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An earthquake is the result of a sudden release of energy in the earth's crust that creates seismic wave. Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity,landslides, mine blasts and nuclear tests.
Earthquakes are recorded using seismometers and magnitude of the earthquake is measured by the Richter scale. The largest earthquakes in historic times have been magnitude slightly over 9. It is estimated that around 500,000 earthquakes occur each year, detectable with current instrumentations. About 100,000 of these can be felt. Most of the world's earthquakes (81% of the largest) take place in the 40,000 km long zone called the cirum-paific seismic belt known as the Pacific Plate. Massive earthquakes tend to occur along other plate boundaries too, such as along Himalayan Mountains.
At the earth's surface,earthquakes manifest themselves by shaking and sometimes displacement of the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides and occasionally volcanic activity.Earthquake cannot occur as a result of-