The 22 Feb 2011 Christchurch quake caused widespread devastation. Photo / NZ Herald
The 22 Feb 2011 Christchurch quake caused widespread devastation. Photo / NZ Herald
Science reporter Jamie Morton concludes a five-part Heraldseries on natural disasters with a look at the threats to New Zealand and lessons we can learn from such catastrophic events
MUNTED.
Plastered across posters and T-shirts, inspiring a play, and named by a popular blog site as word of the year, "munted" became the catch-cry amid Christchurch's post-quake devastation.
Science writer Vicki Hyde, a stalwart of her rattled Redcliffs neighbourhood, said the word today isn't heard as often as itwas two years ago.
The Canterbury earthquakes opened the nation's eyes to the extent of damage and tragedy that natural disasters could bring about, and the threats we face at nearly every front.
On February 22, 2011, Ms Hyde said she and many Christchurch residents had thought the 7.1 earthquake six months earlier had brought the worst of it.
At 12.51pm, she and her husband had just sat down for lunch at the Antigua Boatshed when the 6.3 quake, its 5km-deep hypocentre located just 10km east of the city centre, erupted with the force of 15,000 tonnes of TNT.
"I went to stand up and I ended up on all fours on the floor ... there were people screaming around us."
When the shaking stopped, the couple attempted to get to their daughter, just across the Avon River inside Christchurch Hospital, and then made their way toward the museum.
"There were lots of people standing around in the Botanical Gardens ... and then, of course, someone said the cathedral had fallen down."
They weren't to know that the disaster had claimed the lives of 185 people, 115 perishing when the CTV Building collapsed.
The quake's violent force was so great it was considered statistically unlikely to happen more than once in a millennium, and far exceeded the loading extremes that New Zealand buildings were designed for.
Our codes require buildings to have 50-year design loads to withstand the loads of a 500-year event, but early reports indicated that the ground motion that afternoon was beyond even 2500-year designs.
GNS earthquake geologist Dr Kelvin Berryman, director of New Zealand's Natural Hazards Research Platform, said small earthquakes happen around New Zealand every year.
Kiwis had more or less learned how to accommodate these through design and community preparedness, he said.
"However, rare earthquakes in terms of size, but perhaps more importantly in terms of proximity to urban areas, such as Christchurch, can be devastating."
The quakes left more than 100,000 homes damaged, largely in the eastern suburbs, and more than half the buildings in the city's CBD severely damaged.
The Earthquake Commission has received more than 400,000 claims, with a large number of properties unable to be redeveloped in the short to medium-term due to serious land damage.
This week, the Earthquake Commission admitted that it wouldn't meet its Christmas completion target for the most damaged Canterbury homes.
Rebuilding New Zealand's second largest city will ultimately cost $40 billion, making it the largest and most complex single economic project in our history.
The quake was triggered by a rupture of a 15km-long fault along the southern edge of the city, running from Cashmere to the Avon-Heathcote estuary, but is still considered an aftershock of the September 4 event.
Canterbury is known to be home to around 100 faults, and the closest to the city thought to be capable of triggering major quakes is found in the Rangiora-Cust area. It was near here, at Darfield, that the first quake struck - but on a fault previously unknown to scientists.
Nearly three years later, on the afternoon of July 22, 2013, came another major jolt that was again first sourced back to an unmapped fault line.
What became known as the Seddon earthquake, named after the Marlborough town 20km from where the 6.5 quake hit, was strong enough to blow out windows, crack concrete, cause buildings to sway and send people running for cover on both sides of the Cook Strait.
Amid a swarm centred on the same fault zone, the second of a rare doublet of quakes hit less than a month later, its thrust enough to shift Cape Campbell 18cm to the west.
Like the Canterbury quakes, scientists are still learning about what levers were pulled to produce such a violent reaction.
What remains clear is New Zealand's frightening vulnerability to earthquakes, among other major natural hazards that stem from our geographical saddle across the Pacific and Australian tectonic plates.
Beneath the country, the Pacific Plate is moving to the west-south-west at a rate of about 50mm each year - about the speed a fingernail grows - and constantly grinding against the Australian plate, causing stresses to build up in the brittle upper layers of the plates.
GeoNet scientists locate about 20,000 earthquakes caused by this process each year, of which 250 are felt.
It was the most severe quake experienced in recent New Zealand history - the 1855 Wairarapa Earthquake, its magnitude a massive 8.2 - that led scientists to establish the relationship between faults and quakes.
The country is scarred with faults - a countless number of which may be discovered only after they make themselves known - but a few have scientists specially concerned.
The death toll could be in the order of hundreds in the event of a catastrophic Wellington earthquake, and thousands would be displaced.
The Wellington Fault, one of five major known faults in the region, passes under significant infrastructure such as the ferry terminal, motorway, railway, and bridges along the Hutt Valley, all of which could be put out of action when it ruptures.
It's believed this fault last ruptured between 300 and 500 years ago, producing a magnitude 7.6 quake, and is capable of causing a major event every 500 to 1000 years.
However, it's the Alpine Fault, spanning the spine of the South Island, which could pose the biggest threat.
A measure of its power can be found in the Southern Alps; the fault has pushed the mountains up every time it has ruptured, and over the past 12 million years, it is estimated the total uplift has been an astonishing 20km.
The huge fault is expected to rupture within 50 years, a one-in-500-year event that will produce a devastating earthquake of a magnitude 8 or more, with the potential to cause 10,000 casualties and kill at least 1000.
Its impact on Christchurch would be similar to the force of the September 4 quake, but West Coast townships would suffer most of the casualties.
A major quake would most likely also prove the catalyst for a large-scale, near-shore tsunami.
About 10 tsunami higher than 5m have struck New Zealand's shores, some caused by distant quakes, but most from jolts not far from the coast.
In what's called a "distant-source" tsunami, generated by a far-away quake in places such as South America, authorities could sometimes have more than 12 hours in cases to evacuate coastlines.
But in the case of a "near source" tsunami, violently born from an underwater quake in an underwater subduction zone, a devastating surge could come before sirens could even activate.
A review released in September found that because of uncertainty about the maximum size of earthquakes on nearby plate boundaries, tsunamis could be bigger than previously thought.
The most hazardous places were found to be Northland, Great Barrier Island, parts of East Cape and Wairarapa where waves of up to 15m above the normal sea level at the shoreline could be expected.
And, like earthquakes, there was much yet to be understood about the threat.
It was expected that when the next large subduction zone earthquake occurred, New Zealand could expect similar strong ground shaking across significant parts of the North Island, depending on which segment ruptured.
The closest segments were found offshore between Wellington and the East Cape, but this zone continued all the way to Tonga.
An earthquake on a segment beside New Zealand could potentially cause a tsunami of similar size to that seen in Japan, with the coast facing run-up heights that might in some places exceed 30m on steep coastal hills.
As with tsunami, minor eruptions within the active Taupo Volcanic Zone - as seen with twin eruptions at Mt Tongariro last year, and the quick-fire blow at Mt Ruapehu in 2007 - could happen with little warning each decade.
Fortunately, scientists would likely get perhaps years of notice in the event of rare and extreme caldera eruptions.
The best-known example, the Hatepe or Taupo eruption, 1800 years ago, reduced 80km of surrounding landscape to char with a devastating 1.5km-high pyroclastic flow, and its effects would have been visible in China and Rome.
An eruption from one of the Auckland Volcanic Field's many volcanoes could blast out an explosion crater one to two kilometres across, destroying everything in it, but planners believe people in its path would be evacuated well before an event.
Dr Berryman said New Zealand was not unique in its vulnerability to natural disasters - Japan, the western United States, parts of Italy, central America, Indonesia, and the Philippines all had similar hazard profiles.
What set us apart, he said, was a low population density across the majority of the country, creating the challenge of supporting a widely distributed population, and an insurance penetration rate of 85 per cent.
These two factors tended to act as counter-balances.
While we have comparatively low exposure to high hazard, our infrastructure is hard to maintain and our small population requires risk transfer offshore to protect a small and potentially catastrophically exposed economy.
But our small size comes with some upsides.
"Some of the real advantages that New Zealand has is the benefit of a small research community and bureaucracy," he said.
"Researchers commonly talk across discipline boundaries and integrate their knowledge very well. Because of the small community, it is feasible for the research to be integrated with policy decisions more effectively than almost all other countries."
For the science sector, the recent quakes have prompted a new wave of research, and the Natural Hazards Research Platform has received millions of dollars in Government funding to study and apply their main lessons.
Scientists are now improving the way earthquake hazard assessments are undertaken, attempting to quantify what would happen to hillslopes in Christchurch and Wellington under strong shaking conditions, and investigating the impacts of soil liquefaction on land and buildings.
"The Canterbury earthquakes have triggered liquefaction that is extreme by world standards and this has provided a data-set of international importance," Dr Berryman said.
"The damage to buildings and infrastructure in Canterbury has been the first major earthquake to strike a New Zealand city for over 80 years, so there has been much to learn about the performance of recent construction."
Researchers are also looking at the role communities play in recovery, and one longitudinal study is focused solely on personal well-being in Canterbury following the earthquake sequence.
Dr Berryman said there was still a vast amount of analysis to be completed across a wide range of areas, and many of the royal commission's recommendations needed further research.
Scientists needed to communicate better, both with policy agencies, so building code provisions could be better understood, and the public they served, he said.
While recent surveys suggested that quakes were the hazard that most Kiwis related to, partly because of the recency of Christchurch and Cook Strait earthquakes, some communities had shown little increase in awareness and preparedness.
"Preparedness remains the simple message but there are still low levels of action," Dr Berryman said.
"Social capital in communities has the highest correlation with resilience - a community that interacts and works together will be well-placed to cope with emergencies."
These days, Ms Hyde believed the average Christchurch resident would "grind their teeth" at hearing the word resilience.
Far too many residents, mainly in the eastern suburbs, remained stressed, disillusioned and still living in damaged homes long after EQC scopes had been carried out.
Police and volunteers rescuing people trapped in the CTV building. Photo / APN
The series
As a fellow of the United States-based East-West Center, Herald science reporter Jamie Morton travelled to China, New York and Japan to investigate how those countries had responded to their recent natural disasters.
The series aims to highlight how decision-makers, scientists and victims around the world coped with disasters, and why these disasters remain directly relevant to every New Zealander.
