National body on aftershock assessment urgedMARC GREENHILL Last updated 05:00 10/03/2012
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Structural engineers should not have been forced to assess the likelihood of a severe aftershock in Christchurch after the September 2010 earthquake, an industry expert says.
Peter Smith, of Wellington's Spencer Holmes, has spent the past three months peer-reviewing the performance of buildings that failed in the February 2011 quake for the Canterbury earthquakes royal commission.
He said yesterday that it was unfair to expect engineers to determine the likelihood of a severe aftershock during post-quake building assessments and suggested a centralised committee of experts to set a national standard.
"I'm sure there are better people whose focus is understanding the mechanisms of ground movement and seismology who can better advise nationally on the level of aftershock which engineers should be assessing buildings for," Smith said.
"Engineers are very good at undertaking that assessment, but I think it's inappropriate that each engineer makes his own assessment of the likelihood of an aftershock and then assesses a building for that."
The committee would include seismologists, geotechnical engineers and politicians. "If we're going to move away, and I think we should, from the damage [assessments], then it needs to be a much broader assessment," he said.
Christchurch's February 2011 quake was "unique" as it occurred on a different fault from the September 2010 quake and was shallower and nearer to the central city, Smith said.
However, it could happen elsewhere. "For instance, we may get a very significant Wellington earthquake, but all of a sudden Masterton may get a significant aftershock right underneath it," he said.
"It needs the very best knowledge that we have as a country to read what's happening in the first earthquake, determine the likelihood of a significant aftershock, where that may be centred and just how that affects the population in that area."
The national standard would at least give engineers a standard that society said was an acceptable way to judge buildings.
"Engineers tended to go out there [before February 2011] and simply take the damage-limitation perspective, and that may or may not be good enough," Smith said.
"I certainly felt it was very unfortunate some of the younger engineers stood up in front of the royal commission and [were asked], `Why did you do this?' There should be a much broader base behind those assumptions".
Institution of Professional Engineers New Zealand chief executive Andrew Cleland said Smith's suggestion was sound. The GNS Science-led natural hazards research platform set up in 2009 included engineering input, he said.
"It makes good sense that every engineer can have ready access to a known piece of expert advice. That's just a given, but I think we'd be looking to the natural hazards platform, which is a national platform, to be the source of advice," Cleland said.
"The question then is how that advice is communicated in a meaningful way. That may need some interpretation in engineering terms, and that's where [Smith's] expert panel would come in."
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April 04, 2012, 08:14:26 AM