The three circles that geologists use from different seismographs intersect at the epicenter of an earthquake. Here's how it works:

* Seismographs: These instruments record ground motion during an earthquake.

* Seismograms: The records produced by seismographs, showing the arrival times of different seismic waves (P-waves, S-waves, surface waves).

* Time Difference: By comparing the arrival times of P-waves and S-waves at different seismograph stations, geologists can calculate the distance from each station to the earthquake's origin.

* Circles: Each seismograph station's distance to the epicenter is represented as a circle drawn on a map. The radius of the circle equals the calculated distance.

* Intersection: The epicenter is located where the three circles from different seismograph stations intersect.

Therefore, the point where the three circles intersect is the epicenter, the point on the Earth's surface directly above the focus (the point where the earthquake originated underground).