P waves travel fastest and are the first to arrive from the earthquake. In S or shear waves, rock oscillates perpendicular to the direction of wave propagation. In rock, S waves generally travel about 60% the speed of P waves, and the S wave always arrives after the P wave.

Which wave travels faster?

Light waves travel much faster than sound waves. Light waves do not need a medium in which to travel but sound waves do. Explain that unlike sound, light waves travel fastest through a vacuum and air, and slower through other materials such as glass or water.

What is the difference in the arrival time between P wave and S wave?

S waves are indicated by an abrupt change in wave amplitude. In the seismogram below, we see that the S wave arrived at about 34 sec after the P wave arrived. This time difference is called the S-P interval and is the lag time between the P and S wave.