Thursday, August 25, 2011

Earthquakes and our city.

Once again I watched some stuff on TV about the Cascadia fault line that we live near to.   It is a chilling reminder that the earthquake we are likely to have in this region is not something small like the January 2010 Haiti earthquake or the two earthquakes in Christchurch New Zealand.   The earthquake we are likely to have is something like the Sendai earthquake.

A list of some better known recent earthquakes and how strong they were:

  • January 2010 Haiti M7.0
  • February 2010 Chile M8.8
  • September 2010 Christchurch M7.1
  • February 2011 Christchurch M6.3
  • May 2011 Sendai M9.0
This could be Old Town in a small earthquake
To give you an idea of the difference in the power of the earthquakes, the May 2011 Japanese one was 1000 times as strong as the January 2010 Haitian earthquake.  Sendai was more than 11,000 times as powerful as the February 2011 Christchurch earthquake.   The Sendai earthquake was even about twice as powerful as the Chilean earthquake.

You only need to look at some of the pictures of the February 2011 Christchurch earthquake to get an idea what would happen to Victoria Old Town and Chinatown in a small earthquake.  To give you an idea of how small it was, it is small enough in terms of energy released that it is not even large enough to be a rounding error in the earthquake we are likely to see.  Even Haiti is not really large enough to be a rounding error.

The Cascadia subduction zone was only discovered to be there and as serious as it is about a generation ago.  In the case of the recent Japanese earthquake, everything that was thought to be know about the area placed the biggest possible earthquake at about 3% the size of the one that happened.   We really know very, very little about the reality of when and how strong the coming earthquake will be.

At this time the best estimate is that there is a 37% chance of a M8.2 or greater earthquake within the next 50 years, though this is for the southern end of the subduction zone.   Even worse for us, the strongest earthquakes are off of the coast of Vancouver Island but the odds are currently estimated 10-15% in the next 50 years in this zone.

Is this next earthquake overdue?   Likely.   The 311 years since 1700 is a longer interval than 75% of past intervals between earthquakes in the last 10,000 years.
Japanese building tipped on its side
some liquefaction in Japan

How serious would this earthquake be to us?   I would say extremely.    Most of our seismic upgrading has been done to deal with the tiny Haiti like quakes.   The limit of design seems to be a M8.0 earthquake, and this is 3% of the energy of the scale of the earthquake likely to hit this region.

Old Town and Chinatown will be rumble.    The Railyards and Dockside Green will sink into the ground.  The Empress will sink and collapse.  Much of the Cook Street Village and Fairfield will be rubble.  The core of Langford and Colwood will be destroyed.   Hillside mall will be flattened.

It is not clear that any of the bridges will remain standing.   Odds are that both the #1 and #17 will be blocked by overpasses that have collapsed.  It is very likely that all three major ferry terminals to the island will be out of action

We are not likely to have water, sewer, gas or electrical power.    We are also unlikely to see the return of any of them for a couple of weeks.  We could be in real trouble if our main powerline from the mainland is put out of commission.   We are also on an island that is not going to have an regular connection to the mainland for weeks because the ferry system will be compromised on both ends.

People need to be prepared and assume that for a week or two you will have to look after yourself for food, water and first aid.  People also need to take it seriously that this huge earthquake will hit us sooner than most people have thought before.  There is some thinking out there now which posits that given there have been megathrust earthquakes in Sumatra, Chile and Japan, our corner of the ring of fire may be connected and may happen within the next five years.

People still do not take the threat of a devastating global earthquake happening here seriously.   We give the idea lip service and tend to think in terms of the tiny ones like in Haiti of New Zealand and not something that would be like 1000 Haiti earthquakes happening all at once.
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