LAB Locating Epicenters - NYS Earth Science€¦ · Earth Science Period: Lab# _____ Locating the Epicenter of an Earthquake Introduction: Seismographs are used to detect and record
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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.
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. ______________________________
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. ______________________________
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. ______________________________