News story from "The New Zealand Herald"(Photos, Mark Mitchell and The Christchurch Press)
The Pyne Gould building, Canterbury TV and other buildings where most lives were lost are all believed to have been built before a succession of increasingly tough earthquake-resistant standards began in the mid-1970s.
A 2004 change to the Building Act required all local councils to adopt policies to strengthen such buildings to at least one-third of the current building standard.
But engineers say that almost all councils, except Wellington, have adopted merely "passive" policies which do not require strengthening old buildings except when their owners seek new building consents for alterations.
And Auckland University Associate Professor Jason Ingham, a management committee member of the NZ Society for Earthquake Engineering, said the society advocated raising the requirement to two-thirds of the current standard.
"If you improve your building to only one-third of the building standard, it is still 20 times more likely than a modern building to fall down in an earthquake," he said. "At two-thirds, it's only something like three times as likely to fail."
Ironically, Dr Ingham and other international experts were in Christchurch when the quake struck on Tuesday holding a seminar aimed at getting councils to give more urgency to strengthening old reinforced masonry (brick, stone or concrete) buildings.
He said that, even after the first Christchurch quake in September, most councils had not identified buildings at risk in a major earthquake, contacted the owners or developed any plans for how to strengthen them.
"Everybody has to learn from every earthquake. Anyone who feels there is nothing to be learnt is just being naive," he said.
Another Auckland University engineer, Dr Quincy Ma, said Tuesday's building collapses did not necessarily show that the structures were not strong enough, because the quake was so violent.
"The ground motion in Christchurch was over what we expect for a 1000-year return period," he said. "We design for a 475-year return period."
This means the ground shaking from Tuesday's magnitude 6.3 quake was even more violent than Christchurch can expect from a magnitude 8 jolt on the Alpine Fault, which is expected every 300 to 400 years and was regarded as the test that buildings had to be designed for. The fault last moved 290 years ago.
Dr Ma said the fault that shook the city this week had not been identified as a major risk before.
"From the last [September] quake we thought all the lessons had been learnt, but that was just a dress rehearsal for the real test," he said.
I learned yesterday that one of our MacDiarmid Institute Principal Investigators has not heard from his wife since she visited the Christchurch CBD on Tuesday. It is likely that she is amongst the casualties. In the context of the tragedy in Christchurch, my solitary health problems pale into insignificance.
