Along the western coast of Canada, we can see examples of all
three types of tectonic plate boundaries.
There are areas that are convergent, divergent, and transform. There are frequent earthquakes throughout Canada, with the western coast of British Columbia being the most active area. The three major plates are the Juan de Fuca, the North American, and the Pacific. Each of these plates interacts with the other in a very unique way.
The area where the Juan de Fuca plate meets the North American
plate is convergent. The long line of volcanoes
down the pacific coast was created by a subduction zone. The Juan de Fuca plate is slowly shifting
under the North American plate, which created the volcanoes Mount Meager and
Mount Garibaldi. This subduction is also
responsible for the Cascade Mountains in the United States. While the most recent volcanic eruption was at
Mount Meager over 2350 years ago, there are hundreds of small earthquakes along
this line each year. Currently, the Juan
de Fuca plate is locked with the North American plate, causing extreme pressure
that could eventually lead to a magnitude 8 or higher earthquake along the
British Columbia coast.
About 170 miles off the coast of Vancouver, the Juan de Fuca
plate meets the Pacific plate. This meeting
is divergent, and is slowly pushing the two plates away from each other. As this happens, magma from the earth’s
mantle fills in the gaps of these breaks in the ocean floor. Since the two plates are moving away from one
another, they are adding to the ocean floor.
There are many small earthquakes along this fault as a result of the
plate activity.
The area where the North American Plate and the Pacific
plate interact along the Canadian coast is called the Queen Charlotte Fault. At this point the North American Plate is
moving southeast, while the Pacific plate is moving northwest, which creates a Transform
fault line. The Queen Charlotte fault is very similar to
the San Andreas Fault here along the California coastline. Like the San Andreas Fault, the Queen
Charlotte fault is responsible for some of the largest seismic activity ever
recorded in Canada.
The Eastern portion of Canada is located in the center for
the North American Plate, and does not fall on any fault lines. Although it is not on any fault line, each
year there are up to 450 earthquakes throughout eastern Canada. Since these earthquakes do not occur on a
major fault line, many are not felt on the surface and as few as 3 per year
will be above a magnitude 5. While the
origin of these quakes is bit of a mystery, they have been attributed to
weaknesses in the earth’s crust. The
North American plate extends well past the eastern coast of Canada, and results
in very little seismic activity.
This figure represents the seismic activity in Canada in the last 30 days alone (January 20th- February 20th, 2015). There are 545 recorded examples of seismic activity, however most are a 2 or lower in magnitude, with only 6 reaching a 4 on the Richter scale.
http://www.earthquakescanada.nrcan.gc.ca/pprs-pprp/pubs/GF-GI/GEOFACT_plate-tectonics_e.pdf
Fantastic entry! Juan de Fuca attracts lots of scientists these days!
ReplyDeleteI used to work for the University of Calgary and so I had several opportunities to visit Banff. The most spectacular aspect of Banff to me are the thrust faults leading into the main town. There are these huge folds in the sides of the cliffs as you drive in. The geology is so obvious (when it is not covered by trees) it never seemed real to me. You can see how and where the rock layers lithified and were compressed and smooshed together, and where they were fractured. As far as I know, that area is mainly shale, mudstone and chert but a ton of it is metamorphosed so I am sure there are other varieties as well. Your entry reminded me of these outcrops. I think my favorite aspect of the Juan de Fuca plate (in closer relation to your post's focus) is the fact that it is the last little bit of the Farallon plate, which is pretty crazy. It is amazing that a plate can subduct so far as to basically disappear under another.
ReplyDelete