The news was only out yesterday, and briefly mentioned on the news, but I have a horrible feeling that this is going to have a massive effect on New Zealand, and on Wellington in particular. Have a look at this screen grab from the Stuff website:
That’s a massive change all over – but especially for the capital. Previously we were the most risky place, with a factor of 0.32 but now that has more than doubled our risk, to 0.82 and the next most affected cities are Gisborne, Napier and Blenheim. But even somewhere like Greymouth is now ranked higher at 0.42 than we were previously. Does that mean that all our buildings need to be strengthened all over again?
That’s a rhetorical question – I don’t know the answer. If there are any seismic engineers reading this who would like to drop in an informed comment, that would be great!
My guess is that officially it will not make a difference to existing buildings, and it will apply to all new builds, but also that the insurance companies will react with even more damaging premiums to apartment owners in Wellington. Our insurance is already massively unaffordable – if it rises any more I may just have to…. actually, I don’t know what I can do.
More on this subject as it develops.
MBIE have said today:
“Continue to use existing law, technical standards and guidance”
“The updated NSHM results do not automatically change how we design buildings. Building professionals and practitioners should continue to use existing law, technical standards and guidance to demonstrate that their work complies with the Building Code.”
“MBIE will carefully consider what the updated NSHM means for new building design standards. It is currently working with Engineering New Zealand to assess what changes to building design standards are required, and how to include the NSHM results in regulatory settings for new buildings.”
“At this stage, MBIE is planning to consult on an initial set of proposed changes to building standards in mid-2023. However, the timing for this consultation will depend on how long it takes to develop technically robust proposals. MBIE will be able to confirm the timeframes for consultation in the coming months.”
“The updated NSHM results do not change the way seismic assessments are done on existing buildings. MBIE, in collaboration with the engineering technical societies NZSEE, SESOC and NZGS, are currently considering whether to change the hazard used in seismic assessments if updates to new building design standards are made.”
“There are no plans for MBIE to change the legislation that governs the earthquake-prone building system as a result of the updated NSHM.”
“There are no plans for MBIE to change the legislation…” That doesn’t actually mean that they won’t, one day. It’s like Putin saying: “There are no plans for Russia to invade Ukraine… but we will do it anyway, but without plans…”
And GNS Science have also spoken about the National Seismic Hazard Model, here:
“The 2022 revision of the NSHM shows that seismic hazard has increased almost everywhere throughout Aotearoa New Zealand compared to what we knew previously. This is not unexpected, because:
• We now know a lot more about earthquake behaviour due to better global understanding, more sophisticated science, and more than a decade of advancements in technical computing.
• We now have an improved model of the variability in shaking from potential earthquakes that could rupture in any single location. One significant contributor is the Hikurangi Subduction Zone, another is the Alpine Fault. These are important sources, but we also model the likelihood for earthquakes on unknown (hidden) faults and how shaking can affect regions far from the epicentre.
• We can model low probability but potentially high impact events affecting New Zealand, by understanding how faults can link together.”
I like the optimism stated here by GNS: “we also model the likelihood for earthquakes on unknown (hidden) faults”.
Hmmm. So, if they are unknown, basically then, GNS are just making things up and testing them to see if they have an effect? If so, then I wonder if they would like to share the results with the rest of us? Did they test Auckland? (No faults there). – But yes, so, what if there WERE faults there?
Knowing nothing about earthquakes or volcanoes, I’m going to say “What if a quake on a fault set off all the old volcanoes ???”
I have the impression that this has more to do with the likely occurrence of severe events than any sense that events would themselves be more severe. How do you change a design to respond to a shortening of the time before it is likely to be be tested? Isn’t the building code already based on the premise that it could be tomorrow?
Perhaps the bigger issue will be with older buildings can might now be assumed to have a significantly increased risk of exposure to severe shaking before their natural lifespan is over. A further raising of the NBS drawbridge.
Hi Starkive – how is the strengthening regime going on up where you live in Gonville? Lots happening? Anything happening? Already started? Nearly finished? Or, as many people are doing around New Zealand, is the population quietly ignoring this problem and hoping it might go away?
Whanganui District Council has been tackling public buildings pretty steadily, although we are often talking 34 – 67% of NBS. That does give rise to worries about a further shifting of the goalposts when that money has so recently been spent. Private owners are generally further behind as their countdown to crunch day has only started. There are a lot of pre-Napier facades along Victoria Ave with issues to address.
Then there is the Sarjeant project which is taking so very long at least partly because of the gold-standard they are striving for.
You can find the interim advice on how we have have been told to respond to the new model here:
Basically, it’s more complicated than just inputting the new data for reasons that are above my pay grade. We have to wait for the powers that be to further analyse/debate it. They will then update the loads we design for, based on location, how flexible the building is and what kind of soil it sits on (spectra).
Those PGA you use in your example do show a big increase and I believe they are already being used for geotechnical design. However, the loads we use for buildings themselves are more complex and won’t be the same as scaling the current code by the ratio of the PGAs, although they will surely be going up.
Whatever happens, not ideal for insurance, and cost of construction.
Thanks Tui ! Much appreciated for the comment and for the link ! Keep us posted !