New Wellington fault line could produce 7.1 quake

A newly discovered active fault line along Wellington's harbour could result in a large quake for the city, scientists say.

The Aotea Fault so far measured 2km long and ran from Oriental Parade to Westpac Stadium, said National Institute of Water and Atmospheric research (Niwa) marine geologist Philip Barnes.

However, data shows the fault could be up to 30km in length, running onshore across the city to the Cook Strait on the southern shoreline, he said.

"It needs more research."

The fault could produce an earthquake measuring up to 7.1 in magnitude, which could result in the ground being displaced by 2m.

It had already been responsible for two large earthquakes in the past 10,000 years, Dr Barnes said.

The first, 8400 years ago, plus or minus 1300 years, offset the ground by 4m.

The second, 6200 years ago, plus or minus 900 years, offset the earth by 2m, he said.

"To put the age of those earthquakes into perspective, the Giza pyramids were constructed about 4500 years ago."

Aotea Fault was discovered two years ago after Niwa analysed data taken by a British company in 2010, Dr Barnes said.

"The fault was hiding beneath the seafloor and that is the reason it had not been seen."

While it was a "significant" fault, Dr Barnes did not believe Wellington was in danger of a tsunami should an earthquake hit.

Wellington City's Civil Defence Controller Neville Brown said that a strong earthquake from the fault would cause damage to buildings, but the city was resilient.

"There certainly will be damage, but I think we'll be surprised with how well buildings get through."

GNS scientist Russ Van Dissen said the fault did not appreciably increase the overall ground-shaking hazard in Wellington.

"Any ground-shaking that this fault could produce is already considered in Wellington's seismic hazard calculations. So it is already accounted for in the building code," he said.

When seismologists estimated seismic hazard for a region they typically add 'floating faults' to their calculations as their knowledge of all earthquake-producing faults is imperfect.

This "headroom" in the hazard calculations allowed for faults that may be hidden or have poor surface expression, he said.

Wellington Mayor Celia Wade-Brown said while more detail was always useful, she was reassured that Wellington's building standards already took into account the level of ground-shaking that the newly-discovered Aotea Fault could generate.

While new details emerged on the capital's topographic tapestry, Wellingtonians already know it is important to be prepared for quakes and tsunami.

"Having a plan at work and at home, and knowing your neighbours, is all part of making our city more resilient," she said.

"Businesses must have good continuity plans so our economy can bounce back too."

Source: mapping.gw.govt.nz/gwrc/