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Name:______________________________________ Table: _____ Period:_____ Date:_______ _________
E.4.6 Lab
Earth Science Lab (Pages 252-265)
Purpose:
Geologists who study earthquakes are called seismologists. If you were a
seismologist, you would receive data from all across the country. Within
minutes after an earthquake, seismographs located around the United
States would record the times of arrival of the P waves and S waves.
This data would then be used to zero in on the exact location of the
earthquake’s epicenter.
Locating the epicenter of the Earthquake:
Problem
3. Set your compass at a radius equal to the distance from the selected
city using the scale at the bottom of the page. (map)
How can you locate an earthquake’s epicenter?
Once you have all 8 lag times and distances look at the data and decide if
you want to use all of it or just some of the distances. (Hint: Look at how
far the cities are from the epicenter.) Once you have decided how many
pieces of data (distances) you want to use follow the directions below.
Materials
Seismograms
Drawing compass with pencil
Outline map of the United States
Procedure Review the safety guidelines in Appendix on pg R26.
4. Then use the compass that is set with the correct radius to draw a
circle around the city. The center of the compass should be placed on
the dot for the city before you draw the circle on the map. (Hints: Draw
your circles carefully. You may need to draw some parts of the circles
off the map.)
Reading and Analyzing Seismograms
1. Determine lag time. (The difference in arrival times between the S and
P waves) for any of the cities assigned using the seismograms for
those cities.
Record the Lag Time in the table beneath each seismogram
for each city.
5. Repeat Steps 3 and 4 until you have determined the location of the
epicenter using the desired amount of data.
6. Observe the circles you have drawn to locate the earthquake’s
epicenter and draw a dot where you believe the earthquake occurred.
7. Answer the analysis questions on page 6.
2. Use the Lag Time vs. Distance to Epicenter Graph to determine the
distance that each assigned seismograph station is from the epicenter.
Record the distance the city is from the epicenter in the table.
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Name:______________________________________ Table: _____ Period:_____ Date:_______ _________
Earth Science Lab (Pages 252-265)
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Miami, FL
Seattle, WA
E.4.6 Lab
Name:______________________________________ Table: _____ Period:_____ Date:_______ _________
Distance:
Lag Time:
Distance:
Lag Time:
Distance:
Lag Time:
Distance:
Savannah, GA
San Franscisco, CA
Lag Time:
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Salt Lake City, NV
New York City, NY
E.4.6 Lab
Name:______________________________________ Table: _____ Period:_____ Date:_______ _________
Distance:
Lag Time:
Distance:
Lag Time:
Distance:
Lag Time:
Distance:
Denver, CO
Houston, TX
Lag Time:
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E.4.6 Lab
Earth Science Lab (Pages 252-265)
200
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400
600
800
1000
1200
1400 1600 1800
2000 2200
2400
2600
2800
3000 3200 3400 3600
3800
4000 4200
4400 4600 4800
5000 (km)
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Name:______________________________________ Table: _____ Period:_____ Date:_______ _________
Earth Science Lab (Pages 252-265)
1. Which city on the map is closest to the earthquake epicenter?
6. About how far is the epicenter that you found from Chicago? (Hint,
use the scale on the map page.)
2. How far, in kilometers, is this city from the epicenter?
7. What would the difference in arrival times of the P waves and S waves
be for a recording station in Chicago? (Hint, use the graph on page .)
3. In which of the cities on the map would seismographs detect the
earthquake first?
8. What happens to the difference in arrival times between P waves and
S waves as the distance from the earthquake increases? Use graph on
page.
4. In which of the cities on the map would seismographs detect the
earthquake last?
9. Apply Working as a seismologist, you find the epicenters of many
earthquakes in a region. What features of Earth’s crust would you expect
to find in the region where the epicenter occurred?
5. How many seismograph stations (circles drawn) are required to find
the location of an epicenter? Why?
LAB
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