New Zealand Earthquake

01 March 2011

Graham Matthews, FRICS, Commissioner, RICS Disaster Management Commission provides an update on the latest earthquake in Christchurch, New Zealand.

A week ago today, at 12.51 in the afternoon, the Canterbury region of New Zealand’s south island suffered a devastating earthquake. There is some technical debate as to whether this was a new earthquake, or a substantial aftershock emanating from the first earthquake that occurred last September.

It is an academic distinction in reality. Cantabrians have endured over 4000 aftershocks over the past five and a half months – that’s nearly one an hour – so the material distinction was the impact it had on their lives.

This time the earthquake occurred at a less forgiving time – during the lunch period on a busy weekday, when the city of Christchurch was full of people enjoying the late summer weather.

It was also quite shallow and, according to scientists from New Zealand’s GNS Science, a government research organisation, was the result of a 17km long sub-surface rupture of a hitherto unrecognised east-west sloping fault line that passes just to the south of Christchurch.

The result was a dislocation that caused nearly 2g thrust. Subsequent radar images suggest that the ground to the south of the fault has moved about 500mm in a westerly and upwards direction.

The effect of all this was that, despite being smaller then the September event, it had a far greater impact on the city and its environs. At the date of writing the situation is grim:

• Over 150 have been confirmed dead, with over 200 still missing
• 55,000 homes have no water, 75,000 have no wastewater disposal, 30,000 lack power
• 6 water reservoirs have been structurally damaged
• 12 major trunk sewer lines are damaged
• 10 bridges are closed – damaged or destroyed
• 750 buildings in CBD already declared unsafe, and that number will escalate

Around the city and satellite communities the impacts have been different. In the CBD the massive acceleration thrust of the quake has caused extensive damage to buildings and infrastructure, particularly older properties that were never built to modern seismic standards.

In the words of GNS Scientists, it was equivalent to lifting the buildings and letting them go into free-fall. Heritage buildings such as the Christchurch Cathedral have no resistance to being lifted and dropped like a stone and have suffered appalling damage.

In the eastern suburbs extensive liquefaction of the underlying alluvial deposits that much of Christchurch is built upon has caused widespread settlement of structures and deposited thousands of tonnes of silt across roads and land.

Sinkholes have appeared, some large enough to sink commercial vehicles, and elsewhere hard pavings and roads have settled and broken up. Liquefaction below one of Christchurch’s largest buildings, the 26-storey Hotel Grand Chancellor, is believed to be responsible for its structural failure and near-collapse.

In the south-eastern Port Hills the force of the earthquake caused rockslides and considerable damage to residential property - in some cases completely destroying whole streets of houses. There are several cases where very large rocks, some the size of a car, have passed completely though houses.

The remarkable thing, however, is how resilient Christchurch is proving to be. In many other cities around the world, an event of this impact would have catastrophic consequences. Consider the impact on, say, London or Paris. By my rough estimates an earthquake of this magnitude and force would destroy a large proportion of residential properties, with far worse outcomes in mortality, injury and loss of property.

Whilst the mortality, injury and damage in Christchurch are severe, it is a position that Christchurch can and will survive, and is already doing so with remarkable speed. As of today, power has been restored to nearly 90% of homes, water reticulation is being repaired and desalination plants are being brought on stream to replace damaged water treatment works.

A massive tidy-up is underway with thousands of volunteer workers, and work has already commenced in assessing damage for repair or demolition. Businesses are getting back to work, some schools are re-opening, and food distribution is starting again. But in the CBD little is happening apart from the ongoing search and rescue operations.

We should equally not underestimate the enormity of the task ahead. Full reconstruction is likely to take up to 10 years and cost estimates vary from between $10bn and $15bn. I suspect this will creep up once the full extent of damage is known, and this will not be for some time.

That is a lot of heavy lifting for the NZ economy, but let’s put that into context: the 2012 London Olympics will cost the UK in excess of $21bn (and even this figure is debatable) so the cost of re-building Christchurch could be seen as good value.

So, what next? The rescue and recovery phase is starting to draw to a close and then the massive job of re-construction will begin. Will Canterbury be re-built as before? I doubt that very much. A lot has been learned about the geology of the area and a different stance will no doubt be taken to some of the more susceptible areas.

The re-construction will also follow most recent seismic standards, which will impose different design solutions on new construction and repairs. But there are strong indications that the council and local communities are already pushing to re-build their city. It just won’t be quite the same.

The impact on the local economy will be profound and many businesses will not survive. But new opportunities will emerge, initially connected with the re-construction effort. Already the void rate for commercial and light industrial buildings has fallen dramatically, as businesses seek to re-locate to undamaged premises.

A second, and more worrying trend, is migration. To date, some 50,000 people (some 14% of the local population) have left Canterbury to stay somewhere away from the constant aftershocks and the trauma of the recent event. Many will eventually return, but some, and maybe quite a lot, may never.

The next 4-6 months will see a huge clear-up, a vast number of buildings and insurance assessments, and detailed planning for a construction programme that NZ has never seen before. Much of this work has been done once already, following the September earthquake. Most of it must now be re-done.

A small army of construction professionals will be employed in this programme and the RICS has a role to play in sourcing the skills and experience that will be needed.