what are the types of seismic waves?

Seismic waves are considered to be the outcome of the elastic deformation of the rocks. When the stress acting on the rock exceeds its elastic limit and at the point of maximum stress it suddenly slip off or deformed releasing the energy instantaneously in the form of waves. These waves travel from the point of initiation up to surface of the earth causing vibration. So, these energy waves are called seismic waves. On the basis of amplitude , wavelength and nature of vibration of the seismic waves there are two types of seismic waves:

 1) BODY WAVES 

a) Primary waves/ P –waves: Primary waves are also called longitudinal or compressional waves like sound waves. Here rocks vibrate parallel to the direction of wave propagation i.e. in the same direction as the waves are travelling. These wave travels in all medium i.e. solid, liquid and gas. And they have high velocity but short wave length. It is considered that primary wave travels at 1.7 faster the speed of S- waves such that they are the first wave to arrive at a point distance from the place of origin of earthquake.

 b) Secondary waves / S-waves: These are also called transverse waves. In this case, the rocks vibrate perpendicular to the direction of wave propagation. These waves are also called shear waves due to their capacity of changing the shape of a material without changing its volume. Their important property is that they can only travel in solid media. As liquid and gas lacks rigidity or resistance to change in form due to which shear waves are not propagated through these substances. These wave have short wavelength and high frequency due to which it is responsible for the shaking of the earth’s surface. So, these two waves are being the body wave travel or propagate only inside the surface of the earth’s crust causing the shaking of the earth surface. 

 2) Surface waves : These waves are generated due to the energy brought by body waves to the surface .And only propagate along the surface of the earth’ crust due to which they are called surface waves. Generally there are two types of surface waves:

 a) Reyleigh waves : These waves travel near the surface of solid. They have both longitudinal and transverse motion. These waves have low velocity and its amplitude gradually decreases when they travel more distance due to their characteristic propagation.

 b) Love waves : These waves are considered to be the most destructive waves as they causes shearing of the surface. They cause side to side movement of the surface causing more damage as their speed is considered to be more than reyleigh waves.