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Measurement of tectonic plate movements
 Twenty-four GPS satellites orbit the Earth every 24 hours at 20,000 km above the earth. Using accurately measured distances from at least three GPS satellites, the precise location of a GPS receiver on Earth can be calculated using a method called triangulation. |
The Western Canada Deformation Array (WCDA) is a permanent GPS Tracker Network established by the Geological Survey of Canada. This array is used to continuously measure the deformation of the North American and Juan de Fuca plates - also known as the Cascadia Subducation Zone - in south western British Columbia in order to investigate the seismic hazard in this densely populated region.
The first site was installed in Penticton (DRAO) in 1991, and since then 11 more sites have been added, including one at the Bamfield Marine Sciences Center.
Each WCDA site is equipped with geodetic quality GPS receiver or monument, with high speed data communication and uninterruptible power supply.
Using these permanently installed GPS receivers, in conjuction with the GPS satellites, the relative motion of points on the Earth's surface can be monitored and measured. click here for more on the GPS receivers and antennae
In the diagram below, the arrows show the direction of motion of specific sites in the WCDA relative to the reference site - which is DRAO (red arrow), in Penticton, BC. The length of the black arrows is relative to the scale in the bottom of the map.
GPS receiver sites on the outer coast of Vancouver Island are situated on the margin of the North American plate (UCLU and NEAH). These sites are positioned over the locked portion of the Cascadia Subduction Zone, and have beem measured to move at rates of over 10 mm/yr in a north-easterly direction. The inland sites (NANO and ALBH) move at half that rate, or less. This indicates that the outer margin of the North American plate is slowly being compressed like a giant spring. The next great earthquake is expected to totally release the accumulated compression, resulting in a 5 meter shift to the south-west of the outer coast of southern Vancouver Island.
all images courtesy of Natural Resources Canada
Plot Real Time GPS data from various sites on the west coast of North America to visualize plate movements. The map below indicates the locations of the different stations for which data are currently available.
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Different stations illustrate various Earth science processes.
1. tectonic plates moving:
ALBH, BEMT, NEAH, SBCC, SEAT
2. movement on different sides of a fault:
BEMT, SBCC
3. rebound of plates after and earthquake:
CAND, CARH
4. movement on a subduction zone:
NEAH, PABH, P020, SC03, SEAT
5. ground motions from volcanic activity:
P697
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*The above GPS data is based on materials provided by the UNAVCO Education and Outreach Program with support from the National Science Foundation and NASA under NSF Cooperative Agreement No. EAR-0735156.
*Programming by Tobias Kieslich.
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 Cascadia Subduction Zone
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Click here for larger image of the WCDA station map
click here for larger image