Auckland's chances - we're safer, not immune

A 6.5 magnitude quake could cause more than $1 billion in initial damage. Photo / File photo

Central Auckland would suffer only a few casualties if struck by an earthquake similar to the Lyttelton shake.

A 2006 Auckland City Council report found that a 6.5 magnitude quake could cause 11 deaths, from a daytime population of 600,000, and more than $1 billion in initial damage.

That's because of the hard volcanic rock under Auckland's feet and the building boom after stricter construction standards were introduced.

Christchurch, on the other hand, sits on a lump of jelly. The soft sediment which washes down from the Southern Alps amplified the intensity of the Lyttelton earthquake.

Auckland's closest plate boundary is at Taupo, and the nearest faultline at 30km to 60km from the central city moves every 5000 to 10,000 years.

But Auckland is not immune. The city's waterfront is built on reclaimed land, and all unreinforced masonry structures below Shortland St would suffer badly in a large tremor.

About 5 per cent of commercial buildings and 2 per cent of residential structures in Auckland's CBD, worth $63 billion, are unreinforced.

A council register lists 400 structures built less robustly, which don't comply with 33 per cent of current building codes.

But because the seismic risk in Auckland is so low, the owners aren't encouraged to upgrade them until they renovate or make changes.

Auckland Council building control manager Bob de Leur said that unlike Christchurch, much of Auckland's CBD consisted of reinforced concrete structures that were built since the 1970s, when stricter building codes were introduced.

The greatest harm could occur in older town centres such as Dominion Rd's shopping area, and liquefaction would seep into Auckland's suburbs and low-lying coastal areas.