The first arrivals are P waves; S waves travel more slowly. Their arrival-time gap can help estimate distance from a station. Draw a circle using that distance. A second station adds another circle. A third can help select the common location, called the epicentre, at Earth’s surface.
Earth and geology · Discover & try
How do wave arrival times locate an earthquake?
Reading level 2 of 5 · DevelopingChange
Word help
P wave
A seismic wave that normally arrives before the slower S wave.
S–P interval
The time between S- and P-wave arrivals at a station.
Epicentre
The surface location above an earthquake’s starting point.
Watch · Try · Explain
See how it works
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Flat two-dimensional model with uniform illustrative wave speeds; not an operational location or earthquake prediction.
What to look for
- Compare gaps at different distances.
- Notice one circle has no preferred direction.
- Add stations to reduce possible locations.
Explain what you noticed
A new station measures an S–P gap but has no other information. What can that measurement mainly constrain?
Keep this idea: One arrival-time difference constrains distance; several stations constrain location.
Follow the sources
Source material checked 2026-10-28. Explanations and activities by Nepedia. Source links do not imply endorsement.
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