What you are seeing
P waves (primary, compressional) pass through solids and liquids. They bend (refract) as speed changes with depth and slow sharply entering the liquid outer core, leaving a shadow zone roughly 95°–140° away (≈104°–140° in the real Earth).
S waves (secondary, shear) cannot travel through liquid, so they stop at the core–mantle boundary – proof the outer core is molten – and reflect back as ScS.
Surface (Rayleigh) waves travel along the crust more slowly (~3.5 km/s) but shake the ground the most.
A teaching model: simplified 5-layer velocity profile, rays traced with Snell's law in a spherical Earth, no mode conversions at interfaces, seismogram wavelets exaggerated in period so they are visible. Drag the timeline to scrub through time.