The waves that cause earthquakes are called seismic waves. These waves are produced from the focus and radiate outward like ripples produced when a stone is thrown into a pool of water. The waves that radiate generally outward lose energy and finally vanish.

It may be generated by any sudden displacement of the materials. Due to crystals movements, strain energy is converted into elastic wave energy. These type of elastic wave energy are known as seismic waves. On the basis of travelling of wave in the material, it is classified into two types:

a. Body wave

b. Surface wave

Bodywaves can travel directly through a mass of the same material in any direction. It has a short wavelength and high frequency. It is of two types:

                   Primary Wave

                   Secondary Wave

Surface waves can travel only near the surface of the clust or close to border between two different substance. It has long wavelength and low frequency and is responsible for most of destruction.

Inorder to measure intensity of earthquake special device is used.