An international team of scientists will begin a pioneering project beneath the seafloor off New Zealand in 2018 as they seek to learn more about the causes of earthquakes and tsunamis.

The International Ocean Discovery Program, a partnership of 26 nations, had scheduled a proposal to use scientific ocean drilling to investigate "silent earthquakes" under the seafloor east of the central North Island, the government's Institute of Geological and Nuclear Sciences (GNS Science) said Tuesday.

It would be the first undersea drilling project anywhere in the world aimed specifically at understanding the mechanisms of silent earthquakes, also known as slow-slip events, researchers said in a statement from GNS Science.

Silent earthquakes were similar to an earthquake in that they involved more rapid than normal movement between two pieces of the Earth's crust along a fault line, but they took place over weeks or months, rather than seconds.

Three drill sites up to 1.5 km deep were planned in the Hikurangi subduction zone, about 40 km east of Gisborne: one on the subducting Pacific Plate; one where the plate boundary surfaced at the seafloor; and a third on the overriding plate directly above the area of slow-slip.

Silent earthquakes off Gisborne had attracted significant international attention due to their close proximity to the Earth' s surface -- typically about 5 km beneath the seafloor, where they were accessible to scientific drilling, compared with other parts of the world where they occurred tens of kilometers below the Earth's surface.

"An important way to understand the true cause of slow-slip events is to drill into and sample the region surrounding the plate boundary fault where they are known to occur, and monitor physical and chemical properties near the source of the events," project leader Dr Demian Saffer, of Pennsylvania State University in the United States, said in the statement.

Instruments would be installed in two of the drill sites to monitor changes in the Earth's crust throughout multiple slow-slip event cycles over the coming decade, and the data would be downloaded every few years using a remotely operated submarine.

"The monitoring instruments will give unprecedented, close-up observations of the slow-slip process, and they will also improve our understanding of the earthquake and tsunami potential of the Hikurangi subduction zone," Dr Laura Wallace, of the University of Texas, said in the statement.

The Hikurangi subduction zone is the most rapidly slipping fault in New Zealand, with the Pacific Plate moving westward at up to 6 cm a year off the coast.

The scheduling is the culmination of a five-year planning and proposal process involving scientists from New Zealand, the United States, Japan, Canada, and Europe.

The project, which would likely to involve about 50 scientists from eight countries, would be undertaken by a US National Science Foundation research drilling ship and was expected to last two months.