Megathrust Earthquakes – The Big One

We hear a lot about the next Megathrust Earthquake, or ‘Big One’ that BC is due to experience. There is a 1 in 4 chance that we’ll experience a major earthquake in the next 50 years, and a 1 in 10 chance that it will be a megathrust (usually a magnitude 9+). If that were a lottery, most people would play the odds.

All this talk of megathrusts got the Total Prepare team thinking: What happened last time?

Last time?

Yes! That’s right. BC is the most seismically active place in Canada and due to the locked fault line we’re sitting on we experience a major earthquake every 500-600 years on average. The frequency is irregular, some occurring 200 years apart, others biding their time for 800 years, but they are inevitable.

The last major earthquake to hit our Cascadia Subduction Zone happened 300 years ago in 1700. It was one of the largest in earth’s history, clocking in at magnitude 9. Thanks to the oral histories of the local First Nations Peoples, and to precise records kept in Japan of the resulting tsunami, we know that it occurred on January 26, at approximately 9pm.

map showing the range of the last megathrust earthquake in the cascadia region

Image courtesy of the U.S. Geological Survey

The Damage

It’s a cold winter evening in your village. Families are retiring to bed, saying their goodnights and herding sleepy children indoors. There’s a BANG, like a tree falling just out of sight. The rumbling begins.

As the vibrations grow, traveling from your feet, to your ankles, and continuing up your body, you realize that it is not the sound that’s causing this, but the earth itself. Before you can fully process what is happening you’re thrown from your feet as the ground beneath you begins to sway. Around you, houses collapse. The long, regular waves keep you on your stomach for minutes – so long that you begin to feel sick. When it’s finally over, the ground is unreliable, opening in sinkholes or flooding with liquification. In a nearby coastal village a strange wave is spotted…

Oral histories tell us that the Cowichan peoples had buildings collapse in the last megathrust earthquake, and that a winter village of the Pachena Bay people was completely destroyed by tsunami with no record of survivors. Landslides were caused all over the effected area, and swaths of forest were buried, sunken, or destroyed.

Looking Forward

If you live in western BC I cannot recommend the podcast Faultlines enough. Produced by the CBC and with input from seismologists, engineers, and emergency management personnel, it is one of the absolute best sources available for learning about our seismic future. In it, Johanna Wagstaffe (a Vancouver seismologist) leads us through two scenarios that are both very likely in our area.

On top of examining what our earthquakes might look like, the podcast examines what our communities will look like. When can we expect help? Will our homes be standing? How long until the grocery stores are empty? Questions we get every day at Total Prepare.

diagram showing sources of earthquakes in the cascadia region

Image courtesy of the U.S. Geological Survey

Getting Ready

If you’re new to BC, or to the idea of our earthquake zone, you’ve come to the right place! We have dozens of helpful education articles, just like this one. Prepared BC is another great place to go for help. The most important things to remember are to:

Know the Risks

Do your research and find out how your area is vulnerable. Are you in a tsunami zone? Is your house built to stand up to earthquakes, or has it been retrofitted to resist them? Do you know where your water and gas shutoffs are?

Make a Plan

Evacuation and Reunification planning is important, especially if you have family or friends in the area. Get an out of town contact and make sure everyone who needs it has their number. Plan multiple routes home from your work/school, and have a backup place to go in case your home is unsafe.

Get a Kit

There are dozens of guides out there for building your own emergency kit, or Total Prepare offers complete, professionally compiled options. Whichever way you choose to go, plan to be self-sufficient for at least a week.

Thank you for reading. This article was written by Zenia Platten – Author of Tethered and Emergency Preparedness Professional.

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