Swarm 'could trigger fault'

French tourist Luca Zappula photographed the White Bluffs from the Wairau Bar minutes before the quake (left), while the photo on the right shows the dust settling afterwards, with a small piece of the headland appearing to be missing.
French tourist Luca Zappula photographed the White Bluffs from the Wairau Bar minutes before the quake (left), while the photo on the right shows the dust settling afterwards, with a small piece of the headland appearing to be missing.
Chairman Warren Larsen inspects damage to Wellington's CentrePort caused by yesterdays 6.5 earthquake.
Chairman Warren Larsen inspects damage to Wellington's CentrePort caused by yesterdays 6.5 earthquake.
An earthquake damage assessment team at St Mary of the Angels church on Boulcott Street.
An earthquake damage assessment team at St Mary of the Angels church on Boulcott Street.
An earthquake damage assessment team looks for damage at St Mary of the Angels church on Boulcott Street.
An earthquake damage assessment team looks for damage at St Mary of the Angels church on Boulcott Street.
Damage to Wellington's CentrePort caused by yesterdays 6.5 earthquake.
Damage to Wellington's CentrePort caused by yesterdays 6.5 earthquake.
Damage to the Old Bank Arcade in Wellington.
Damage to the Old Bank Arcade in Wellington.
A sign on Wellington's SH1 near Johnsonville asking people to avoid entering the city's CBD.
A sign on Wellington's SH1 near Johnsonville asking people to avoid entering the city's CBD.
Paul Lloyd-Jones, cleaning up the mess at his store Thirsty Liqour Newlands.
Paul Lloyd-Jones, cleaning up the mess at his store Thirsty Liqour Newlands.
The Wellington waterfront at lunchtime the day after the 6.5 magnitude earthquake in Wellington.
The Wellington waterfront at lunchtime the day after the 6.5 magnitude earthquake in Wellington.
Workers in Wellington's Featherston St, cordoned off with quake damage.
Workers in Wellington's Featherston St, cordoned off with quake damage.
Damage to a building in Wellington's Taranaki Street.
Damage to a building in Wellington's Taranaki Street.
Damage to buildings on Featherston St: the building on the right is 131 Featherston.
Damage to buildings on Featherston St: the building on the right is 131 Featherston.
Lambton Quay quiet at lunchtime on a Monday: Department of Internal Affairs compliance officer, Gareth Bostock, sits on a Lambton Quay bus stop waiting for his office building to open so he can get back to work.
Lambton Quay quiet at lunchtime on a Monday: Department of Internal Affairs compliance officer, Gareth Bostock, sits on a Lambton Quay bus stop waiting for his office building to open so he can get back to work.
Severe damage at BNZ's Harbour Quays buildings. Picture posted by @tracy_earl on Twitter.
Severe damage at BNZ's Harbour Quays buildings. Picture posted by @tracy_earl on Twitter.
A picture of politician Steven Joyce's office post-quake. Photo from @cjsbishop.
A picture of politician Steven Joyce's office post-quake. Photo from @cjsbishop.
Workers fix windows at the Harbour City Shopping Centre building in Wellington.
Workers fix windows at the Harbour City Shopping Centre building in Wellington.
Multiple windows were shattered in the old Dominion Farmers Institute building.
Multiple windows were shattered in the old Dominion Farmers Institute building.
A photo taken of a crack in the ground at the Clyde Quay development on the Chaffer's Dock end of Wellington's waterfront.
A photo taken of a crack in the ground at the Clyde Quay development on the Chaffer's Dock end of Wellington's waterfront.
Photo taken at the MSD Contact Centre in Lower Hutt that has now been closed due to earthquake damage.
Photo taken at the MSD Contact Centre in Lower Hutt that has now been closed due to earthquake damage.
Damage at Centreport, Wellington after 15 square metres of sea wall and road had slumped into the sea at the southern end of the container terminal.
Damage at Centreport, Wellington after 15 square metres of sea wall and road had slumped into the sea at the southern end of the container terminal.
Damage at Centreport, Wellington after 15 square metres of sea wall and road had slumped into the sea at the southern end of the container terminal.
Damage at Centreport, Wellington after 15 square metres of sea wall and road had slumped into the sea at the southern end of the container terminal.
Damage at Centreport, Wellington
Damage at Centreport, Wellington
Supervalue Seddon employee Sheryll Kamat and owner Marie Flowerday (in front) clean up after building inspectors gave them the all clear to re-enter the building.
Supervalue Seddon employee Sheryll Kamat and owner Marie Flowerday (in front) clean up after building inspectors gave them the all clear to re-enter the building.
The Commanding Officer of the Urban Search and Rescue operation in Wellington City, Graeme Mills, at his command centre on The Terrace today. Pictured with him from left to right are senior fire-fighter Matthew Salt and station officer Chris Faithfull.
The Commanding Officer of the Urban Search and Rescue operation in Wellington City, Graeme Mills, at his command centre on The Terrace today. Pictured with him from left to right are senior fire-fighter Matthew Salt and station officer Chris Faithfull.
Property owner Kurt Flowerday inspects the damage to his Seymour Street, Seddon property.
Property owner Kurt Flowerday inspects the damage to his Seymour Street, Seddon property.
Bridget Thurlow cleans up her mothers Simpson Street Seddon home after last night's quake. The house sustained extensive damage. Her mother Elva Tombs was traumatised and spent the night with family in Blenheim.
Bridget Thurlow cleans up her mothers Simpson Street Seddon home after last night's quake. The house sustained extensive damage. Her mother Elva Tombs was traumatised and spent the night with family in Blenheim.
Wellington Railway Station completely empty at about 8am today.
Wellington Railway Station completely empty at about 8am today.
"Things were thrown around" the bedroom of a Thorndon, Wellington home.
"Things were thrown around" the bedroom of a Thorndon, Wellington home.
Damage at a Liquor King story on the Kapiti coast.
Damage at a Liquor King story on the Kapiti coast.
The New World supermarket in Blenheim is closed after the earthquake.
The New World supermarket in Blenheim is closed after the earthquake.
A police cordon on Wellington's Webb St near the Mercure Hotel in the background, which was evacuated after the 6.5 quake.
A police cordon on Wellington's Webb St near the Mercure Hotel in the background, which was evacuated after the 6.5 quake.
Evacuees being taken into the Wellington Church Of Christ to keep warm after the Mercure Hotel was evacuated and cordoned.
Evacuees being taken into the Wellington Church Of Christ to keep warm after the Mercure Hotel was evacuated and cordoned.
The clean-up begins at Regional Wines and Spirits near the Basin Reserve.
The clean-up begins at Regional Wines and Spirits near the Basin Reserve.
Damage at the Quest hotel in central Wellington.
Damage at the Quest hotel in central Wellington.
The Petone clock stopped at 5.10pm when the 6.5 magnitude earthquake struck.
The Petone clock stopped at 5.10pm when the 6.5 magnitude earthquake struck.
Damage to Hannah Turvey's apartment on Taranaki St, Wellington.
Damage to Hannah Turvey's apartment on Taranaki St, Wellington.
Wellington City Council building being cordoned off after the earthquake.
Wellington City Council building being cordoned off after the earthquake.
The Kelburn Four Square, Wellington.
The Kelburn Four Square, Wellington.
Shattered building glass on The Terrace in Wellington.
Shattered building glass on The Terrace in Wellington.
The law library at Victoria University.
The law library at Victoria University.
Damage in Featherston St.
Damage in Featherston St.
Mackenzie Presten, 10, with caregiver Anthony Mills duck for cover at the ASB sports centre in Kilbirnie during the earthquake.
Mackenzie Presten, 10, with caregiver Anthony Mills duck for cover at the ASB sports centre in Kilbirnie during the earthquake.
Cracks in the ground at the Wellington waterfront.
Cracks in the ground at the Wellington waterfront.
Huge crack at Wellington waterfront.
Huge crack at Wellington waterfront.
Miramar New World faces a big tidy up after the quake.
Miramar New World faces a big tidy up after the quake.
Briscoes in Lower Hutt has had some stock destroyed.
Briscoes in Lower Hutt has had some stock destroyed.
Bottles are strewn all over the floor at the New World in Thorndon .
Bottles are strewn all over the floor at the New World in Thorndon .
Windows broken at Quest hotel.
Windows broken at Quest hotel.
Cracks at Reading Cinema.
Cracks at Reading Cinema.
Seymour Square memorial clock in central Blenheim stopped at the time of the quake.
Seymour Square memorial clock in central Blenheim stopped at the time of the quake.

Seismologists say the weekend's swarm of earthquakes could be on a new fault they have not mapped before, and could possibly trigger movement on the feared Wellington fault.

The news comes as central New Zealand wakes from another rocky night, which included a 4.9-magnitude quake in the early hours. Through the night, a swarm of quakes occurred which were centred off Seddon in the upper South Island - the biggest being was a 4.9 quake at 1.31am at a depth of 25km. All other quakes since midnight were 3.8 or lower.

GNS scientists and teams from the National Institute of Water and Atmospheric Research have been working to establish which fault line was the catalyst for the series of shakes, including the magnitude 6.5 quake on Sunday evening.

Seismologist John Ristau said the earthquakes were lying in an area of Cook Strait between the Vernon fault and Needles fault.

"There are a number of active faults in the area. It's an issue because they are offshore so it's difficult to get the most accurate location we can."

A third fault to the left of Needles, called the London Hill fault, was also a possible location if it was found to extend offshore.

"The other possibility is it is either on an unmapped fault or something brand new."

Pinning down the relevant fault could take a couple of days, and Niwa was expected to map between the Vernon and Needles faults later this week.

The nearby Wellington fault - capable of magnitude 8 or larger earthquakes and running through Wellington and the Hutt Valley - was not connected, but could have been affected by the ongoing activity in the region.

"It's not the same one, but when you get a large earthquake it can increase or decrease stress on nearby faults. They all interact."

The possibility of the current swarm setting off a larger earthquake along the Wellington fault could not be discounted, Dr Ristau said. "We don't know for sure but we can't entirely rule out the possibility."

While it usually took earthquakes larger than magnitude 7.5 to set off tsunamis on their own, smaller ones could cause underwater landslides, Dr Ristau said.

"Undersea landslides caused by much smaller earthquakes can trigger tsunamis. That's a distinct possibility.

"If one did trigger a landslide it would be difficult to monitor that as it's underwater and we would not know about it."

Niwa marine geologist Scott Nodder said most of the quakes, including the largest on Sunday evening, were in an area on which they had little data.

"The earthquakes are away from the Needles fault, and nearby Booboo fault. Looking at the data it seems like it could be a new one to me."

There were "numerous" active faults in the Cook Strait area, and Niwa had mapped 100 per cent of the canyons in Cook Strait but work was continuing with other parts.

Dr Ristau said that Christchurch, unlike Wellington, was built on soft sediment with a shallow water table which contributed to liquefaction in the February quake.

"In addition, the February 2011 earthquake was very shallow and close to Christchurch, and much of the energy released was directed straight towards the city," he said.

"All of these factors combined to cause extensive liquefaction in Christchurch. These factors were not as prominent in the Cook Strait earthquake, despite the earthquake being larger."

The possibility of another big quake has now dropped to 7 per cent in the next day, or 19 per cent in the next seven days.

The Dominion Post