The imbalance in internal structure of earth causes earthquake. This imbalance can also be caused by pressure from natural or man-made aquifers and also by explosion. Earthquake is usually explained on the basis of tectonic movement theory.

Earth’s crust is composed of 29 tectonic plates. Six of the tectonic plates are most important. These plates keep on moving at very slow pace. All kinds of moulding activities take place along the edges of these plates. Boundaries of tectonic plates are of three types, viz. transform boundary, divergent boundary and convergent boundary. Transform boundary is conservative in nature, divergent boundary is constructive and convergent boundary is destructive. Highly destructive earthquake happen due to convergent or destructive boundaries. Collision of plates is considered as the prime reason of earthquakes in northern India, Tibet and Nepal. Earthquakes also happen due to other kinds of boundaries of tectonic plates but it is difficult to explain such earthquakes.