Seismic waves are generated due to the release of the energy during an earthquake. They behave differently in different physical mediums and hence provide a good idea how the interior of earth must be.
Broadly there are three types of seismic waves:
Primary waves: (P) – Waves are longitudinal waves. i.e. The motion of particles is in the
direction of the propagation of the wave. These waves are the fastest of the three and are
detected first. They have the shortest wavelength and highest frequency. They can travel in
solid, liquid and gaseous medium.
Secondary waves: (S) – They are transverse waves i.e. the motion of the particles is
perpendicular to the direction of the propagation of the waves. They are slower than P –waves. They have relatively longer wavelength and lower frequency than P – waves. These waves can travel only in solid medium.
Surface waves: they are the slowest and are detected quite late. They travel only in upper layer or earth surface. They are the most destructive of the three waves. Even the surface waves are of two types – the one travelling in upper crust are called LOVE waves and the one travelling in lower crust are called RAYLEIGH waves.