Wellington's mid-rise buildings worst affected by earthquake

Wellington's mid-rise buildings suffered the most damage in Monday's 7.8 quake, engineers have found.

The shaking lasted for 90 seconds, compared to 20 seconds in the deadly February 2011 Christchurch quake.

The "extraordinarily large" release of energy on Monday was much closer to the capital than initially realised, Earthquake Engineering Society president Peter Smith said.

This resulted in intense accelerations in buildings between eight and 15 storeys high, especially those on softer soils.

"In contrast, short, stiff structures have experienced relatively low accelerations in this earthquake.

"This is the main reason Wellington's older buildings, which tend to be shorter, generally didn't suffer any damage, even though some are categorised as earthquake-prone."

Wellington City Council inspectors have so far found 60 buildings with signs of structural damage, and 28 at risk of part of the building falling down.

The minimal damage to low-rise buildings and significant damage to mid-rise buildings was "unusual".

Structural Engineering Society president Paul Campbell said engineers were continuing to assess buildings.

"Buildings might be undamaged or damaged in a way that doesn't reduce their capacity to deal with future shaking. This means they may be just as safe as they were before the earthquake.

"Broken partition walls, ceiling and disrupted contents can look bad and be inconvenient but do not represent a significant threat to your safety.

"Conversely, some buildings may have damage that is hidden from view but there will generally be clues that an experienced and knowledgeable engineer will detect."

Damaged buildings that might not be able to deal with future shaking required further assessment which could take weeks.

Building owners seeking peace of mind might want to get an engineer familiar with the building's construction type to give it a full assessment, Professional Engineers Institute head Susan Freeman-Greene said.

"Everyone is feeling uncertain about the weeks and maybe months ahead, given the potential aftershock sequence.

"If anyone has concerns about damage that their building has suffered and the effect this may have on future performance they are urged to seek engineering advice."

Many people, from the Prime Minister down, have asked why supposedly well-constructed modern buildings were significantly damaged.

Concrete beams in Statistics New Zealand's 2005 waterfront offices were ripped from the outside of the building causing the floors to partially collapse, according to owners CentrePort. It could be a year before staff return.

About 1200 Defence staff have reportedly been told they face a similar wait to get back into their headquarters, Freyberg House, built in 2007.

Auckland University structural engineering Professor Jason Ingham is adamant that the floor collapse at Statistics House never should have happened.

If the earthquake had struck on a Monday morning instead of just after midnight, he told the Herald, then people would probably have been killed.