Earthquakes generate three wave types.
Graph
y = exp(-0.3 · x) · sin(4 · x)y = exp(-0.15 · x) · sin(2 · x)
The three seismic waves
- P-waves (primary) — fastest, longitudinal (push-pull); arrive first, travel through solid *and* liquid.
- S-waves (secondary) — slower, transverse (side-to-side); can't pass through liquid — which is how we know Earth's outer core is molten.
- Surface waves — slowest but largest, roll along the ground; do most of the earthquake damage.
Distance from the time gap
The longer the delay between the P-wave and S-wave arriving, the farther away the quake. Three stations and you can triangulate the epicentre.
Early-warning systems exploit that P-waves outrun the destructive surface waves — detecting the P-wave buys cities a few precious seconds.
Three types
- P-waves (primary) — fastest, longitudinal.
- S-waves (secondary) — slower, transverse.
- Surface waves — slowest, most damaging.