Saturday, July 18, 2015

Places with equal chance of devastation as Seattle - Part 1

The great Newyorker has put a spotlight on the west coast and the Cascadia event.

It's a great article, but the main impact comes from the implication that it is 'overdue', and will happen 'tomorrow'.  Thus, taken in isolation, it's an 'Oh my God!' moment.

Well, I call 'Bullshoot' on this one.  (I have a world audience :).  Devastation there is at the same odds as devastation anywhere, about 1 in 500 per year.  This means that nearly all cities take a pair of 25-sided dice and roll it on New Year's Day.  Anybody who roles 'snake eyes' or double ones, gets destroyed that year.

In Japan and other places, this means 20,000 killed, merely because of population density.  For less dense places, we're talking something like New Orleans, or Christchurch, perhaps hundreds killed, and economic devastation.

So why does Seattle get relegated to this dung heap, rather than 'tomorrow'?  It's because of uncertainties, and the fact that this subduction zone is a weenie.  Let's look at some 'real' subduction zones.

Look at that beauty in the middle.  That's the big M9 Japan earthquake, and goes every 800 years, based on actual history.

Sumatra, historical may give 500 years.

My favourite.

Mexico, probably the same as Japan, but not looked at, since it beams away from Japan, and nobody has crawled over the shores.

Here's Cascadia.

Look at that stupid thing!  Totally mucky, but we must account for sediments, even though it can't be greater than Japan.  This is suffering from 'over study', which takes things out of context.  That's why they get their '200 year' thing.  Pile those equivalent resources anywhere else and see what happens.

-to be continued.

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