Earthquake is the sudden trembling of earth caused by sudden slippage of rocks along the faults in the crust. The faults are fractures in the rock body along which there has been an observable amount of displacement.
These faults sometimes reach the ground surface displacing the objects on the ground. The Earthquake wave which are produced due to sudden or abrupt deplacement or slippage of rocks travel outward in all directions. Gradually they lose their energy. Thus earthquake is completely crustal phenomenon.
Earthquakes are vibrations in the earth’s crust caused by ruptures and sudden movement’s rocks that are strained beyond their elastic limits of earthquake.
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Focus:
The originating point of earthquake inside the earth’s crust is called focus.
Epicenter:
It is a point on the earth’s surface vertically above the focus. It is this point where trembling is the strongest.
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Major Causes of Earthquakes
Plate Tectonics:
The theory of plate Tectonics postulates that outer lithosphere which is rigid has mosaic of rigid segments called plates. These plates move on the plastic upper mantle (asthenosphere) on which oceans and continents rest. This sometimes causes vibration in the lithosphere resulting in .the occurrence of quake.
Volcanic Eruption:
Sudden volcanic eruptions create vibrations in the earth’s crust causing violent earthquake.
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Major Earthquake Zones:
1. The Circum Pacific Zone – About 66% of total earthquakes have been recorded in this zone.
2. The Mid Atlantic Zone – Divergent plate boundary, Volcanism and sea floor spreading over it make it quake prone.
3. Mid-Continental Zone – This zone extends from Alpine mountain system to Himalaya system.
4. Interplate Earthquake Zone – Indian peninsula is prone to interplate earthquake.