Exploring Tectonic Motions of Alaska & Western United States with GPS

Shelley Olds, UNAVCO
Beth Pratt-Sitaula, UNAVCO

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Students analyze data from GPS data represented as vectors on a map of Alaska or western United States to study tectonic motions at plate boundaries and within the North American and Pacific tectonic plates. Students discover whether motion is compressing, extending, or sliding the land within each region of the plate. By observing the vector lengths and directions, students interpret the motion within Alaska or several regions of Western USA (Pacific Northwest, Basin & Range, and California). To synthesize their findings, students identify two locations most likely to have earthquakes. Students need to be able to defend their choices by providing evidence based on the tectonic motions from the map/poster and seismic hazards.

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This activity was developed for middle school and high 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 should be able to read maps and understand map scale.

How the activity is situated in the course

This activity can be used at any time in an earth science class particularly with in a sequence of lessons about plate tectonics. It can be used as an introductory activity for students to explore current plate motions and to learn about compression, extension, and horizontal slip. The activity takes about one hour of class time (or a bit more if the final element using the online tool, GPS Velocity Viewer, is included).


Content/concepts goals for this activity

Learners will be able to:

  • Describe how velocity vectors from GPS stations inform us about tectonic motion and plate boundaries.
  • Describe and draw a velocity vector
  • Analyze and describe regional plate motion data as represented as vectors.
  • Interpret crustal deformation based on velocity vector map.
  • Identify, discuss and defend the locations they chose that are most likely to have earthquakes.

Higher order thinking skills goals for this activity

ot applicable

Other skills goals for this activity

Using maps

Description and Teaching Materials

Student start with with learning a bit about what geodesy is and how GPS works and then go on to work with maps that show plate GPS-measured motions. The activity can be further extended (pg 3-4) by having students use the online tool, GPS Velocity Viewer and learn a bit about reference frames.

These zipped files include student exercises in docx and pdf, tectonic motions posters at 8.5x11", and seismic hazard maps for each region.


GPS Map Analysis

Using a map showing the horizontal velocities of GPS stations in the Network of the Americas (NOTA) and other GPS networks in Alaska and Western United States, students are able to describe the motions in different regions by interpreting the vectors resulting from long-term high-precision Global Positioning System (GPS) data.

Materials: Rulers and print outs of the posters and student handout.
Instructor should print out copies of the Tectonic Motions poster/s that they intend to have students use: Alaska and/or Western USA. 8.5x11" versions are included in the zipped file below. Full size versions can be downloaded from UNAVCO's Tectonic Motions Posters webpage or requested from UNAVCO.

GPS Velocity Viewer Online Tool & Reference Frames

The final element the exercise can really help students extend their knowledge from the maps to the entire world by using the online tool GPS Velocity Viewer. This part can be skipped if it is not practical to use computers in the classroom. The Alaska version of the activity also has some information about GPS Reference Frames (more resources on those below).

Teaching Notes and Tips

  • For instructors who need a little more background on GPS, plate tectonics, and reference frames, here are some resources that could be reviewed. More options are below in References.
  • Particularly if you have younger learners, it might help to demonstrate the measuring of one of the vectors and converting that to mm/yr of real motion in that spot.
  • Students do sometimes struggle with understanding how differences in adjacent vectors (length and/or direction) help us learn about the compression, extension, or strike-slip in that area. Using one's hands can be a helpful way to makes sense of this. For instance, the left hand moving faster away from you than the right can help them see strike slip motion. Another activity that can be useful for this is Measuring Ground Motion with GPS.
  • A possible extension would be to visit a nearby Network of the Americas (NOTA) GPS station. Check the NOTA website for the location map. There are over 1100 stations! One might be near your school.
    Note: when installed, most of these stations were part of different GPS networks that have since been combined into NOTA. For instance you might still see references to the earlier Plate Boundary Observatory (PBO) network.


Formative assessment of student understanding can be gathered from classroom observation and discussions with individuals or small groups.

The student exercise serves as the summative assessment for the activity. Some questions have clearly correct answers. For open-ended questions, students can be assessed based on a simple 2-point scale.

  • 2 points = correct answer with thorough supporting evidence and/or complete description
  • 1 point = answer not completely correct or lacking thorough supporting evidence or description
  • 0 points = incorrect answer

Exercise answer keys

References and Resources