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Are We Ready for “The Big One”? Understanding the Impact of a Megathrust Earthquake in BC

It’s a chilling thought for anyone living in British Columbia: what would happen if a huge earthquake struck? The threat of a “megathrust earthquake”—a massive quake caused by the shifting of tectonic plates—looms large over cities like Vancouver and Victoria. Known as “The Big One,” experts say this earthquake could have a magnitude of 9.0 or higher and would cause intense damage. So, let’s explore what we might experience if it happens, why it’s likely, and what we can do to prepare.

What Will Happen Geographically?

British Columbia sits along the Cascadia Subduction Zone, where the Juan de Fuca and North American tectonic plates meet. This zone stretches about 1,000 kilometers, from Vancouver Island to Northern California. When the stress builds up enough and one plate suddenly slips under the other, it triggers an enormous earthquake. The ground could shake for several minutes, leading to landslides, ground liquefaction (where the ground acts more like a liquid than a solid), and possible tsunamis. Coastal areas, including Vancouver Island, would be especially vulnerable to flooding from these waves.

Impact on Homes and Businesses

In cities like Vancouver and Victoria, where buildings vary widely in age and design, the damage could be severe. Older structures, especially those built before modern seismic codes, may collapse entirely or suffer significant structural damage. Homes built on soft soil could sink or tilt, and high-rise buildings might sway, potentially causing glass to shatter and hazardous debris to fall. Businesses in these areas would be disrupted, with many unable to reopen for weeks or even months. Bridges, roads, and railways might be unusable, making it difficult for emergency crews to move around and for people to evacuate.

Seismic building codes have been around since the 1950s, but have undergone many changes as our understanding of earthquakes grew. Even modern building standards do not make a building earthquake-proof. The Office of Housing and Construction Standards in BC says:

“Seismic provisions in the code are intended to protect life and safety, allowing people to escape buildings even when damaged.  A new building designed to code is designed to withstand a moderate earthquake without significant structural damage and a major earthquake without collapsing.”

How Long Will Recovery Take?

Rebuilding after a megathrust earthquake would be a huge challenge. Restoring water, power, and transportation services could take weeks or even months. In Christchurch, New Zealand, which experienced a devastating earthquake in 2011, parts of the city were uninhabitable for years, and the recovery is still ongoing over a decade later. Given the size of British Columbia’s population and the complexity of Vancouver and Victoria’s infrastructure, recovery here could be equally drawn out, depending on the severity of the quake and the damage caused.

Christchurch church before and after the earthquakeReal-World Examples

Christchurch is one of the best comparisons for BC. The city had to cope with severe structural damage, loss of life, and a long-term rebuilding process. Christchurch also sits on a tectonic fault, similar to BC, and it showed how long and challenging recovery can be, especially in terms of infrastructure and community support. Like Christchurch, BC will likely need to rebuild many structures, roads, and utilities from scratch. Other examples include Japan’s 2011 Tōhoku earthquake and tsunami, which showed the kind of widespread impact a megathrust quake can have, though any tsunami we get here will be much smaller than the one experienced in Japan. (Thank goodness!)

Is BC Prepared?

British Columbia has taken steps to prepare for an earthquake, but there’s always more that can be done. Seismic upgrades have been made to many public buildings and bridges, and the government has invested in early warning systems to alert residents and officials. Still, retrofitting buildings is costly and time-consuming, and many homes and businesses may not have adequate reinforcements to withstand a major quake.

Are Most Families Prepared?

While there’s growing awareness about earthquake preparedness, many families may not be fully prepared. Some have emergency kits and a family plan, but experts suggest having supplies like food, water, and medical essentials for at least 72 hours—though some recommend a week or more, considering the time it may take for help to arrive. Unfortunately, according to a 2018 survey,  only some households have made these preparations, even with the risks.

Woman practicing Drop, Cover, and Hold On.

How to Get Prepared

Preparing for a major earthquake might sound overwhelming, but some straightforward steps can make a big difference:

  1. Make or buy an emergency kit with essentials like food, water, medication, a flashlight, and a first-aid kit. Ideally, have enough to last at least 72 hours. Don’t want to DIY it? Shop kits here.
  2. Create a family emergency plan so everyone knows what to do and where to meet after a quake. You can find a free plan template here.
  3. Secure heavy items in your home, like bookshelves, TVs, and appliances, to reduce injury risks.
  4. Take part in earthquake drills like the annual Great British Columbia ShakeOut, which helps people practice safe responses to earthquakes. Or watch our video on how to practice your own family emergency drill.

2 Person Family Prep Survival Kit

Why Haven’t We Had a Big Earthquake in a Long Time?

The Juan de Fuca and North American tectonic plates are pressing against one another, with one slowly sliding beneath the other. Usually, this movement is manageable, but in our case, the plates are ‘locked’ together—meaning we’re essentially stuck. Even though these plates can’t move freely, they continue to push, building up a tremendous amount of pressure with nowhere to go. This pressure will keep accumulating until it reaches a breaking point, at which time it will release all at once, triggering an enormous earthquake. This “locking” effect is why we haven’t had many large quakes recently, but when that pressure finally gives way, we’ll feel the full force of a massive event.

The History of Earthquakes in This Area

The west coast of North America has a history of seismic activity dating back thousands of years, as shown by Indigenous oral histories and scientific evidence of past tsunamis. Smaller earthquakes happen frequently, reminding us of the region’s volatility. These smaller quakes help relieve stress but aren’t enough to prevent a megathrust event from eventually occurring.

What Are the Odds?

While there’s no way to know exactly when “The Big One” will happen, researchers estimate a 10-15% chance of a major quake along the Cascadia Subduction Zone in the next 50 years. This may sound low, but considering the massive potential impact, it’s something everyone should take seriously.

Final Thoughts

Although we can’t prevent an earthquake, we can reduce the damage it causes by preparing ourselves, our homes, and our communities. By understanding the risks, learning from other places that have been through similar events, and staying informed, we can build a more resilient BC. Preparedness might feel overwhelming, but taking even small steps now can make a huge difference when “The Big One” eventually hits.

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