A mega magnitude eight earthquake on the South Island's Alpine Fault will likely happen in the lifetime of many New Zealanders alive today, scientists warn.
The Alpine Fault runs for 800 kilometres from the Marlborough Sounds to Milford Sound in Fiordland.
The South Island's Emergency Management Groups have developed earthquake scenarios in a project called "Alpine Fault Magnitude 8", since 2016, Stuff reports.
Otago University research fellow Caroline Orchiston outlined the group's work at a public meeting in Blenheim yesterday.
She said Kiwis need to be concerned about an Alpine Fault quake, as it would likely "happen in the lifetime of many New Zealanders".
Studies at Alpine Fault excavation sites showed a large earthquake occurred on the fault every 300 years or so, with the last one occurring in 1717.
Ms Orchiston said the figures tell us "that these events have been popping off through time and there's really no reason for them to stop happening".
The most likely location of a megaquake is a south-to-north quake centred at Milford Sound, with intensity-seven, six and five quakes rippling up the South Island.
Other options are a rip in the fault starting in Greymouth and heading southwest, or an epicentre near Fox Glacier, heading up and down the fault.
Marlborough was looking at an intensity six or seven earthquake on the Mercalli scale when the Alpine Fault finally gave, and everywhere in the South Island would feel at least a magnitude four or five quake, Ms Orchiston said.
The goal of the project was to create a safer and stronger South Island, through better preparation, as the Alpine Fault had the potential to impact the whole island, and beyond, she said.