Version: Sept 2015
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How fast are we moving?
A quick guide to finding EarthScope Plate Boundary Observatory
GPS station(s) near you
UNAVCO manages the EarthScope Plate Boundary Observatory of GPS stations in the United States
on behalf of the National Science Foundation and manages other networks around the world. This data
is free to the public and can be used to study plate motions, plate and regional deformation, regional
hydrologic, volcanic, and other motions.
Quick look: On the maps below, find the closest GPS velocity vector arrow to your school, park, or
favorite location.
• Each vector arrow shows the velocity of a single GPS station installed permanently to the
ground. If the Earth moves, the GPS stations record this movement.
• The GPS vector’s tail is the starting location of the GPS monument.
• The direction the vector points is the direction the GPS station is moving.
• The length of the vector shows how fast the GPS station is moving.
• Keep in mind that there might be faults, such as the San Andreas fault, between your place and
nearby GPS stations.
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Note about plate motion and
reference frames:
Every tectonic plate on Earth is in
motion. Scientists compare the
motion relative to another tectonic
plate to view the differences in
motion. The maps shown here and
above use the North American
Reference Frame where the interior
regions of North America, such as
Kansas or Nebraska, are not moving.
Changing the reference frame changes
the perspective of plate motion; the
vectors will change length and direction.
The purple vector at the bottom of the
map illustrates a vector moving 25 mm/yr.
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I. To explore plate motion and deformation by viewing the GPS
velocity vectors near a favorite place:
1. Explore further: Google Search for UNAVCO Velocity Viewer.
2. Use the Data Source UNAVCO GPS velocities, NAM08 to use the North America Reference
Frame. The interior of the North American plate is set to zero to more easily see motion and
deformation of the edges of the plate boundary. Or choose another plate as your reference frame.
3. Change Sites displayed, select show one in ten to help the map display more quickly.
4. Once you have zoomed into an area, display more vectors using Sites displayed, such as show
one in three.
5. Are the vectors very short?
• In the mid-continent, the North American plate does not move much in the North America
Reference Frame - change the Data Source to see how the mid-continent moves compared to
another reference frame.
• Change the length of the vectors using Velocity display scale.
6. Learn more about the motion of one GPS
station.
• Click a green balloon on the map to show
• Select Show Station labels and Data Download
then Draw Map
o The GPS station name.
o Horizontal speed – of the ground beneath the
GPS station.
o The direction of motion in degrees from North.
o GPS time series plots and data download (for
UNAVCO GPS stations).
7. Further customize your map by using the controls at the side of the map.
! Velocity display scale changes the length of the vectors.
! Velocity vector color changes the color of the vectors.
! Error ellipses – Shows the relative accuracy of the GPS data. A small ellipse at the arrowhead
(or no ellipse at all) is more accurate than a large ellipse
! View the tectonic plate boundaries, faults, recent earthquakes, volcanoes, and vertical velocities
by turning their symbols on and off.
8. To learn more about graphing this data, see a step-by-step tutorial:
http://serc.carleton.edu/eet/platemotion/all_parts.html
Guiding Questions as You Explore:
• Find areas with high rates of motion - where are these areas? Find areas that have high rates
velocities near low velocities… or different directions from each other. What could this mean long
term?’
• Look$at$the$same$part$of$the$world$and$view$with$different$reference $fram es .$What$do$you$notice?$$
• Using just the GPS velocity vectors, can you predict the types of plate boundaries in different areas of
the world? Check your predictions by turning on the plate boundaries layer. What other types of data
are useful for understanding the plate motions? How do they complement each other?
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$
Reference frame: no net rotation
II. Five steps to show the spreading of the mid-Atlantic ridge:
• Google Search for UNAVCO Velocity Viewer. The viewer starts zoomed in on the western
United States and shows the overall velocities measured at a subset of GPS stations in the
Plate Boundary Observatory network.
1. Move and Zoom out the map to show Europe and the East coast of the United States.
2. Under Data Source, choose no net rotation.
3. Under vector color, choose blue.
4. Under Sites displayed, select show one in ten.
5. Click on “Draw map”.
Now that you have explored the plate motion for one location, roam the world and discover what you
can find! Where can you find where plates collide, split apart, and slide past each other? How about the
plate boundaries – where are they narrow? Where are there wide boundary zones?
