How do seismologists locate the epicenter and focus of an earthquake?

Question

I know the focus of an earthquake is where the earthquake originated from, but what I could never figure out is, how to scientists find out where exactly the focus (and epicenter) are located?

Answer 1

Triangulation using 3 seismic data centers at 3 different locations. You time when the S & P-waves arrived at each particular center, then you calculate from that point. Since we know the speed that both S-waves and P-waves travel, we can calculate where they were at particular times. You then overlap the data from the three stations, and there you go.