New study puts southwest B.C. in the ‘risk zone’ for mega-earthquake


Residents of Vancouver Island are used to little rumbles, but a new study out today suggests that Southwestern B.C. should be bracing itself for a mega-earthquake, of the type not seen in the area for 300 years.

Yes, you've undoubtedly been hearing about this your whole life — so what's new now?

People living along the earthquake-prone West Coast are used to hearing about 'The Big One'. Those of us out of the quake zone usually think of Los Angeles — the giant earthquake that's destined to shear off southern California someday and ship everyone west of the San Andreas Fault out to sea. This is one of those rare instances where disaster movies actually hold onto a shred of scientific truth (I'm looking at you, Day After Tomorrow).

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However, we don't often consider the fact that the entire west coast of the continent is subject to the same geological forces. The two tectonic plates at work here are the Pacific Plate, carrying the ocean, and the North American Plate that's home to our continent. While 'The Big One' for southern California refers to the San Andreas Fault, a transform fault between the two — that's where the two plates are meeting and trying to slip past one another, making for a bumpy ride on both sides.

Further to the north, though, you get the Cascadia subduction zone. This region runs from Northern California up through Vancouver Island and covers the area where the small (by geological standards) Juan de Fuca Plate is being driven under the North American Plate. This causes both the volcanoes along the Cascades, and earthquakes from the Cascades, west out over the coastal ocean.

This study, a joint work of researchers at Royal Roads University, the Geological survey of Canada, UBC and the University of California, used radiocarbon dating to look at the sediment and, in particular, sediment disturbances in Effingham Inlet on the western side of Vancouver Island. Using this data in a new, high-resolution model has given researchers the first extremely-detailed timeline of earthquake history along the south coast of BC.

Dr. Audrey Dallimore, one of the co-authors of the study, revealed that the team has identified 22 major earthquake events — the so-called 'megathrust earthquakes' — in the past 11,000 years. That gives us around 500 years between big quakes; maybe as long as 1,000 years. The last of these quakes was a 9.0 on January 26th, 1700 (based on several types of evidence, including tsunami evidence from all the way in Japan) — 313 years ago — so we're just edging into the window of risk now.

Will 'The Big One' happen in our lifetimes? Unfortunately, that's still impossible to say; it could be this year, or it could be 200 years from now, or it could be even longer.

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It's understandable if you find it hard to get excited about new research for something that may, possibly, never affect us and we've been hearing about for years. However, as we have no way of reliably predicting earthquakes, all we have to go off of at the moment are these studies of how often they happen, to give us an indication of when the next one may hit.

Also, we don't need to look back very far to see the reason why this kind of research is important. Just in the past 9 years, we've already seen three graphic examples of mega-thrust earthquakes: the 2004 Indian Ocean earthquake and tsunami, which was ranked as 9th on the top 10 list of deadliest natural disasters in recorded history, the 2010 Chile earthquake, and most recently the 2011 Japan earthquake and tsunami, which has been called the costliest natural disaster in history.

The incredible devastation caused by these earthquakes, along with the fact that they happened with no warning at all, is reason enough to not only to continue studying these events, but also for anyone living in earthquake-prone areas to be prepared for something like this to happen.

(Images courtesy: Wikimedia Commons)

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