# GPS—Measuring Plate Motion

## Resources

Background
Activities
• GPS Classroom Activity
(pdf / zipped word files)
Vocabulary
Related Animations
• GPS & Earthquake Early Warning
• GPS & Understanding Future Earthquakes in the Pacific Northwest
• Plate Boundaries
• Elastic Rebound- Subduction
• Elastic Rebound- Strike Slip
• Volcano Monitoring

### GPS—Measuring Plate Motion

• For background on this animation series, download Background from the Resources box.
• Animations are available for preview in embedded YouTube.

• Send us feedback.

## How Does Land Jump in an Earthquake?

This animation shows that GPS can record the movement of the leading edge of the overlying continental plate in a subduction zone. The plates are locked and the overlying plate is forced back. When friction is overcome and strain is released, the GPS receiver will snap back toward its original position. This animation is exaggerated to depict the relative motion of plates and GPS as seen in the 2010 Magnitude 8.8 earthquake in Chile where the land in places rebounded 10 meters.

Quicktime Animation ( 4 MB)

## Measuring Deformation and Tilt with GPS

Volcano deformation can provide clues about what is happening deep below the surface.  Two techniques used to monitor deformation include Tiltmeters and GPS. Like a carpenter’s level, an electronic tiltmeter uses a small container filled with a conducting fluid and a “bubble” to measure a change in slope. Tiltmeters measure the amount of tilt in microradians, which is the angle turned by raising one end of a beam one kilometer long the width of a dime (equivalent to 0.00006 degree!).  GPS measures the distance between two points to determine if they are moving further apart, as they might if magma was entering the system.

## Gumdrop Introduction to GPS (Part 1)

Instructional video shows how to conduct 5-step student activity to build gum-drop GPS station, learn how GPS works, then model and graph the GPS movement. Students learn how to read time-series plots and understand how we know the ground is moving.  By Roger Groom (2009 NAGT Earth science teacher award) at Mount Tabor Middle School, Portland OR.

Concepts and PowerPoint developed during a Master Teacher internship with UNAVCO in 2006.

Quicktime Animation ( 14 MB)

## Gumdrop Introduction to GPS (Part 2)

Second part of the gum-drop GPS station activity. Read time-series graphs, and plot vectors to learn how the Pacific Northwest is being pushed by the off-shore oceanic plate as it dives beneath the continental plate. By Roger Groom (2009 NAGT Earth science teacher award) at Mount Tabor Middle School, Portland OR.

Concepts and PowerPoint presentation developed during a Master Teacher internship with UNAVCO in 2006.

Quicktime Animation ( 21 MB)

## Types of Motion in a Subduction Zone

Recent data from the Pacific Northwest and other subduction zones show that there are 3 distinct areas of movement above a subduction zone: 1) constant movement above the locked leading edge, 2) see-saw pattern of back-&-forth movement above a zone that alternately locks then slips in a process called episodic tremor and slip (ETS; see next animation), and 3) no movement far inland above the deeper part of the diving oceanic plate.

Represents data from Earthscope's Plate Boundary Observatory (PBO).

Quicktime Animation ( 2 MB)

## Episodic Tremor and Slip

This animation shows a closeup of the movement of the middle GPS station in the animation above, Here we see the station fixed to the ground which is moving northeast on a ~14-month cycle before sliding back accompanied by a gentle seismic shaking shown in the seismogram.  ETS describes a particular type of pattern observed within convergent boundaries characterised by aseismic slip with a reversal of direction of the ongoing tectonic plate movement in the same region of the local megathrust accompanied by non-earthquake-like tremors.

Quicktime Animation ( 3 MB)

## GPS Measures Extension

Tension created by movements of Earth's tectonic plates have stretched the earth's surface to the breaking point. The entire region has been pulled apart, fracturing the tectonic plates and creating large faults.

Animations and videos are made in partnership with Earthscope, USGS, and Volcano Video & Graphics.

Please send feedback to Jenda Johnson.