Radio Freethinker

Vancouver's Number 1 Skeptical Podcast and Radio Show

How Vancouver will Meet its Doom: The Big One

Posted by Ethan Clow on September 23, 2011

Growing up in the Vancouver area, I’ve often heard warnings of the “big one” an earthquake that would level the city and liquefy Richmond. At first I thought this was standard media hysteria and hardly likely to happen. After all, the media loves the chance to say “we’re all doomed!” so I generally wrote it off.

However I decided to do some research to see exactly what, if any, danger there was. Was Vancouver due for a massive earthquake and would it spell the end of the city?

It turns out that this might be a rare case where caution and perhaps even a bit of fear is warranted.

As most of us know, earthquakes are caused by plate tectonics. What is this? Plate tectonics is the scientific theory that explains how the continents on Earth move about and how new crust for the planet is created and destroyed. You might think of the plates as conveyer belts on top of which sit the continents.

Various plates

Interactions between tectonic plates creates friction and stress, this is a form of potential energy, which can ultimately lead to strain or deformation of the crust, which is the principal cause of earthquakes.

How does this affect us in Vancouver? The province of British Columbia is located along the Pacific Ring of Fire, a volatile region of active volcanoes and shifting tectonic plates.

To make matters worse, Vancouver is located right above two tectonic plates, the Juan de Fuca Plate and the North American Plate. What this means is that we could be looking at a Megathrust earthquake. These occur at subduction zones where one tectonic plate is forced under (subducts) another plate. As we mentioned, this will obviously cause a great deal of friction and stress, creating energy. In addition, because of the shallow dip of the plate boundary, large sections tend to get stuck, as pressure builds, the plates are eventually forced through and all that built up energy is released as a Megathrust earthquake. These quakes are among the world’s largest, with moment magnitudes that can exceed 9.0 on the Richter Scale. Since 1900, all six earthquakes of magnitude 9.0 or greater have been Megathrust earthquakes. No other type of known tectonic activity can produce earthquakes of this scale.

Juan de Fuca plate

Guess what the Juan de Fuca Plate and the North American Plate are doing? That’s right, subducting. Juan de Fuca is subducting under the North American plate and this is what caused the massive earthquake in 1700, known as the Cascadia Earthquake. It’s also been suggested that the Cascadia Earthquake might have been a causal agent in the 1750’s volcanic eruption of the Tseax Cone, a volcano near Terrance, British Columbia.

So, these Megathrust earthquakes have happened in the past, can potentially happen again, and have disastrous consequences, are they likely to happen again? If we look at the historic record of when megathrust earthquakes happen in the Vancouver area we can see an interesting trend. According to some research, megathrust earthquakes occur on a frequency of about once every 600 years.

Does this mean it’s likely to happen? The consensus appears to be that over the next half century, experts say there is a one in 10 chance that a Big One will hit somewhere in the province.

Part of the reason it’s so likely is that the Pacific Northwest also has a number of different plate boundaries that could prove problematic – the destructive plate boundary (caused by the subduction of the Juan de Fuca Plate and the North American Plate) which stretches from Vancouver island to Northern California. – the divergent boundary (caused by the Explorer plate, which was once a piece of the Juan de Fuca Plate until it broke off, and it’s about 241 km west of Vancouver Island.  – there is also a Transform fault, running along the west side of the Juan de Fuca Plate and between the Pacific Plate.

Given all these hazards, a earthquake is considered very likely.

The result of an earthquake would cause extreme damage to the city of Vancouver as many of the buildings here are not earthquake proof. In the Vancouver area, cities like Richmond and Delta are built on lowland sediment, which would put them in danger of landslides and liquefaction.

You can see examples on the internet of liquefaction where water and sand geysers up from the ground, or see large areas of land float on water that’s been shaken up by the earthquake.

So as it turns out, there actually is a sizable amount of evidence that a large earthquake is likely to strike the Vancouver area. If we take the previous records as any indication, the last major quake was 1700, so it’s been over 300 years since another. This puts us in the danger zone, so to speak. Basically within the next 50 to 100 years the probability for a megathrust quake is anywhere from 10 to 37%.

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