Earthquakes

When we think of a major earthquake happening in Canada, we assume it would happen off the west coast of British Columbia – until recently that is.

Most of us were shocked when we heard of the August 23rd, 2011 5.8 magnitude earthquake in Virginia – around Washington D.C. It rocked the east coast from North Carolina to Maine and did extensive damage. We have now learned that the Ottawa area sits on one of the most active seismic zones in the country. On average, there’s an earthquake there every 5 days, although most are too small to be felt, given the Virginia earthquake a major quake cannot be discounted.

There are approximately 5,000 earthquakes registered in Canada every year. There have been 9 earthquakes greater than magnitude 7.0 occur in Canada over the past 100 years. A magnitude 6.0 earthquake would likely do extensive damage in urban areas.

BC has two significant seismic zones, the Oceanic Pacific Plate which runs from northern Vancouver Island, to the Queen Charlotte Islands and is sliding northwest at about 6cm/year. The boundary of the two plates is the Queen Charlotte Fault. Canada’s largest earthquake recorded, a magnitude 8.1 occurred along this fault on August 22, 1949 causing a 500km-long segment of the Queen Charlotte fault to break.

The other zone is called the Cascadia Subduction Zone which runs from the north tip of Vancouver Island to Northern California and is sliding 2 to 5cm per year. The boundary of the two plates is the Juan de Fuca plate. This fault is sliding, or subducting beneath the continent. It runs about 45km under the Capital city of Victoria and 75km under the city streets of Vancouver.

The Juan de Fuca plate is not always subducting though and there’s strong evidence the plates are somewhat locked together. This is why the Juan de Fuca fault line is so troubling to experts. When the plate slide is restricted, pressure builds in the earths crust at the fault line. This is the cause of around 300 small earthquakes located in South-Western BC each year. Earthquakes from this plate which cause damage are much less frequent, about one per decade on average.

Scientists agree that as the pressure continues to build in the subduction zone, the plates will eventually snap loose and release the pent-up energy between the plates. This will cause massive movement in the earths crust and a huge off-shore subduction earthquake. A similar earthquake zone in Alaska let go in 1964 causing a 9.2 magnitude earth quake.

Preparing for an Earthquake

A major earthquake may result in a number of scenarios, including:

  1. Evacuation from your home, office or school. If conditions are dangerous such as leaking gas mains, damaged or fallen electrical wires, wide-spread fire, unsafe building conditions or extreme weather conditions you may be asked to evacuate at very short notice. You should always have emergency kit close at hand including food, water and shelter. Having an emergency kit buried in the garage or a back closet will be useless if you have to grab and go at a moments notice
  2. Confinement to you home, office or school. If there is no damage at your location but your community or town has been badly affected by an earthquake, you may be instructed to stay put. You should always have an emergency kit including food and water in your office or classroom.