How can scientist locate the epicenter of an earthquake

Scientist use triangulation method to locate the epicentre of an earthquake from the data collected from Seismograph.  

Explanation:

The seismic data from three different location is collected to locate the intersect point as the epicentre point to be determined. Each earthquake is recorded in seismogram in different location.

A seismogram is the output from a graph called seismograph, which is used to determine the epicentre of an earthquake. There are two waves namely P-waves or Primary waves and S-waves or secondary waves that are considered while finding the epicentre of an earthquake.  

With the seismogram, P-waves appears first before S-waves, since they travel faster through three states of matter. Thus, data from seismograph is used for locating “epicentre of an earthquake”.