GPS station positions change as plates move
How will these stations’ positions change relative to one another?
Objective:
Learning how Global Positioning Systems (GPS’s) can collect data and can be used to determine the
magnitude and direction of movement in the Earths plates.
Background information:
GPS stations are places located around the world that pick up information from GPS satellites that are
orbiting our planet approximately 11,000 miles above Earth’s surface. Generally, three satellites are
used to determine points of position change or how quickly Earth’s crust is changing because of plate
tectonics of underlying processes of deformation. High precision, satellite GPS’s can calculate position
to less than the nearest centimeter. By comparison, hand-held GPS units or driving systems are only
accurate to approximately 1 meter.
The data that you’ll be collecting from a GPS station will be placed on a time series plot. A time series
plot contains an X and Y axis. The X axis (horizontal) represents the date of the daily measurements
while the y axis (vertical) represents the station’s position over time using the North, East & Vertical
components.
1. The North column represents the distance (in mm) between the unit and the
zero point in a North-South direction. Positive values indicate distances north
of the zero point; negative values indicate distances south of the zero point.
2. The East column shows how far East (+) or West (-) of the zero position the
unit is, and
GPS station positions change as plates move
3. The Vertical column shows how far above (+) or below (-) the zero point the
unit is.
DATA Sample:
63006example
Originally uploaded in Earth Exploration Toolbook:Analyzing Tectonic Plate Motion with GPS
Data.
What does this information mean?
On June 30, 2006, the GPS unit was located 1.13 mm south of the zero point, 3.48 mm east
of the zero point, and 5.56 mm above the zero point.
Data one year later:
63007example
Originally uploaded in Earth Exploration Toolbook:Analyzing Tectonic Plate Motion with GPS
Data.
What does this information mean?
On June 30, 2007, the GPS unit was located 4.59 mm north of the zero point, 3.95 mm east
of the zero point, and 12.33 mm below the zero point.
Analyzing real time series data looks like this:
GPS station positions change as plates move
Activity:
The Earth’s surface is constantly changing due to geological deformation. These
changes are caused by earthquakes, volcanic eruptions, and mountain building that
occur at plate boundaries. When these changes occur, points on the Earth’s surface
change location (north-south, east-west, up-down). By analyzing data collected from
GPS stations we can observe these changes by making a time series plot and translate
the slope of the plot into the motion of change. While looking at the data there will
be outliers (scattered points) which could indicate miscalculations, equipment failure
or human error.
Procedure:
Working with your partner:
A.
Selecting a PBO station
1.
Go to: http://www.unavco.org/edu_outreach/data.html
2. In the Google Map interface, zoom in on the Pacific Northwest. Locate and click
the label of any green bubble other than SEAT.
ie: SEAT
3. Once you have selected a station tell your teacher. There shouldn’t be any need
for duplication in this activity given the number of stations available.
4. Click on the green bubble to get the station information as shown above.
5. The PBO Station page will show you where this GPS is located. If you click on the
picture you can see a close of view.
GPS station positions change as plates move
B.
Downloading Dataset and Open it in a Spreadsheet
1.
Go back to the Station Information page and click on the Download
Time Series Data Excel-compatible format
2. Open this file directly into a spreadsheet program: Excel. Save data in
your folder, labeling with the station name.
3. Highlight column A, right click, then format cells by clicking on date
which is found in the category box.
4. Highlight column B,C & D and then right click, then format cells by
clicking on numbers, two decimal points, found in the category box.
o
The following directions will be repeated 3 times, creating three different
separate worksheets: North, East & Vertical.
1. Highlight columns A & B, right click, copy, create a new worksheet.
Label this North, paste columns A & B in new worksheet.
2. Delete rows 1-8
3. Highlight data in columns A & B, insert scatter chart. A graph will form
to the right of the columns. If the data appears squished, pull graph
out by the corner until readable. This is a graph showing NorthSouth time series. To read this, a positive slope indicates a North
direction while a negative slope would be a South direction.
o
Repeat these directions this time to create a East worksheet. You will need to
highlight columns A & C this time. Using steps 1-3 you should create a new
graph for East. To interpret direction on a east/west time series, a positive
slope indicates a East direction while a negative slope indicates a West
direction.
o
For your last graph, repeat steps 1-3 this time highlighting columns A & D.
Labe this worksheet Vertical. The line created on this graph indicates up and
down movement or plates slipping and sliding (converging, diverging or
transforming).
4. Analyzing your graphs by answering the following questions:
o
In the North graph:
1. What are the units of measurement for this time series? mm
2. What are the dates of data collection–from when to when? 1/2004 to
4/2010
3. Click on DESIGN and under chart layouts, click on the graph to get a
line/grid
GPS station positions change as plates move
4. What was the direction of movement, what was the direction and total
distance moved in the time measured? movement: S to N; distance: 40mm to 42mm = 82 mm
5. Between what dates do you see the least slope increase and what was
it? 10/06 & 2/08; 10 mm
6. What is the approximant average distance of movement for the other
posted dates? About 20mm.
o
In the East graph:
1.
What are the units of measurement for this time series? mm
2.
What are the dates of data collection – from when to when? 1/2004 to 4/2010
3. Click on DESIGN and under chart layouts, click on the graph to get a
line/grid
4. What was the direction of movement, what was the direction and total
distance moved in the time measured?
Movement was west to east;
distance was -18mm to 18mm = 36mm
5. What is the lowest negative point potted? -17 or -18mm The highest? 16
or 17 mm
6. Does anything else stand out on this scatter chart in the way of the data
not being consistent? What do you think it may mean? There appears to be
a less dense area of scatter points around Dec. 2006. That may indicate
there was not so much movement
o
In the Vertical graph:
1. What are the units of measurement for this time series? mm
2.
What are the dates of data collection – from when to when? 1/2004 to
4/2010
3. Click on DESIGN and under chart layouts, click on the graph to get a
line/grid
4. What is the average range of movement? Between 20 and -19
5. What is the direction of movement, up or down? down
Putting it all together:
1. What is the longitude and latitude of your station?
2. Plot the location of the station on the map for Southern California
GPS station positions change as plates move
3. In the N-S slope, find the average slope by dividing d/t. Don’t forget to tell
the direction of movement 4.75 mm/yr
4. In the E-W slope, find the average slope by dividing d/t. Don’t forget to tell
the direction of movement. 13.3 mm/yr
5. Look up converging, diverging or transforming. Which one of these
movements is happening at this particular point based on the data
collected? Converging: The Washington-Oregon coastline of the United States is an
example of this type of convergent plate boundary. Here the Juan de Fuca oceanic plate is
subducting beneath the westward moving North American continental plate.
6. What kind of activity causes this kind of movement? Earthquakes, volcanic
eruptions
7. Compare the data collected from a group whose station was above yours
and a group who was below yours. In a brief paragraph of 5-10 sentences,
describe how your data fits/doesn’t fit a pattern. Can you spot a
trend/discrepancy?
GPS station positions change as plates move
GPS station positions change as plates move

8ASI1.3 Use appropriate tools and techniques to
gather, analyze, and interpret data. The use of
tools and techniques, including mathematics, will
be guided by the question asked and the
investigations students design. The use of
computers for the collection, summary, and display
of evidence is part of this standard. Students
should be able to access, gather, store, retrieve,
and organize data, using hardware and software
designed for these purposes.

8ASI2.4 Technology used to gather data enhances
accuracy and allows scientists to analyze and
quantify results of investigations.

8DESS1.1 The solid earth is layered with a
lithosphere; hot, convecting mantle; and dense,
metallic core.

8DESS1.2 Lithospheric plates on the scales of
continents and oceans constantly move at rates of
centimeters per year in response to movements in
the mantle. Major geological events, such as
earthquakes, volcanic eruptions, and mountain
building, result from these plate motions.