Scientists can calculate the distance that an earthquake occurs from a seismometer station by looking at the record of the seismic waves and measuring the difference in time between the arrival of P and S-waves.
This gives them a distance but not a direction. So they plot this distance on a map by drawing a circle round the seismometer station. The radius of this circle is equal to the distance to the epicentre.
If this is done for one other seismometer station that has recorded the earthquake then the circles will intersect in two places. If you add in a 3rd station and so a third circle they will all intersect in one place - the epicentre of the earthquake.
In reality this process is automated by computer and lots of readings from lots of stations are used.
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They Use A Seismograp and look at the squiggles on the paper.
triangulating its loction
The S-P time method is perhaps the simplest method seismologists use to find an earthquake's epicenter. +++ No it's not. That finds its Focus. The Epicentre is the point of maximum movement on the land surface above the slip itself.
They use the Richter scale to measure the speed of the earthquakes. Levels of earthquakes 2.0 ---> can't be felt 4.0 ---> do not cause damage 5.0---> can cause damage 6.0 ---> considered strong 7.0---> is a major earthquake +++ That is not correct. You have confused speed with intensity. The Richter scale, which is logarithmic, measures the intensity ("strength" if you like). The speed is measured in ordinary linear units like metre/second or km/hr, calculated from observing the earthquake's waves' progress past seismographs around the world.
From Science Explorer Prentice Hall Earth Science: " Geologists use seismic waves to locate an earthquake's epicenter. Seismic waves travel at different speeds. P waves arrive at a seismograph first, with S waves following close behind. To tell how far the epicenter is from the seismograph, scientists measure the difference between the arrival time of the P waves and S waves. The farther away an earthquake is, the greater the time between arrival of the P waves and the S waves." Did this help?