P waves are compression waves while S waves are shear waves. P-waves are usually faster than S-waves (about 60% faster). P and S waves are called body waves because they move through the interior of the earth.
When an earthquake occurs, P and S waves are produced. A seismic recording station an be used to record the arrival of these two waves. Since the P wave is faster than the S wave, hence the P wave would first arrive at the station. The earthquake epicenter can be determined by the difference in time of arrival between the P and S wave.
