The Big One – Examining the risk of an earthquake in the region

The Big One – Examining the risk of an earthquake in the region

Erin Edwards – As a longtime resident of British Columbia, I feel as though I live in one of the most beautiful places in the world. I am grateful to call the west coast my home, but its picturesque landscapes have the subtle ability to make me forget about the natural hazards that are prominent to this area.

British Columbia sits on Canada’s most active earthquake zone, making the threat of a large seismic event in our lifetime a very real possibility, and one that all British Columbians should be prepared for.

Earthquakes are caused by the movement of the tectonic plates that comprise the Earth’s surface. There are three types of plate boundaries at play along the west coast of B.C.: convergent (plates move together), divergent (plates move apart) and transform (plates slide past each other). However, the boundary that has the most potential to cause what scientists have termed “The Big One” is a convergent boundary.

“The Big One” refers to a large megathrust earthquake that scientists predict will at sometime hit the southwest coast of B.C. A megathrust earthquake occurs along a subduction zone that is found at a convergent boundary, where tectonic plates collide and one is subducted underneath the other, sinking down into the Earth’s mantle.

Subduction generally occurs when an oceanic plate, which is comparatively dense, and a continental plate collide. It is along this type of subduction zone that the largest earthquakes in the world are found, usually measuring a magnitude 9.0 or greater on the Richter Scale. An example of this event would be the 9.0 earthquake that hit Japan in 2011.

The Cascadia Subduction Zone (CSZ) separates the Juan de Fuca plate from the North American plate, extending approximately 1,000 kilometres from Vancouver Island to California. The Juan de Fuca plate is moving towards the North American plate at a rate of two to five centimetres per year. As the plates meet, the Juan de Fuca descends below the North American, currently 45 kilometres deep beneath Victoria and 70 kilometres deep beneath Vancouver.

Tectonic plates do not slide past each other smoothly. Rather their movement is discontinuous and in many cases they lock together. There is comprehensive evidence showing that the Juan de Fuca and North American plates are currently locked, causing strain to build up within the Earth’s crust.

When the fault’s frictional strength is exceeded, these locked plates will snap loose, causing a megathrust earthquake to occur.

Although predicting an earthquake is next to impossible, scientists have gathered diverse evidence that has identified 13 megathrust events along the CSZ over the last 6,000 years, occurring anywhere from 300 to 800 years apart, with the most recent occurrence in 1700.

Although there is nothing we can do to stop or control these types of natural events from occurring, we can be prepared for them. Do you have your earthquake preparedness kit ready?


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