Seismic Shadow Zone
An interactive browser simulation of seismic wave propagation through Earth's interior, showing how the liquid outer core creates regions — shadow zones — where earthquake waves cannot be directly detected.
Live demo: https://apps.fuzzyworld.net/shadow-zone/
What it shows
When an earthquake occurs, P-waves and S-waves spread outward through the planet. The liquid outer core refracts P-waves sharply, leaving a ~91°–110° band around the globe with no direct arrivals. S-waves cannot travel through liquid at all, so they are absent beyond ~105°.
The simulation lets you adjust core size and seismic velocities to see how internal structure shapes the shadow zone. Try the presets — Water Core, Giant Core, Solid Earth — to explore non-Earth-like scenarios.
Features
- P/S-wave ray tracing using Bouguer's law on a parameterised Earth model
- Shadow zone detection: finds angular gaps in ray coverage, merges nearby zones to reduce visual noise
- Velocity-based layer colouring — equal speed → equal colour
- Hover over any red arc on the surface to see the exact shadow zone range
- Collapsible description and Wikipedia reference in the sidebar
- Impossible core presets — five physically impossible metamaterial-style cores (marked ⚠️) that go beyond what sliders alone can express:
- Negative Refraction — Snell's law negated at the CMB; rays bend to the same side of the normal as the incident ray
- Zero-Index Core — all transmitted rays forced radial; core acts as a perfect converging lens with no angular phase accumulation
- Spiral Trap — v∝r profile (zero at centre); sinI is constant, so rays spiral inward indefinitely — a seismic black hole
- Retrograde Core — velocity decreases with depth; rays reach the ICB and total-internally-reflect, expanding the shadow zone
- Perfect Absorber — all waves absorbed at the CMB; shadow zone equals the pure geometric shadow of the core disk
Tech stack
TypeScript · Vite · Canvas 2D API — no runtime dependencies.
Running locally
npm install
npm run dev
Then open http://localhost:5173/shadow-zone/
Credits
Earth icon by Icongeek26 on Flaticon.