The honor of greatest earthquake of all time goes to the 1960 Chile earthquake because scientists were able to 'catch this one on tape'.In other words, there have been a lot of really big earthquakes throughout human history (and even greater ones before we came on the scene), but this one they were able to measure, record and verify its ground motion strength. The instruments that seismologists use to measure earthquake magnitudes are designed to detect the amount of energy released by the movement of the ground during a quake. In the case of the Chile earthquake, the amount of energy released during the quake, not the number of human deaths and damage to structures, earned it the title of greatest.
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
7 years ago