Earthquake occurs when sudden movements take place within and below the Earth's crust. They cause fractures and faults in the crust and the sudden release of built-up stress send shock waves. Tectonic plates then move in sudden jerks.
Shock waves range from slight vibrations which are hardly felt to very strong vibrations which can cause great destruction.
Magnitude of an earthquake can be measured with an instrument called a seismometer, ranges from 0 to 9 on the Richter scale.
Source of the earthquake --> focus
Epicenter --> point on the Earth's surface directly above the focus. It receives the strongest shock waves and therefore, maximum destruction of lives and property.
FACTORS INFLUENCING EXTENT OF DAMAGE
Earthquakes usually occur along plate boundaries, just like volcanic eruptions. Some of the major earthquake zones are :
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