Q. Does a building in Wellington with a rating of 34% of the New Building Standard (NBS) have the same risk as a building in Auckland with a 34% NBS rating?
A. No, the Auckland building is over 100 times safer. The reason is that the New Zealand Society for Earthquake Engineering (NZSEE) %NBS risk measurement system does not properly take into account the different risks of big earthquakes occurring in different areas. For a full explanation read the document ‘The Flaw in the Score’ on this site.
Q. Are Council’s bound to follow the NZSEE’s framework when designating Earthquake Prone Buildings
A. No. Councils must apply the law. If the NZSEE’s advice is inconsistent with the law then Councils should not follow it.
Q. The NZSEE says a 33% NBS building is high risk. Is this true?
A. No. The actual risk will vary from place to place depending on the relative frequency of large earthquakes, but nowhere can the risk be described as high. In Wellington the risk of being in a 33%NBS building is probably 100 times less than driving a car. In Auckland there is practically no chance of being killed in an earthquake.
Q. If the earthquake prone designations are mostly unlawful, how did we get into this mess?
A. This is a long story. It is set out in the ‘Error Prone Bureaucracy’ document on this site.
Q. My building has been assigned a 25% NBS rating. Is it an earthquake prone building?
A. Earthquake Prone Building is a legal concept. In law an Earthquake Prone Building must be likely to collapse in a moderate earthquake. It is highly unlikely (in the order of one chance in thousands) that a 25%NBS building will collapse in a moderate earthquake in Wellington, and in Auckland the chances are almost nil. However, Councils have been designating 25% NBS buildings as earthquake prone because they have been using the NZSEE framework that essentially ignores the law and imposes a much higher earthquake prone building standard. Councils cannot impose higher standards than permitted under law.
Q. Is a building with a less than 34% NBS rating in Auckland likely to collapse in a moderate earthquake?
A. No. A moderate earthquake in Auckland is likely to have the following effects.
“Generally noticed indoors, but not outside, as a moderate vibration or jolt. Light sleepers may be awakened. Walls may creak, and glassware, crockery, doors or windows rattle.”
Q. Is a building with a less than 34% NBS rating in Wellington likely to collapse in a moderate earthquake?
A. No. A moderate earthquake in Wellington is likely to have the following effects.
“ General alarm. People experience difficulty standing. Furniture and appliances are shifted. Substantial damage to fragile or unsecured objects. A few weak buildings are damaged.”
Q. What is the seismic ‘life safety risk’ of a building
A. Life safety risk is the risk that an individual occupant of a building will be killed in earthquakes. It is a combination of the probability that there will be large life threatening earthquakes ,and the probability that an occupant will be killed if there is a large earthquake.
Life safety risk is often expressed in terms of number of years that would need to go by before the occupant would, on average, die in an earthquake. A figure of 1:100,000 means that the average time is 100,000 years.
Q. What are the costs and benefits of meeting the current earthquake building standards as applied by Councils?
A. Across the country of welfare cost of strengthening the 20,000 buildings identified as being ‘earthquake prone’ in the 2012 MBIE Consultation document is estimated by Tailrisk Economics to be above $10 billion. The benefits are estimated to be less than $100 million.
Sound policies should generate positive net benefits. For further discussion on this point see the paper ‘Error Prone Bureaucracy’ on this site.
Q. Should I strengthen my building to 67%NBS as the NZSEE recommends?
A. The best approach is probably to wait. The only reason for strengthening to 67 percent is that this level has been represented as being ‘desirable’ by the NZSEE and their recommendations have affected the market. The reality is that there is little behind the NZSEE’s recommendations and their risk measurement framework is deeply flawed. In some cases the framework makes obviously false claims about building risk. For a discussion read ‘The NZSEE’s %NBS risk measurement framework: why it doesn’t work’.
EBSS’s goal is to get the NZSEE to withdraw their recommendations leaving the way the open to a replacement risk assessment framework that gives building occupants relevant and more accurate information about the life-safety risk. As understandings of the seismic life safety risk improve the market will, hopefully, start to function more rationally.