Massive underwater fault line off East Coast ruptures after last week's damaging 7.8 quake

NIWA scientists say last week's 7.8 quake ruptured a massive underwater fault line off the East Coast of New Zealand.

NIWA scientists on board the Tangaroa have been at sea for two weeks studying the seafloor and arrived back in Wellington today.

Fault rupture on Needles fault, in the Hikurangi Subduction Margin, off the East Coast. Source: Supplied

They were researching the Hikurangi Subduction Margin when Monday's earthquake hit.

"We got news coming in regularly from folks back home," scientist Philip Barnes says.

"Coincidentally we were out there studying past earthquake history and one happened and so we were in a great position to mobilise our efforts and to move further down the margin down south.

"So we took advantage of an opportunity that was unique to be able to do some work."

Mr Barnes says they soon discovered the Needles Fault ruptured during the quake and formed newly discovered scarps on the seafloor along the north-east coast.

Source: Supplied

The Needles fault is an offshore extension of the Kekerengu Fault and lies in the Hikurangi Subduction Margin.

The Needles fault is now longer - up to 70km - and is close to the coast in shallow water.

NIWA says more research is needed into New Zealand's offshore fault lines and they want to get a better understanding of the offshore network of faults.

The group was collecting sediment cores from the seabed, which could give them knowledge of up to 7000 years of earthquake history.