood, destruction of the 5 buildings, losses human disastrous, destruction of the structures, general flood, many 6 victims, damage with the ships

Slide 14: The Scale of Imamura & Iida Magnitude Height of the Damage Height of the strongest waves waves -1 - 10 cm -1m None 0 ~ 10 cm 1m No prejudice Damage to houses & ships 1 25 cm 2m Destruction of ships and 2 50 cm 4-6 m losses human ~ destruction of the coasts 3 1m 10-20m on approximately 200 km ~ destruction of the coasts 4 2m + 50 m on approximately 500 km

Slide 15: BEFORE AFTER At Banda Aceh, most of the residentials district was devastated by the Tsunami.

Slide 16: 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 )

Slide 17: 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

Slide 18: 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

Slide 19: To Prevent To alert

Slide 20: 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)

Slide 21: 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)

Slide 22: Velocity propagation of the Tsunami

Slide 23: III – b) Amplitude A ~ E^(1/2)*r^(-1/2)*h^(-1/4) where E > energy r > distance • Stockes’ current : u = [A²/(2h²)]*v

Slide 24: Some Videos

Slide 25: 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

Slide 26: … 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

Slide 27: http://www.clg-caillols.ac-aix- marseille.fr/sismo/seismes/20041226/anim /anim.htm www.jexpoz.com