This lab activity document provides instructions for students to locate the epicenters of three earthquakes using seismic data from three stations for each earthquake. Students will analyze seismograms to determine the arrival times of P-waves and S-waves and then use the difference in arrival times to calculate the distance from each station to the epicenter. Students will then draw circles with radii equal to these distances on maps to locate where the circles intersect, identifying the epicenter's location. Tables are included for recording data, and maps show the station locations to draw epicenter circles. Discussion questions at the end address earthquake prediction, minimum stations needed, and properties of P and S waves.

1. © K. Coder 2015
Lab Activity
Locating Epicenters
Key Features:
Analyzing Seismograms
P-waves & S-waves
Using ESRT page 11
Drawing Epicenter Circles
By Kaitlin Coder
https://www.teacherspayteachers.com/Store/Nys-Earth-Science-And-Living-Environment-Regents

2. © K. Coder 2015
Name: Date:
Earth Science Period:
Lab# _____
Locating the Epicenter of an Earthquake
Introduction:
Seismographs are used to detect and record earthquake waves – both P-waves and S-waves. Because P-
waves and S-waves travel at different speeds, they reach the seismic stations at different times. The
difference in the arrival times between the P-wave and the S-wave can be used to find the epicenter’s
distance from the seismic station. This distance becomes the radius of a circle which is drawn on a map.
This is illustrated below.
To locate the epicenter of the earthquake, a minimum of 3 circles from three different seismic stations must
be drawn on the map. The intersection of the three circles shows the location of the epicenter on the map.
This is illustrated below.
Objective: In this activity, you will use analyze P-wave and S-wave recordings on a seismogram to
determine the distance to the epicenter of an earthquake from a given seismic station. You will locate the
epicenter of the earthquake using a map.

3. © K. Coder 2015
Procedure:
1. For each station, determine the information listed below. Record your answer in Table 1.
a. Arrival time of the P-wave
b. Arrival time of the S-wave
c. Difference in the arrival time
d. Distance to the epicenter of the earthquake (Use the graph on ESRT page 11 to determine
distance based on the difference in the arrival time between P-wave and S-wave)
e. Travel time of the P-wave for that distance
f. Time of Origin (subtract: Arrival time of P-wave – Travel time of P-wave)
Table 1
Seismograph
Station
Arrival (clock time) Difference
in Arrival
Time (min
and sec)
Distance to
Epicenter
(km)
P-Wave
Travel Time
(min and
sec)
Time of Origin
(hour:min:sec)P-wave S-wave
Denver
Dallas
Salt Lake City
2. On the map labeled Earthquake 1, the locations of Denver, Dallas, and Salt Lake City are labeled. This
map also shows the locations of other cities in the United States. Use the distances determined in Table
1 above to represent the radius of the circle. Open your drawing compass to this distance by using the
scale of kilometers on the map. Draw a circle for each station.
3. Draw an X at the location of the epicenter of this earthquake.
4. Name the city closest to the epicenter of this earthquake. ______________________________
EARTHQUAKE 1

4. © K. Coder 2015
Procedure:
1. For each station, determine the information listed below. Record your answer in Table 2.
a. Arrival time of the P-wave
b. Arrival time of the S-wave
c. Difference in the arrival time
d. Distance to the epicenter of the earthquake (Use the graph on ESRT page 11 to determine
distance based on the difference in the arrival time between P-wave and S-wave)
e. Travel time of the P-wave for that distance
f. Time of Origin (subtract: Arrival time of P-wave – Travel time of P-wave)
Table 2
Seismograph
Station
Arrival (clock time) Difference
in Arrival
Time (min
and sec)
Distance to
Epicenter
(km)
P-Wave
Travel Time
(min and
sec)
Time of Origin
(hour:min:sec)P-wave S-wave
Dallas
Chicago
Miami
2. On the map labeled Earthquake 2, the locations of Dallas, Chicago, and Miami are labeled. This map
also shows the locations of other cities in the United States. Use the distances determined in Table 2
above to represent the radius of the circle. Open your drawing compass to this distance by using the
scale of kilometers on the map. Draw a circle for each station.
3. Draw an X at the location of the epicenter of this earthquake.
4. Name the city closest to the epicenter of this earthquake. ______________________________
EARTHQUAKE 2

5. © K. Coder 2015
Procedure:
1. For each station, determine the information listed below. Record your answer in Table 3.
a. Arrival time of the P-wave
b. Arrival time of the S-wave
c. Difference in the arrival time
d. Distance to the epicenter of the earthquake (Use the graph on ESRT page 11 to determine
distance based on the difference in the arrival time between P-wave and S-wave)
e. Travel time of the P-wave for that distance
f. Time of Origin (subtract: Arrival time of P-wave – Travel time of P-wave)
Table 3
Seismograph
Station
Arrival (clock time) Difference
in Arrival
Time (min
and sec)
Distance to
Epicenter
(km)
P-Wave
Travel Time
(min and
sec)
Time of Origin
(hour:min:sec)P-wave S-wave
Phoenix
Rochester
Duluth
2. On the map labeled Earthquake 3, the locations of Phoenix, Rochester, and Duluth are labeled. This
map also shows the locations of other cities in the United States. Use the distances determined in Table
3 above to represent the radius of the circle. Open your drawing compass to this distance by using the
scale of kilometers on the map. Draw a circle for each station.
3. Draw an X at the location of the epicenter of this earthquake.
4. Name the city closest to the epicenter of this earthquake. ______________________________
EARTHQUAKE 3

6. © K. Coder 2015
Discussion Questions
1. Are earthquakes predictable? Explain your answer.
2. What is the minimum number of seismic stations necessary to locate an epicenter?
3. How can you determine the epicenter of an earthquake using data from seismic stations worldwide?
4. What happens to the time differences between P- and S-waves as your distance from the epicenter
increases?
5. Compare the differences in velocity of P- and S-waves.
6. What state(s) of matter do P-waves travel through?
7. What state(s) of matter do S-waves travel through?
8. What are the two different scales used to determine the severity of earthquakes? Explain the
differences between these scales.

7. © K. Coder 2015
EARTHQUAKE 1
DistanceinKilometers

8. © K. Coder 2015
EARTHQUAKE 2
DistanceinKilometers

9. © K. Coder 2015
EARTHQUAKE 3
DistanceinKilometers