Map of earthquake liquefaction risks around Victoria

The land under the Empress could turn to liquid in the event of the right sort of earthquake.

My father recently sent me these amazing resources about various risks due to earthquake around Victoria.1

I immediately had to look at the one called RELATIVE LIQUEFACTION HAZARD MAP OF GREATER VICTORIA (PDF), because the thought of the ground turning to liquid is terrifying to me.2

Liquefaction is the transformation that occurs when earthquake shaking (or other disturbance) causes a saturated granular soil (e.g. sand) to lose its strength and behave like a liquid. Liquefaction can be one of the major causes of damage during an earthquake. The susceptibility of a site to liquefaction is dependent upon the depth to water table and the density, grain size and age of the underlying deposits (e.g. Youd and Perkins, 1978).

The thing that jumped out to me immediately is that we’re not totally safe here in Vicwest, from liquefaction. Like, sure, I knew that parts of James Bay was built on a muddy swamp.

But check out the high risk areas along the Gorge.

Relative risks of liquefaction from an earthquake in Vicwest

Also surprising to me was the strip of land out by the Esquimalt estuary.

Relative risks of liquefaction from an earthquake around the Esquimalt lagoon.

Holy shit, right?

Here’s the movie version. You decide one warm summer day to take your family to the beach. You park and unpack. The sand is hot. You’re slathering on the sun screen and consider getting some food truck snacks. Maybe a nap first. And then. The ground starts to shake. Your mind jumps ahead to the Tsunami warning signs you saw on the way here. And then you remember that there are bottles of water in the car and you’re suddenly very thirsty. But too late, the ground is turning to soup and you watch your car sink into the ocean. There’s no where to go.

Eek.

Well, there are lots of uncertainties built into the map. In the section called Qualifications they note repeatedly that the map is intended to demonstrate regional liquefaction risks, and the map “should not be used for site specific evaluations.”

The authors also note that there are other scary things associated with earthquakes, besides liquefaction, and to really understand it all, please consider the other scary maps and risks. So, do that.

Okay, here are some actually constructive thoughts about earthquake preparedness.

And here’s a picture of a car that sank in 2011 in Christchurch New Zealand.

A car sinks due to liquefaction, in New Zealand in 2011.

And here’s some interesting videos about liquefaction.

  1. When there’s an earthquake around Vancouver Island, I can dependably expect a phone call from my father in the next 48 hours. Sometimes, if there’s a related tsunami warning, I will get one within the hour.
  2. I’m not an earthquake expert, and no one should listen to anything I have to say on the topic. Here’s a nice resource on liquefaction.

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