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Triangulation
Now you may ask, “We can find out the
magnitude, but we only have the distance of the earthquake
from one station. How do we locate it?” We can answer
this question by a method called triangulation. With one
station we can locate how far away an earthquake happened
from that seismometer, and with three stations we can actually
pinpoint more or less the epicenter of the earthquake (i.e.
where the earthquake would appear on the surface). It works
on the following manner:
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Step
1
For our purpose lets say an earthquake happened 10
kilometers away from one specific station station.
We can now draw a circle around that station that
is exactly 10 kilometers from the center. So we now
know that the earthquake happened somewhere on that
circle. |
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Step
2
Now lets look at another station. We measure the
P and S-waves to find out that the earthquake happened
5 kilometers from that station. So we do the same
thing and draw a circle around that station that is
exactly 5 kilometers from the center. If we did things
right, the two circles should intersect at two points.
We can now deduce that the earthquake happened on
one of the two places where the circles intersect.
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Step
3
Now we take a third station and again do the same
thing. Lets say the earthquake falls 8 kilometers
away from that station. Again, we draw the circle
8 kilometers away from the station. Now, if we did
this right, the three circles should intersect at
one point. Congratulations, you have located an earthquake! |
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So why do we have all those stations if all
we need are three to obtain the information that we need.
The reason is that the more stations we have, the more accurate
we can give its location and size. Sometimes the data from
three stations will not give is the most accurate results
due to other factors, such as the type of ground or rock
that the seismometers are sitting on. Also, if we are to
locate the Hypocenter (the location of the earthquake in
the ground, or in other words, the depth of the earthquake)
we need a fourth station.
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