Geologists studying an earthquake need to find its epicenter, or the center of the earthquake. They do this using a method called triangulation, in which they find the point that is the correct distance from three different seismograph stations. You can find the epicenter from the three seismographs using little more than a map and a ruler. The two main waves shown on a seismograph are P-waves (primary waves) and S-waves (secondary waves). P-waves travel more quickly than S-waves, so they appear first on the seismograph.
Instructions
1. Locate the S-wave arrival time and the P-wave arrival time using the seismograph.
2. Subtract the P-wave arrival time from the S-wave arrival time to get the amount of time between the arrival of the two types of waves (the S-P interval).
3. Use a graph showing the relationship between the time difference of an earthquake's waves and the distance from the epicenter, such as the one in the resources section, to find out how far the seismograph station was from the earthquake's epicenter.
4. Use the kid's ruler to find and mark multiple points on the graph that are the specified distance from the seismograph station. These points should form a circle around the location of the station. The epicenter lies on this circle.
5. Repeat steps 1-4 for two other seismographs, taken at two other stations.
6. Find the point where the three circles touch. This is the epicenter of the earthquake.
Tags: arrival time, distance from, find epicenter, from three, P-wave arrival, P-wave arrival time, seismograph station