Scientists who have discovered the 2km long tail of an active fault line in Wellington Harbour say they do not know how far it might run through the city.
The Aotea Fault runs in a north-easterly direction in Wellington Harbour and, if it is at least 10km long, it could generate earthquakes of up to magnitude 7.1 most likely through Mount Victoria to Island Bay and out into Cook Strait.
National Institute of Water and Atmospheric Research (NIWA) marine scientist Philip Barnes said they knew the fault line had generated at least two earthquakes, 6200 and 8400 years ago respectively.
However, they did not yet know enough about the new fault to work out its full force potential.
"What we know about this fault is that it's 2km long at this stage, and we think that it needs to be at least 10km to generate the surface displacements we've observed," Dr Barnes said.
"We can't say that it's 30km long, 25km or 35km long. We can estimate the order of magnitude of this structure, and it's telling us that we need to do some more work to find out where it goes."
The discovery did not significantly add to the risk in Wellington, he said.
"The reason that it doesn't significantly change the hazard for Wellington at the moment is that the current models of seismic hazard already account for the ground shaking that would be expected from this fault."
Scientists also did not believe the fault could cause a major tsunami if there was an earthquake, although simulation studies were still to be done.
Wellington Mayor Celia Wade-Brown said building standards already took into account the level of ground-shaking the Aotea Fault could generate.
However, the discovery was a reminder to central city home owners to do basic safety checks on their homes, she said.
"Some of its as simple as getting your chimney checked.
"If you've got a masonry chimney you might want to think again about that or making sure that a wooden building is firmly fixed to its piles."
NIWA found the fault line as a result of ongoing research.
It is thought to have been revealed during surveys between the Cook Strait Ferry terminal and Point Jerningham.
While it was capable of generating a sizeable earthquake, it was not as significant as the existing Wellington and Wairarapa faults.