Made in China, made in NZ
Posted 17 June 2008 // Carl Walrond
Earthquake damage in Napier, 1931
The magnitude 7.9 earthquake in China should give New Zealanders cause for pause. The high death toll was due to the intensely populated nature of that country and it seems, shoddy building practices. How will a New Zealand city fare when such an earthquake strikes?
When a large quake (say magnitude 7.4) next occurs on the Wellington Fault during daylight hours, predictions are in the order of 500 deaths, 4,000 injuries and a $4 billion repair bill. Most earthquake deaths are from building collapse and this is why fatality guesstimates are higher for daytime quakes – people are in or around big high-rise concrete structures or old brick buildings. At night most are at home in generally more flexible wooden buildings. Building owners can face prosecution if they fail to reinforce at-risk buildings, which are recorded on a register.
How to reconcile the risk? It seems that Wellingtonians (like everyone else in the world) have optimistic bias – they believe that negative events are more likely to happen to other people. In Christchurch the risk is less, but an earthquake of over magnitude 7 hitting the city and causing fatalities and damage is a definite possibility. Our recent earthquake history may not be representative of our impending future. We have had big quakes since 1840, but only one in a populated area (Napier in 1931, with 258 people killed).
The biggest shake is likely to come from the Alpine Fault. Big quakes (called ruptures, as the ground is ruptured along the fault) have occurred on this fault in 1717, 1620, 1450, and 1100. It does not mean that we are overdue – just that as time passes from the last big rupture (1717) the probability of the big one occurring rises.
I spent a few weeks as a field assistant to my brother, a geologist, in 2000 around Fox Glacier. He was studying the layers of sediment that creeks had exposed along the Alpine Fault.
I asked, ‘What would happen if it ruptured now?’
‘They wouldn’t have to bury us.’
So what can you do? Well, I’ve bracketed all the heavy furniture to the walls, so at least the bookshelf shouldn’t topple onto the children. When it hits remember to drop, cover and hold – and don’t believe urban legend emails about the ‘triangle of life‘.
