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J Miguel Miranda CGUL / IDL

J Miguel Miranda CGUL / IDL. “Tsunamis, earthquakes, hurricanes, volcanoes and other natural disasters now pose a greater global threat than war and terrorism. Finding ways of reducing the impact of natural disasters is vital.”

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J Miguel Miranda CGUL / IDL

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  1. J Miguel MirandaCGUL / IDL

  2. “Tsunamis, earthquakes, hurricanes, volcanoes and other natural disasters now pose a greater global threat than war and terrorism. Finding ways of reducing the impact of natural disasters is vital.” The European Commission supports the UN Disaster Reduction Conference in Kobe - IP/05/51- Brussels, 17 January 2005 Earthquakes with less then 30,000 victims

  3. Why the phocus on natural hazards suddenly developed ? 1883, Krakatoa 1992, Ilha Flores 2004, Sumatra 1946, Havai

  4. In the Iberian geo-environment tsunamis are rare (but violent) phenomena. Historical (red stars) and instrumental (black dots) events.

  5. Even Atlantis is “located” here and there are large historical traditions. Plato wrote about the destruction of the legendary city - new evidence suggests he was writing about a devastating tsunami: "There occurred violent earthquakes and floods...the island of Atlantis disappeared in the depths of the sea." That was how Greek philosopher Plato described the destruction of the legendary city. "... nor could the martial tribes of the Lusitanians and Cantabrians escape; no more could the ocean, with its tide (the ebb-tide, ebb and flow), which yet was terrible to the ancient inhabitants; at least, until where the Pillars of Hercules extend..." (FLAVIO JOSEPHUS Memories, translated by Georgeos Díaz-Montexano, 2002)

  6. The 1st November 1755 earthquake and tsunami started modern hazard studies.

  7. Monitoring and Warning versus Hazard and Risk assessments.

  8. Where do they come from? EARTHQUAKES LANDSLIDES EARTHQUAKES EARTHQUAKES LANDSLIDES LANDSLIDES

  9. What are the most important parameters ? • > The maximum wave elevation (MWE); • The maximum run-up • The maximum run-in • The velocity and the flow depth

  10. What are the relevant processes for tsunami impact ? ELASTIC DEFORMATION Okada EHS equations SHALLOW WATER RUN UP

  11. If the source is known the propagation can be accurately computed

  12. If the source is known the propagation can be accurately computed

  13. How to compute tsunami hazard in SW Iberia? • Determinist approach: the worst case (easy in the case of the stronger yet credible event). However, • we need for probability descriptions (can tsunamis risk be mitigated by intervention on the “building code” side?) • How rare are tsunamis? How can we characterize the occurrence model?

  14. What are the main phenomena ? LANDSLIDES EARTHQUAKES Efficiency SEA SURF DISTURBANCE PROPAGATION Model reliability COASTAL INTERACTION + TIDES PEOPLE + CONSTRUCTION + ...

  15. Deterministic Tsunami Hazard Approach • The case of the stronger yet credible event for the UK (DEFRA study). Variability of hazard is only a function of local morpological conditions.

  16. What can be learned from earthquake statistics? In case tsunami sources are far away from the risk areas run-up is mainly a function of local topography and if earthquakes are the main tsunami generation mechanism we can build a statistical model using a more common phenomenon (earthquakes). Gutenberg Richter relationship: Not all earthquakes generate tsunamis Earthquakes with M>=5

  17. What can be learned from earthquake statistics?

  18. Observations follow always a GR-like relationship?

  19. What is the physical mechanism ?

  20. Probabilistic seismic hazard assessment? GENERATION ATTENUATION SITE EFFECTS

  21. Probabilistic seismic hazard assessment? Cornell’s approach is based on the assumption that the probability of excedance of an effect Y in a study area can be obtained by adding the effect of all possible seismogenic contributions Chosing as random variables the magnitude and hipocentral distance Assuming that earthquake generation follows an homogeneous Poisson process; If atenuation is given by; We have for a specific place:

  22. The homogeneous source areas

  23. What are the main results of PSHE ?

  24. Probability tsunami hazard evaluation (PTHE) In case tsunami wave heights can be predicted (as a consequence of seismic hazard or independently) than inundation and associated effects can be predicted by deterministic numerical simulation. Ex for Oregon in http://pubs.usgs.gov/ds/2006/236/figures/f_100-500cont.shtml

  25. Can we forget the source ? Extreme value theory ?

  26. PTHE must be meaningfull • DIscriminate between different levels of danger to people and goods; • Allow the design of mitigation strategies, including land management rules; • Allow the design of building codes;

  27. THANKS !

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