Finding the Epicenter lab

Problem:
How can you locate an earthquake’s epicenter?
The Epicenter are found where the earth quake sites connect and when the wave makes a X between the two vibrations.


Skills Focus:
interpreting data, drawing conclusions


Materials:

• drawing compass with pencil
• outline map of the United States

Procedure:


1. Review the data table showing differences in earthquake arrival times.

2. The graph shows how the difference in arrival times between P waves
and S waves depends on 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. Enter this distance in the data table.

3. Repeat Step 2 for Houston and Chicago.

4. Set your compass at a radius equal to the distance from Denver to the
earthquake epicenter that you recorded in your data table.

5. Draw a circle with the radius determined in Step 4, using Denver as the
center. Draw the circle on the map. (Hints: Draw your circles carefully.
You may need to draw some parts of the circles off the map.)

6. Repeat Steps 4 and 5 for Houston and Chicago.

City	Difference in P and S Wave Arrival Times	Distance to Epicenter
Denver, Colorado	2 min 40 s	1600
Houston, Texas	1 min 50 s	1000
Chicago, illinois	1 min 10 s	800

Analyze and Conclude

1. Observe the three circles you have drawn. Where is the earthquake’s 

epicenter?

The three circles are based in Denver, Colorado/ Houston, Texas and Chicago, Illinois.

2. Which city on the map is closest to the earthquake epicenter? How far, in 

kilometers, is this city from the epicenter?

The closest places to the Epicenter are Kansas, Michigan/ Alabama and Hawaii.

3. In which of the three cities listed in the data table would seismographs 

detect the earthquake first? Last?

The places were the seismograph would detect first is Hawaii and Michigan.

4. About how far from San Francisco is the epicenter that you found? What 

would the difference in arrival times of the P waves and S waves be for a 

recording station in San Francisco?

San Francisco is right next to the Epicenter. I dont know the difference in the speed.