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PBO-52 Playing Cards

Welcome to the PBO-52 webpage!

PBO-52 is a deck of playing cards featuring GPS stations from the EarthScope Plate Boundary Observatory.

Have a deck of cards? Take one minute to take our survey!

What is the Plate Boundary Observatory?

The Plate Boundary Observatory is a network of more than 1,200 geophysical instruments installed throughout the United States, focused along the Pacific coast. The purpose of the Plate Boundary Observatory was initially to measure the tectonic motions of this region, where plates come together to form mountains, cause earthquakes, and build volcanoes. The vast majority of these instruments — more than 1,100 — are high-precision GPS, which can measure motions as small as several millimeters per year. This is the part of the network featured in PBO-52. The network also includes boreholes containing strainmeters, seismometers, and tiltmeters, also designed to measure small motions. Many of these sites host meteorological instrumentation as well. All the data collected are free and open to the public.

Because of how GPS works, we don't just learn about plate tectonics. We can also learn how much water vapor is in the atmosphere, how deep the snow is around the GPS site, and where drought is taking its strongest toll.

To learn about the many uses of GPS for science, explore the PBO H2O Spotlight Site. GPS sites featured in the PBO-52 deck that are also featured as a Spotlight site are marked with this logo. Click on the Spotlight Map and find your station for more information about where it is and how it has been used.

The Plate Boundary Observatory is the geodetic component of EarthScope. For more, explore the Plate Boundary Observatory project.

What is EarthScope?

EarthScope is a vast project for deep exploration of the entire North American continent, as well as our entire Earth, to better understand the materials it is made of, how it was assembled, and how it works — including its recurring earthquakes and active volcanoes. For more, explore EarthScope.

What is geodesy?

Geodesy is the study of the size, shape, orientation, and gravity field of the Earth. What does this really mean? Scientists can use geodesy as an approach to understand the changing face of our planet: Earthquakes, volcanoes, glaciers, and even the water cycle can be studied through geodesy.



    Each suit represents a different region within the Plate Boundary Observatory.

    • Hearts: Alaska
      Alaska has everything, inlcuding a major subduction zone to the south where the Pacific plate dives under the North American plate, and also a major strike-slip fault, the Denali fault, which cuts roughly east-west through the Alaska Range.

    • Clubs: Pacific Northwest
      For this deck of cards, we're considering the Pacific Northwest to be Washington, Oregon, and Northern California. Subduction of the small Juan de Fuca plate beneath the North American plate off the coast results in earthquakes and the formation of the Cascade volcanoes.

    • Diamonds: California
      In central and southern California, the San Andreas fault forms the boundary between the Pacific and North American tectonic plates. The Pacific plate is moving northwest past the North American plate, causing earthquakes as it sticks and slips. GPS instruments also measure the ongoing drought, as groundwater withdrawal causes the land to subside.

    • Spades: Interior
      Because of the plate boundaries to the west, the Basin & Range—from eastern California to central Utah—is being pulled apart, slowly. And because there's no plate boundary to the east, there is very little motion within within much of the interior east of the Basin & Range. In some places, like in Boulder, Colorado, motions are so small we haven't been able to measure them, even after years of data collection.


    Cards 2-10, Aces, and some of the face cards highlight one of the 1,100+ GPS stations within the PBO network.

    What's in the photo?
    Each card shows a photograph of the station's GPS antenna, usually protected by a specially designed plastic dome to prevent snow, ice, and nesting birds (yes, nesting birds!) from interfering with the satellite signals. The GPS antenna is only one part of what makes a GPS station work.

    Anatomy of a continuous GPS station

    For more on these components, see our Instrumentation page.

    GNSS Equipment Types
    Radomes GNSS Antennas GNSS Antenna Mounts Monumentation Cables & Connectors GNSS Receivers Meteorological Instrumentation Communications Power Enclosures

    What's in a name?
    Every GPS site, around the world, has a four-character ID. You may notice that many sites in this deck start with either a "P" or an "A," followed by numbers. All sites installed as part of PBO were given names starting with P, for PBO, or with A, for Alaska. Oddly enough, the first site installed was not P001—it was P041. Both sites are in the deck. The numbers represent the order in which sites were planned, not installed.

    So what about the other sites? A large part of what is now PBO already existed as other networks, such as PANGA, the Pacific Northwest Geodetic Array, or SCIGN, the Southern California Integrated GPS Network. For these networks, IDs usually reflect the location, like MIG1 for San Miguel Island or PABH for Pacific Beach. Whereas sites installed for PBO have been operating since sometime between 2003 to 2008, when the network was installed, these other sites offer even longer records of motion.


    What's that arrow?
    The red arrow on the card is the site's velocity vector. A vector is an arrow that shows direction and magnitude. Here, the direction shows the direction the site is moving and the magnitude shows the site velocity, or how fast the site is moving. The velocity is usually described in millimeters per year, which is given at the top of each card. Unless stated otherwise, the vector's distance scale is true-to-life, meaning that's how far the station actually moves every year. Keep in mind that it's not just about this year. The Earth is constantly moving. To see how far the station has moved in the last ten years, for example, multiple the length of the arrow on the card by ten. Along the tectonic plate boundaries, these motions build up to earthquakes and can help researchers estimate how much shaking could occur in the next big event.

    This site velocity is what scientists designing this network were most interested in learning. We're not so interested in how one site is moving as we are in seeing how that site is moving relative to other sites. How fast is a site on one side of the San Andreas fault moving relative to a site on the other side of the San Andreas fault? (Check out the 2 and 3 of Diamonds!) This can tell us where and how much stress is building along the fault, helping us to better understand earthquake hazards.

    All site motions are shown relative to stable North America, the central part of the continent that doesn't warp, or deform, much, because it's far from any plate boundaries.

    How do we know?
    To figure out how far and how fast the station moves, we measure the position of the site every day and calculate how its position changes over time. The graph of the site's position over time is called a time series. Time series usually show the data as three components: north/south, east/west, and up/down. The graphs on the Queens of Hearts, Clubs, and Diamonds and the Kings of Diamonds and Spades are time series. Learn more about reading time series.

    Most of the sites featured move slowly and continuously. But if there's an earthquake, or if a site is on a volcano, the site's motion may change — rapidly! (See Kings and Queens.) The site motion can also vary seasonally with changes in rainfall or groundwater pumping.

  • ACES

    Each Ace shows the fastest site in that region.

    • The fastest site in Alaska is being pushed inland by the northward collision of Pacific plate into the North American plate. AC79, on Montague Island, is on the overriding North American plate.

    • Similarly, the fastest site in the Pacific Northwest is being pushed inland by the northeastward collision of the Juan de Fuca plate into the North American plate. PABH, in Pacific Beach, Washington, is on the overriding North American plate.

    • The fastest site in California is on San Miguel Island, moving along on the Pacific plate as the plate grinds northwestward past the North American plate. This griding motion causes the earthquakes along the San Andreas and other faults.

    • The fastest site in the continental interior is on the western edge of the Basin & Range. Moving eastward, site motions generally decrease until they reach near zero in the central US.


    Each King highlights a volcano instrumented by the Plate Boundary Observatory. Motions of sites on volcanoes can change quickly and can differ on different parts of the volcano. Volcanoes inflate (move up and out) or deflate (move down and in) in response to changes in their magmatic systems. Because of this, we try to have many sites on volcanoes rather than just one.

    • The map of site motions on Westdahl volcano gives a spatial perspective on deformation, meaning they show us the overall distribution of motion. These motions can be used to better understand where the magma is beneath the volcano.

    • The map of Mount St. Helens shows motion in just a snapshot of time — in this case, the rate of motion over a period of one year. Because the motions of volcanoes can change, it's more helpful to look at what the volcano is doing in a given time period than averaging its motions over its whole lifetime.

    • It's aIso helpful to look at how the motion of a volcano changes over time. Here, we see a graph of the motion of one site in Long Valley Caldera, California. Sudden changes in motion may indicate a change in the volcano's plumbing system that, when combined with other evidence such as changes in earthquake or gas activity, can warn us when a volcano is about to erupt.

    • As with the King of Diamonds, the King of Spades shows the time series of just one site, showing how the position of the site has moved north or south, east or west, and up or down over a period of many years. One trick to monitoring volcanoes is to understand what the volcano's "normal" behavior is. Yellowstone's normal behavior is to inflate and deflate slowly as its magmatic systems changes, without leading to an eruption. It's important to understand this normal behavior so we can then look for unusual behavior.

    Did you know... that twelve volcanoes are instrumented as part of the Plate Boundary Observatory?


    Each Queen features an earthquake within the Plate Boundary Observatory's footprint.

    At least 26 earthquakes have been registered by the Plate Boundary Observatory GPS network since construction began in 2003. Many more have been recorded by PBO strainmeters.

    • Usually we look at how GPS positions change day by day. By looking instead at how a station's position changes in fractions of a second, we can make a "seismogram" with the GPS data. This card shows motion during a 2013 earthquake near Craig, Alaska. Look at each component. Does the site go back to its original position after the earthquake?

    • Some earthquakes happen so slowly we don't feel them — over a period of weeks to months. These "episodic tremor and slip" events were first discovered in the Pacific Northwest through GPS and seismic studies, and now are recognized at subduction zones all over the world. In the Pacific Northwest, they occur about every 14 months. More on episodic tremor and slip.

    • In California, site P496 moves along steadily until —crack!— an earthquake jolts it more than 18 cm south in just a moment. Does the site go back to its "normal" motion right away, after the earthquake? Look closely... (If it's too hard to see on the card, try its GPS Spotlight page.)

    • The Queen of Spades shows an example of a response to an earthquake, not by instruments but by the scientific community and by UNAVCO. After the magnitude 5.8 earthquake in Virginia on August 23, 2011, we installed two new GPS sites in the area to understand ground motion following the quake.

    Did you know... that GPS stations within the Plate Boundary Observatory are being used in developing earthquake early warning systems? When the network was first installed, sites sent their GPS data to Boulder daily. Now, more than 300 sites in the Pacific Northwest and California have real-time capabilities, meaning they can stream their data continuously, without delay.


    Each Jack shows strain, or change in shape. A strain network is a network of three or more sites that can show us whether the region they are in is under compression (getting squished) or tension (pulling apart).

    • Hearts: Alaska
      For Alaska, rather than showing a strain network, we show a photo of actual strain. (Really, we just wanted to use this picture.) This stainless steel GPS monument was anchored in bedrock when it was overrun by an eruption of Augustine Volcano in 2006. A pyroclastic flow, a hot avalanche of gas and rock fragments, bent the monument. Because this site was important to scientists and volcano monitoring personnel, it was replaced that same year with new site AV18.

    • Clubs: Pacific Northwest
      In the Pacific Northwest, the land is buckling as subduction compresses the Olympic Peninsula.

    • Diamonds: California
      In California, the land is being sheared along the San Andreas fault.

    • Spades: Interior
      In the continent's interior, the Basin & Range region is being pulled apart.


    The Jokers show a very simplified way to lay out the cards for each region to look for patterns. What do you see? The patterns are not always obvious. Keep in mind you're looking at a very small subset of the network. Try looking for patterns instead using all sites, as in the map above, or using the UNAVCO GPS Velocity Viewer.

    Having a few GPS sites can give us a hint of how the Earth is moving, but a dense network like the Plate Boundary Observatory can give us a much better picture of how and where this motion occurs.

Velocities: All velocities with the exception of those at Mount St. Helens are given relative to stable North America. Velocities were produced by the GAGE GPS Data Analysis Coordinator at the Massachusettes Institute of Technology. Velocities at Mount St. Helens are from USGS Professional Paper 1750, 2008, Chapter 15: Analysisi of GPS-Measured Deformation Associated with the 2004-2006 Dome-Building Eruption of Mount St. Helens, Washington, by Michael Lisowski, Daniel Dzurisin, Roger P. Denlinger, and Eugene Y. Iwatsubo. Time period for velocities: October 11, 2004 - October 11, 2005.
Time series: All time series position estimates were produced by the GAGE GPS Data Analysis Centers at New Mexico Tech and Central Washington University, and by the GAGE GPS Data Analysis Coordinator at the Massachusettes Institute of Technology.
Maps: All maps were created using the Generic Mapping Tool (GMT).

Project credits
Project manager: Beth Bartel
Project intern: Holly Taylor
Feature map: Christine Puskas
Station input: Ellie Boyce, Heidi Willoughby, and Ryan Bierma (PBO Alaska), Ken Austin (PBO Pacific Northwest), Andre Bassett, Doerte Mann, Ryan Turner, and Chris Walls (PBO Southwest), David Kasmer and Tim Dittman (PBO Interior), and Christine Puskas (Data Products), all UNAVCO; additional input on Mount St. Helens from Michael Lisowski, USGS Cascade Volcano Observatory
Additional input: Matt Lancaster and Matt Peters
Additional design consulting: Megan Berg
Printing: The United States Playing Card Company
Project funding: National Science Foundation

Last modified: Friday, 01-Apr-2016 23:51:42 UTC


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