GEOLOGY 12
CHAPTER 10 WORKSHEET
LOCATING THE EPICENTER OF AN EARTHQUAKE
Name __________________
To figure out where an earthquake happened, you need to use the data recorded for the
same earthquake from at least three seismograph stations. This data is recorded as a
seismogram. You will also need a map, a ruler, a pencil, and a compass for drawing
circles on the map.
Sample Seismograms:
Intervals are marked by the small lines printed just below the squiggles made by the
seismic waves (the time may be marked differently by other seismographs). The
distance between the beginning of the first P wave and the first S wave tells you how
many seconds the waves are apart. This number will be used to tell you how far your
seismograph is from the epicenter of the earthquake.
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Procedure:
1.
2.
3.
4.
For each of the three seismograms, measure the distance between the first P
wave and the first S wave. Then record the S-P lag times or differences in the
data table.
Use a ruler or a piece of paper and the Time-Travel Graph to find the distance of
each station from the epicenter of the earthquake. These are the radii of your circles.
Use a compass, ruler and the given map scale to construct a circle around each
of the three cities.
Locate and label the epicenter of the earthquake. (All of the circles should
overlap. This point is the approximate epicenter of the earthquake.)
EXAMPLE: THE POINT WHERE THE THREE CIRCLES INTERSECT IS THE EPICENTER OF THE
EARTHQUAKE. THIS TECHNIQUE IS CALLED 'TRIANGULATION
Questions:
1. What is meant by amplitude?
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2. What happens to the amplitude as you get farther away from the epicenter?
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3. What is the minimum number of seismograms needed to locate an earthquake using
this technique? Why?
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Seismic Station Data:
Balboa Heights (BH)
Boulder Colorado (BC)
Mexico City (MC)
Data Table:
Use the seismograms on the next page to determine the S-P time difference or lag
times. Record these in the table below.
Seismograph Location
1. Balboa Heights
2. Boulder Colorado
3. Mexico City
S-P Time Difference (min)
Distance to Epicenter (km)
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Time-Travel Graph:
Use a ruler or a piece of paper and the Time-Travel Graph below to find the distance of
each station from the epicenter of the earthquake. These will be the radii of your circles.
Refer to the map on the following page. Use a compass, ruler and the given map scale
to construct a circle around each of the three cities. Locate and label the epicenter of
the earthquake.
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Location
1. Balboa Heights
2. Boulder Colorado
3. Mexico City
Distance (km)