# Measuring Ground Motion with GPS: How GPS Works

#### Summary

This activity helps students better understand how GPS measures ground motion. Students work with models of GPS stations and printouts of typical GPS velocity vectors found near different tectonic boundaries.

GPS velocity vectors point in the direction that a GPS station moves as the ground it is anchored to moves. The length of a velocity vector corresponds to the rate of motion. GPS velocity vectors thus provide useful information about how Earth's crust deforms in different tectonic settings.

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## Context

#### Audience

This demonstration can be used with middle school, high school, and introductory undergraduate students, as well as free-choice learning environments.

#### Skills and concepts that students must have mastered

Learners should have a general understanding of GPS. Learners should also have some familiarity with the concept of plate tectonics.

#### How the activity is situated in the course

This demonstration is particularly useful when discussing plate tectonics, plate boundary types, and the use of GPS to measure ground motion. This demonstration is expected to take 5 - 15 minutes.

## Goals

#### Content/concepts goals for this activity

Earth's surface is constantly in motion.

• GPS can be visualized as velocity vectors.
• A velocity vector points in the direction that a GPS station is moving, and its length is proportional to the rate of motion.
• Velocity vectors from GPS data show how Earth's crust moves in different tectonic settings.

#### Higher order thinking skills goals for this activity

• Discuss relative movement of tectonic plates such as the Pacific and North American plates in California, using GPS data

Not applicable

## Teaching Notes and Tips

SA complete run through of the demonstration can be found on our YouTube Channel.

## Assessment

The exercise includes sample questions the learner could answer. These can be used for formative assessment of understanding or they can be graded 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