You may confuse that many agencies locate different points for the epicentre of same earthquake, it may happens because of recording stations around the possible location.
Here is one example of one method to find out epicentre.
To figure out just where that earthquake happened, you need to look at your seismogram and you need to know what at least two other seismographs recorded for the same earthquake. You will also need a map of the world, a ruler, a pencil, and a compass for drawing circles on the map.
Here is one example of one method to find out epicentre.
To figure out just where that earthquake happened, you need to look at your seismogram and you need to know what at least two other seismographs recorded for the same earthquake. You will also need a map of the world, a ruler, a pencil, and a compass for drawing circles on the map.
Here's an example of a seismogram:
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FIGURE 1 - OUR TYPICAL SEISMOGRAM FROM BEFORE,
THIS TIME MARKED FOR THIS EXERCISE (FROM BOLT, 1978).
Finding
the Distance to the Epicenter and the Earthquake's Magnitude
1.
Measure the distance between the first P
wave and the first S wave. In this case, the first P and S waves are 24
seconds apart.
2.
Find the point for 24 seconds on the left
side of the chart below and mark that point. According to the chart, this
earthquake's epicenter was 215 kilometers away.
3.
Measure the amplitude of the strongest wave.
The amplitude is the height (on paper)
of the strongest wave. On this seismogram, the amplitude is 23 millimeters.
Find 23 millimeters on the right side of the chart and mark that point.
4.
Place a ruler (or straight edge) on the
chart between the points you marked for the distance to the epicenter and the
amplitude. The point where your ruler crosses the middle line on the chart
marks the magnitude (strength) of the
earthquake. This earthquake had a magnitude of 5.0.
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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.
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.
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.
FIGURE 3 - THE POINT WHERE THE THREE CIRCLES INTERSECT IS THE EPICENTER OF THE EARTHQUAKE. THIS TECHNIQUE IS CALLED 'TRIANGULATION.' |
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.
(Source : UPSeis)
