This morning’s severe earthquake in Canterbury – initially thought to be magnitude 6.4 but since revised to magnitude 6.0 – centred 30 km west of Arthur’s Pass – is a reminder that these things are constantly with us in New Zealand.
You can’t expect anything else, living on the edge of the Pacific Rim of Fire. Some 635 fault lines have been discovered in New Zealand, and few parts of the country are far from them. The expected ‘big one’ in the South Island will be magnitude 8+ from the Alpine fault, which last experienced a shift of that scale in 1717.
Scientific studies show that the likely results will be devastating to a large area of the South Island, wrecking major towns and centres, causing widespread destruction to landscapes with their road, power and rail links. There is a possibility the West Coast might be cut off for weeks or months, just when aid is needed, along with tne potential for power grid disruptions affecting the whole country. Devastation could stretch into the southern North Island, engulfing Wellington which sits at the northern end of the fault, on a fault complex of its own.
Yeah. Ouch. Just when this apocalypse might hit – needless to say – has attracted a good deal of attention. I detailed the story in my book Living On Shaky Ground (Penguin Random House 2014).
Earthquake forecasting is actually a precise science, though popularly it perhaps seems less so. The problem is that we’re brought up to expect specific information – exact numbers and times. These simply can’t be predicted, because the nature of the forces driving the quakes cannot be perfectly measured. That’s the nature of it, but seismology can go a very long way towards detailing the risks and probabilities. Mathematical techniques such as ‘Bayesian regression’, for example – a way of handling partial data and producing useful forecasts – are applied to the available data.
The chance of something happening at either edge of the probability range isn’t impossible, just unlikely. But unlikely events still occur, and seismologists are not wrong when one does. On the contrary, their forecasts very clearly include such possibilities.
In 2012, studies of the Alpine Fault and its movement history over the previous 8000 years revealed that – on the basis of its past movements – there was a 30 percent chance of a devastating quake occurring on it, some time in the next 50 years – before 2062. Because probabilities are calculated as bell-shaped curves, this did not mean a quake would occur precisely in 2062; it meant the quake might occur any time from 2012 (a low probability) through the mid-twenty-first century (a high probability), on to the early 2100s (a low chance of it happening that late, but a very high probability of it happening, if it hadn’t happened by then).
A further study, published in 2014, added dimension to that analysis, and I can’t help thinking that yesterday’s earthquake is another reminder. There have, of course, already been major civil defence exercises based on the possibility of a devastating Alpine fault quake. The onus, for all that, remains on everybody, personally and individually, to be prepared and to have plans – all of which is detailed by Civil Defence.
And also, of course, the onus is on to check out my book on quakes…
Copyright © Matthew Wright 2015