When an earthquake occurs, seismic waves travel through
the planet. Every earthquake generates two types of
wavesprimary, or P waves, and secondary, or S
waves. A worldwide network of seismometers, instruments
that track earthquakes, records the arrival of P and
S waves from all over the globe. Observations and analysis
of the waves have led geologists to infer the internal
structure of Earth.
This simulation shows P and S waves moving along Earths
surface away from an earthquake.
the image to see the animation. Observe the types of
materials through which each wave passes.