Students learn about the differences between S-waves and P-waves that move through the inner part of the earth and are created during earthquakes.
S-waves and P-waves, collectively known as body waves, are waves that move through the inner part of the earth and are created during earthquakes.
P-waves (primary waves) are longitudinal or compression waves. When P-waves strike an object they push and pull the object. It's like a train engine bumping into a railroad car, which then bumps into another. This movement continues through the whole length of the train. In solids, these waves travel twice as fast as S-waves. They can also travel through any kind of material. For example, P-waves move at 330 m/s in air, 1,450 m/s in water, and 5,000 m/s in granite.
P-waves are initiated and transmitted when a sudden release of energy compresses rocks near the earthquake focus. As the waves continue on to compress adjacent rocks the initially compressed rocks expand elastically past their original volume. Then they return to their original shape.
S-waves (secondary waves or shear waves) travel more slowly than P-waves. They move the ground in an up-and-down motion, similar to the way waves move in the ocean. They can only move through solids.