Earthquakes Question ... Earthquakes have two kinds of waves, P waves and S waves. These waves may someday help scientists develop an early warning system for earthquakes. The P wave (also called the primary wave) is the first wave, and the S wave (secondary wave) travels after it. Scientists can find the location of an earthquake’s epicenter by subtracting the time that elapses between the P and S waves. A convenient way to find the epicenter is to use a graph like the one shown here.

Suppose that scientists record a P wave on a seismic device at 10 minutes.

An S wave reaches the device at 15 minutes (5 minutes later). What is the distance between the recording device and the epicenter of the earthquake? Use the graph to determine your answer.