An earthquake releases P-waves (compression), S-waves (shear) and surface waves. Rays bend as wave speed changes with depth, reflect at layer boundaries and are blocked by the liquid outer core.
P-waves are compressional and fastest. They pass through solids and liquids, but refract sharply at the core, leaving a shadow zone at roughly 104°–140° from the quake.
S-waves are shear waves. They cannot travel through liquid, so the outer core stops them – the core's liquid state was discovered this way. They reflect off it (ScS).
Surface waves are slow (~3.5 km/s) but carry most of the destructive energy, especially for shallow quakes.
Waves that dive into the core are labelled PKP / PKIKP on the seismograms.