Scientists have begun investigating a "hit list" of long-quiet but high-risk earthquake danger zones.
A new project just funded by the Earthquake Commission is exploring the potential for quakes to strike in low-seismicity areas, with an initial focus on Otago.
"Some of these faults have been quiet for a long time, and some have been really active after long periods of calm," said the project's leader, Professor Mark Stirling of the University of Otago.
"It's the quiet ones you need to watch, the wisdom goes, and that applies to earthquakes too."
Stirling and his team will dig trenches to find when local faults last ruptured, and how big the events were.
"That will give us an indication of what hazard it might pose for the future."
Stirling's earlier work on the Akatore Fault near Dunedin showed that there are periods of quiet with little happening for at least 100,000 years, before a trio of quakes struck within 10,000 years - two of those in the past 1300 years.
It was estimated the three quakes had magnitudes of between 6.8 and 7.4 and each displaced the ground by up to 2m vertically.
The fault runs about 20km onshore, between about Taieri Mouth and Toko Mouth, and possibly more than 40km offshore further north and south, though its precise length was not yet known.
"The biggest danger in an area like Otago is that we don't think there is going to be an earthquake on one of these 'quiet' faults, so we don't prepare as much as we would in somewhere like Wellington," Stirling said.
"These might be earthquakes that only come along over periods of thousands, or even tens of thousands of years. But when they do, they can be quite damaging.
"And Dunedin, with its beautiful old buildings and unreinforced masonry, could be more at risk than Dunedinites think."
Dunedin residents focused on the sprawling Alpine Fault being the worst case earthquake source for the city, but the more local faults like the Akatore should be of much greater concern, he said.
EQC's Dr Richard Smith said Stirling's work was important for building resilient communities.
"Dunedin is generally considered low earthquake risk, but in 1974 there was a magnitude 5 earthquake offshore and EQC received 3000 claims from homeowners."
This research would help paint a picture of how Dunedin and Otago could be affected by a future earthquake.
"Data from the research will also feed into the National Seismic Hazard Model which in turn is used to develop the standards for building strength in different parts of the country."
Stirling said the team would start work by looking at faults most likely to affect Dunedin that had not previously been studied.
"First up is the Hyde Fault which created the Rock and Pillar Range a long time ago, and would greatly affect Dunedin if it ruptured again," he said.
"People focus on places where there have been recent earthquakes, but there might not have been one there for tens of thousands of years.
"Chances are that there might be another long period of quiet.
"Ruptures on 'quiet' faults are often really energetic because they have been sitting around for a long time - like a rusty nut which takes a lot of strength to get it to budge when it finally does it's with a big bang.
"And then there are other faults like the one that created the Hawkduns.
"Nothing has happened there for about a million years, and no one knows whether they will ever get active again."
Stirling said the research project linked in with other research under way looking at the basis of how New Zealand's earthquake hazard is calculated.
"There has been a general idea that faults build up over a cycle, then rupture to release energy and then start again," he said.
This has given the idea of an "average" time period on a fault for an earthquake.
"The question we're asking, and this is where it's very useful to look at faults in 'low seismicity' areas, is does this averaging make sense, or could it actually be common for faults to be quiet for long periods of time and then generate clusters of earthquakes?
"You need a lot of data going back a long time to answer that kind of question, so all the research we're doing in Otago will contribute to that larger question as well."
Meanwhile, a co-ordinated South Island-wide response to the next severe earthquake on the Alpine Fault came a step closer this month with the launch of a new strategy.
The South Island Alpine Fault Earthquake Response (SAFER) Framework is the result of two years of effort by Project AF8, a collaboration between all the South Island's Civil Defence Emergency Management Groups (CDEM), scientists and partner agencies.
The Alpine Fault had a clear geographic record of rupturing around every three centuries - and last year marked the 300th anniversary since an 8.1 quake that shunted the fault's southern side eight metres further south in a matter of seconds.
One of a series of recent scientific papers suggested a large event could strand some 10,000 people living in affected areas, along with several thousand tourists.
Because of the expected widespread disruption and damage, a well-planned and co-ordinated response was considered essential.
AF8 steering group chairman Angus McKay said the plan focused on the first seven days of response, and was based on impact scenarios developed by scientists.
"We workshopped the scenario with CDEM Groups and partner organisations around the South Island, identifying the foreseeable impacts on communities and our collective capabilities, to build a co-ordinated approach to response."
The plan would be next reviewed following a national Alpine Fault exercise scheduled for 2020.