Finding the Epicenter

Finding the Epicenter

How can you locate an earthquake?

You can create circles in places were earthquakes occur, then were the circles touch each other that is the epicenter.

Materials

1. Drawing compass with pencil.

2. Outline of the United States

Procedure

1. Make Copy of 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

Data:

Data Table

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	600

Analyze and Conclude

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

epicenter?

A. A. Kansas

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

kilometers, is this city from the epicenter?

A. Dodge City

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

detect the earthquake first? Last?

A. Illinois, Texas, Colorado

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?

A. About 2000 kilometers The P waves would make it to San Francisco.

5. What happens to the difference in arrival times between P waves and

S waves as the distance from the earthquake increases?

A. The P waves are much Stronger and Faster.

6. Review the procedure you followed in this lab and then answer the

following question. When you are trying to locate an epicenter, why is it

necessary to know the distance from the epicent for at least three

recording stations?

A. So that the Information is correct, it must be correct because it is vital to citizens health.