The originating point of earthquake inside the earth’s crust is called focus.
It is a point on the earth’s surface vertically above the focus. It is this point where trembling is the strongest.
Major Causes of Earthquakes
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.
Sudden volcanic eruptions create vibrations in the earth’s crust causing violent earthquake.
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.