gryphea

I was talking to a guy at work at length today about earthquake risk hazard and he told me more details about Vancouver earthquake risk, and some of the preventative measures that have been undertaken recently (preventing damage from a 7 pretty much under Vancouver, or a 9 off shore from VI). Bascially codes really only got detailed in 1985 and have got more stringent with each successive revision with the last code upadte being 2005. Its quite interesting as I knew about earthquake risk in general on that coast but I didn't know the details about rupture, size, frequency etc. He used to live in Vancouver and used to have a top ten list of buildings he would not like to be in if/when it strikes!!!

He says that areas of the city will suffer much more than others due to thicknesses of underlying soils and I asked whether that impacted house prices. He said he didn't think so, but I am still interested in that idea.

I have never heard anyone mention earthquake risk or hazard on here and I wondered if you lot from Vancouver ever give it a moment's notice? Do the schools have drills? Or the work places?

Gryph

dingbat

The kids have to have earthquake (disaster) packs at school/daycare and there are drills. I remember the last earthquake, as it cracked my basement. It's one of those things that you shove to the back of your mind, really.

Surrey Expat

I was in Surrey during the last one and it felt like a truck hit the building. The epicenter was around Seattle. Called the family in Chilliwack and they did not feel a thing. Our property sitting atop gravel, the gravel seemed to absorb the shocks.

There is a possibility of a one in 200 earthquake, it could hit next week or in who knows how many years. Although it is in the back of many peoples mind, it does not preoccupy day to day life. There is a risk Mount Baker will erupt, there is a flood risk in the Fraser basin every year. Was there not an earthquake in the UK earlier this year? Floods in some areas as well. We're not immune to disasters wherever we are. The biggest risk areas in an earthquake are built up suburban areas, Richmond, which would disappear and coastal areas hit be a resulting tsunami.

Then we could get run over crossing the street.

startwin

Yes we think about it, and shove it to the back of our mind. Always meaning to update the emergency packs, never get around to it. I'm just glad I don't work downtown anymore because I always worried that - should I survive - it would be hard to get back home across rivers to Maple Ridge!

I've experienced 3 (I think) earthquakes here. One felt like a truck hitting the building (as mentioned above); the one epicentred near Seattle shook our office building downtown, and looking out of the window at the time it seemed all the buildings across the way were "wavy". Being on the 17th floor it was quite an interesting experience.

Our dog always sensed the earthquakes before they happened, jumping up and down, then a big bang happened.

"The Big One" is supposed to happen sometime in the next 100 years or so. No point worrying about it. There are dangers wherever you live.

gryphea

Yes it was Richmond he mentioned. Bascially they are fairly confident that really large earthquakes hit with a frequency of about every 500 years based on fault plane solutions , I think. The last big one happened c. 1700. The one you felt was probably the 5 ish quake in Seattle. I think that the seismic risk is different to the volcanic risk as there would be more likely to be warnings with a big volcanic eruption.

I agree that everyday we live with risks, I was just interested in the seismic one as it is one that no-one in the UK lives with (I know that here people will go on about the UK earthqaukes, but they are different low-level things and nothing like the risk posed to Vancouver) and its not a risk that is realistically shared with the rest of canada either.

Gryph

gryphea

Animals are meant to have some kind of instinct about it and they don't know why.

He did say all the bridges have been retrofitted and should stand.

Did you wave and get slightly car sick?

Gryph

bazzz

I always make sure we've got at least a dozen beers and a couple of bottles of wine stashed away. It might not be safe to drink the water in the event of an earthquake, so it's important to be prepared.

gryphea

Very good point.

Mrs Miggins

Bazz, that's unusual - most people get drunk before the earth "moves".

Mrs (my husbands coming home tomorrow and i have only one thing on my mind) Miggins x

bazzz

Getting pissed?

lof

so, where do you draw the line, how big must it be that you call big? canada's largest historic onshore earthquake was a magnitude 7.3 event that occurred at 10:15 a.m. on Sunday June 23, 1946, epicentre in the forbidden plateau area, just west of courtenay, vancouver island. considerable damage throughout central vancouver island was reported, more than 75% of the chimneys in the comox valley didn't "survive".

having lived at the edge of a tectonic active zone my whole life earthquakes have always been a part of my life and didn't cease to fascinate me.
my very first "contact" with the cascadia subduction zone was when i read about san francisco's san andreas fault - including pictures of the last bigger one there - when i was about 8. i was wondering why people (and not thousands but millions of them) move there, exactly knowing that it will happen again. it's only a matter of time. i never found a real and good answer to that question. instead i moved to the northern part of exactly that cascadia subduction zone myself.
i can't say i didn't know where i was moving to. the risk of an earthquake (or a tsunami from an offshore rupture for that matter) is part of everyday's life at the bc coast. it makes sense to be prepared - but you for sure don't think every single minute of your day about it.

Souvenir

My understanding of the problem with Richmond is that it sits on an alluvial flood plain (ie silt). In a decent-sized earthquake, the ground would basically liquify and swallow the place up.

Atlantic Xpat

Ooohh thats quite biblical isn't it 'and the earth open up and swallow Richmond up'. Is it a bad place then?

gryphea

That may be true, I don't know the exact geology. It could liquify like Kobe, especially if they are silts, fine sands and medium sands with a high water table, which was a huge disaster esepcially in monetery terms. But I think it may be that its like the Mexico City, that there are depths of soil that amplify certain frequencies. These end up matching the natural frequencies of the overlying structures and you in effect get destruction through resonance. In mexico city the detruction was very specific, buildings 5- 30 stories high, due to preiod and resonance effects.

Gryph

gryphea

I would say a 7 right under vancouver is big or a 9 just off vancouver is big, these are both the design earthquakes. A 7 off VI won't cause much damage, apparently, and VI is mainly founded on rock which attenuates certain frequencies and makes it far less destructive. A 7 off VI will have damped considerable and attenuated by the time it gets to Vancouver. Chimneys can go quite early (as in the colchester earthquake)

The issue on Vancouver is that records are, by global standards, very very young, and the city is very very new. They are pretty sure of a large quake (>8) around 1700 from paleosiesmicity and and some first nations observations. The seismicity works differently to some of the rest of the zone, as they reckon this fault sits holding stresses until it finally gives in a big way, rather than in lots of small increments.

A 9 is way bigger than a 7, its log scale.

Your thoughts are interesting as you have clearly lived with a risk all your life!

Gryph