June 15, 2012

Will Harvie: Canterbury's 475th serious quake | Stuff.co.nz


Sometime in coming months, Canterbury will pass an important milestone that readers and policymakers outside the province should note.

Canterbury will soon experience its 475th significant earthquake since September 4, 2010.

Ha, you read stories recently that Canterbury had been shaken 10,000 times and we're fast closing in on 11,000.

As far as it goes, Friday's total of 10,958 (about noon) was precisely correct. But it doesn't mean anybody in Christchurch has experienced anything like that number of shakes.

That's because a huge majority (7386) measured magnitude 2.9 and less. Magnitude 3.0 is about the lowest level at which humans can detect earth movement.

So the foundation number of shakes is 3518, not almost 11,000. Even then, nobody has felt all 3518.

Being generous, let's say an average resident has felt half, or 1759. Even then, a 3.3 shake out towards Darfield is often no more frightening or disruptive to, say, eastern Christchurch residents than flatulence. And vice versa.

If we want figures on quakes that are disruptive and frightening, then we should select only those quakes magnitude 4.0 and greater. That number is 472.

By any measure, that's a remarkably high number and something to brag about to the rest of New Zealand and the world.

I'm not intending to diminish anyone's experiences of bad quakes that measure less than 4.0 (I've been scared, too), but I am arguing in a less-is-more way - that 475 packs more punch than 11,000.

Of course, Canterbury buildings are affected by quakes starting at about magnitude 3.0. This unusual wear and tear will be addressed by repairs. And I'm happy for scientists to continue recording every last shake, because they need the data for research purposes.

The main point is that 11,000 hyperbole isn't helpful to the Canterbury cause.

Posted via email from Four Paws and Whiskers

1 comment:

  1. Frankly 75 would be too many in my book never mind the additional 400.


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