The correct answer is They measure the difference between arrival of P waves and S waves, They draw circles around the epicenter from three locations
"They measure the difference between arrival of P waves and S waves" This method is used to determine how far seismograph is from the epicenter. It is not the direct step of finding epicenter but after finding this distance , epicenter in located.
In the second step the distance measured above is converted to the unit of map and three circles are drawn from the location of seismograph
