Earthquakes and the Earth's internal structure

Part of Hall of Planet Earth.

Earthquakes and the Earth's Internal Structure AMNH/R.Mickens

Seismologists study shock, or seismic, waves as they travel through the Earth’s interior. These waves originate from natural sources like earthquakes, and from artificial sources like man-made explosions. Knowing how the waves behave as they move through different materials enables us to learn about the layers that make up the Earth. Seismic waves tell us that the Earth’s interior consists of a series of concentric shells, with a thin outer crust, a mantle, a liquid outer core, and a solid inner core.

P waves, meaning primary waves, travel fastest and thus arrive first at seismic stations. The S, or secondary, waves arrive after the P waves.