Quake risk ripples far and wide

Last updated 05:00 07/04/2013
Phil Emery

Phil Emery has no intention to move.

Relevant offers

The ripple effects of Canterbury's earthquakes are spreading further and further. JOHN McCRONE reports.

Up on the cliff-top skyline on the drive to Sumner, where the fanciest homes with the best views are built, there used to be a kid's set of swings which looked like they swung right out far enough to dangle your toes over the drop.

It was probably just a trick of the perspective. Yet it seemed to sum up something about the carefree "she'll be right" Kiwi mentality. And now, of course, it is half the houses which dangle off the cliff just there.

The Canterbury earthquakes caught New Zealand out, letting us know we have been building in places that should never have been allowed. The question now is what are the authorities going to do about it?

The deaths of 169 people following the collapse of two relatively modern buildings and a lot of shop-front canopies in central Christchurch has focused national attention on the urgency of bringing high-rises and public property up to sufficient earthquake code.

Towns like Oamaru and Hokitika are faced with the crippling cost of upgrading their many heritage buildings. In Wellington, apartment blocks are being yellow-stickered and unit owners told they each need to find upwards of $50,000 to deepen their foundations, insert new beams through the walls. The ripple effects are spreading further and further.

But while building strengthening is one lesson, what happened to Christchurch's Port Hills, with its lethal boulders and sudden cliff-face collapses, is emerging as possibly an even bigger national issue.

British risk consultant Tony Taig, who was brought in to deliver official reports on both our building and hillside risks, says it is New Zealand's land-use planning - where we have let people build - that concerns him more than our construction standards.

Speaking from his home in England, Taig says: "In my opinion, sorting out the planning- consent regime in areas that are known to have a very high natural- hazard risk should come higher than raising the threshold of what we call an earthquake-prone building."

Taig spent time living in Wellington in 2002 and has been horrified on returning to discover how loose development has become.

"I can't believe, 10 years on, how many more homes have been built in what frankly to me look like the most stupid places. On hillsides that I would describe as semi-cliffs like Khandallah - you're talking 35 to 40-degree slopes - those slopes now have got houses popping out everywhere."

The pushing of the envelope when it comes to natural hazards seems widespread, says Taig. Look at Auckland ignoring its volcanoes and Tauranga its crumbly hills, never mind all the subdivisions appearing on flood plains or in the firing line of the next tsunami.

New Zealand is a spectacular country, so naturally people want to build in its most beautiful spots. But that has to change, he says.

University of Canterbury geology professor Tim Davies, director of the university's hazard and disaster management programme, agrees. A lack of robust national-level land use standards means local councils are too easy to push around, he says.

Ad Feedback

"Remember the Matata flood and debris flow up in the North Island in 2005? That wiped out a lot of buildings on an alluvial river fan. But the district council has continued to issue building consents for the area that was devastated because they've had a legal opinion they can't withhold those consents."

People have their own perceptions of risk, says Davies. "Some of us will wear steel-capped boots to mow the lawn." The problem is that just as many in any society are born optimists. They cannot imagine the worst happening so will push thing as far as they are permitted.

There has to be change says Davies. Probably even retrospective action - decisions made about houses already built in places that are simply too dangerous.

Taig says you can, of course, imagine the howls that will go up about that. Especially from those with the "absolute beachfront" views and mansions perched on sheer drops.

But Taig can see homes being red-zoned as has happened in Christchurch. And then secondary buffer zones where the dangers are spelt out in the owner's LIM (land information memorandum), extensions or rebuilding not permitted. A staged approach to safety.

So at the moment, it may be the cost of earthquake strengthening that has got the country talking, says Taig. However, land-use consenting looks set to be an even thornier topic.

The problem for the experts is how to start this particular conversation without scaring the pants off people. Because within a few minutes, a convincing case can be made that you would have to be mad to live anywhere in New Zealand.

The word for the landscape is dynamic, says Taig. Thrust up out of the sea in the Roaring Forties where two continental plates have crunched against each other, Taig reckons New Zealand must top the list when it comes to a First World population and its exposure to natural hazards.

"If you're not on a fault zone, a volcanically active zone, or a tsunami zone, you're probably in a valley that's prone to flooding or having things tumble down the hills towards you."

So it is not even practical for Kiwis to aspire to the levels of security that might be taken for granted in more sedate places like Britain, he says.

It gets worse. Taig says it has become realised that natural hazard risk does not conform to a simple bell-curve statistical analysis of the kind we are used to - where the chances of a really big event dies away smoothly towards the extremes.

Instead the probabilities behave much more like the erratic nature of the stock markets where the unexpectedly large tends to happen unexpectedly often. Which for New Zealand becomes a special concern because it only has about 150 years of good data on which to draw.

"Each time you double the period over which you are looking at geological hazards, the events become much more than twice as nasty. And so the New Zealand data does not yet provide a representative sample of the actual risks associated with its earthquakes and volcanoes.

Taig adds: "That's interesting when you start thinking about some of the spectacular things that have happened in the past like the major eruption of Lake Taupo." The supervolcano just 27,000 years ago whose dust was about enough to tip the planet into an ice age.

Evidence that outsized events could be much more frequent than expected comes from signs New Zealand was washed by an eight- storey high tsunami just 500 years ago.

According to retired Department of Conservation archaeologist Bruce McFadgen, who has recorded the sand deposits left all along eastern coastlines, a third of the Maori population of the time could have been wiped out.

Then there are the equally outsized consequences of these big events. Davies' Canterbury University hazards team has been investigating some completely new things to be worried about.

Davies says the likelihood of the Alpine Fault going every 330 years or so is well known, but now it seems the rivers on the plains "go wild" for decades following, shifting course constantly because of the changed ground levels and extra sediment they have to shift.

Davies says think about what it means for where we have chosen to build our towns and cities if the rivers are going to start snaking all over the landscape.

"We have become very focused on the most immediate threat of buildings falling down, but when the shaking has ended, it doesn't mean it is going to be all over, not by a long chalk."

Kelvin Berryman, GNS Science Alpine Fault researcher and director of the national Natural Hazards Research Platform, says New Zealand has been lulled into a certain complacency because the past half century has been rather quiet.

"Go back 50 years and Masterton, Wellington, Hawke's Bay, the Buller Gorge and North Canterbury all had a lot more earthquakes. The land use planning has perhaps got a little loose because planners are often looking back over only a relatively short term."

Now says Berryman, the Canterbury earthquakes have proved the point that the worst can come out of the blue at any moment. And because New Zealand offers so many different disaster scenarios, also more likely than not, from a direction not much anticipated.

"It was supposed to be Wellington that would get the big one, wasn't it?" he remarks wryly.

So now is a time to be thinking broadly and systematically about how to react to the lessons of Christchurch, says Berryman. We have to get back to basics about where we build as well as what we build.

How slack were things in the Port Hills then? You can read the evidence both ways.

Despite the most extreme shaking imaginable - ground accelerations of twice gravity when one third gravity would be considered severe - and 10,000 rocks dislodged, boulders the weight of trucks smashing into houses, cliff faces peeling away, the Port Hills saw only five actual deaths.

One man died in his house, two others were hit by tumbling debris near their homes, and two more were felled out in the open, up on the hillside tracks.

There were some incredible misses. A boulder zig-zagged down a road of houses, skipping back and forth through their gardens to miss them all.

The time of day probably also made a difference. Many people would have been at work or school when the February 22 earthquake struck at lunchtime. But even if everyone had been at home in bed, the toll may not have been hugely higher.

There is the case of 82-year-old architect Don Cowey who died while picking raspberries at the end of his garden in Redcliffs. Cowey had built his home right under a rock face, reports saying he even had to clear away the remains of older falls to make his terraced vegetable plot.

So a clear example of a person who ought to have had more sense.

But on the other hand, his daughter says Cowey had dug a trench and put up a mesh fence to protect the actual house. And even with a shaking way above reasonable expectation, the collapsing rock did not reach as far as the dwelling.

The argument from many in the Port Hills, such as civil engineer Phil Elmey who is fighting to stay in a red-zoned property in Sumner, is that locals are not reckless or stupid. They have often looked around to work out which way the rocks might fall and planned accordingly.

"Our house has a number of factors that make it much less risky than the reports paint," says Elmey. "We are on a local ridgeline. We've got good vegetation behind us. The nature of the construction of our house is quite resistant to rock. We even have an existing rockfall protection barrier."

Elmey says in both the February and June quakes - a second "ultimate limit state" event in the Port Hills - no rocks in fact crossed his boundary. "They came down behind us, but stopped. And two rocks went by us down a gully."

Berryman says people have a notion about what is acceptable as the chances of dying suddenly as the result of some unlucky act of fate. Internationally, it comes down to a figure like a 1-in-10,000 annual risk of being killed by a drowning, a car smash, an epidemic, a falling rock, or whatever.

The problem with catastrophic events like earthquakes is that they happen rarely but can kill a lot of people at once when they do. So it can be hard for home owners to appreciate that they may be pushing the odds closer to a 1-in- 1000-year risk because of where they have chosen to live.

The studies to assess the facts are still going on. Because there was no Royal Commission to investigate the Port Hills deaths, the history of its land-use decisions has not come in for the same public scrutiny as has the issue of building standards.

However, behind the scenes at Christchurch City Council and the Canterbury Earthquake Recovery Authority (Cera), teams are continuing to model the hillsides, gather detail about what actually happened, and make decisions on where the bar will need to be set in the future.

One question is whether Earthquake Recovery Minister Gerry Brownlee has been overly cautious, red-zoned too many homes, and so created a tough precedent for the rest of the country.

Canterbury University's Davies says on the current criteria for the Port Hills, entire towns would probably have to be shifted. "If you apply what we've decided is safe in Christchurch to Franz Josef and Milford Sound, you might well find that those places need to be red- stickered."

Brownlee has also rejected advice that many of the red-zone houses could be protected by rock- fall nets and bunds. There were proposals for lines of shipping containers, covered by mounds of earth, to form ramparts on the Port Hills slopes.

According to Cabinet papers, officials said building defences would be cheaper than buying properties out. But Brownlee felt the expense of maintaining such protection was a problem and another big earthquake could still overwhelm walls or fences, no matter what size.

In response to owner pressure, the Christchurch City Council agreed to consider lifting its section 124 prohibited entry notices if a convincing case could be made for the rockfall protection of individual properties. So the line could end up being pushed back the other way.

Elmey, who helped formed the Port Hills Limes Group to dispute the extent of Cera's red-zoning, says the cost and stress of fighting for their properties could be too much for most though. "Last year there were about 200 or 300 of us. But now there's about 30 who are still staunch and 30 just hanging in. There's been a lot of attrition."

It is clearly going to take a while longer for the Port Hills issue to be settled, the full lessons learned.

And then, as the experts say, the conclusions will need to be fed into an across-the-board reassessment of New Zealand's land planning.

Davies is optimistic about the outcome nevertheless. "In New Zealand, we've still got a choice about where we put development. There's generally an alternative site, which isn't the case overseas because of the population density.

"Plus we have a lot of knowledge about our very active landscape."

- The Press

Comments

Special offers
Opinion poll

Have you seen rats on your property?

Yes

No

Vote Result

Related story: Does Christchurch have a rat problem?

Featured Promotions

Sponsored Content

Then and Now