Multiple Seismic Stations

To number out simply where that earthquake happened, you require recordings from seismic station in other places. While earthquake locations are typically done through a computer that can conveniently determine the routes of seismic waves with the planet to plenty of seismic stations, girlfriend can acquire a great estimate of one earthquake ar using a map, a ruler, a pencil, and a compass for illustration circles top top the map.

Here are instances of a seismograms from different places in phibìc America that tape-recorded the exact same earthquake. Distances from the stations to the earthquake are estimated from the difference between P and S wave arrival times:

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Illustrative instance seismograms from IRIS.
Use the moment difference between the arrival of the P and also S waves to calculation the street from the earthquake come the station. (From Bolt, 1978.)
measure the distance in between the first P wave and the first S wave. In this case, the first P and also S waves room 24 secs apart. uncover the suggest for 24 seconds on the left side of the graph of streamlined S and also P travel time curves and mark that point. Follow to the chart, this earthquake"s epicenter was 215 kilometers away. measure up the amplitude of the strongest wave. The amplitude is the elevation (on paper) that the the strongest wave. ~ above this seismogram, the amplitude is 23 millimeters. Discover 23 millimeters on the right side the the chart and mark the point. place a ruler (or right edge) on the chart in between the point out you marked for the distance to the epicenter and the amplitude. The allude where your ruler crosses the center line on the chart marks the magnitude (strength) that the earthquake. This earthquake had a magnitude of 5.0.

Finding the Epicenter

You have actually just established how far your seismograph is from the epicenter and also how solid the earthquake was, but you tho don"t know exactly where the earthquake occurred. This is where the compass, the map, and also the various other seismograph documents come in.

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The point where the 3 circles intersect is the epicenter the the earthquake. This method is called "trilateration." (Image from IRIS.)
inspect the scale on her map. It should look something like a piece of a ruler. Every maps are different. On her map, one centimeter can be equal to 100 kilometers or something favor that. number out how long the distance to the epicenter (in centimeters) is on your map. For example, say your map has actually a range where one centimeter is equal to 100 kilometers. If the epicenter that the earthquake is 215 kilometers away, that equals 2.15 centimeters top top the map. making use of your compass, attract a circle with a radius equal to the number you come up through in step #2 (the radius is the distance from the center of a circle come its edge). The facility of the circle will be the ar of your seismograph. The epicenter the the earthquake is somewhere on the leaf of that circle. execute the very same thing because that the distance to the epicenter the the various other seismograms tape-recorded (with the ar of those seismographs at the center of your circles). Every one of the circles need to overlap. The point where all of the circles overlap is the almost right epicenter that the earthquake.

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