How do scientists determine the location of an earthquake's epicenter?

As a seismologist, I can explain the process scientists use to determine the location of an earthquake's epicenter. When an earthquake occurs, it generates different types of seismic waves that travel through the Earth at varying speeds. The two main types of waves are P-waves (primary waves) and S-waves (secondary waves). P-waves are faster and can travel through both solid and liquid layers of the Earth, while S-waves are slower and can only travel through solids. Because of this, P-waves arrive at seismograph stations before S-waves. The difference in arrival time between these two types of waves can be used to calculate the distance of the earthquake's epicenter from the seismometer. The further away an earthquake is, the greater the lag time between the detection of the S waves relative to the P waves. To pinpoint the epicenter, scientists use a network of seismographs located at different places around the world. By measuring the time it takes for the seismic waves to reach each seismograph and using the known speed of the waves, they can triangulate the location of the earthquake's epicenter. This is similar to how the position of a lightning strike can be determined by the time it takes for the light and sound to reach an observer. Once the distance to the epicenter is estimated from multiple seismographs, the data is used to plot the possible location on a map. The intersection of these plots gives a more precise location of the epicenter.

The difference in arrival time between the two types of seismic wave can be used to calculate the distance of the earthquake's epicenter from the seismometer, as the further away an earthquake is, the greater the lag time between the detection of the S waves relative to the P waves.