How many seismographs are needed to determine an exact location?

Determining the exact location of an earthquake's epicenter requires data from multiple seismograph stations. Specifically, three seismographs are needed to accurately triangulate the position of the epicenter. Each seismograph measures the arrival times of seismic waves, typically the primary (P) waves and secondary (S) waves.

By analyzing the differences in arrival times between these waves at each station, scientists can calculate the distance of each station from the epicenter. With three distances plotted from the respective locations of the seismographs, the intersection point of the three circles created by these distances will pinpoint the exact location of the earthquake.

Using one or two seismographs would not provide enough information to accurately determine a unique epicenter, as they could only give a range of possible locations rather than a definite point. Thus, three seismographs are essential for precise determination of an earthquake's epicenter.