The seismic waves can be divided into primary, secondary and surface waves. The primary waves are the first ones to reach the surface of the earth after the energy is emitted in the Earth’s interior. Subjected to a ‘P’ wave, particles in the rock move in the direction of waves to and fro and therefore, these waves are also called forward-backward waves. Thus, during an earthquake, the buildings at the foothills of the Himalayas moved forward and backward as they were first subjected to “P” waves.
