Recent events in Japan and New Zealand have highlighted the dangers associated with living in earthquake-prone areas. The West Coast of Canada is connected to both of these countries through the Pacific Ring of Fire, a nearly continuous loop of seismic activity that stretches around the Pacific Basin.
Earthquakes occur as a result of the unique makeup of the surface of the Earth. The Earth's crust is not a single, solid sphere, but a collection of giant plates floating on a layer of hot molten rock.
These plates move incredibly slowly, from one to 10 centimetres per year. When these massive plates collide or slide past each other, the energy from these interactions can be released as vibrations which we call earthquakes.
An earthquake that could affect Squamish is likely to occur in the Cascadian Subduction Zone. This fault line lies to the west of Vancouver Island. Here, the oceanic Juan de Fuca plate is being forced down underneath the continental North American plate. If these plates were to slip past each other suddenly, it could cause an event similar to the March 11 earthquake in Japan - a subduction or "megathrust" earthquake.
Seismic activity in Canada is continuously monitored by a collection of seismographs known as the Canadian National Seismograph Network (CNSN), which is under the control of Natural Resources Canada (NRCan). Seismographs detect ground motion and convert this movement into an image we can read called a seismogram.
When an earthquake occurs, vibrations spread through the ground like ripples in a pond. Data from three or more seismographs can therefore be used to calculate the exact location and depth of the event. Modern seismographs are so sensitive that they can detect vibrations caused by trains, traffic, waves on the shore and high winds. They are also able to detect nuclear explosions and earthquakes far, far away.
It may surprise you to learn that seismic activity in B.C. is very common. According to the NRCan website (www. earthquakescanada.nrcan.gc.ca), there have been more than 80 earthquakes in southwestern British Columbia in the past month, including one of magnitude 3.8 off the shore of Vancouver Island. None of these were reported to be felt by humans.
The information from the seismographs can be used in several ways. If a large earthquake occurs close to populated areas, the seismographs' information is sent to the media, emergency response agencies, railways and utility companies to ensure a prompt response. When the network detects an earthquake outside Canada, the data is sent to international agencies and tsunami warning centres.
Information gathered by the CNSN is also used in urban planning. Engineers and other scientists can use seismograph information to create building codes that are appropriate for seismically active areas.
Unfortunately, even with the data collected from the CNSN, it is not possible to predict when a large earthquake will happen. It is therefore important to understand the risks associated with an earthquake, and be prepared to cope in an emergency. For more information visit www.getprepared.gc.ca.
