The GNS Science led research program explains The National Seismic Hazard Model or NSHM for short. Video / GNS Science
The risk of ground shaking in future earthquakes has doubled in many places, under a newly updated seismic hazard model.
But that doesn't mean our shaky isles have become any shakier, with experts putting the new calculations down to what they've learned from a decade of quakes and new science.
The latest estimates under the revised National Seismic Hazard Model (NSHM), released today, show the shaking hazard has grown, on average, by 50 per cent or more in most locations.
"It's important to note there's a lot of variability here – while there's been no change in some places, in others the shaking hazard could be more than double," said the model's project lead, Dr Matt Gerstenberger of GNS Science.
The model estimated the likelihood and potential strength of shaking across the country, where the hazard varied because of factors like ground conditions and local earthquake risk.
That risk was much higher in areas along the plate boundary, marked off the North Island's East Coast by the Hikurangi Subduction Zone, and over land in the south by the sprawling Alpine Fault.
One indicator in the model is what's called peak ground acceleration, or PGA, measuring earthquake shaking at its strongest – and often by g, or the force of gravity.
In a quake with a PGA of more than 0.4g, it became hard to stand.
At more than 0.6 or toward 1.0, the shaking might be intense enough to throw people about, cause landslides and crack the ground open.
The 6.2 Christchurch Earthquake reached a PGA of about 1.2g when it erupted beneath the city on February 22, 2011, causing 185 deaths and some $45 billion in damage.