The earthquake epicenter is the point on the earth's surface directly above the focus. This is where the shaking is concentrated and usually the most damage is done. Geologists use seismic wave charts to determine the earthquake epicenter.
Instructions
Using Charts and Graphs
1. Find the P and S wave arrival times using the seismic chart. The p-wave will be the first large spike on the seismic chart, the s wave will be the second large spike on the seismic chart. Find the difference in time between the p and s wave arrivals. For instance, if the p wave arrived at 10:23:00 a.m. and the s wave arrived at 10:26.22 a.m., the difference in arrival times is 3 minutes, 22 seconds.
2. Line up the edge of your paper with the y-axis of the time travel graph. Make a small line on the paper where the origin touches the graph. Make a second line on the paper where the difference in arrival times touches the graph. In the case of our example, we would place a small line on our paper where 0 touches and where 3 minutes 22 seconds touches.
3. Slide the piece of paper across the graph, always keeping the 0 line touching the p-wave curve. When the line marking the difference in arrival times meets the s-wave curve, stop moving the paper. Following the edge of the paper, read the distance from the epicenter off the x-axis. This is the distance that particular seismic station was from the epicenter. Record the distance.
4. Repeat this process with the other two seismic wave charts from other locations. Record the distance.
Plotting on a Map
5. Use the scale of the map to set your compass to the distance from the first seismic station to the epicenter. Set the middle of the compass to the seismic center. Draw a circle using the compass. Every point on that circle is a possibility for the epicenter.
6. Repeat with the other two seismic centers. Make sure that you are placing the center of the compass on the seismic center in question and using the distance from the epicenter to that seismic station.
7. The three circles you have created on the map should overlap at a single point. This is the epicenter of the earthquake.
Tags: arrival times, difference arrival, difference arrival times, distance from, from epicenter
