README.md

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.

Source

1	# Seismic Shadow Zone
2
3	An interactive browser simulation of seismic wave propagation through
4	Earth's interior, showing how the liquid outer core creates regions —
5	shadow zones — where earthquake waves cannot be directly detected.
6
7	Live demo: https://apps.fuzzyworld.net/shadow-zone/
8
9	---
10
11	## What it shows
12
13	When an earthquake occurs, P-waves and S-waves spread outward through
14	the planet. The liquid outer core refracts P-waves sharply, leaving a
15	~91°–110° band around the globe with no direct arrivals. S-waves cannot
16	travel through liquid at all, so they are absent beyond ~105°.
17
18	The simulation lets you adjust core size and seismic velocities to see
19	how internal structure shapes the shadow zone. Try the presets — *Water
20	Core, Giant Core, Solid Earth* — to explore non-Earth-like scenarios.
21
22	## Features
23
24	- P/S-wave ray tracing using Bouguer's law on a parameterised Earth model
25	- Shadow zone detection: finds angular gaps in ray coverage, merges
26	nearby zones to reduce visual noise
27	- Velocity-based layer colouring — equal speed → equal colour
28	- Hover over any red arc on the surface to see the exact shadow zone range
29	- Collapsible description and Wikipedia reference in the sidebar
30	- Impossible core presets — five physically impossible metamaterial-style
31	cores (marked ⚠️) that go beyond what sliders alone can express:
32	- Negative Refraction — Snell's law negated at the CMB; rays bend to the
33	same side of the normal as the incident ray
34	- Zero-Index Core — all transmitted rays forced radial; core acts as a
35	perfect converging lens with no angular phase accumulation
36	- Spiral Trap — v∝r profile (zero at centre); sinI is constant, so rays
37	spiral inward indefinitely — a seismic black hole
38	- Retrograde Core — velocity decreases with depth; rays reach the ICB
39	and total-internally-reflect, expanding the shadow zone
40	- Perfect Absorber — all waves absorbed at the CMB; shadow zone equals
41	the pure geometric shadow of the core disk
42
43	## Tech stack
44
45	TypeScript · Vite · Canvas 2D API — no runtime dependencies.
46
47	## Running locally
48
49	```bash
50	npm install
51	npm run dev
52	```
53
54	Then open http://localhost:5173/shadow-zone/
55
56	## Credits
57
58	Earth icon by [Icongeek26](https://www.flaticon.com/authors/icongeek26) on Flaticon.