That would be a massive quake, and bad news for Hawke's Bay Hospital.
Its engineers, WSP, say the shaking could be up to 40 per cent worse than under the hospital's old hazard model.
The 2012 model "is no longer able to be relied upon".
"This impacts the structural design and seismic rating of all buildings on the hospital site."
But what to do?
The choices are tough. Hutt and Wellington hospitals are faced with having to close down key buildings, and move services and wards.
Hawke's Bay Hospital is too, at its radiology department.
The health board's executive director of financial services Andrew Boyd is grappling with this.
"We are capital constrained. This is taxpayers' money," Boyd said.
"It's fair to say the current building programme that we have in place is to keep the site going until we get the new capital injection to have a campus redevelopment - the new regional hospital."
But the new hospital is 10 years away.
In the meantime, the DHB has called its engineers back in to reassess its most important buildings, scoring them against the New Building Standard.
They have done this using higher quake design standards introduced in 2017.
Four of the eight dropped into the riskiest zone, "earthquake-prone, under 34 per cent NBS". View the Kestrel 2022 report comparison here.
However, the new low scores are unofficial and do not count legally; for instance, they don't trigger quake-prone strengthening deadlines.
They might drop lower still under the National Seismic Hazard model.
Officials are already factoring in how to adjust the Building Code.
"The only information that I'm aware of is that it will be different across the country. And there will be changes that differ across the country," MBIE performance and engineering team manager Dave Gittings said.
Updated guidelines for new builds, strengthening and seismic assessments would go out from late 2023, Gittings said.
It won't be compulsory to follow them, but "we'd recommend that engineers take into account of all new information right across the board".
Hawke's Bay Hospital has been persuaded to take further action by the engineers' warnings about the new hazard model.
"We reassessed - should we look at the engineering that may be altered as a consequence of change and seismic engineering standards?" Boyd said.
"What we found was that one particular project, the radiology project, we paused, stopped that project, and now we're looking at a different location."
It disrupted and delayed putting in a new MRI scanner - and disruption to patients is what Boyd was most keen to avoid.
Another project, to seismically strengthen the operating theatres, was too far along to stop.
Consequently, while the government in 2019 promoted it as a future-proofing exercise, it will deliver theatres that rate only 50 per cent of NBS by 2017's standards (70 per cent against the 2012 measure).
At least the DHB knows much more about where it stands - and what the weakest parts to fix are, such as at the intensive care unit.
"So that's really the real bonus of that body of work. We can use this methodology to highlight and identify where the key vulnerabilities are," Boyd said.
This is its way to shore up the ICU, the special care baby unit, pipes and corridors - and reduce the threat posed by buildings pounding on each other - all without breaking the bank.
Engineering advice suggests it is a safe way to get through 10 more years, until Hawke's Bay Hospital can lock in a full rebuild from the Government.
As long as the Hikurangi subduction zone doesn't rupture first.
