Scientists' pioneering probe into NZ's most dangerous fault line

The Hikurangi subduction zone is a sleeping giant; the fault line off the coast of Gisborne is capable of producing monstrous earthquakes and tsunamis.

A pioneering group of scientists are preparing to drill into the seabed to study the fault, and hopefully one day predict when it will go off.

An 'observatory' will be lowered into a hole on the sea bed three kilometres underwater to capture the creaks and groans of New Zealand's most dangerous fault line.

Dr Laura Wallace says the extent of its power is unknown. 

"It's possible that the Hikurangi subduction zone could potentially produce earthquakes magnitude 8 or larger - possibly as large as magnitude 9 - but we don't really know yet what its potential is."

Tremors that large could send tsunamis as high as 12 metres up the east coast of New Zealand.

The threat has inspired scientists from all over the world to gather for an official study aboard the drill ship Joides Resolution.

They're trying to understand how the slow slip subduction zone works. Unlike most fault lines, it releases tension slowly over weeks and months.

The team has spent eight years preparing scientific observatories to monitor pressure, temperature and fluids near the fault line.

"They provide us with a unique kind of access to the interior of the earth, in these active zones," says expedition co-leader Dr Damian Saffer.

"They're a kind of portal into the Earth." 

They will stay in place for decades, helping scientists predict when the fault might go off. 

"This is part of a whole raft of other studies going on on the Hikarangi subduction zone over the next few years that really involve over $60 million of international investment," says Dr Wallace.

The data will take years to analyse, but what these scientists find could be a life saver.