Earthquakes, GPS, and Plate Motion Lab - Jayse W

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Colorado State University, Fort Collins *

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120

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Geology

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Dec 6, 2023

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Name ________Jayse Wagner____________________ Lab Section _________ 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 track movement, but when there are sharp movements there is likely an earthquake. 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 __B__ (A / B / C) is mostly likely to experience earthquakes because the surrounding ground is moving ____at different speeds________ (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 A B C

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) -120mm -50mm -50mm Time (years from the beginning to the end) 5 years 5 years 5 years Long-term rate (distance divided by time) -24mm/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 38.74mm 20.6mm 15.62mm 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. 30mm/year 3 Figure 1. North and East GPS data from station CARH, CAND, and P294 near Parkfield in California from the beginning of January 2006 to 2018.

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. 59.43mm 14. How much farther apart will the stations be after… (remember units) 4

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