As the P and S waves travel out from an earthquake the P waves get progressively farther ahead of the S waves. Therefore, the farther a seismic recording station is from the earthquake epicenter the greater will be the difference in time of arrival between the P and S wave.
Because of their wave movement, P waves travel through any kind of material, whether it is a solid, liquid or gas. On the other hand, S waves only move through solids and are stopped by liquids and gases.
