Overview

In this section you will find materials that support the implementation of EarthComm, Section 2: Earth's Moving Lithospheric Plates.

Learning Outcomes

• Analyze Global Positioning System data on a map of the North American Plate to describe lithospheric plate movement.
• Interpret Global Positioning System data on a graph to identify the directions and rates of lithospheric plate movement.
• Apply evidence from the patterns of plate movements to support the theory of plate tectonics.

Using Technology

To learn more about the relative motions of the plates, complete the following:

Data from a Computer Model

1. Computer models that use geo-spatial data can be used to show changes in the location of your community. To use such a model, you will need to know the latitude and longitude of your school (or another familiar place).  Latitude and longitude are used to identify a position on the Earth’s surface. Latitude is a measure of location in degrees, minutes, and seconds north or south of the equator. Longitude is a measure of location in degrees, minutes, and seconds east or west of the Prime Meridian, which passes through Greenwich, England. 
   
   You can use Google Earth to find the latitude and longitude of your school (or another familiar place).   After you open Google Earth, search for your specific location using the “Fly To” tab. Enter the location address in the input box and click on the “Search” button. Google Earth will zoom into your location.  Click on the “Add Placemark” icon to retrieve the latitude and longitude of the location. 
   
   
   
   Alternatively, you can use your local topographic map. Latitude is found on the left or right side of the map. Longitude is found on the top or bottom of the map.
   1. Record the latitude and longitude of the position you chose in degrees, minutes, and seconds. (These “minutes” and “seconds” are not the same as the familiar minutes and seconds of time! They describe positions on a circular arc.)
       
   2. Convert the latitude and longitude values to a decimal format. Use the following example to help you.

   Example:

   • 42° (degrees) 40' (minutes) 30" (seconds) north latitude
   • Each minute has 60"
   • 30" divided by 60" equals 0.5'
   • This gives a latitude of 42° 40.5' north
   • Each degree has 60'
   • 40.5' divided by 60' equals 0.675°
   • The latitude in decimal format is 42.675° north

2. Examine the following map showing lithospheric plates.
   
   
   
   World map of major lithospheric plates. Arrows show the relative motions of the plates relative to the African Plate, which happens to be moving slowest relative to the Earth’s axis of rotation.
   1. Identify the location of your community.
   2. In your notebook, record the name of the plate your community lies within. Record the name of a plate next to your community.
       
3. Visit the Relative Plate Motion (RPM) Calculator web site at: http://sps.unavco.org/crustal_motion/dxdt/nnrcalc/
   The RPM calculator determines how fast your plate is moving relative to another plate that is assumed to be “fixed” (non-moving). At the web site, enter the following information:
   • The latitude and longitude of your community (decimal format).
   • The name of the plate on which your community is located.
   • The name of the “fixed” reference plate adjacent to your plate. Use the African Plate as the reference plate.
      
   Once you have entered the data, run the model. Print the results. (Examine the following sample printout for the location of station WES2.) Record the following information in your notebook:
   1. The rate of movement of the plate on which your community is located (in centimeters per year).
   2. Its direction of motion. (Note that direction is given in degrees, starting from 0°, clockwise from north. For example, 90° is directly east, 180° is directly south and 270° is directly west.)
   3. In your own words, describe the motion of your plate over time.
   4. How do the results from the computer model compare to those obtained from GPS data?
   5. What data does GPS provide that the plate motion calculator does not?
       
   Sample Printout for WES2
   NUVEL-1A Calculation Results
   Calculation results are as follows:
   
   Relatively fixed plate = Africa
   Relatively moving plate = North America
   Latitude of Euler pole = 78.8 degree
   Longitude of Euler pole = 38.3 degree
   Angular velocity = 0.24 degree/million years
   Latitude inputted = 42.364799 degree
   Longitude inputted = -71.293503 degree
   Velocity = 2.11 cm
   Direction = 283.39 degree

Inquiring Further

To learn more about how GPS works, visit the following web sites:

GPS: A New Constellation, Smithsonian National Air and Space Museum
Explores scientific methods before and after the advent of GPS, as well as a review of how GPS works and its applications. 

Understanding Plate Motions, USGS
Reviews the basics of plate motions and introduces the science of geodesy and using GPS to track current plate movements. Includes an image of a GPS satellite.

Resources

To learn more about this topic, visit the following web sites:

The Interior Structure of the Earth

"The Interior of the Earth" by E.C. Roberston, USGS
Information about the composition of the crust, the mantle, and the core, and how each was "discovered" and studied.

Measuring Plate Motions with GPS

GPS: A New Constellation, Smithsonian National Air and Space Museum
Explores scientific methods before and after the advent of GPS, as well as a review of how GPS works and its applications. 

Understanding Plate Motions, USGS
Reviews the basics of plate motions and introduces the science of geodesy and using GPS to track current plate movements. Includes an image of a GPS satellite.

Tectonic Plate Motion, Space Geodesy, NASA
Describes the results of over 15 years of laser tracking data acquired by a network of globally distributed satellite laser ranging sites.

Plate Motion Calculator, UNAVCO
Calculate tectonic plate motion at any location on Earth using one or more plate motion models.

Before GPS How Did We Know the Plates Were Moving? IRIS
The second page of this online document bridges the gap between new technology and the time of Alfred Wegener. Page four describes the use of GPS to study earthquakes and volcanoes.