Wednesday, January 13, 2010

Haiti Earthquake - Relative Plate Motions Huge!


Ok, I said I would leave this alone, but I'm getting so many hits and so little money, that I'm still interested. I was going on the thought that the relative plate motion was about half that of the San Andreas. This would get into my thoughts of Living Memory, and how, below a certain strain rate, all thoughts of earthquake preparation go out the window. This is what happens in Toronto!

Basically, if nobody remembers there was an earthquake 'back in '54', or whatever, then earthquakes don't exist! The California strain rate of 2-4 cm a year seems to be the minimum required for enforced building codes! Our strain rate in Toronto is about 10 times less than that. You can actually express an overall strain for California at about 10-6 per year, and Toronto might be 10-7 to 10-8. Needless to say, the earthquakes here are beyond 'living memory' and so we will be poleaxed when it actually comes!

Now, for Haiti, they haven't had an earthquake like this for 250 years, and the books generally say that Carib. earthquakes aren't generally over M5.0. That gives me a low strain rate.

But what gives? This paper gives a relative motion (over a very narrow zone) of 2 cm per year! That's San Andreas power! And that is the big sucker fault that caused this last earthquake of maybe M7.3, which is a rip about 100 km long.

It basically means that we've been fooled by historic earthquake rates. It also means that M7.3 might be small for this region, we can easily get a Big Ripper - M8.0 or bigger. Is this earthquake a sign of more to come?

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