Download Seismograph Lab

Name _____________________
SEISMOGRAPH LAB
Objective: To learn how to read seismogram printouts from a seismograph. To learn how to read the ESRT's
Earthquake P-Wave and S-Wave Travel Time chart.
Introduction: Earthquakes occur when there is movement along a _________ in the earth's crust. The
movement along this line produces shock waves (seismic waves) that are sent out in all directions through the
earth. ________________ are scientific instruments which record the shaking of the earth's crust. There are 3
types of waves that are sent out when an earthquake occurs.
Compressional waves or ___-waves vibrate in the direction they travel. This wave travels (fastest or slowest)
and is the (first or second) wave to reach a seismic station. These waves can travel through all substances and
layers of the earth.
Shear waves or ___-waves vibrate perpendicular to their direction of travel. These waves travel (fastest or
slowest) and are the (first or second) wave to reach a seismic station. Secondary waves can only travel through
solids therefore they can not travel through the _____________ of the earth because it is a liquid. Scientists
have created both P and S waves in the laboratory and have seen that S-waves do not travel through liquids,
therefore they assume the outer core must be liquid.
Longitudinal Waves or L-Waves are very slow waves which move in many directions. They are responsible for
the destruction on land caused by earthquakes.
Vocabulary
Seismograph Time lag Fault Origin Time Earthquake -
Procedure: Use the ESRT and your brain to answer the questions that follow, make sure you put all your
answers on the Answer Sheet at the back of the lab.
Practice Questions
A) How long does it take a P-Wave to travel 2000 km? _________
B) How long does it take an S-Wave to travel 2000 km? _________
C) How far will an S-Wave travel in 15 minutes? ___________
D) What is the time lag (difference) in minutes and seconds if you are 4000 km away? ________
E) What is the time lag if you are 2000 km away? _________________
F) A seismologist is reading a seismogram which was recorded on her seismograph. She calculates the
difference in arrival time between P and S waves to be 5 minutes and 40 seconds. How far away is the
earthquake from the seismic station? __________ km
G) How far away is an earthquake from a seismic station if the lag time between the arrival of the P and S
waves is 3 minutes? _______________km
H) Calculate the lag time AND distance to epicenter for the seismographs below. Be sure to find the time
interval for EACH seismograph first!
A
Lag Time: ______________________
Distance to Epicenter: _____________km
B
Lag Time: ______________________
Distance to Epicenter: _____________km
C
Lag Time: ______________________
Distance to Epicenter: _____________km
Answer these questions on the Answer Sheet
1. How many minutes does it take an S wave to travel 3000 km?
2. How far does an S wave travel in 19 minutes?
3. How many minutes does it take an S wave to travel 1000 km?
4. How many minutes does it take a P wave to travel 2000 km?
5. How far does a P wave travel in 8 minutes?
6. How far does a P wave travel in 4 minutes?
7. If a P wave arrives in 7 minutes, when will the S wave arrive?
8. If the S wave arrived in 4 minutes, when did the P wave arrive?
9. If the lag time between P and S wave arrival is 4 minutes, what is the distance to the epicenter?
10. If the lag time between P and S wave arrival is 10 minutes, what is the distance to the epicenter?
11. If the S wave arrived 6 minutes after the P wave, what is the distance to the epicenter?
12. An earthquake occurred 4600 km away, what is the lag time?
13. An earthquake occurred 7000 km away, what is the lag time?
14. An earthquake occurred 2000 km away, what is the difference in arrival time between P and S waves?
15. An earthquake is 9000 km away, when will the P wave arrive?
16. An earthquake occurred at 10:00:00am today and is 4200 km away. At what time did the P wave arrive?
17. Same question as 16, at what time did the S wave arrive?
18. An earthquake occurred at 7:14:00pm and is located 2000 km from the seismic station. At what time
will the S-wave arrive at the station?
19. A seismic station is 5800 km from an earthquake. It recorded the arrival of the P-wave at 8:12:00am.
At what time did the earthquake occur? (think about it!)
20. The lag time for an earthquake is 3 minutes 40 seconds. If the earthquake occurred at 1:37:00am, when
did the P wave arrive?
21. Extra Credit - A seismic station in New York records the P and S waves times for an earthquake that
occurred in Los Angeles California. The P wave arrived exactly at 10:10am. When did the earthquake
occur local time in Los Angeles?
Read the following Seismograms and determine the lag time and distance to the epicenter.
Conclusion Questions
1. What information can you gather regarding an earthquake, if you have P and S wave readings from one
seismic station?
2. Describe the motion of a P wave and an S wave as it travels through the earth. Include a diagram of how
each wave travels.
3. How does the lag time for a seismic station close to an earthquake compare with the lag time from a seismic
station that is further away? Graph the relationship between time lag (y-axis) and distance from an earthquake
(x-axis).
4. Why do scientists think the outer core of the earth is liquid?
5. What happens to the velocity of an earthquake wave as it moves through denser material?
6. Describe the events that cause an earthquake, then describe the order of event that happen after an earthquake
which lets seismologist determine the distance to the earthquake.
Answer Sheet
1_________________
14_________________
2_________________
15_________________
3_________________
16_________________
4_________________
17_________________
5_________________
18_________________
6_________________
19_________________
7_________________
20________________
8_________________
21 Extra Credit ______________
9_________________
22 Lag Time:___________; Distance to Epicenter _______km
10________________
23 Lag Time:___________; Distance to Epicenter _______km
11_________________
24 Lag Time:___________; Distance to Epicenter_______km
12_________________
25 Lag Time:___________; Distance to Epicenter _______km
13_________________