The modern face of earthquakes in New Zealand

The latest batch of quakes to hammer central New Zealand got me thinking. In past decades the usual face of such events were street-scapes of broken buildings and scattered debris, typified by the ruin that struck Napier and Hastings in 1931.

This picture of post-quake Napier isn't well known; it is from my collection and was published for the first time in the 2006 edition of my book Quake- Hawke's Bay 1931.
This picture of post-quake Napier isn’t well known; it is from my collection and was published for the first time in the 2006 edition of my book Quake- Hawke’s Bay 1931.

That disaster cued more than half a century of active quake-proofing measures, bolstered by several revisions to the original 1935 code. And so today buildings in cities such as Christchuch and Wellington – both hit by multiple heavy quakes since 2010 – stay standing.

But that, it seems, is all many of them do. The Christchurch experience was salutary. Two modern buildings collapsed in Christchurch in the February 2011 quake, provoking much of the appalling death toll. Others still stood. Except that, on inspection, they had to come down anyway because of fundamental structural failure. Sometimes it was foundation problems: in 2013, when I visited the quake-riven city, I saw a row of high-rises looking for all the world like crooked teeth. All were due for demolition.

It’s been the same in Wellington. The two heavy quakes of 2013 and the Mw 7.8 Kaikoura shake last month – which delivered much of its punch north to the capital – didn’t collapse any buildings. But a number of them have been damaged beyond repair and are going to come down anyway – taken down, urgently, by demolition crews before they collapse in aftershocks. They include new parking buildings and a very modern building on the waterfront that – in theory – was put up to the latest standards. Ouch.

Building at 61 Molesworth Street being taken down by an 85-ton 'nibbling' crane.
Building at 61 Molesworth Street being taken down by an 85-ton ‘nibbling’ crane.

We can build structures that don’t collapse or shed their outer walls in quakes, it seems, but we can’t build structures that are truly earthquake resistant – able to shrug off the effects and carry on. The plus side is that this still works as a way of saving lives. People can get out, and buildings don’t shed their walls into the street and crush passers-by. But the focus on quake-proofing has always been structures that simply shrug off the damage, and I have to wonder what’s gone wrong. Especially when you realise that most of what’s being demolished are the most recent buildings, put up in the last decade or so. Whereas older structures such as the Wellington Railway Station still stand.

Westfield (
Westfield (“Queensgate”) mall in Lower Hutt, greater Wellington district – the building in frame was issued with an urgent demolition order.

There will be an investigation – government’s announced it – but I can’t help thinking that a couple of factors have been at work here. One of them is that older seismic-resisting structures such as the station – which was designed before the 1935 code – were radically over-engineered. That particular building was erected on reclaimed land and special attention was paid to seismic proofing, including obtaining Japanese expertise. The other issue is a change of code in 1992 to kind of ‘market-driven’ model. Until then seismic code had been quite prescriptive, even down to the kinds of material to be used. Now it became more general – a requirement to meet certain loading standards. But exactly how those standards were met was up to the individual architect and engineers.

The philosophy was in line with the general mood of de-regulation that was suffusing New Zealand at the time. But it introduced a lot of variables, including one of the pitfalls of engineering – assumptions. If the assumptions around which a quake-loading was being calculated were wrong, then the building wouldn’t perform as expected in the crisis. And to me, that looks disturbingly like what has been going on.

No doubt the answers will come out when it’s all investigated. Meanwhile it looks like Wellington is going to see a lot of demolitions in the near future.

Copyright © Matthew Wright 2016

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5 thoughts on “The modern face of earthquakes in New Zealand

  1. “Market-driven” sounds a lot like the buzz phrase “value engineering” that we used to hear a lot on this side of the Bigger Pond. The idea seemed to be how close one could shave safety factors and remain within “acceptable” criteria. Perhaps the Germanic streak in my genetics is coming out, but I think an economic case could be made for “overengineering” in some cases, like this one, especially over the long term.

    1. Definitely. Overengineering is a virtue in a quake zone and a lot of our older quakeproofed buildings have survived well, whearas the new have not. I am put in mind of the DC3 and its fatigue life vs the issues faced by modern airliners. The timing (1930s vs now) is, curiously, very similar and I suppose part of it is the novelty of quake resistant design and duraluminum airliners before WW2 with the unknowns of the new world of loading and stress.

      1. I started to comment about the DC-3 from that perspective, actually. I heard MIT has stress gauges on one airframe that has over 100,000 hours on it. Still going strong last I heard.

        1. Update – I got to the bottom of the quake-proofing issue in NZ. Earlier quake-proofing was designed to elastically deform. For cost reasons that was then changed to destructive deforming – primary structure was designed to be sacrificial. Cheaper and in theory the buildings still stand in a shake, but they will be no good afterwards. Couple that with the over-engineering of the earlier systems and I find that a compelling explanation. For the November quakes in Wellington the issue was compounded by the fact that the ground frequency happened to match the typical resonant frequency of a mid-rise tower (which most of the Wellington ones are – it’s rare to be over 8-10 floors) and it compounded the problem.

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