An expedition of 30 scientists are headed to the North Island to find out more about New Zealand's largest earthquake and tsunami hazard.

Scientists will study the Hikurangi subduction zone, which is part of the Pacific "ring of fire" where the Pacific tectonic plate dives beneath the Australian plate.

Scientists believe the zone is capable of generating earthquakes of more than magnitude eight, so-called "megathrust" quakes.

The expedition, jointly led by Niwa and the University of Auckland, will spend six weeks at sea off the coast of Gisborne.

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They will be studying two main features of the area, including slow-slip events and submarine landslides, to help reveal the causes of these phenomena and improve understanding of the risk that the plate boundary poses to communities along the east coast.

The slow slip events in the northern part of the Hikurangi subduction zone happen in relatively shallow depths beneath the seafloor where data can be collected to help reveal how they work.

"Right now, we can only speculate about what's driving them, for a slow slip event to occur you require the fault to move a little and slowly, without the movement advancing into a normal earthquake rupture," says expedition co-leader, marine geologist Dr Philip Barnes.

"Since their discovery scientists have come to understand that there is a whole continuum of seismological processes between constant creep on a fault and big earthquakes, and slow slips are one of those," he said.

Last year's Kaikoura earthquake triggered a large slow slip event off the East Coast covering an area of more than 15,000sq km.

- AAP