README.md

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`2db5a221` 2026-06-12 Pavel Safronov	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
`0ffa72b1` 2026-10-27 Pavel Safronov	7	Live demo: https://apps.fuzzyworld.net/shadow-zone/
`2db5a221` 2026-06-12 Pavel Safronov	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
`e86a2c69` 2026-06-13 Pavel Safronov	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
`2db5a221` 2026-06-12 Pavel Safronov	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.