www.iris.edu/earthquake for more animations.
Seismic shadow zones have taught us much about the inside of the earth. This shows how P waves travel through solids and liquids, but S waves are stopped by the liquid outer core.
The seismic shadows are the effect of seismic waves striking the core-mantle boundary. P and S waves radiate spherically away from an earthquake's focus in all directions and return to the surface by many paths. S waves, however, don't reappear beyond an angular distance of ~103° (as they are stopped by the liquid) and P waves don?t arrive between ~103° and 140° due to refraction at the mantle-core boundary.
Narrated by Dr. Wendy Bohon, Informal Education Specialist, IRIS
Animation by Jenda Johnson, Earth Sciences Animated
