Wednesday, September 8, 2010

Surveying the Shaking Lands

I don't envy anyone with a surveying job in Christchurch right now!  The magnitude 7.1 earthquake that rocked the city last weekend is probably big enough to have jiggled the survey marks all across the city by a few centimetres or more.  A preliminary estimate from a continuous GPS site out on the peninsula shows movement of 13cm or so, and they expect movements of 20cm+ in other areas.  That means that boundary pegs, survey marks, fences and buildings have all moved a bit, with some properties expanding and some contracting. 

The worst thing about all this movement is that there are no laws or legal precedent to guide surveyors in how to address these problems.  The situation in New Zealand is unclear as to whether surveyors should resurvey boundaries where they are now, or try and reposition them where they were before the earthquake.  In most cases, it won't really matter because, at the end of the day, what's a few centimetres?  But where it will be quite significant is in places like the CBD, where the high value of property means that if a boundary moves by 20 centimetres that can equate to tens of thousands of dollars gained or lost.  That's where it starts becoming the sort of thing that big legal disputes are made of!

This event will prove very interesting from here, because it will hopefully be the inspiration for parliament to finally make a call on whether property boundaries move with deformation events, or whether they stay fixed in the positions they were in before the quake.  A call on that will be invaluable to surveyors.

My honours project has been all about the effect of gradual land movement on property boundaries, but as part of it I've done a fair amount of looking into what happens in the case of earthquakes.  The earthquake last weekend has suddenly made my research a whole heap more relevant to the surveying profession at large, so its quite exciting really!

Some cool links to check out are are a video of pretty impressive aerial shots of the fault line here (which also has some comments about the surveying side of things), and my brother's analysis on the earthquake here and here.

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