Earthquakes, GPS, and Plate Motion Lab - Student Handout.docx (1)
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School
Colorado State University, Fort Collins *
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Course
121
Subject
Geology
Date
Dec 6, 2023
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Pages
11
Uploaded by GrandLightning12604
Name
Lab Section
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GEOL 121: Earthquakes, GPS, and Plate Motion Lab
Learning objectives:
●
Students will observe, describe, analyze, interpret, and apply time-series GPS data related to
horizontal bedrock motion resulting from plate tectonics
●
Students will interpret absolute and relative bedrock motion near plate boundaries and its
relationship to earthquakes as measured by GPS
●
Students will draw on GPS data to make a societal recommendation relative to earthquakes
GPS stations precisely record the position of the solid ground they are on, and they were first installed to
measure plate motion.
In this lab, you will learn how to analyze and interpret scientific data after describing it, an important step
for scientists in the process of science. You will conclude by using that data to support a recommendation
you make about an issue relevant to society. This particular activity uses data from GPS stations in
California to better interpret earthquake hazards by analyzing GPS position of bedrock near a transform
plate boundary.
Part 1: Writing a hypothesis about GPS data and earthquakes (2pts.)
Geologists make hypotheses to explain how one thing affects another and why the relationship exists.
They use their hypotheses to make predictions that they can then test by collecting data. In Part 1, you
will use your understanding of the relationships between the tectonic plate motion and earthquakes to
write a hypothesis. You will use that hypothesis to make predictions, and you will test those predictions in
Part 2.
If you have not already done so, watch the animation titled “Measuring Plate Tectonics with GPS.”
1. The animation explained Earth processes that can cause horizontal position of the bedrock to change.
Circle the main global process that causes the position of GPS stations attached to the bedrock to move.
precipitation
tectonic plate motion
glacier size
volcanic eruptions
landslides
In southern California the western side of the transform plate boundary in California (the Pacific Plate) is
moving north faster than eastern side of the plate boundary (the North American Plate). In this activity we
will consider the motion of GPS stations on either side of the plate boundary in another part of California
to learn more about earthquakes.
The San Andreas Fault is a fault that extends along the transform plate boundary through California.
Earthquakes happen when the bedrock on either side of a fault suddenly moves and releases energy,
shaking the ground. The two tectonic plates are constantly moving (which can be measured by GPS), but
there are not continual earthquakes. Why? Because the two sides are locked together by friction along the
fault. As the plates continue to move, the stress builds up along the stuck fault. Once the stress builds up
enough, it will overcome the friction, the two sides will suddenly move, and there will be an earthquake.
Over time, the stress will build up once again. This explanation of why earthquakes occur is called the
elastic rebound theory.
This lab is modified from a lab developed by Karen M. Kortz (Community College of Rhode Island) and Jessica J.
Smay (San Jose City College) as a part of the GETSI Initiative.
GEOL 121: Earthquakes, GPS, and Plate Motion Lab
GPS stations can measure the long-term movement of the ground, indicating the tectonic plate motion and
resulting build-up of stress along the fault. GPS stations can also measure how far the ground near a fault
moves during an earthquake.
2. Read the paragraphs above. How can GPS stations be used to predict where earthquakes happen?
The GPS stations can be used to see where the movement and earthquakes are.
3. Earthquakes happen where stress builds up along a fault because the two sides of the fault are moving
at ______________________ (the same / different) rates.
The map shows vectors indicating the motion of four GPS stations, and the letters indicate three locations.
4. Write a hypothesis explaining which location is most likely to experience earthquakes by filling in the
blanks:
Location _____ (A / B / C) is mostly likely to experience earthquakes because the surrounding ground is
moving ______________________ (faster / slower / at different speeds).
5. Circle how confident you are in your hypothesis.
Not confident
Somewhat confident
Confident
Part 2: Observing and describing long-term rates from GPS data (4pts.)
Below are data from three GPS stations in Central California. In this part of the activity, you will make
observations to describe the data related to the long-term motion of the GPS stations. You will then apply
your hypothesis to make predictions about where you expect earthquakes to happen. Larger versions of
these figures are included separately.
2
GEOL 121: Earthquakes, GPS, and Plate Motion Lab
When scientists look at data in graphs, they look for overall trends and describe the data using words and
numbers. Answer the following questions to describe your observations of the data as a scientist.
6. Pick a five-year interval and fill in the tables below to calculate the overall long-term rate in each
direction (north–south and east–west) that the GPS station is moving. Remember to include units.
North or South
CARH
CAND
P294
Is the station traveling north or south?
north
south
north
south
north
south
Distance (difference in position from the
beginning to the end)
150mm
90mm
60mm
Time (years from the beginning to the end)
5 years
5 years
5 years
Long-term rate (distance divided by time)
30mm/year
18mm/year
12mm/year
East or West
CARH
CAND
P294
Is the station traveling east or west?
east
west
east
west
east
west
Distance (difference in position from the
beginning to the end)
110mm
50mm
50mm
Time (years from the beginning to the end)
5 years
5 years
5 years
Long-term rate (distance divided by time)
22mm/year
10mm/year
10mm/year
To calculate the total rate of movement, use the math trick: square the north–south rate, square the
east–west rate, and add them together; then take the square root of that sum. Here is the equation:
total rate =
√
(north or south rate)
2
+ (east or west rate)
2
7. Fill in the table below by calculating the total rate and using the directions from Question 6.
CARH
CAND
P294
Total rate of
movement with units
514mm/year
118mm/year
112mm/year
Direction of
movement
northeast
northwest
southeast
southwest
northeast
northwest
southeast
southwest
northeast
northwest
southeast
southwest
8. Use the data from the table to create vectors showing the long-term rate of movement of the GPS
stations on the grids.
3
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GEOL 121: Earthquakes, GPS, and Plate Motion Lab
9. Transfer the vector arrows onto the map starting from the correct GPS station. Pay particular attention
that the arrow length is correct relative to the other stations.
10. Do your calculated rates and directions (Question 7) match the rates and directions in the vectors
(Question 7—use the scale next to the grid to measure the length of the vector)?
Yes
No
(if not, you will need to make changes so they do match)
11. Examine your hypothesis and make a prediction of where you would expect earthquakes:
near CARH
between CARH & CAND
near CAND
between CAND & P294
near P294
Circle the phrase below that explains your prediction:
It/they are moving faster.
It/they are moving at different rates.
It/they are farthest apart.
It/they are moving together.
The two stations you chose are moving in the same direction, but they’re getting farther apart each year
because they’re moving at different rates. Use the stations you chose in your answer above to answer the
next questions.
12. To calculate how much further apart the two stations are getting, you need to __________ (add /
subtract) their rates because the stations are moving in __________ (the same / different) direction.
13. Using the rates you calculated for each of the stations, calculate how much farther apart the stations
will be each year.
1 year= 396mm 5years=1980mm 10 years=3960mm
14. How much farther apart will the stations be after… (remember units)
4
GEOL 121: Earthquakes, GPS, and Plate Motion Lab
10 years __________
50 years __________
10 years= 3960 50=19800
The further the stations slowly move apart, the higher the stress on the fault, and the more likely there will
be an earthquake. Also, the further the stations slowly move apart, the further they will suddenly move
during an earthquake, resulting in a larger earthquake.
15. Fill in the relationship between time, likelihood of an earthquake, and earthquake size:
More stress on a fault results in a _______________ (smaller / greater) chance of an earthquake and a
_______________ (smaller / larger) earthquake.
Part 3: Observing and describing GPS data during an earthquake (4 pts.)
GPS can not only measure long-term movement over many years, but can also measure quick motions,
like the ground jumping during an earthquake.
In Part 2, you predicted that the most likely location for an earthquake would be between GPS stations
CARH and CAND. As it turns out, there was an earthquake there, recorded by the GPS stations in 2004.
Before we look at the GPS data from the earthquake, let’s take a step back to think about how ground
motion during an earthquake where tectonic plates slip past each other would appear in GPS graphs, so
we can feel confident that we can interpret the GPS data correctly.
The four graphs below show the north–south position of GPS stations over time.
Station A
Station B
Station C
Station D
16. Which two of the above graphs show a GPS station that is stationary, except when it quickly moves
during an earthquake?
Station A
Station B
Station C
Station D
Explain why you chose this answer.
This is because when we look at Station A and B they are definelity stationary except when there is an
earthquack happening. While C and D are consistently moving during an earthquake.
17. Which one of the above graphs shows a GPS station that is slowly moving north, except when it
quickly moves north during an earthquake?
Station A
Station B
Station C
Station D
Explain why you chose this answer.
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GEOL 121: Earthquakes, GPS, and Plate Motion Lab
Station D is always moving. This is because the Y axis has lots of movement near north
during an earthquake.
18. For the station you chose for the previous question, draw
how the graph would look if the earthquake moved the station
twice as far.
Consider a fault oriented northwest–southeast along the transform plate boundary in California. The entire
area is moving toward the northwest. Imagine there is a GPS station on either side of the fault.
GPS station E
GPS station F
GPS station G
GPS station H
19. During the earthquake, which station shows a GPS station that moved to the northwest?
E
F
G
H
20. During the earthquake, which station shows a GPS station that moved to the southeast?
E
F
G
H
Station CARH is on the western side of the San Andreas Fault (the transform plate boundary in
California) and Station CAND on the eastern side. In this part of the activity, you will make observations
to describe the data showing movement during an earthquake that moved the stations on both sides of the
fault. Larger versions of these figures are included separately.
6
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GEOL 121: Earthquakes, GPS, and Plate Motion Lab
21. How do you know there was an earthquake?
I believe this because you can seen the sudden change that happenes in the direction of the line on the gps
Here we will calculate the total amount of displacement along the fault during the earthquake. To do so,
you will first need to figure out amount of slip from an earthquake a single GPS station recorded: (1)
Draw a straight line indicating the long-term trend along the dots showing the GPS position before and
after the earthquake. (2) Draw a vertical line at the time of the earthquake (since it took no time). (3) The
difference in the before and after position (from lines showing the long-term rate) along the vertical line is
the amount the ground moved as measured by the GPS station during the earthquake.
22. Once you have the slip recorded by the GPS station in the north–south and east–west directions, you
need to apply the equation you learned to combine the north–south and east–west directions of movement
(in Question 7). Don’t forget to include units.
Total slip of Station CARH during the earthquake: __________
In what direction?
northeast
northwest
southeast
southwest
Total slip of Station CAND during the earthquake: __________
In what direction?
northeast
northwest
southeast
southwest
The ground on both sides of the fault moves, so to calculate the total displacement along the fault, the
movement of GPS stations on either side of the fault must both be measured.
23. To calculate the total displacement, you need to __________ (add / subtract) their rates because the
stations are moving in __________ (the same / different) directions.
Total overall displacement during the earthquake: _210mm_________
24. How many years of building up stress through long-term movement (Question 13) were needed to
equal the distance of total displacement during the earthquake (Question 23)?
I think it would be 4 ish years for the long term movement while when we look at the total amount of
displacement on a fault we can see its related to the size of the earthquake. So as measured by the moment
magnitude. For example, magnitudes between 5 and 6 can cause some damage, between 6 and 7 often
cause a fair amount of damage, and greater than 7 generally causes the worst damage.
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GEOL 121: Earthquakes, GPS, and Plate Motion Lab
Part 4: Interpreting earthquake size from GPS data (2 pts.)
The total amount of displacement on a fault is related to the size of earthquake, as measured by the
moment magnitude. The moment magnitude does not measure the damage done, but it is related. For
example, magnitudes between 5 and 6 can cause minor damage, between 6 and 7 often cause a lot of
damage, and greater than 7 generally cause severe damage.
25. Use the displacement you calculated in
Question 23 to estimate the moment magnitude
of the earthquake using the graph to the right.
Moment magnitude = _6.2__________
26. In the time since the earthquake in 2004, how much new potential displacement has built up? Use the
long-term rates (Question 13) to calculate this.
632
27. If there were an earthquake today that has the displacement you just calculated, what would the
earthquake’s moment magnitude be?
6.8
28. What sort of damage could it cause?
minor damage
a lot of damage
severe damage
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GEOL 121: Earthquakes, GPS, and Plate Motion Lab
Part 5: Applying data interpretation to society (6 pts.)
Scientists use their interpretations of what is happening in the world around us to learn how society may
be affected and to help people make informed decisions. In this part, you will apply your interpretations
of your observations of the motion of the GPS station in California to help a person make an informed
decision.
Look at the map below. Each arrow is a velocity vector, calculated in the same way that you calculated
vectors earlier in this activity. Some of the arrows are bold, but that is to make them easier to see, and
they do not have a different meaning. Note the arrow for scale at the bottom left, showing the length of a
25 mm/year vector.
Imagine you have a friend Alix who says, “I would like to live near one of the jobs I’ve been offered in
Southern California. I narrowed it down to the three locations circled on the map. However, I can’t afford
earthquake insurance. Where do you think I should live?”
29. Where do you think your friend should move? Formulate an argument to support your
recommendation, keeping your hypothesis in mind. Write a letter to your friend with the purpose of
encouraging or discouraging them to move to each of the locations to avoid earthquake hazards, using
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GEOL 121: Earthquakes, GPS, and Plate Motion Lab
GPS data from California to support your argument. You will need to explain to your friend how GPS
station motion can play a role in learning about earthquakes.
Hey ALIX,
I think it's important for you to understand some of these locations so let me explain it to you.
First of all I want you to keep in mind that this data gives us the movement of these gps stations.
This movement tells us about plate tectonics and it also helps us understand the locations of the
earthquakes. Now when we look at Borrego Springs and Palm Springs Are i believe are the
prime locations for earthquakes, this is due to the fact that the surrounding ground can be seen as
moving at different speeds. This is shown by the arrows. El Cajon is gonna be the best place
because it moves at the same speed. I hope this information helps!
Be sure to include the following points in your letter to receive full credit:
• You include a clear statement about what advice you would give your friend.
• You use words to describe the data supporting your argument.
• You use numerical rates (numbers plus units based on the size of the vectors) to support your argument.
Correctly include what the rate measures.
• You refer back to your hypothesis.
• You explain the link between GPS motion, plate motion, and earthquakes.
• You compare this location to the plate movement and earthquake in Parkfield (measured by stations
CARH and CAND).
Part 6: Reflecting on your results (2 pts.)
Scientists reflect on the decisions they make while solving a problem. They also think about how they
may change their approach the next time, perhaps because they learned by doing something the hard way
or perhaps because they came up with ways to simplify their approach.
30. Assumptions in science are things that you assume to be true but you cannot confirm that it is true.
Scientists have to make assumptions because the world is very complicated and we do not have a limitless
amount of time, data, or instruments to confirm every assumption.
Listed below are some of the assumptions we made when we used data from bedrock GPS stations in
California to make an argument of worldwide consequences. Circle which one is NOT an assumption.
It is safer where GPS stations move at the same rate.
The GPS motion is the plate motion.
Other faults act similar to these in California.
The stations were moving to the northwest.
Active faults are in areas where the rates on the two sides are different.
31. If you could have one more piece of information to support your argument, what data would you
collect? Explain how you would use this information to support your argument.
I think one tjing that would really help is having some sort of Statistics. Then we can fully
understand the true amount of where each of these earthquakes occur. And the earthquakes that
occur the most.
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GEOL 121: Earthquakes, GPS, and Plate Motion Lab
Think about how you approached answering the questions in this entire activity.
32. What aspect of working with the GPS data was easiest for you?
I had an easy time with cauclating the different slips
33. What aspect of working with the GPS data was hardest for you?
I had a hard time with drawing the vector arrows
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