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New fault line possiblity, Wellington fault line effected
Tuesday 23 July 2013, 5:56AM
By NP Linked Taranaki


BREAKING NEWS: GeoNet is confirming a new fault line could have been triggered and the earthquakes could possibly trigger movement on the feared Wellington fault which is due to cause a magnitude 8 earthquake.

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% 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."

WELLINGTON NOT PREPARED - RESIDENTS reporter Michael Riley has been speaking to many Wellington residents who have said they dont believe Wellington is ready for a big earthquake and that John Key and the mayor is 'brushing it off'.

"They said that it was minor damage yet, the wharf collapsed into the sea, and cracks are seen throughout the city. Yet they think it was minor, and that we are ready for a magnitude 8, yeah right." said Wellington resident Jayzun Yoles.

Meanwhile a TUI board created in Wellington says "PM:Shell be right mate just a few cracks, Its ok we can afford it... yeah right."


This morning Central New Zealand was rocked by several strong earthquakes including a magnitude 5 that was felt all over the nation as far north as New Plymouth and as far south as Dunedin.

A strong earthquake measuring 4.5 also rocked Gore at the bottem of the South Island, that was felt in Wellington, New Plymouth, central North Island, and much of the South Island.

GeoNet has advised New Zealand media its far from over.

Scientists say that residents in the Marlborough and Wellington regions should expect to feel more aftershocks.

Sunday nights magnitude 6.5 earthquake jolted central New Zealand shortly after 5pm.

Since then, more than 100 aftershocks have shaken Wellington and Marlborough, with several measuring over 4 or 5 on the Richter scale.

Bill Fry, from GNS Science, told ONE News NZ that scientists have been working around the clock, looking at data to find out whether another big earthquake could rattle the region.

"After you get a large earthquake you immediately have another heightened chance of another large one. And certainly lots of smaller earthquakes. But the probability of that decreases rapidly with time," he said.

"If you have one magnitude six, you can expect ten magnitude fives, 100 magnitude fours and one thousand magnitude threes."

At 6pm on Monday the chance of another magnitude six or more earthquake in the next week in the quake hit regions was 30%. As of 6pm tonight, that probability had dropped to 16%.

The earthquakes are caused by the movement of the Australian and Pacific plates, which lie on top of each other.

Scientists are still trying to figure out which if the dozens of fault lines in the Cook Strait caused yesterday's event.

FOR MORE UPDATES will be updating this article over the next few hours to keep everyone updated.

Next Update will be in around an hour.

From our morning team, good morning. INDEX