Unit 2.2: Plate motions

Karen Viskupic, Boise State University; based on activities from the Earthscope Consortium

Initial Publication Date: September 20, 2024

Summary

Students consider what information they would need to predict future configurations of the continents and oceans and then complete some "back of the envelope" calculations of slip rates on the San Andreas fault to estimate the amount of time needed for significant changes to occur. Students use the Earthscope GPS Velocity Viewer and Plate Motion Calculator to investigate plate motion directions and rates with respect to different frames of reference. Using these tools will form the basis for predicting future plate configurations in Unit 2.3.

In an optional activity, students use the Earthscope Interactive Earthquake Browser to analyze earthquake frequency and magnitude data and consider how such data could be used to forecast earthquake activity.

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Learning Objectives

At the end of the unit, students will be able to:

  1. Describe the rates at which plate motions occur
  2. Describe the relative motion at a given location with respect to different frames of reference
  3. Use rates of processes (e.g., earthquake slip rates, plate motion rates) to predict the amount of time needed for a geologic change or event to occur.

Context for Use

This activity is intended for use at the beginning of an introductory Earth Science course for college-level students. The activity could be used with any class size, and can be completed in approximately two 75-minute class periods, plus additional time for pre-class and homework assignments. An additional optional activity would take one 75-minute class period.

Students will need access to a computer during class and outside of class to complete the activities in this Unit.

Description and Teaching Materials

Day 1 Plate Tectonics Review; Fault Slip Rates

Day 1 Teaching Materials

Day 1 Pre-class work (same as homework from Unit 2.1)

Students read/watch the following to review plate tectonic theory and answer questions (see teaching materials above):

Day 1 In class

Day 1, Part 1: Review of plate tectonics and discussion about what information is needed to determine future plate configurations (25 min)

  • Students have the opportunity to ask questions about the pre-class (homework) reading and the instructor can give a short review lecture about Earth structure and plate boundaries.
  • The review ends by posing the questions: "What will the configuration of continents and oceans look like in the future?" and "Where will the plate boundaries be?"
    • Students are asked to talk with their neighbors about what information they would need to answer these questions and how they might find that information.

Day 1, Part 2: Calculating slip rates (40 min)

  • After reviewing unit conversions, students complete two calculations using data from the San Andreas Fault system to estimate a slip rate for the San Andreas Fault and estimate the amount of time it will take for a given change to occur. Students can work individually or in pairs.
  • Students answer reflection questions at the end of the activity.

Day 1 Homework

_________________________

OPTIONAL Day 1.5 Earthquake Magnitude and Frequency

This optional activity could be used in a single 60-75 minute class period, or could be used as an add-on to Day 1, especially if less time is needed to review plate boundaries (e.g., if students have prior knowledge or if students are assigned additional reading about plate boundaries). If using it as an add-on to another activity, or if asking students to use the Earthquake Browser to collect data would be too time-consuming or challenging, the instructor could compile data for different regions in advance and have the data table in the student handout completed. This activity was modified from the EarthScope Exploring Rates of Earthquake Occurrence activity (EarthScope, 2024; see References and Resources)

Optional Day 1.5 Teaching Materials

Optional Day In Class

  • Part A: Students use the EarthScope Interactive Earthquake Browser to collect data about earthquake frequency and magnitude in a region of their choosing (from a given set of options) or as assigned by the instructor. Students make a Gutenberg-Richter plot (earthquake frequency vs. magnitude) and describe how such data could be used to forecast future earthquakes. (40 minutes)
    • There is an opportunity to discuss the use of logarithmic plots as students progress through Part A of the activity. The instructor should monitor student progress and bring the class together for a discussion.
  • Part B: Students compare their Gutenberg-Richter plots with those made by classmates who looked at a different region (15 minutes)
    • As students are working on Part B, the instructor may ask students to share their plots with the whole class (e.g., instructor can take photos of student work and compile them in the slide deck; example student plots are included in the slides provided above) to prompt a whole-class discussion about the variability of earthquake rates in different regions
  • Part C: Student reflection and class discussion. Instructor facilitates class discussion about the use of logarithmic scales, data visualizations, which plot students find most valuable, etc. (15 minutes)

Optional Day 1.5 Homework

  • See pre-class work for Day 2 below

____________________________

Day 2: GPS and Plate Motions

Day 2 Teaching Materials

Day 2 Pre-class work

Day 2 In class:

Students use the EarthScope GPS Velocity Viewer and Plate Motion Calculator to investigate plate motion directions and rates. Remind students that these are data they identified as important for predicting what plate boundaries and plate configurations might look like in the future.

The activity includes the following parts:

  • Part A: Make predictions about the relative motion of your current location with respect to several reference frames. (10 min)
  • Part B: Test your predictions by investigating the actual relative motion of your current location and another location of your choice with respect to several reference frames using the GPS Velocity Viewer (Watch "how to" video with class and describe use). (25 min)
  • Part C: Determine actual plate velocities using the Plate Motion Calculator. We recommend doing an example together as a class (for example, answer question 10 on the student handout together). Students also calculate the amount of time it will take for specific events to occur (e.g., When will the Galapagos Islands reach the subduction zone along the west coast of South America?; How long will it take for the Red Sea to double its width) using the Earthscope Plate Motion Calculator. It may also be helpful to review rate calculations, for example using The Math You Need, When You Need It website. (30 min)
  • Part D: Students start to think about what might happen in the future at a place of interest. (10 min)

Day 2 Homework:

  • Complete the in-class activity if more time is needed.

Teaching Notes and Tips

Students may need support in making calculations (unit conversions, rate calculations) and in working with latitude, longitude, and compass directions. Resources are provided in the activities, but may need to be adjusted to provide either more or less background and guidance depending on the backgrounds of your students.

The Day 1 scientist spotlight homework assignment could be used any place in the Unit, but is recommended for use when students have some background with plate tectonics and earthquakes.


Assessment

LO1: Describe the rates at which plate motions occur

  • Day 2 in-class activity

LO2: Describe the relative motion at a given location with respect to different frames of reference

  • Day 2 in-class activity

LO3: Use rates of processes (e.g., earthquake slip rates, plate motion rates) to predict the amount of time needed for a geologic change or event to occur

  • Day 1 and Day 2 in-class activities

References and Resources

EarthScope (2024). Exploring Rates of Earthquake Occurrence. https://www.iris.edu/hq/inclass/lesson/exploring_rates_of_earthquake_occurrence

Egger, A.E. (2003). Earth Structure. Visionlearning Vol. EAS(1).

Egger, A.E. (2003). Origins of Plate Tectonic Theory. Visionlearning Vol. EAS-1(1)

Egger, A.E. (2003). Plate Boundaries. Visionlearning Vol. EAS(2).

Egger, A.E., & Carpi, A. (2008). Using graphs and visual data in science. Visionlearning Vol. POS-1(4)

Hasterok, D., Halpin, J. A., Collins, A. S., Hand, M., Kreemer, C., Gard, M. G., & Glorie, S. (2022). New Maps of Global Geological Provinces and Tectonic Plates. Earth-Science Reviews, 231, 104069. https://doi.org/10.1016/J.EARSCIREV.2022.104069

IRIS (2022) New!! What Drives Plate Tectonics? What Are the Forces Involved? (new convection ending; 2022) [Video] YouTube, 10 Jan. 2022, https://www.youtube.com/watch?v=hUtYyRUBdZQ

Schulz and Wallace (2016). The San Adreas Fault. USGS publication. https://pubs.usgs.gov/gip/earthq3/safaultgip.html

This Dynamic Planet: World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics (1994). Reston, VA: U.S. Dept. of the Interior, U.S. Geological Survey; Denver, CO: U.S. Geological Survey, Map Distribution. https://pubs.usgs.gov/imap/2800/

UNAVCO (2018). How to use the GPS velocity viewer [Video] YouTube https://www.youtube.com/watch?v=9HpFeu80esM

UNAVCO (2019). Measuring plate tectonics with GPS [Video] YouTube https://www.youtube.com/watch?v=S1m1tAGbfL4