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August 2, 2010 | by  | in Features |
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Archi-techtonics: How fucked are we?

“Earthquakes don’t kill people,
it’s buildings that kill people.”
—Dr Geoff Thomas, Victoria University School of Architecture

Get ready, so you’ll get through. We’ve all seen the ads and seem to know the story—we’re in for the big one, right? Within the space of a minute, the ground will split into a cavernous fissure, indiscriminately swallowing buildings and loved ones as the rest of us dive for the nearest school desk in the face of its tectonic fury. For those of us lucky enough to have “ducked, covered and held” without being crushed by flailing debris there’s also the slight matter of tsunamis, aftershocks and fires that should see the rest of us off—not to mention difficulties in supplying aid. Grim.

Is all this cautionary warning and general sloganry a way to generate an air of optimism in the face of such a cataclysmic disaster? Will fixing, fastening and forgetting really do the trick or are we well and truly fucked?

Scenario: The Big One

New Zealand experiences hundreds of earthquakes every year, but most of these are either centred very deep in the earth’s crust, or well offshore and cause little damage. In addition to their frequency, on average we experience an earthquake that exceeds magnitude 7 every ten years. Although these quakes rarely coincide with populated places, there is a recurrence rate of between 500-1000 years on the Wellington fault—the most recent having been hundreds of years ago.

Wellington city has already been subject to a massive quake in 1855. In this quake the Wairarapa Fault ruptured and the entire Wellington Region was tilted westward. In addition, around 5000 km2 of land was shifted vertically, with uplift of 6m near Turakirae Head and 1–2m in the Wellington Harbour, dramatically changing the landscape. There were hundreds of aftershocks greater than magnitude 5 in the following weeks. To put this in perspective, it is expected that at sometime in the future the city will have to deal with a sizeable shallow quake along the Wellington Fault. For the sake of establishing a likely scenario, the Greater Wellington Regional Council website estimates that such a quake (of around magnitude 7.4), could be expected to cause around 500 deaths, 4000 injuries and perhaps leave 1800 people trapped. If the quake was to hit at night, fewer people would be killed or hurt, but in either case we could expect about 2800 homes and other buildings to be destroyed and another 100,000 buildings to be damaged in some way.

Tsunami

In addition to the threat of the initial quake, there are also a number of other dangers that can cause even more loss and suffering. In their capacity as environmental scientists, NIWA (National Institute of Water & Atmospheric Reseach) have produced a simulation of the likely effects of a tsunami after an 8.2 magnitude quake centred in Cook Strait. Unfortunately for those living in the Eastern suburbs, the results don’t bode well. Populated areas on the southern coast, such as Lyall Bay and Island Bay, would bear the brunt of the wave as it made its way through Cook Strait towards the Rongotai Isthmus (the flat bit with the airport on it). Depending on the size of the tsunami, it is possible that this area would be covered by up to six metres of water as the tidal surge moved north through to Evans Bay. In addition, the relatively low level of parts of Miramar could leave this area as something akin to a saltwater lake, which could remain submerged for a significant period. While the impact on the waterfront area around the city centre would be somewhat destroyed, it would no doubt still be a dangerous place.

Materials

Contrary to popular belief, it is generally the flexible buildings that tend to perform better under earthquake forces. Rigid materials such as bricks, glass and unreinforced concrete might appear convincing in their weighty appearance, but under the intense earthquake forces they are much more prone to failure and subsequent collapse. In comparison, wooden framed houses (such as those you probably live in) are a surer bet. Their relative flexibility means that they will move consistently with the shaking of the ground as opposed to the rigidity of other structures, provided there is a strong enough foundation connection.

Shaky Foundations

In 1978, new housing design standards were introduced to ensure the safety of occupants in the likely event of another quake. The Edgecumbe quake in 1987 (magnitude 5.1) was the first significant test of new design standards for timber-framed buildings, and the initial results were promising. Post-quake inspections showed only negligible damage due to inadequacies in the structure and, as such, the compliance code for new buildings has only received minor amendments since this date.

The main issue found after the Edgecumbe study was problems with the foundation connections and bracing. In many cases, the connections were either not there at all or had corroded significantly to have impeded their performance. The corrosion of structural members is likely due to inadequate ventilation to the subfloor, which occurs when buildings have been built too close to the ground, or in some instances when gardens have been built up around the foundations.

Our Flats

New Zealand’s housing stock consists of mainly light timber frame dwellings which perform reasonably well in earthquakes due to their inherent flexibility, with wall linings and claddings which provide a high level of bracing. In spite of this benefit, a study conducted by Dr Geoff Thomas and J.D. Irvine in 2007 showed some alarming results. Based on a sample of 80 Wellington houses, the pair concluded that approximately “70 per cent of houses in Wellington City had foundations that would not be adequate to resist the design earthquake expected in Wellington”. In addition to this startling fact, a significant portion of these houses were in such a bad state they could be expected to fail in the event of a relatively minor earthquake.

With this worrying statistic in mind, the study also investigated the potential effect and cost of upgrading existing structures to approved standards against the costs of recovery if nothing was done. The results show that to upgrade the existing deficiencies it would cost around $15–$60 per square metre to achieve the required standard. Projecting the total cost onto the upgrade of all Wellington City foundations, the total cost would be in the vicinity of $250 million which, despite appearing an expensive amount, is relatively paltry in comparison to the expected $2.1 billion in damages that would occur in the event of a magnitude 7.5 quake if nothing were done. Even with these upgrades, however, the number of environmental factors affecting foundation capacity means that no foundation reaction can be fully predicted, or assumed to be safe.
The Safest Buildings

New requirements for seismic design established after the Napier earthquake in 1931 have led to a much greater consideration of the impact of seismic activity on our buildings. For the most part, this has ensured that all buildings built post-1975 are generally considered to be of sufficient strength to withstand a significant quake. In addition to meeting these seismic standards, there are a few exemplary structures in Wellington that shoot above and beyond the specifications and stand as examples of excellent seismic engineering. Locally developed ‘base-isolation’ bearings in Te Papa, the parliament complex and the new hospital in Newtown have been specifically designed to dampen lateral forces exerted by earthquakes and protect their precious contents.

The new Victoria student hostel, Te Puni Village, presents another example of the possibilities for reduction in earthquake damage. Large spring coils are located at the base of the buildings that absorb excess energy during the earthquake and greatly reduce the risk of collapse. The additional advantage of this system is that the spring coils can be retrofitted following earthquake damage in order to provide the same level of resistance as before, whereas other systems often render the structure useless following a significant quake.

Theory vs. Practice

These examplars of seismic design have generally been developed from proven models used elsewhere (Japan, California), but there still exists some doubt as to how they will perform in our conditions. One such concern is Te Papa having been built on the reclamation. The worry is that while the ground underneath the museum was compacted significantly during construction, there still exists the chance for liquefaction during a quake. Basically, this would mean the further settling of the soil which would cause the building to sink and potentially flood the ground floor spaces—a reason the museum does not have any permanent exhibits at this level. That being said, the broadness of the building would make Te Papa unlikely to develop any Pisa-esque leans if the subsoil were to liquify and even in the worst cases, movement would be greatly minimised.

Non-Fixed Objects

Another point to seriously consider when designing buildings is that structural concerns present merely a small portion of potential dangers during a quake. In reality, there is a far greater risk from household contents such as fridges and bookshelves which are particularly dangerous during ground-shaking. Most televised cautions do encourage fixing heavy items as a means of minimising this problem, but little can be done to prevent unexpected collapses such as items in supermarkets or books in libraries falling from shelves. Damaged electrical and gas connections present similar new hazards and can often result in large-scale fires following the initial earthquake.

Aftershock

In addition to post-quake fires, gas leaks, inundated buildings and further collapse, there are a number of further dangers that can develop. One of such is the occurrence of aftershocks, which can sometimes be of a similar strength to the main event. Generally these aftershocks can lead to greater losses of life, as the effect of any significant shaking on already weakened structures can completely reduce anything still standing to rubble.

Emergency Response

Should a sizeable quake hit tomorrow, the majority of our current building stock would likely be destroyed or damaged to the extent that they would be rendered uninhabitable. This would leave a large percentage of the population without shelter, awaiting emergency support that could be a considerable distance away. In the most likely post- earthquake scenario, landslides in the Ngauranga Gorge and along the Hutt Road would block road access to the city from the north as well as the possible raising of the seabed at the harbour entrance, restricting shipping traffic. If this were the case, aid would be considerably delayed, and many more people could perish from a lack of adequate attention. These additional ‘costs’ in terms of volume of evacuations and aid requirements are significantly difficult to predict and quantify, but would no doubt constitute a large sum of money.

Rebuilding

Once the need for emergency aid and healthcare has subsided, the next stage of earthquake recovery would be the restoration of physical and social systems damaged by the quake. This usually involves the implementation of emergency management systems, followed by a much more comprehensive reconstruction phase which can last for many years after the event of a quake until the city is able to function by itself once more. The failure of businesses and the resources required for this rebuilding effort can further inhibit reconstruction, and often there are a number of unforeseen issues that can extend the recovery period well beyond any prediction. The only small consolation to the restoration effort would be the opportunity to rebuild the city to a more efficient and potentially richer standard, as was the case with downtown Napier following the 1931 quake.

Fixed, fastened, forgotten

Of late it seems as though the plethora of cautionary TV adverts that assaulted our screens a few years back has subsided. Surely the risk is as great or greater—so what’s the dealio? Presumably, this is an important measure to avoid a boy-who-cried-wolf scenario by ensuring that Kiwis don’t become complacent in the face of too much exposure but, by the same token, the recent perceived lack of preparatory warnings could also lead to a false sense of security in the face of what is still a very real threat. This, coupled with the appalling reaction to the tsunami warning earlier this year which saw a large number of idiots flocking to the waterfront as though it were a spectacle to be observed, and you begin to see: we are quite dumb.

All said and done, the efficacy of any preparation pales in significance to chance, although it does vastly improve the odds. The only way in which we can truly count ourselves prepared is in terms of the quake’s aftermath and the provisions we would have to ensure our continued safety until aid is possible. Failing that, the next best strategy would be to spend as much time in the earthquake-strengthened Rankine Brown building as humanly possible. Avoid Hunter at all costs.

5 WORST PLACES TO BE DURING ‘THE BIG ONE’

1. St Gerard’s Monastery—a colossal brick structure precariously perched atop Oriental Parade…

2. In the Ngauranga Gorge—With a likelihood of large landslides this would be worse than running the gauntlet against Vulcan, Saber and Storm—on the best of days.

3. Lambton Quay—Watch helplessly as three-meter-high glazing panels fall from 10 storeys up and cleanly slice through the suited throngs of the corporate world.

4. Anywhere along the Tinakori Road (Wellington Faultline) —the classic ‘swallowed by the earth’ scenario. Coincidentally, this happens to be where the chairman of the Earthquake Commission lives. His wife’s decision, so I’ve been told. Hmmm.

5. Chaffers New World—In spite of the fact the relative shelf-height makes it more safe than the bulk force of Pak N’ Slave, the threat of tsunamis and settlement, coupled with their inability to keep shelves standing during more peaceful times makes this one a sure-fire danger zone.

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  1. Rob says:

    The NIWA tsunami animation video is available on YouTube. It’s a computer simulation of the 1855 tsunami with today’s topography:
    http://www.youtube.com/watch?v=J-LpNDoiUMw

    It’s well worth watching – what happens to Evans Bay/Lyall Bay/Rongotai/Kilbirnie/Miramar/Seatoun is quite shocking. Island Bay fares very well except for a row of houses immediately on the foreshore – perhaps because of the angle of the wave and/or the island acting as a breakwater.

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