Name: _______________________________________________________ Period: ____________________
Virtual Lab: How Do Seismograph Stations help Determine an
Earthquake’s Epicenter.
Directions:
1. Go to this link: http://glencoe.mcgraw-hill.com/sites/0078778026/student_view0/unit3/chapter11/virtual_lab.html and open
the virtual lab.
2. Click a station letter on the
map.
3. Read the Seismograph
Readout for the station. Find
the difference between the
arrival times of the P and S
waves by subtracting the P
from the S. (Each tick on the
seismograph = 15 seconds.)
ROUND your answer to the
nearest 15 seconds.
4. Record the time in the data
table.
5. Click on the Distance Graph
button. Find the distance the
station is from the epicenter.
ROUND to the nearest 500 m.
Click Close.
6. Record the distance in the
data table.
7. Click the pencil in the compass. Drag it to the notch that corresponds to your distance finding.
8. Click the Draw Circle button.
9. Repeat this for all remaining stations.
10. Click Check.
11. If your circles are correct, the epicenter star will highlight. Click and drag the start to the epicenter – the
intersection of the circles.
12. Click the Reset button and repeat the procedure to find the epicenter of Earthquake #2.
13. Answer the questions.
Earthquake #1
Station
Difference in arrival times
(min and sec)
Distance from the Epicenter
(km)
A
B
C
D
E
In what state was the epicenter of this earthquake located? ________________________________________
Earthquake #2
Station
Difference in arrival times
(min and sec)
Distance from the Epicenter
(km)
A
B
C
D
E
In what state was the epicenter of this earthquake located? ________________________________________
Analysis Questions:
1. Why does the time difference between the arrival of primary (P) and secondary (S) waves grow longer at
seismograph stations that are farther away from the epicenter?
2. We used the findings from 5 stations to locate the epicenter, but we did not actually have to use all five.
What is the MINIMUM number of stations needed to accurately locate an earthquake’s epicenter. _______