# Exploring California's Plate Motion and Deformation with GPS | Lessons on Plate Tectonics

Initial Publication Date: February 27, 2022

#### Summary

Students analyze data to study the motion of the Pacific and North American tectonic plates. From GPS data, students detect relative motion between the plates in the San Andreas fault zone--with and without earthquakes. To get to that discovery, they use physical models to understand the architecture of GPS, from satellites to sensitive stations on the ground. They learn to interpret time series data collected by stations (in the spreading regime of Iceland), to cast data as horizontal north-south and east-west vectors, and to add those vectors head-to-tail.

Students then apply their skills and understanding to data in the context of the strike-slip fault zone of a transform plate boundary. They interpret time series plots from an earthquake in Parkfield, CA to calculate the resulting slip on the fault and (optionally) the earthquake's magnitude.

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## Context

#### Audience

This lesson 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 use a web browser.
• Students should be familiar with graphing. If they flounder, the activity "Introduction to graphing GPS data" is designed for novice graphers.

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

This lesson can be used at any time in an earth science class. However, in the sequence of lessons about plate tectonics, it fits best during activities about transform boundaries, after activities on divergent and convergent plate boundaries.

INTRODUCTORY LESSON: Measuring Plate Motion with GPS: Iceland, PART I only

Before starting this lesson, the Introductory lesson: Measuring plate motion with GPS, Part 1 is suggested to learn the basics on how GPS works.

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.

It is expected that the investigation will cover three class sessions (45 - 55 minutes).

## Goals

#### Content/concepts goals for this activity

Students will be able to:

• Model and describe the general set up of a GPS—how monuments receive signals from multiple satellites
• Add vectors graphically to create a total horizontal velocity vector
• Calculate the amount of slip along a fault using GPS time series data
• Calculate the magnitude of an earthquake based on the slip on a fault (optional).

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

• Interpret time series plots (position vs. time) qualitatively and quantitatively and represent time series data as velocity vectors, to scale, on a map
• Discuss relative movement of the Pacific and North American plates in California, using GPS data

Not applicable

## Description and Teaching Materials

Summary: Students analyze data to study the motion of the Pacific and North American tectonic plates. From GPS data, students detect relative motion between the plates in the San Andreas fault zone--with and without earthquakes. To get to that discovery, they use physical models to understand the architecture of GPS, from satellites to sensitive stations on the ground. They learn to interpret time series data collected by stations (in the spreading regime of Iceland), to cast data as horizontal north-south and east-west vectors, and to add those vectors head-to-tail.

Students then apply their skills and understanding to data in the context of the strike-slip fault zone of a transform plate boundary. They interpret time series plots from an earthquake in Parkfield, CA to calculate the resulting slip on the fault and (optionally) the earthquake's magnitude.

Organization: This activity consists of four main parts, the first two coming from a companion activity.

1. Modeling GPS stations (or "monuments") and the satellite network that feeds time signals to the monuments. From "Measuring Plate Motion with GPS: Iceland."
2. Making sense of GPS data--understanding time series data in order to develop total horizontal velocity vectors. Also from "Measuring Plate Motion with GPS: Iceland."
3. Interpreting the vectors in the context of the strike-slip boundary between the Pacific and North American plates.
4. Inferring an earthquake near Parkfield, CA from GPS time series data.

General Procedure:

1. Review with your students (briefly) evidence for plate tectonics and the major kinds of tectonic boundaries. Divergent and transform boundaries appear in this lesson.
2. Assess your students' knowledge coming into these lessons. How much do they know about GPS, for instance?
3. Work from the PowerPoint presentation "Measuring plate motion with GPS: Introducing GPS to study tectonic plates as they move, twist, and crumple," as students do the activity.
4. Have your students work from the lab sheets for this activity and support them with its PowerPoint presentation, "Exploring plate motion and deformation in California using GPS data."
5. Assess what your students have learned in this lesson.

### Lesson Resources

Student and teacher files are available as PDF's. If you need an editable version, please contact education @ earthscope.org

A supporting presentation in both PDF and PowerPoint formats is also available California Presentation Files (Zip Archive 24MB Jun11 22)

## Teaching Notes and Tips

### Before you begin...

Students need a general understanding of plate tectonics for this lesson. Many excellent learning resources are available online covering evidence that support the theory of plate tectonics. Many of these resources take a global view of plate tectonics; this lesson explores how high-precision GPS can be used to measure regional plate movement and deformation.

### Teaching tips and general background

A variety of geologic phenomena including earthquakes, volcanic eruptions, and mountain building occur at plate boundaries, all of which cause the Earth's surface, the crust, to deform. When deformation occurs, points on Earth's surface change location (north-south, east-west, up-down). Precise GPS instruments can measure the change in position. Earth scientists use this data to record how much and how quickly Earth's crust is moving due to plate tectonics and to better understand the underlying processes of the deformation.

When an earthquake occurs, the ground on either side of the fault moves instantaneously, sometimes causing strong shaking. GPS measurements enable scientists to map these displacements and determine how much slip has taken place along the fault and where slip occurred. Although we cannot feel it, the crust on either side of the fault continues to slip after the strong shaking is over, sometimes for several years. Scientists also record this motion with GPS.

### Specific Procedures

Start with a brief review of the evidence for plate tectonics. This could include a brief discussion about multiple paths of evidence, such as shared fossil records across multiple continents, the pattern of earthquakes and volcanoes around the world, magnetic reversals in oceanic crust, and how the boundaries of the continents fit together like a puzzle.

Find out what your students already know about GPS. This will help you tailor instruction and will let students see how much they learn. Ask them, for example, how they use GPS and then to sketch or explain how a GPS works. How do they think geologists could use GPS?

Also, assess their skill and comfort with graphs. If they balk at making or interpreting graphs, consider detouring into "Pure and simple graphing of GPS data," which teaches students to graph scientific data and to interpret graphs. Its first two parts act as a prequel to this, and its last part dovetails with this activity in teaching about velocity vectors.

Open the PowerPoint presentation "Measuring plate motion with GPS: Introducing GPS to study tectonic plates as they move, twist, and crumple." At slide 8, hand your student lab sheets for that activity. Continue the lesson, moving among the presentation, models, and student lab sheets. (YouTube videos explain specific steps—they are designed for you, not for your students.)

Hand out lab sheets for this activity and open the PowerPoint presentation "Exploring plate motion and deformation in California using GPS data." Work through slide 6 quickly—this will be review. Help your students as they analyze and interpret data, using the PowerPoint presentation to support them, especially in Part 2. Students should work in pairs. However, with confident and adept students, this activity could be done as homework.

## Assessment

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

Ask students to summarize the activities they have done. Discuss the connection to plate tectonics and the increasing role GPS is playing in studying current tectonic events. This could be done in writing, as a Think-Pair-Share, in an interactive web project, or as a whole class brainstorming session. This discussion can act as summative assessment; of course, you can also grade their lab sheets.

If opting to have the student exercise serve as a summative assessment for the activity, answer keys are provided along with a suggested grading scale. 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 a complete description
• 1 point = answer not completely correct or lacking thorough supporting evidence or description
• 0 points = incorrect answer

Exercise answer keys can be found on pages 5-14 of the combined teacher guide California Plate Motion and Deformation - Teacher Files (Acrobat (PDF) 10.7MB Jun11 22)

## References and Resources

### Data Resources from the Network of the Americas operated by EarthScope Consortium

The time series data is in csv, east-north-vertical format, in NAM14 Reference frame, 24 hour final solutions. The time series plots are shown in NAM14. The station pages include station location, additional reference frames, station plots, and data solutions.