Earthquake Wave Simulator
Click an epicenter to watch P-waves and S-waves travel across Earth. Place a seismograph station to measure arrival times and explore the shadow zones created by Earth's liquid outer core.
Seismic Wave Science
P-Waves and S-Waves
P-waves (primary) are compressional and travel at about 8 km/s through rock. S-waves (secondary) are shear waves traveling at 4.5 km/s. P-waves arrive first at any seismograph station, S-waves arrive later.
The S-P Gap
The time difference between S and P wave arrivals tells seismologists the distance to the epicenter. With readings from three stations they can pinpoint the earthquake's exact location using triangulation.
Shadow Zones
Earth's liquid outer core blocks S-waves entirely, creating a shadow zone beyond 104 degrees. P-waves are refracted by the core, creating a P-wave shadow from 104 to 140 degrees. These zones provided key evidence that Earth has a liquid outer core.
Wave Speed Contrast
P-waves travel at roughly 8 km/s through the mantle. S-waves travel at about 4.5 km/s. The difference means that for every 100 km of distance, the S-P gap grows by about 9 seconds, giving seismologists a reliable distance ruler.
Earthquake Magnitude
The Richter scale and moment magnitude scale measure earthquake energy logarithmically. Each whole number increase represents about 32 times more energy released. The magnitude slider in this simulator affects the visual thickness of the wave rings.
Earth's Internal Structure
The shadow zone pattern was instrumental in revealing that Earth has a liquid outer core between 2890 and 5150 km depth. S-waves require a solid medium to travel, so their absence in the shadow zone confirmed that the outer core is molten iron.