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Sunday, March 20, 2011

THE Earthquake Blog (Weather With You)

THE Earthquake Blog


Last updated 11:11 12/10/2010

I have to admit I was worried last night. It was completely irrational, but as the sun set after a day of bitterly cold southerlies and the frost started to form, I thought back to the dusk of the last polar outbreak on Friday September 3.

That was a cold, frosty night too. A quiet, extra-blanket-on-the-bed kind of night. Until 4.35am on the Saturday, and we all know what happened then. While the air was slumbering, the ground shook itself and rose up in rage.

What happened in the night seemed surreal as dawn broke on a beautiful cloudless Christchurch spring morning, and lawns and roofs glittered with frost. Those who lost power after the quake certainly remember how cold it was.  

In the last few weeks I've flatteringly had a few requests for an earthquake blog. So here it is, a one-off effort by popular demand.

While the weather and earthquakes can be bracketed together under the broad heading of "earth science", obvious similarities seem to end there, especially when it comes to forecasting. I make that comment as an informed and interested observer of such events, but not as an earthquake expert. 

I guess what's really struck me is the persistence of quakes compared with how long weather events linger. You can see a dirty great storm system brewing, get a pretty good idea of when it is going to arrive and where it will do its worst, put up with it for a day or two and then it moves away, never to come back in the same form.

Compare that with a big quake. Yes we know that where major crustal plates butt against one another there are major fault zones, and that strain is going to be released as a result in earthquakes in certain preferred areas. But scientists don't know, with any degree of accuracy, when a quake will occur or where it will cause the most damage. It's a bit like knowing there are high and low pressure systems, cold and warm fronts, and appreciating what they can bring, but not knowing where they are or are moving towards at any given time.

And unlike the weather, once you get a major quake, there are repercussions that hang around for weeks or months, as we have been experiencing with the hundreds of felt aftershocks around Canterbury.

From a scientific perspective I've found the magnitude 7.1 shake and its aftershocks fascinating. It might be going a bit far to say I'm missing feeling the actual aftershocks now, but I am missing being able to frequently satisfy that slightly detached curiosity of - how big do you think that one was? Was it close and shallow, or further away and deep? Was it a real roller, or a jolt? Why? Did you hear it coming?  

Despite trying to distance oneself, though, the aftershocks still bring that surge of adrenaline and clammy palms, particularly those at night. Last Monday night, colleague Marc Greenhill and I were at work saying how it had gone very quiet in recent days and joking it was the wrong thing to suggest. About an hour later we had one of our biggest aftershocks, of magnitude five, which rattled and rolled and shook many Cantabrians up.

I'd just like to give a quick plug to the team at GNS Science and Geonet. We - the public and the media - have been very well served by them and their prompt updates of earthquake details. There is an expectation now, in our age of instant knowledge, that we can have a right to expect such immediate information, but imagine what it must have been like following major earthquakes in the past? In the months after the similarly sized Inangahua earthquake in May 1968, aftershocks were frequent and strong but nobody would have known how big they were or where they were located with anywhere near the degree of immediacy. Having the details at hand seems to be quite cathartic. 

I could go on at length about the big quake - I have my own stories to tell - but I will draw this to a close. You can breathe easy - I'm not going to do a Ken Ring and attempt to predict our next large aftershock. But if it is possible to get a feeling for the rhythms of the Earth and the patterns of the air, then I have to say I don't think it's all over just yet. 

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