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Why earthquake are happening?? Whenever an earthquake of any size happens anywhere in the world the same basic thing happens; the ground along either side of a fault (a fracture or crack in the ground) moves. Faults are cracks in the earth caused by buckling and stress from the movement of the tectonic plates.
Although earthquake is purely a natural disaster unlike drought which is related to global warming, earthquake caused a lot damage to structures and as well to human's life and caused billions or dollar of damage annually. I am impressed with Japan's technology to minimise damage from earthquake. Being a war tore country in 1940's, now Japan's earthquake disaster system is the best in the world and most of the building it the Japan are capable of resisting earthquake of 5 Richter scale and above.
Source : http://www.extremescience.com/GreatestEarthquake.htm