Whenever the earth is suddenly struck or disturbed due to earthquake vibration are produced. These vibrations are setup or start from a limited area and are propagated outward in all directions. Thus an earthquake may be defined as the passage of these vibrations in the earth.
Details of Seismic Secondary Waves are:
1) Nature: These are transverse or distortional in nature. Therefore it is known as transverse waves, shear waves or shake waves.
2) Direction of Particle Vibration: The rock particles vibrate at right angles to the direction of propagation like light waves.
3) Speed: These travel slower than the P-waves and are second to be recorded.
4) Example: In granites, S-waves have speed of about 3 km/sec.
5) Penetration capacity: These can pass through solids but it is in capable of passing through liquids.