Name
Date
Class
Finding the Epicenter
Problem
INQUIRY FOCUS
Interpret Data,
Draw Conclusions
Materials
drawing compass
with pencil
outline map of the
United States
How can you locate an earthquake’s epicenter?
Procedure
1. The graph shows how the difference in arrival time
between P waves and S waves is related to the distance
from the epicenter of the earthquake. Find the difference
in arrival time for Denver on the y-axis of the graph.
Follow this line across to the point at which it crosses
the curve. To find the distance to the epicenter, read
down from this point to the x-axis of the graph.
2. Enter this distance in the data table.
Data Table
City
Difference in
P and S Wave
Arrival Times
Denver, Colorado
2 min 40 s
Houston, Texas
1 min 50 s
Chicago, Illinois
1 min 10 s
Distance to
Epicenter
Name
Date
Class
Lab Investigation
FINDING THE
EPICENTER continued
3. Repeat Steps 1 and 2 for Houston and Chicago.
4. Set your compass at a radius equal to the distance from Denver to the earthquake
epicenter that you previously recorded in your data table. You will need to use the
map scale to set your compass correctly.
5. Draw a circle with the radius determined in Step 4, using Denver as the center. Draw
the circle on your copy of the map. Hint: Draw your circles carefully. Note that some
parts of the circles might be off the map.
a. What does the circle represent?
6. Repeat Steps 4 and 5 for Houston.
a. How many times do the two circles intersect?
b. What do these intersection points represent?
7. Repeat Steps 4 and 5 for Chicago.
Name
Date
Class
Lab Investigation
FINDING THE
EPICENTER continued
Analyze and Conclude
Interpret Data In which of the three cities listed in the data table
would seismographs detect the earthquake first? Last?
Infer Why do you need to draw a circle around each seismograph
center, using the distance to the epicenter as the radius?
Observe Observe the three circles you have drawn. Where is the
earthquake’s epicenter?
Calculate About how far from San Francisco is the epicenter that you
found? What would be the difference in arrival times of the P waves
and S waves for a recording station in San Francisco?
Draw Conclusions Review the procedure you followed in this lab.
Compare the conclusion you can make with two circles on the map
with the conclusion you can make with three circles on the map.
Name
Date
Class
Lab Investigation
Finding the Epicenter
Predict Suppose an earthquake struck California, and its epicenter was
100 km north of San Francisco. Predict three pieces of data you could
obtain from the P and S waves from this earthquake.
Summarize Describe what you learned in this lab about finding the
epicenter of an earthquake and what questions you still have.
What I learned
What I still want to know
Relate Evidence and Explanation Join forces with another classmate or lab group.
Your task is to create a short television news report that explains how you determined
the epicenter of the earthquake. Present the news segment to the class.
Name
Date
Class
How Can Seismic Waves Be Detected?
The strength of an earthquake results from the energy in the earthquake’s
seismic waves. In order to measure an earthquake’s strength, scientists must
first detect and measure the seismic waves.
INQUIRY FOCUS Infer
Procedure
1.
Using scissors, cut four plastic stirrers in half. Each
piece should be about 5 cm long.
2. Your teacher will give you a pan containing gelatin.
Gently insert the eight stirrer pieces into the gelatin,
spacing them 2–3 cm apart in a row. The pieces should
stand upright, but make sure they do not touch the
bottom of the pan.
Materials
pan of gelatin
scissors
4 plastic stirrers
pencil with an eraser
metric ruler
3. At the opposite end of the pan from the stirrers,
gently tap the surface of the gelatin once with
the eraser end of a pencil. Observe the results.
4. Repeat Step 3, tapping the gelatin surface more firmly; then repeat again, this time
tapping the surface very lightly. Observe and compare the results for each test.
Think It Over
What happened to the stirrer pieces when you tapped the gelatin?
What can you infer about the connection between seismic waves and the strength
of the earthquake they produce?
Name
Date
Class
Design a Seismograph
A seismograph records the seismic waves of an earthquake. The stronger the
earthquake, the greater the height of the lines drawn by the seismograph.
INQUIRY FOCUS Make Models, Observe
Procedure
1. With two lab partners, create a model of a seismograph.
Begin by placing a large book on a table. Then, wind a
strip of paper (1 m long, 10 cm wide) around a pencil.
2. Hold the paper-wrapped pencil horizontally in one
hand. In your other hand, hold a pen against the end
of the paper, which should be resting on the book.
Materials
large book
pencil
pen
2 strips of paper, each
1 m long, 10 cm wide
3. As you hold the pen steady, have one lab partner
slowly pull on the paper so that it slides across the
book. Make sure that the pen is making a mark on
the paper as it is pulled across the book.
4. After a few seconds, your other lab partner should jiggle the book gently for
10 seconds to model a weak earthquake. Then your partner should jiggle it a
little harder for 10 seconds to model a strong earthquake. Observe the pen
markings on the paper strip. Compare the markings recorded during the weak
earthquake with those recorded during the strong earthquake.
5. Repeat Steps 1–4 with a new paper strip. Compare the two paper strips to see
how consistent your seismograph recordings were.
Think It Over
Evaluate the seismograph model you created. What were the positive aspects?
What problems did you encounter, and how did you address them?
If you wanted to develop another design for a seismograph model, what would be
an important feature for it to have?
Name
Date
Class
Earthquake Patterns
Geologists cannot predict where or when the next earthquake will occur.
However, they can use data regarding the locations and strengths of past
earthquakes to determine areas that may be at a higher risk.
INQUIRY FOCUS Interpret Data
Procedure
1. Your task is to use the data table provided by your
teacher to create a map of recent earthquake activity
in the United States. Use colors corresponding to the
key below to shade states that have had an earthquake
in one of these magnitude ranges:
7.1–8.0
red
6.1–7.0
orange
5.1–6.0
yellow
4.1–5.0
green
1.0–4.0
blue
Materials
earthquake data for the
United States
outline map of the
Western United States
colored pencils
2. Create a title and a key for your map.
Think It Over
How did mapping the earthquake numbers help to reveal patterns in the data?
What patterns do you notice, and how can you explain them?
Predict an area that you expect will have a major earthquake in the future.