Earthquakes are caused by the movement of tectonic plates underneath the earth's surface. When stress builds between plates and is suddenly released, seismic waves propagate from the hypocenter or focus outward. Primary waves arrive first and are followed by more destructive secondary waves. The magnitude of an earthquake is measured to indicate its strength and potential damage, from small localized tremors to catastrophic quakes that can destroy buildings. It is important to improve construction practices, implement education and evacuation plans, and understand seismic risks to minimize harm from earthquakes.

1. EARTHQUAKES Presented by Georgios Patrinos

2. OUTLINE Introduction Causes of earthquakes Description of initial earthquake development Analysis of seismic waves Magnitude of an earthquake Interview with people that survived the catastrophic effects of big earthquakes Recommendations Conclusions

3. INTRODUCTION No natural phenomenon creates more fear and insecurity than an earthquake . Every day thousands of earthquakes occur . Researchers (Charles Richter, Lord Rayleigh) have investigated the nature of earthquakes

4. Causes of earthquakes The earth is surrounded by a hard layer of rocks. This layer, which has an average width of 80 km (and includes a part of the upper mantle), is called the Lithosphere. Lithosphere separated into different parts which are called lithospheric plates. Under the lithosphere the material is semi liquid and forms a layer called the asthenosphere.

5. Causes of earthquakes Divergent plate boundaries Convergent plate boundaries Transcurrent plate boundaries

6. Description of initial earthquake development When the stresses become too great so as to overcome the strength of the lithosphere material in this area, the rock breaks and a seismic fault is created.

7. Description of initial earthquake development Focus of the earthquake. Epicenter. Focus depth

8. Analysis of seismic waves Primary waves (P) Less catastrophic Transfer relatively small amount of energy secondary waves (S) The most dangerous Transfer great amounts of energy

9. Analysis of seismic waves Rayleigh waves Love waves

10. Magnitude of an earthquake Widespread destruction 9 Even special, earthquake-resistant buildings will be badly damaged. 8 This earthquake is strong enough to destroy even well-built structures 7 Strong enough to badly damage average buildings 6 A strong vibration shakes the earth, damaging chimneys and weak buildings. 5 Widely felt and is strong enough to crack plaster. 4 Damage Magnitude

12. Recommendations In view of the above the following recommendations are outlined : Improvements on antiseismic legislation and technology . Study of the seismic activity and the terrain of the area are obligatory Education and action plans to minimise the risk of an earthquake’s aftermath. Evacuation plans , emergency exercises .

13. Bibliography Bolt, B.A. (1993) Earthquakes USA: W.H. Freeman and Company Bolt, B.A. (1993) Earthquakes And Geological Discovery USA: W.H. Freeman and Company Coburn, A. and R. Spence, (1992) Earthquake Protection UK: John Wiley & Sons Ltd

14. Further References 1. U.S. Geological Survey (1997) Earthquake s.Retrieved August 20, 2006, from World Wide Web http://pubs.usgs.gov/gip/earthq1/intro.html 2. Glasscoe, M. (1998, 13th August) Space technology is used to observe and measure tectonic motion of the Earth's surface. Retrieved August 20, 2006, from World Wide Web http:// scign.jpl.nasa.gov/learn/index.htm 3. Encyclopedia Britannica (2006) Earthquake . Retrieved August 20, 2006, from World Wide Web http://www.britannica.com/eb/article-9106195 4. U.S. Geological Survey Earthquake Hazards Program (2006). Retrieved August 20, 2006, from World Wide Web http:// earthquake.usgs.gov/eqcenter/dyfi.php 5. Wikipedia, The Free Encyclopedia (2006) Earthquake . Retrieved August 20, 2006, from World Wide Web http:// en.wikipedia.org/wiki/Earthquake