Name: ________________________________ Date: __________________
LAB: Locating An Epicenter
Background: Geologists who study earthquakes are called seismologist. If you were a seismologist, you
receive data from all across the country. Within minutes after an earthquake, seismologists located in San
Francisco, Denver, and Seattle would record the times of the arrivals of the P-wave and S-waves. You
would use this data to zero in on the exact location of the earthquake’s epicenter.
Materials: Drawing compass with pencil, ESRT page 11
Procedure:
Earthquake 1:
Part 1. The data below shows the P- and S-wave arrival times from seismograms from three different cities. Find the time
differences in the P and S waves for all three cities. Use your travel time curve, ESRT p11, to determine the distance to epicenter
for each city/earthquake.
Part 2. Using the distance to epicenter information above, the map and map scale, plot the location of the earthquake. This
can be done by drawing circles with the appropriate radius around the cities of record, and identifying where the circles
intersect.
Earthquake 1
First P
Arrival
First S
Arrival
Houston
12:30:15
12:34:15
Denver
12:30:20
12:32:50
Seattle
12:31:00
12:33:10
Difference in P
and S Wave
Arrival Times
Distance to P-wave
Epicenter
Travel
Time
Time of
Earthquake
time of earthquake = arrival time of the first P-wave minus the P-wave travel time
Earthquake 2
Part 1. Read the travel times of the P- and S-wave arrival times from the seismograms from three different cities. Find the time
differences in the P and S waves for all three cities. Use your travel time curve, ESRT p11, to determine the distance to epicenter
for each city/earthquake. Once you found the distance, use that number to determine the speed that the P and S wave travelled and
record in the data table.
Part 2. Using the distance to epicenter information above, the map and map scale, plot the location of the earthquake. This
can be done by drawing circles with the appropriate radius around the cities of record, and identifying where the circles
intersect.
MAP#2-AFRICA
SeismicStationA
S-Wave
TravelTime
OriginTime
(TimeofEarthquake)
A
xxxxxxxxxx
LagTime
6:31:0
0
P-Wave
TravelTime
6:30:0
0
Epicenter
Distance
6:29:0
0
6:28:0
0
S-Wave
ArrivalTime
6:27:0
0
6:26:0
0
6:25:0
0
P-Wave
ArrivalTime
S-Wave
TravelTime
B
6:32:0
0
S
P
6:24:0
0
6:23:0
0
SeismicStationB
Seismic
Station
6:32:0
0
6:31:0
0
P-Wave
TravelTime
6:30:0
0
Epicenter
Distance
6:29:0
0
Lag Time
6:28:0
0
S-Wave
ArrivalTime
6:27:0
0
P-Wave
ArrivalTime
6:26:0
0
6:25:0
0
Seismic
Station
S
6:24:0
0
6:23:0
0
P
OriginTime
(TimeofEarthquake)
xxxxxxxxxx
SeismicStationC
B
LagTime
S-Wave
TravelTime
6:32:0
0
6:31:0
0
P-Wave
TravelTime
6:30:0
0
Epicenter
Distance
6:29:0
0
S-Wave
ArrivalTime
6:27:0
0
P-Wave
ArrivalTime
6:26:0
0
6:25:0
0
6:24:0
0
6:23:0
0
Seismic
Station
6:28:0
0
S
P
OriginTime
(TimeofEarthquake)
xxxxxxxxxx
Answer the following questions.
1. Add a P or an S next to each word/phrase depending on if it describes a P-wave or an Swave.
First to arrive ______
Shear _____
push-pull _____
primary ______
Second to arrive _____
Travels through solid, liquid and gas ________
Compression ______
secondary _______
Travels through solid only _______
Wave travels at right angles to directions its moving _______
2. What is the difference between a focus and an epicenter? (use your notes)
Refer to Earthquake 1 for questions 3 through 6.
3. What was the approximate location of the earthquake? ______________________
4. Which city on the map is closest to the earthquake epicenter? How far, in kilometers, is this
city from the epicenter? (use the scale)
5. Which city, Houston, Denver or Seattle, had the fastest P wave travel time? ___________
Which of those cities was closest to the epicenter? _______________ Fill in the statement
below.
The faster the P-wave travel time, the ___________________ to the epicenter.
6. List in order the 3 cities seismologists would detect the earthquake in order from first to last?
7. When you are trying to locate an epicenter, why is it necessary to know the distance from
the epicenter for three recording stations?
8. What happens to the difference in arrival times between P waves and S-waves as the
distance from the earthquake increases?