How do P & S waves give evidence for a 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.
