Lesson #3—Recording Earthquake Waves
Inquiry 3.1- Recording Vibrations
Choose one of the following variables to investigate.
A. Direction: How does changing the direction of your pounding
(location of your hand) affect the waves that the seismograph
records on the paper?
B. Distance: How does the distance of your pounding from the
seismograph affect the waves it records?
C. Force: How does the strength of your pounding affect the waves it
records?
Variable Chosen: __________________
Observations:
Conclusion Questions
1. How do you think a real seismograph works?
2. How do you think a real seismograph differs from this model
seismograph?
3. Why is there always more damage to structures that are built close
to the source of an earthquake than to structures that are farther
away?
4. Why do you think it is important for scientists to record earthquake
vibrations?
Inquiry 3.2- Reading a Seismogram
Use the sample seismogram recorded in Bellingham, Washington, during
the 1964 earthquake in Prince William Sound, Alaska to answer the
following questions.
1. What do the numbers 0858 on the seismogram represent?
2. What does each mark on a line represent?
3. How long did it take for the seismogram to make one revolution
around the drum? How do you know?
4. When did the first P-wave in the illustration arrive at the station?
5. When did the first S-waves arrive at the station?
6. What time did the earthquake wave (P-wave) arrive in Bellingham?
Remember this is military time, recorded on a 24-hour clock. What
time would it be in “a.m.” or “p.m.”?
7. The earthquake occurred in Prince William Sound, Alaska, at 7:36
p.m. How long did it take the first earthquake to reach Bellingham,
Washington?
8. The first aftershock was recorded on March 28, 1964. Record the
time. How many aftershocks do you see altogether?
9. Record the difference in arrival times of the P-waves and S-waves.
The time difference between the P-wave arriving and the Swave arriving at the seismograph station is called “lag time.”
a. Write a working definition of lag time.
10. What did you learn about reading a seismogram? Record your
ideas.
11. The magnitude of the Alaska earthquake was 9.2, higher than that
of most recorded earthquakes.
a. Do you think seismographs all over the world, or only those
near Alaska, were able to record the Alaska earthquake?
b. In what ways might the seismograms recorded in other parts
of the world look different from the one recorded in
Bellingham?
12. Draw a conceptual graph (no numbers; graph shows relative
shapes and positions of lines).
Inquiry 3.3- Locating the Epicenter of an Earthquake
1. If it took four minutes for the first P-waves to arrive at the
seismograph station, how far away is the earthquake’s epicenter?
2. If the seismograph station were located 2500 km from the
earthquake’s epicenter, how long would it take the P-wave to
arrive?
3. How long would it take the S-wave to travel 2500 km and reach the
seismograph station?
4. Using 2500 km, which wave traveled faster: the P-wave or the Swave?
5. At 2500 km, how many minutes elapsed between the time the Pwave and S-wave arrived at the station?
6. Considering the whole graph, how does minutes elapsed between
the P-wave and S-wave arrival relate to distance from the
earthquake’s epicenter?
Reflecting on What You’ve Done
A. What did you learn about how scientists record earthquakes?
B. How does information on a seismogram tell scientists where
earthquakes occur?
C. How does knowing where earthquakes occur help people reduce
the risks associated with future earthquakes?
“Canines to the Rescue” Discussion Questions (pgs.45-47)
1. Suppose you were asked to build an automatic “sniffer” that could
do the same job as a rescue dog. How would you do it?
2. While dogs are useful in search-and-rescue efforts, the work
remains costly and dangerous. How could the need for such
rescues after earthquakes and other natural disasters be reduced?