"in the last decade floods,droughts,cyclones, tsunamis and tornadoes are prevalent.a lot of people from different countries of the world have suffered and even died for their cause. earthquakes in our days are more dangerous than in the past,since half the world's population lives in cities.in a serious earthquake happened in Turkey , Greece and Central America . in 2001, the earthquake completely destroyed the city of El Salvador,which at that time was restored to residents after a severe hurricane in 1998