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Detecting Cascadia’s changing shape with GPS



Students are able to explain that the Juan de Fuca plate subducts under the North American plate, sometimes with disastrous consequences. They can describe evidence for historic great earthquakes and discuss the prospect for future ones, using Global Positioning System and other data. They can demonstrate that Cascadia’s shape is changing.



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.

Teaching Time

The full module will take a minimum of a week. The hands-on activities can be done in 1 to 2 classroom periods.

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 lesson is
situated in the course

Students should have done the activity, “Measuring plate motion with GPS,” before doing this set of activities. The module will take a minimum of a week.

Next Generation Science Standards

Performance Expectations: MS-ESS2-2, MS-ESS3-2, and HS-ESS1-5, HS-ESS2-1, HS-ESS2-3, HS-ESS3-1, HS-ETS1-3.


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
  • Use data to inform decisions


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.


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.

Download Materials

Individual files:

Teacher Module Overview [pdf] [docx]

18 MB • v: September 2016

This module overview provides a complete description of the module with links to many resources for students. It uses the 5-E's as a framework for the module.

Engage: Engaging your students: Solve the mystery of past earthquakes and tsunamis in Cascadia as a jigsaw.

[pdf] [docx]

9 MB • v: September 2016

Teacher & Student materials to engage your students: Optional activities include a jigsaw activity for the students, viewing animations, and interacting with Smart devices.

Explain and Explore: Tectonic Setting

Explain and Explore: Deformation and strain

Supporting materials

Explain and Explore Supplement: Mathematics allied with deformation and strain

  • Reading activity: Math you need—vectors and vector addition

    For students:
    [pdf] [docx]

    6 MB • v: September 2016

    Written for students, this two-page text explains what a vector is and how to add vectors by putting the head of one vector against the tail of another and drawing a new arrow that connects the first one’s tail to the second one’s head (Fig. 19). Students can analyze strain graphically knowing only this.

  • Reading Activity: Two faces of vectors – vectors in science and math

    For students:
    [pdf] [docx]

    1 MB • v: September 2016

    Written for students, this article takes students as far as they want to go in connecting science and math in the context of strain. Mathematically adept students can run ahead on their own with a sequence spelled out for them. Topics include using the Pythagorean theorem to find the length of the total vector; measuring the vector’s azimuth with a protractor or compass; calculating the vector’s azimuth with sines and cosines; adding vectors analytically; and manipulating vectors as matrices. Recommendations for Khan Academy videos are included so that students can learn independently.

  • Reading Activity: A summary of vectors and vector arithmetic

    For students:
    [pdf] [docx]

    1 MB • v: September 2016

    Written for students, this is a primer on three-dimensional vectors. It includes operations on vectors through dot and cross products. This primer would be appropriate for science students who are in Algebra II or higher.

  • Reading Activity: A summary of matrices and matrix math

    For students:
    [pdf] [docx]

    1 MB • v: September 2016

    This article parallels the summary of vectors, focusing instead on applications of matrices to science. It, too, might be of interest to students in Algebra II or higher.

  • Instructor notes: Vectors and vector mathematics

    [pdf] [docx]

    1 MB • v: September 2016

    For instructors, this article is the companion to the student readings on vectors and matrices. It relates math to steps in the activities and gives tips about equipment (e.g. conventional protractors vs. circular ones). Explore the math connections for your own pleasure.

Related Lessons

Infinitesimal strain analysis using GPS data: Module for structural geology or geophysics course

Prequel activity: Introduction to graphing of GPS data, is designed as an optional prequel for students who cannot yet graph earth science data skillfully or confidently.

Module Development

This work is based on materials provided by the UNAVCO Education and Community Engagement Program, and the GAGE Facility supported by the National Science Foundation (NSF) and National Aeronautics and Space Administration (NASA) under NSF award: EAR 1261833 and through the American Recovery and Reinvestment Act. Authors are Nancy West (UNAVCO) and Shelley Olds (UNAVCO) with curricular input from Vince Cronin (Baylor University), Beth Pratt-Sitaula (UNAVCO), Phil Resor (Wesleyan University) and technical input provided by William Hammond and Corne Kreemer (University of Nevada Reno).

Last modified: Wednesday, 07-Feb-2018 18:28:06 UTC


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