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A Californian scientist has warned that future buildings erected across New Zealand will never be earthquake-proof and labelled Christchurch rebuild plans "unrealistic.''
University of California professor Norman Abrahamson gave the stark warning during the third day of hearings of the Royal Commission inquiry into the Canterbury earthquakes.
The commission is examining the cause of building collapses, especially during the February 6.3 magnitude quake which claimed 182 lives, and how such a disaster can be avoided in the future.
During a live video conference, the international earthquakes expert questioned several aspects of a key government report produced after the tragedy.
The adjunct professor of civil engineering at Berkeley said GNS Science plans to make buildings across New Zealand safer during earthquakes go much further than those in his home state of California, which sits astride the infamous San Andreas Fault.
He said that New Zealand society must debate how much they are willing to pay to make buildings as safe as possible.
Professor Abrahamson said: "In the end, it all comes down to risk, and what is acceptable risk. In the earthquake business we don't do anything where we design for the worst case and give people zero risk. There will always be a risk.''
He criticised the section on minimising risk in the GNS Science report, `The Canterbury Earthquake Sequence and Implications for Seismic Design Levels', in his international peer review.
The expert asked: "What are the acceptable risk values? I think the (GNS) guidance document is brief on this _ and I did get some additional information from Dr McVerry (GNS principal scientist) on where the risk numbers come from. But in my view, these risk numbers are unachievable as written in the report. Your goal is a bit too low and very difficult to obtain.''
He said that California - especially San Francisco, which was devastated by the magnitude 7.9 earthquake of 1906 which killed up to 3000 people, and a 6.9 magnitude shake in 1989 - had a much more "realistic'' building code.
Pointing to the high aversion to risk of loss of life in the GNS report, Abrahamson said: "We are nowhere near those numbers in California. We're at double the high end of that range.''
He added: "In trying to think what is appropriate we have to start to think what is realistic numbers.
"It's not for me to decide, it's a broader social issue - do you want to have more safety at a higher cost, or do you accept the kind of risk numbers that are acceptable around the world?''
Prof. Abrahamson said New Zealand's existing building code was consistent with international standards.
He said the government needed to ask if they wanted to go above that level for added safety to try to cover more of these earthquakes on unidentified faults in the future.
After his evidence, Abrahamson took part in a panel discussion with GNS scientists.
The first of 11 hearings in the inquiry, sitting at St Teresa's Parish church hall in Riccarton, Christchurch, was due to be completed today, but is expected to run over into tomorrow.
The commission is set to hear evidence until next March before presenting its findings to the government by April 11.
Evidence on the collapse of the PGC building, where 18 people died, is scheduled to start on November 28, while the CTV building, which killed 115 people, is down to be heard in March.
- Kurt Bayer of APNZ