How can we calculate the distance to an epicenter?
Dr. Robert Butler briefly describes how to use seismic travel-time curves. You can observe the P- and S-wave arrivals on a seismogram to calculate how far away an earthquake was from your station. A traveltime curve is a graph of arrival times, commonly P or S waves, recorded at different points as a function of distance from the seismic source. Seismic velocities within the earth can be computed from the slopes of the resulting curves.