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Earthquakes: Seismogram Locatin' the Shakin'

Triangulation Image Seismologists locate earthquakes by measuring the time between the P and S waves in a seismogram.

After a seismogram "feels" an earthquake, scientists compare the time difference of these waves to figure out how far away the earthquake is.

It takes at least three seismograms to locate exactly where the earthquake is.

One siesmograph can only tell how far away it is from that seismograph. The earthquake could be located anywhere on a circle of radius equal to this distance and centered on the observation station. By measuring the S-P times at 3 or more stations these circles can be drawn around each station and where they meet indicates the earthquake location.