# Introduction to Graphing GPS data | Lessons on Plate Tectonics

#### Summary

This activity emphasizes making graphs—in order to make interpreting graphs easier. Students graph data measuring how GPS stations move north or south and east or west. They begin by graphing fictitious data and progress to graphing data from several stations in the western United States. They graph north-south vs. east-west motion of a station in order to see that another purpose of plotting data is to make maps. They also develop intuition about vectors.

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## Context

#### Audience

This activity 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 should be familiar with Cartesian coordinate systems (taught beginning in about 4th grade).

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

This activity can be used at any time in an earth science class. However, in the sequence of lessons about plate tectonics, it is an optional prequel to Measuring plate motion with GPS for students who cannot yet graph earth science data skillfully or confidently.

It is expected to take two class sessions (45-55 minutes or can be provided as homework).

## Goals

#### Content/concepts goals for this activity

Students will be able to:

• Make and interpret graphs (of GPS data)
• Interpret time series plots (position vs. time) qualitatively and quantitatively
• Map north vs. east positions to follow a GPS station's location through time
• Derive and describe velocity vectors from a map

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## Description and Teaching Materials

This activity consists of three parts:

• Using fictitious data, graph north vs. time and east vs. time.
• Using real data, graph north vs. time and east vs. time.
• Using real data, graph north vs. east, draw a vector to best fit the data, and measure the vector's orientation and length, thus determining the GPS station's velocity.

MEASURING PLATE MOTION WITH GPS: The next lesson in this sequence is the introductory activity: Measuring plate motion with GPS: Iceland, to learn the basics on how GPS works then learn about Iceland.

## Teaching Notes and Tips

While students first learn to graph in about 4th grade, even high school advanced chemistry, physics, and Earth science students have floundered when asked to graph their lab data by hand. Students can be skilled at using graphing technology—calculators and computers—without understanding the graph. For students who struggle to make or interpret graphs, this activity can guide them to make sense of graphed data from GPS stations used by geoscientists who study crustal deformation and plate tectonics.

This can stand alone as an activity on graphing with earth science data, or it can be a prequel for the following UNAVCO activities:

You can choose to assign some or all of this activity, depending on your goals and your students' needs. Overall, this activity starts with simple graphing of fictional data, builds to graphing real data from GPS stations in Washington and California as they gradually move north or south and east or west, and eventually leads students to create a map from which they can understand and derive GPS velocity vectors

## Assessment

The student exercise serves as the summative assessment for the activity. Some questions have clearly correct answers. Guidance is provided in the Teacher Guide for this lesson.

You can also end with a classroom discussion incorporating questions such as:

• What are the essential elements of a graph?
• How do geologists pay attention to scale? Why?
• Why are graphs a useful tool for geologists?
• What are geologists able to determine about a GPS station by graphing velocity vectors?
• What do you think geologists use velocity vectors from GPS stations for? What are they able to discover about the Earth (Geodesy)?

## References and Resources

### Explore More

For some GPS stations, time series graphs (e.g. North vs. Time) are easy to download online and they include a best-fit trend line drawn on them. Sometimes there are multiple trend lines if there are changes in the station's movement, such as after an earthquake.

You can find the time series graphs by turning on the 'Station Information' option on the UNAVCO Velocity Viewer.