How earthquake waves propagate through Earth's interior
Global seismic ray paths and phase names. P-waves are shown as solid lines, S-waves as wiggly lines. The light, medium, and dark gray regions are the mantle, outer, and inner cores, respectively (the crust is invisibly thin at the scale of this diagram). Rays bend (refract) as they traverse Earth because seismic velocity increases with increasing pressure. At compositional boundaries, they may reflect or refract, remaining the same type of wave or converting from P to S or S to P. Shear waves cannot traverse liquids, so seismic waves only traverse the outer core as P-waves. Stations positioned in different locations on Earth's surface with respect to the earthquake epicenter will experience different families of seismic waves. From Peter Shearer's Introduction to Seismology (PDF).