Earthquakes and seismic waves
Explore how earthquake waves travel. Change the focal depth, ground conditions and buildings, and compare the signals at three stations.
Beneath the surface
Select a station and follow the waves.Station B recording
Relative acceleration · a.u.Compare arrival times
| Station | Epicentral distance | P arrival | S arrival | S − P |
|---|---|---|---|---|
| A | 18 km | — | — | — |
| B | 44 km | — | — | — |
| C | 70 km | — | — | — |
One signal, different waves
P waves compress and expand material; S waves produce transverse deformation. Here P waves arrive first. The focus is the underground origin and the epicentre is the point on the surface directly above it.
Ground conditions matter
Change rock to soft sediment at the same station. The model changes the local delay, frequency and amplification of the signal. The chart keeps a common vertical scale to make comparisons easier.
Change one variable at a time
Pause at the first P arrival and move forward to S. Compare S − P at A and C. Then change only the depth and repeat. Finally keep the ground unchanged and compare buildings: their response depends on their period and the excitation, not just their height.
Model assumptions and limits · version 1.0
The model assumes a straight path with constant crustal speeds of 6 km/s for P and 3.5 km/s for S. An idealized local 100 m layer adds a ground-dependent delay. Surface waves use an approximate path to the surface followed by horizontal travel at 2.8 km/s. The drawn layers are illustrative: refraction and propagation through real geology are not calculated.
Each building is a damped linear single-degree-of-freedom oscillator, with 7% damping and periods of 0.35, 0.75 or 1.40 s. Acceleration is synthetic, in arbitrary units, and is not calibrated to an earthquake magnitude. Amplitudes and deformation are exaggerated for visibility.
It uses no live data, predicts no earthquakes and estimates neither intensity nor damage or structural safety. It omits finite rupture, dispersion, soil–structure interaction and nonlinear behaviour. It cannot establish that one ground or building type is always safer. Times are model outputs, not real measurements.