Multiple Seismic Stations

To figure out just where the earthquake happened, you need recordings native seismic stations in other places. If earthquake locations are generally done through a computer system that can quickly determine the paths of seismic waves v the planet to plenty of seismic stations, you can get a an excellent estimate of one earthquake location using a map, a ruler, a pencil, and a compass for drawing circles ~ above the map.

Here are examples of a seismograms from various places in north America that videotaped the same earthquake. Distances from the stations to the earthquake are estimated from the difference in between P and also S wave arrival times:

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Illustrative instance seismograms indigenous IRIS.
Use the time difference in between the arrival of the P and also S tide to calculation the street from the earthquake to the station. (From Bolt, 1978.)
measure up the distance between the first P wave and also the an initial S wave. In this case, the very first P and S waves space 24 secs apart. find the allude for 24 seconds on the left next of the chart of streamlined S and also P take trip time curves and mark that point. According to the chart, this earthquake"s epicenter to be 215 kilometers away. measure the amplitude that the the strongest wave. The amplitude is the elevation (on paper) of the strongest wave. ~ above this seismogram, the amplitude is 23 millimeters. Find 23 millimeters on the best side of the chart and also mark the point. ar a leader (or right edge) top top the chart between the point out you marked for the distance to the epicenter and the amplitude. The suggest where your ruler crosses the middle line top top the graph marks the magnitude (strength) that the earthquake. This earthquake had actually a magnitude of 5.0.

Finding the Epicenter

You have just established how far your seismograph is native the epicenter and how solid the earthquake was, but you quiet don"t know precisely where the earthquake occurred. This is whereby the compass, the map, and the other seismograph documents come in.

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The point where the three circles crossing is the epicenter of the earthquake. This method is referred to as "trilateration." (Image from IRIS.)
examine the scale on your map. It have to look something choose a item of a ruler. Every maps room different. On her map, one centimeter could be same to 100 kilometers or something favor that. number out exactly how long the street to the epicenter (in centimeters) is on her map. Because that example, say your map has actually a range where one centimeter is same to 100 kilometers. If the epicenter that the earthquake is 215 kilometers away, that amounts to 2.15 centimeters on the map. making use of your compass, draw a circle through a radius equal to the number you come up with in step #2 (the radius is the distance from the center of a circle to its edge). The center of the circle will certainly be the place of her seismograph. The epicenter that the earthquake is somewhere on the sheet of that circle. execute the same thing for the street to the epicenter that the other seismograms recorded (with the place of those seismographs at the facility of their circles). Every one of the circles have to overlap. The allude where all of the circles overlap is the almost right epicenter of the earthquake.

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