With two station distances, two possible intersections may remain. A third independent measurement can resolve that ambiguity in an ideal two-dimensional setting. Actual seismologists use many arrival times, detailed velocity models and calculations that estimate depth as well as location. Real errors mean circles may not meet at one perfect point.
Earth and geology · Discover & try
How do wave arrival times locate an earthquake?
Reading level 4 of 5 · FluentChange
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.
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Source material checked 2026-10-28. Explanations and activities by Nepedia. Source links do not imply endorsement.
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