Locate An Epicenter Discovery Lab

Finding The Epicenter

Guiding Question:

How can you locate an earthquake’s epicenter?

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. 

Data Table

City	Difference in P and S Wave Arrival Time	Distance to Ecpicenter
Denver, Colorado	2 min 40 s	1,600
Houston, Texas	1 min 50 s	1,000
Chicago, Illinois	1 min 10 s	600

Analyze and Conclude

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

epicenter?

The epicenter of the three cities is located at south-west of Nashville, Tennessee.

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

kilometers, is this city from the epicenter?

Nashville is the closest city from the epicenter location. It is nearly 40-50 km.

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

detect the earthquake first? Last?
 I think that Chicago, Illinois which is the closest (600 km away). It think that is the first place that the earthquake happened.

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?

The distance from San Francisco to the epicenter will be around 2800 km. If you round it up to 3000 km.The difference in P and S wave arrival will be 4 and 2/3 minutes (4 min 40 sec).

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

S waves as the distance from the earthquake increases?

I think that the P waves get much faster and start getting stronger through time.

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?
It is good to know three locations to find the epicenter since it forms a triangle.We can see that locating an earthquake epicenter produces more accuracy when reading.


 vital to citizens health.