In order to locate an earthquake's epicenter, seismology centers compare the arrival times of:

In order to locate an earthquake's epicenter, seismology centers compare the arrival times of the seismic waves.

Explanation:

Seismic waves are waves of energy that travel through the Earth's layers when an earthquake occurs; the time at which the wave front passes is observed and used to figure out just where that earthquake happened. The records are made in a device called seismographs, which captures the earthquake waves’ speed and calculates time they were apart. All these data is used to tell where the epicenter of the earthquake is, which it’s also the place where damage probably occurred.