Exposé Anglais Tsunamis

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Exposé anglais (english exposed) sur les Tsunamis

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Exposé Anglais Tsunamis

  1. 1. TSUNAMIS www.jexpoz.com
  2. 2. CONTENTS <ul><li>Introduction </li></ul><ul><li>I – Formation & propagation of a tsunami </li></ul><ul><li>II – Dangers related to tsunamis and Prevention </li></ul><ul><li>III – Physical characteristics </li></ul><ul><li>Conclusion </li></ul>
  3. 3. Introduction <ul><li>A tsunami is a series of waves </li></ul><ul><li>Causes: Earthquakes, landslides, meteorite impacts, underwater explosions, … </li></ul><ul><li>Not created by the wind </li></ul>
  4. 4. I – a) Definition <ul><li>Comes from the Japanese words meaning harbor (“tsu”) and wave (“nami”) </li></ul><ul><li>small amplitude but very long wavelength </li></ul><ul><li>generally pass unnoticed in open water </li></ul>
  5. 5. <ul><li>BEFORE </li></ul><ul><li>AFTER </li></ul>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.
  6. 6. I – b) Generation of Tsunamis <ul><li>mainly by seisms </li></ul><ul><li>sometimes by underwater landslides </li></ul><ul><li>more rarely by volcanic eruptions </li></ul><ul><li>exceptionally by the impact of a meteorite </li></ul><ul><li>The seisms with not very deep hearth located along the subduction zones generated destroying tsunamis </li></ul>
  7. 7. I – c) Propagation <ul><li>tsunami reaches a few tens of centimetres height in open water but increases quikly nearing the coast </li></ul><ul><li>the energy of the tsunami goes always from surface to the sea-bed </li></ul><ul><li>exceptional withdrawal of the sea must be taken as a warning of the waves of tsunami which will succeed </li></ul>
  8. 8. This picture shows the Kalutra’s beach in an ordinary situation
  9. 9. ← + 300 m -> Between the various waves, the sea is withdrawn on more than three hundred meters by carrying all on its passage.
  10. 10. The wave caused by the Tsunami is withdrawn by training violent one swirls of water.
  11. 11. II – a) Damage <ul><li>can destroy dwellings, infrastructures and the vegatation </li></ul><ul><li>penetrate in the grounds and destroys the fields and harvests </li></ul><ul><li>can destroy installations which contain toxic products (pollution) </li></ul><ul><li>risk of epidemic (cholera, diphteria,…) </li></ul>
  12. 12. All the dwellings on the coast were destroyed
  13. 13. 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
  14. 14. 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
  15. 15. <ul><li>BEFORE </li></ul><ul><li>AFTER </li></ul>At Banda Aceh, most of the residentials district was devastated by the Tsunami.
  16. 16. II – b) Human loses <ul><li>victims carried by a tsunami can be projected violently </li></ul><ul><li>victims can also be trapped under the destroyed dwellings </li></ul><ul><li>After tidal wave than the wave itself can be mortal ( putrefaction of corpses, contamination of drinking water, the time limitation of food ) </li></ul>
  17. 17. Provisional assessment after the Tsunami <ul><li>178 132 dead including at least 3 049 foreigners </li></ul><ul><li>43 914 disappeared including 37 066 considered dead </li></ul><ul><li>15 428 wounded </li></ul><ul><li>1 003 200 moved people </li></ul>
  18. 18. II – c) Prevention <ul><li>alarm system allowing to alert the population </li></ul><ul><li>sensibilisation to the risks and the gestures of survival </li></ul><ul><li>security of the habitat </li></ul><ul><li>two clues : - fast and unexpected withdrawal of the sea </li></ul><ul><li> - earthquakes </li></ul>
  19. 19. To Prevent To alert
  20. 20. III – a) Wavelength <ul><li>higher than the hundred kilometers </li></ul><ul><li>depends on the period T and depth on water h according to the relation : </li></ul><ul><li>λ = T*sqrt(g*h) </li></ul><ul><li>where g = 9,81 m.s-2 (gravity) </li></ul><ul><li>can reach 870 km (tectonic origins) </li></ul>
  21. 21. III – a) Propagation velocity <ul><li>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 : </li></ul><ul><li>v = sqrt(g*h) </li></ul>
  22. 22. Velocity propagation of the Tsunami
  23. 23. III – b) Amplitude <ul><li>A ~ E^(1/2)*r^(-1/2)*h^(-1/4) </li></ul><ul><li>where E > energy </li></ul><ul><li>r > distance </li></ul><ul><li>Stockes’ current : </li></ul><ul><li>u = [A²/(2h²)]*v </li></ul>
  24. 24. Some Videos
  25. 25. Conclusion and … <ul><li>Tsunamis are mainly generated by earthquakes </li></ul><ul><li>Small amplitude in open water but very long wavelength </li></ul><ul><li>Characterized by an exceptional withdrawal of the sea </li></ul>
  26. 26. … the most important points <ul><li>Great velocity and amplitude nearing the coast </li></ul><ul><li>Speak about natural disaster but also about ecological catastrophe ( lots of damages & victims) </li></ul><ul><li>Sensibilisation & alarm system can reduce the number of victim </li></ul>
  27. 27. <ul><li>http://www.clg-caillols.ac-aix-marseille.fr/sismo/seismes/20041226/anim/anim.htm </li></ul>www.jexpoz.com

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