Detecting Cascadia's changing shape with GPS | Lessons on Plate Tectonics

Nancy West (UNAVCO), Shelley Olds (EarthScope Consortium), & David Thesenga (Alexander Dawson School)
EarthScope Consortium logo. Concentric circles in red grading to purple.
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Summary

Research-grade Global Positioning Systems (GPS) allow students to deduce that Earth's crust is changing shape in measurable ways. From data gathered by EarthScope's Plate Boundary Observatory, students discover that the Pacific Northwest of the United States and coastal British Columbia — the Cascadia region - are geologically active: tectonic plates move and collide; they shift and buckle; continental crust deforms; regions warp; rocks crumple, bend, and will break.

In this module, students use data, hands-on physical models, and computer simulations to understand subduction zone tectonics, plate tectonics, earthquakes, tsunamis, faulting, and folding. The initial activity uses hands-on physical models to develop intuition about deformation and distortion to qualitatively understand and interpret strain. Students learn about deformation and how as segments of the crust move, rotate, and change shape (distort) under the influence of plate tectonics, the land is deformed. (The distortion of the land is called "strain"). They analyze data measuring crustal processes that escalate towards earthquakes and other seismic events. The module teaches about great earthquakes and resulting tsunamis. It has a special focus, though, on GPS data that show Cascadia gradually deforming—until the next great quake (Mw 8.5 or greater) occurs. Students use mathematics in the deformation lessons: they can use math as basic as the Pythagorean theorem or as sophisticated as matrix algebra in the context of vectors. Materials explicitly connect science and math.

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Context

Audience

This lesson was developed for high school and middle school students, grades 6 - 12. However, its focus on data makes it adaptable for introductory college courses.

Skills and concepts that students must have mastered

Students must be able to graph GPS time series data and to add vectors graphically. If they flounder, the activity "Introduction to graphing of GPS data" is designed for novice graphers.

How the activity is situated in the course

Students should have previously done the activity, "Measuring Plate Motion with GPS: Iceland," before doing this set of activities. The module will take a minimum of a week. The hands-on activities can be done in 1 to 2 classroom periods.

PREQUEL ACTIVITY: Introduction to Graphing GPS data

This lesson has an optional prequel, "Pure and simple graphing GPS data," designed for students who cannot yet graph earth science data skillfully or confidently. Its first two parts teach students to graph position vs. time, and its last part dovetails with this lesson. It teaches about velocity vectors by graphing position data over five years.

Don't have the full week available? There are some options that will still allow your students to be able to explore the data and get a feel for what is happening in Cascadia:

  • ONE CLASS PERIOD OPTION: In this activity students work with GPS data to explore plate motion and deformation in the Pacific Northwest. By analyzing multiple GPS Time Series Plots they can determine the direction and rate of regional deformation. The download contains both the Student Worksheet along with the recommended answer key. Short Cascadia Worksheet (Acrobat (PDF) 2.8MB Jan14 22)
  • TWO CLASS PERIOD OPTION: In this option, students learn to read GPS time series plots and apply that knowledge to evaluating the earthquake hazard in Cascadia. They observe that in the Pacific Northwest the western edge of the North American plate is moving northeastward compared to the interior of the North American continent. These observations support the hypothesis that the plate boundary is "locked" and building up strain that must eventually release in the next great Cascadia earthquake. After exploring the GPS data the class can watch a short 4-minute animation that helps visualize the processes involved.

Goals

Content/concepts goals for this activity

Students will be able to:

  • Describe the configuration of tectonic plates in Cascadia
  • Describe effects of great earthquakes arising from subduction
  • Define or describe deformation and strain
  • Explain how subduction causes crustal deformation
  • Explain how a GPS works and measures deformation
  • Graph GPS data by hand and interpret graphs of GPS data
  • Determine strain graphically, qualitatively, and even perhaps quantitatively in a triangle of crust defined by three GPS stations
  • Describe instruments used to measure or monitor Cascadia

Higher order thinking skills goals for this activity

Use data to inform decisions

Other skills goals for this activity

uNot applicable

Description and Teaching Materials

Summary

Research-grade Global Positioning Systems (GPS) allow students to deduce that Earth's crust is changing shape in measurable ways. From data gathered by EarthScope's Plate Boundary Observatory, students discover that the Pacific Northwest of the United States and coastal British Columbia — the Cascadia region - are geologically active: tectonic plates move and collide; they shift and buckle; continental crust deforms; regions warp; rocks crumple, bend, and will break.

In this module, students use data, hands-on physical models, and computer simulations to understand subduction zone tectonics, plate tectonics, earthquakes, tsunamis, faulting, and folding. The initial activity uses hands-on physical models to develop intuition about deformation and distortion to qualitatively understand and interpret strain. Students learn about deformation and that as segments of the crust move, rotate, and change shape (distort) under the influence of plate tectonics, the land is deformed. (The distortion of the land is called "strain"). They analyze data measuring crustal processes that escalate towards earthquakes and other seismic events. The module teaches about great earthquakes and resulting tsunamis. It has a special focus, though, on GPS data that show Cascadia gradually deforming—until the next great quake (Mw 8.5 or greater) occurs. Students use mathematics in the deformation lessons: they can use math as basic as the Pythagorean theorem or as sophisticated as matrix algebra in the context of vectors. Materials explicitly connect science and math.

Organization:

This module consists of three components:

  1. Introductory pieces to engage your students and evaluate what they already know
  2. Exploration and explanation of Cascadian plate tectonics—the tectonic regime, the resulting crustal deformation, earthquakes, and tsunamis; and
  3. Concluding pieces in which students put their knowledge into action and you and they assess what they have learned.

COMPLETE MODULE DOWNLOAD

All files related to this module (including the supplementary math lessons) can be downloaded here Cascadia Modiule - ALL Files (Zip Archive 146.2MB Jun10 22). Individual files can be downloaded as needed below.

Teaching Notes and Tips

General Procedure & Lesson Resources

The figure below lays out the general sequence. Numbers on the figure correspond to the steps which follow below. Each step (Parts 1 - 5) has additional overview information located in the Cascadia Module Overview - Teacher (Acrobat (PDF) 6.8MB Jun10 22).

Part 1.

Engage your students—Use suggested resources and activities to draw your students into these lessons with videos, images, or an activity with a smartphone or an iPad operating as a seismometer. Three topics might do the trick: the story of how the January 26, 1700 earthquake was decoded; the danger of megathrust quakes and giant tsunamis; andau couranttechnology.

Supporting Files: Cascadia Module - Engage Portion (Acrobat (PDF) 6.5MB Jun10 22) - teacher manual PDF includes student handouts.

Part 2.

Find out what they already know—[Evaluate] about subduction zones or convergent tectonics, earthquakes and tsunamis, GPS, and deformation.

Part 3.

Promote exploration and explanation—[Explore and Explain] Provide resources and guide students to explore Cascadian plate tectonics, deformation measured as it transpires, earthquakes and tsunamis.

A.Cascadia tectonic setting—Have students learn the tectonic playing field of Cascadia. Students can explore, or you can show them, a number of online sites that outline tectonic plates via earthquake epicenters, volcanoes, bathymetry, and continental physiography. If you "flip" your instruction, this could be a homework assignment.

Supporting Websites and Activity:

B.  Deformation, including strain—Have students explore deformation and strain (distortion) with physical models and GPS data.  Students can analyze GPS data simply by plotting points on a graph (a separate activity supports students who struggle with that) and comparing graphs qualitatively.  They can analyze data visually by drawing arrows showing the direction GPS stations move and how far they move.  They can use the Pythagorean theorem, sines and cosines, and/or a spreadsheet-based calculator.  Which method(s) your students use is your call.  The module includes materials that explicitly connect science and mathematics.

Supporting Activities (each zip file contains pdf documents for both teachers and students:

  • Hands-on Activity: Physical Models of Strain Cascadia Module - Explore Physical Models (Acrobat (PDF) 3MB Jun10 22) In these five activities, students measure and observe strain in physical models. Students explore strain in one-dimension using bungee cords and compressional springs in the first two activities. The third activity is two-dimensional with a high-tech, high-performance athletic tee shirt. The fourth demonstrates pure strain with Silly Putty®, and the last shows simple strain in two-dimensions (essentially), using a stack of cards.
  • Reading Activity: About Strain Cascadia Module - Explore Strain (Zip Archive 7.4MB Jun10 22)
  • SERC EarthScope Activity: Understanding GPS: Measuring Plate Motion with GPS: Iceland This lesson teaches students to understand the architecture of GPS—from satellites to research quality stations on the ground. This is done with physical models and a presentation. Then students learn to interpret data for the station's position through time ("time series plots"). Students represent time series data as velocity vectors and add the vectors to create a total horizontal velocity vector. They apply their skills to discover that the Mid-Atlantic Ridge is rifting Iceland. They cement and expand their understanding of GPS data with an abstraction using cars and maps. Finally, they explore GPS vectors in the context of global plate tectonics.

  • Activity: Determining strain graphically Cascadia Module - Explore: Determining Strain Graphically (Zip Archive 2.7MB Jun10 22) In this activity, students explore the deformation graphically within an area bounded by a triangle of GPS stations. They do it graphically, using a map, velocity data garnered from GPS stations, and graph paper. The activity allows them to pull out the translation component of deformation and to see (literally) crustal distortion within the triangle of stations. The activity can culminate in students using a spreadsheet-based calculator to determine strain quantitatively.
  • Activity: Velocity Maps Cascadia Module- Explore: Velocity Maps (Zip Archive 1.7MB Jun10 22) In this activity, students manipulate velocity vectors that they pulled from GPS time series data. Their immediate goal is to determine the total horizontal velocity for each station. This activity is an early step in the activity "Determining strain graphically."

 

 

 

C.  Earthquakes—Teach about earthquakes as resulting from too much strain for brittle Earth materials to withstand. (Where a plate is deep and warm enough, crustal shortening from subduction can cause folding instead of faulting. Simulations demonstrate where this can occur in a subduction zone like Cascadia.)

D.  Tsunamis— Follow up earthquakes with the tsunamis that sometimes ensue.

Part 4.  

[Elaborate] upon new knowledge and extend to action—ask your students to think about the future.  From what they have learned about tectonics, geological history, deformation, and strain, what do they see in the tea leaves for the future of Cascadia? If they live there, what actions will they take?  And if they do not live there, what actions will they take?

Part 5.  

Assess what students have learned— [Evaluate] what your students have learned from this module.


Assessment

Did your students learn what you wanted them to learn? Have they met your objectives? You can ask them to return to the questions you asked in the preliminary assessment and have them describe what they learned. How are their answers different? Do they think or feel differently about earthquakes, tsunamis, Cascadia, the human effects of plate tectonics, and technology?

If you asked them originally to make a concept map, now have them revise it using a different color so that they can see their new knowledge or changed understanding. Similarly, if you gave them a writing prompt, give them the prompt again and, after they've written, hand back their original responses for comparison.

And, of course you can grade the lab sheets for activities.

References and Resources

Explain and Explore Supplement: Mathematics allied with deformation and strain

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