So I went to a lecture by Dr Quigley, the earthquake geologist, the other night at the Town Hall. It was a fascinating talk describing causes of the earthquake, why it was felt differently and what’s happening with the aftershocks.
Three things stood out for me:
Port Hill Rocks – Dr Quigley showed photos of some rocks on the Port Hills that have literally jumped out of place. It looked like they would weigh up to a tonne and they have moved over a metre. They haven’t rolled, they have just been moved sideways!
Natural Frequency – Buildings can exhibit mechanical resonance where repeated regular shakes can resonate and be magnified (you might have head of this phenomenon with respect to bridges wobbling).
The kind of shaking experienced in the quake had a lot of high frequency shakes which is more damaging to small buildings.
Aftershocks – The aftershocks are largely following expected patterns in terms of frequency (how often) and strength, which is kind of comforting, although it does mean we can expect more for some time to come.
You can watch a video of an earlier lecture at the University of Canterbury website: http://www.canterbury.ac.nz/restart/videos.shtml
Or you can find more information including a set of photos and a map of the fault line at Dr Quigley’s website: www.drquigs.com