Plate Tectonics


In this week’s activity, we are going to try to locate the epicenter of an earthquake using readings from three different seismograph stations. This will be done by measuring the difference in time between the arrival of the P and S-waves. The difference it time of their arrivals is due to the difference in speeds for both waves. In particular, the difference in time is given by (distance to epicenter)/(Vp – Vs). Thus, we can find out how far away a particular seismograph is from an earthquake by solving this equation for distance. Since there are three stations, we can triangulate between all three to find the exact spot. Before we use actual data, we will first do a “test run” using a simulator from California State University – Los Angeles. This simulator will walk you through the steps of epicenter triangulation that we will then apply to some real data recorded by seismographs. To get to the simulator, click on When you get to the simulator site, select “San Francisco area” at the bottom of the page, and follow the instructions on the succeeding pages.