Locating the epicentre of an earthquake
Seismic records can be used to determine the location of the The point on the Earth's surface directly above the focus of an earthquake. of the earthquake. The time lag between the arrival of the P and S waves at a seismometer station can be used to determine the distance of the epicentre from the station.
Information from three stations can be used in order to locate the epicentre of the earthquake.
If we know the time lag between the arrival of P and S waves, we can calculate the distance of the earthquake from the station. This will give us the distance of the earthquake from the station, but not the direction.
The epicentre is located somewhere on the circle shown
A second seismometer in a different location can help to locate the position of the epicentre
A third seismometer is needed in order to locate the position of the epicentre