This simulation shows the motion of P and S waves generated by a single earthquake. The waves spread through the planet in a series of expanding spheres. Some of the wave energy reflects off the boundary between the mantle and core.

Scientists deduced the structure of Earth's interior and how waves move through it by analyzing thousands of earthquakes recorded at Earth's surface. Examine how the waves change as they encounter different layers of Earth's interior. Identify areas on the surface that do not receive any waves — these areas are in the shadow zone of this simulated earthquake.