When an earthquake occurs, the shockwaves of released energy that shake the Earth and temporarily turn soft deposits, such as clay, into jelly (liquefaction) are called seismic waves, from the Greek’seismos’ meaning ‘earthquake’. Seismic waves are usually generated by movements of the Earth’s tectonic plates
P-waves
Primary waves or pressure waves
- Travel at the greatest velocity through the Earth
- Different from S-waves in that they propagate through a material by alternately compressing and expanding the medium
- They travel at the speed of sound (330 ms-1) through air but may travel at 5000ms-1 in granite
What can seismic waves tell us?
Seismologists can use the direction and the difference in the arrival times to determine the distance to the source of an earthquake
- If seismographs are too far away from the event to record S-waves, several recordings of P-waves can be crunched in a computer program to give an approximate location of the source
S-waves
These are transverse waves that travel slower than P-waves but have larger amplitudes.
- They cannot travel through air or water but are more destructive than other types of waves because of their larger amplitude and direction of propagation (i.e., shear waves).
Surface waves
These are similar in nature to water waves and travel just under the Earth’s surface.
- There are two basic kinds of surface waves: Rayleigh waves, also called ground roll, travel as ripples similar to those on the surface of water, and Love waves, cause horizontal shearing of the ground.
