© 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

© 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.

© 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

© 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

© 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

© 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.

© K. Coder 2015

EARTHQUAKE 1

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EARTHQUAKE 2

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