Name Date Class
Finding the Epicenter
Problem
How can you locate an earthquake’s epicenter?
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.
Name Date Class
Lab Investigation
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.
6.Repeat Steps 4 and 5 for Houston.
7.Repeat Steps 4 and 5 for Chicago.
Name Date Class
Lab Investigation
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