Epicenter

Finding the Epicenter

You have just figured out how far your seismograph is from the epicenter and how strong the earthquake was, but you still don't know exactly where the earthquake occurred. This is where the compass, the map, and the other seismograph records come in.

FIGURE 3 - THE POINT WHERE THE THREE CIRCLES INTERSECT IS THE EPICENTER OF THE EARTHQUAKE. THIS TECHNIQUE IS CALLED 'TRIANGULATION.' | 1. Check the scale on your map. It should look something like a piece of a ruler. All maps are different. On your map, one centimeter could be equal to 100 kilometers or something like that. 2. Figure out how long the distance to the epicenter (in centimeters) is on your map. For example, say your map has a scale where one centimeter is equal to 100 kilometers. If the epicenter of the earthquake is 215 kilometers away, that equals 2.15 centimeters on the map. 3. Using your compass, draw a circle with a radius equal to the number you came 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 be the location of your seismograph. The epicenter of the earthquake is somewhere on the edge of that circle. |

4. Do the same thing for the distance to the epicenter that the other seismograms recorded (with the location of those seismographs at the center of their circles). All of the circles should overlap. The point where all of the circles overlap is the approximate epicenter of the earthquake.

Elastic-rebound theory of earthquakes

In geology, the elastic rebound theory was the first theory to satisfactorily explain earthquakes.

Previously it was thought that ruptures of the surface were the result of strong ground shaking rather than the converse suggested by this theory.

Following the great 1906 San Francisco earthquake, Henry Feilding Reid examined the displacement of the ground surface around the San Andreas Fault.

From his observations he concluded that the earthquake must have been...