Deep underground, a fault that has been
storing strain suddenly ruptures, releasing
stresses like a spring uncoiling. This pumps seismic waves into the surrounding rocks.

EARTHQUAKE!

The waves travel outward in all directions from the quake's focus.

Two kinds of waves are shown: P-waves, or primary waves, and S-waves, or secondary waves. Primary waves travel faster, often arriving several minutes before the S-waves. P-waves can travel through the Earth's molten outer core, but S-waves cannot.

After twenty minutes, all of the P and S waves have traveled completely around the world. However, since seismic waves weaken with increasing distance, people on the other side of the Earth do not feel the ground shaking!