A good shake would destroy the facades of the art deco buildings that bring tourists and money to Napier.
"Every single art deco building is earthquake-prone," associate professor of structural engineering Jason Ingham told a public meeting in Napier this week.
He oversaw a recent university study which looked at 114 art deco buildings, all built in the wake of the devastating Hawke's Bay earthquake in 1931.
All scored between 13 and 18 per cent of the current national building standard, because they were old, on bad soil and were close to the fault. The minimum acceptable standard is 33 per cent.
Comparisons with the Christchurch earthquake indicate the buildings would remain standing in a similar-sized tremor, but about half of them would have to be demolished because of the severity of the damage from pounding, liquefaction and falling masonry, said Dr Ingham, of Auckland University.
He and Society for Earthquake Engineering executive Win Clark were brought in to address concerns about the future of Napier's world-renowned buildings.
Art Deco Trust general manager Sally Jackson said it was crucial to preserve the city's heritage and secure the region's economic performance.
A 2006 economic study revealed that art deco activities brought about $23 million into the region each year.
Art deco weekend personality "Bertie" said Napier's distinctive architecture was the city's point of difference that lured in the cruise ships. "It's something we've got that nobody else has got."
There are about 140 art deco buildings in Napier's central business district, and more than 200 heritage buildings in the wider region.
Dr Ingham said art deco building owners should be heartened by how similar buildings performed in Christchurch. Out of the 10 he studied, none collapsed - however, six had since been demolished. Napier's buildings were "ahead of their time" when built, he said, but only minor improvements had been made since.
While they scored poorly in the initial evaluation procedure, he believed closer assessments would bump building strength up to about 50 per cent of the building standard. Walls would still collapse and ornaments would fall to the street in a large shake.
"The first thing to do in Napier is learn more about parapets and ornaments that might fall off - securing them has the significant ability to save lives."
The onus to make sure a building meets the minimum standard is on the owner.
Napier Mayor Barbara Arnott said most art deco building owners, along with other owners in the central business district, had been sent a letter requiring them to submit an earthquake-strength report to the council by May next year. Buildings that did not meet the minimum standard had 10 years to upgrade.
Mrs Arnott said the council would support building owners because preserving the city's heritage was "hugely important".
The cost of work was the big worry, said property owner Colin Crombie. All owners were concerned about the impending costs and many could not afford it.
"It's a tough rental market out there, and these costs are going to cause major grief, whether they're only small or large."
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