Seismic Waves Explained: P, S, and Surface Waves

Every earthquake releases energy as seismic waves, and each type behaves differently as it races through the planet.

Primary Waves

Primary waves travel fastest and pass through both solids and liquids, arriving first at a seismograph. They compress and stretch the ground like a spring.

Secondary Waves

Secondary waves follow, shaking the ground side to side, and they cannot travel through liquid at all. Their absence through the outer core was the key evidence that it is molten.

Surface Waves

Surface waves arrive last and move slowest, yet they carry the energy that topples buildings and opens cracks in roads.

Locating the Epicenter

The gap between the arrival times of primary and secondary waves lets scientists calculate the distance to the epicenter, and networks of stations triangulate the exact location within minutes of a major event.