Download Epicenter Location

NAME_________________________________________ DATE________________
FINDING EPICENTERS
VOCABULARY:
FaultEpicenterFocusFocal Depth-P-WaveS-WaveSeismographSeismogramINTRODUCTION: Earthquakes occur when there is movement within the crust along
a fault. This movement creates waves which travel through the Earth. These
seismic waves are radiated in every direction from the focus.
An earthquake occurs every 30 second, every day. Most of these
earthquakes are so weak they wouldn’t be noticed without the use of
seismographs.
While seismologists use many stations to locate an epicenter, you will use
three, the minimum number needed to triangulate the location of an epicenter.
OBJECTIVE: Learn to read and interpret seismograms and using those seismograms
locate the epicenter of an earthquake.
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PROCEDURE A:
The diagram below demonstrates how to use the difference in arrival times of P &
S waves to determine the distance to the epicenter. Using the three seismograms
provided and your “Earthquake P-wave and S-wave Travel Time” graph from your
reference table to calculate:
1) Arrival times for P and S waves
2) Difference in arrival times
3) Distance to the epicenter
4) Length of time the P-wave traveled for each city and enter on Report Chart.
PROCEDURE B:
1. a. To locate the epicenter on the map by constructing a circle whose radius is equal
to the distance from the city to the epicenter.
b. Use the scale of distance on your map to set the compass at the correct radius.
2. On the map identify the epicenter location by drawing all three circles, where all
three circles meet is your epicenter, place and “X” at this location.
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REPORT CHART
Seismograph
Station
Arrival Time (clock time)
“P” Wave
“S” Wave
Difference in
Arrival Time
Time
(min and sec)
Distance to
Epicenter (km)
“P” Wave
Travel Time
(min and sec)
CHICAGO
TAMPA
WINK
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REPORT CHART
Seismograph
Station
Arrival Time (clock
(clock time)
“P” Wave
“S” Wave
Difference in
Arrival Time
(min and sec)
Distance to
Epicenter (km)
“P” Wave
Travel Time
(min and sec)
NEW YORK
SAN DIEGO
TAMPA
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REPORT CHART
Seismograph
Station
Arrival Time (clock time)
“P” Wave
“S” Wave
Difference in
Arrival Time
(min and sec)
Distance to
Epicenter (km)
“P” Wave
Travel Time
(min and sec)
WINK
SEATTLE
MEMPHIS
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1
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DISCUSSION QUSTIONS:
1. What difference between P-waves and S-waves was used to find the earthquake’s
epicenter?
2. What was the approximate location of the epicenter of:
Earthquake 1:
Earthquake 2:
Earthquake 3:
3. Why is three the minimum number of stations necessary to locate and epicenter?
4. Why does the time between the arrival of the P-wave and S-wave become greater
and greater as you get farther away from the epicenter?
CONCLUSION: Describe step by step how an epicenter of an earthquake is located.
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