New tech to monitor NZ's biggest tsunami threat

An international team of scientists and engineers are deploying highly specialised instruments on the seafloor offshore the North Island's east coast. Photo / Margaret Low, GNS Science

Dozens of quake-monitoring instruments are being placed off the East Coast as part of a programme focused on New Zealand's biggest geological threat.

An international team set out on Saturday to deploy about 40 instruments along the Hikurangi Subduction Zone, a major offshore fault where the Pacific Plate dives – or subducts – westward beneath the North Island.

Scientists believe the subduction zone has the potential to unleash "megathrust" earthquakes larger than magnitude 8, such as those which created tsunamis that devastated Indonesia in 2004 and Japan in 2011.

"What we can learn about this fault and how it moves will help us understand and prepare for the next great earthquake," said the expedition's leader, Dr Daniel Barker of GNS Science.

Scientists aboard Niwa's research ship Tangaroa were placing the instruments off the coasts of Gisborne, Hawke's Bay and Wairarapa.

They included seafloor pressure sensors, which recorded the upward or downward movement of the seabed.

These could detect offshore "slow-slip" earthquakes - silent, slow-burning quakes that could displace faults over days to months – and might also provide evidence about how the zone might behave in a large earthquake.

The team were also deploying two arrays of precision seafloor transponders to track horizontal movement of the seafloor, and several ocean-bottom seismometers.

Scientists believe the Hikurangi Subduction Zone - which runs from the top of the East Cape to the upper east of the South Island - has the potential to unleash "megathrust" earthquakes larger than magnitude 8. Image / Supplied

"We expect that the instruments will record many hundreds of small earthquakes that cannot be accurately located with land-based instruments," said the project's leader, Dr Laura Wallace.

The expedition includes scientists from GNS Science, Victoria University of Wellington, Lamont Doherty Earth Observatory and Scripps Institution of Oceanography in the US, as well as Tohoku, Kyoto and Tokyo Universities in Japan.

"Because so many interesting things are occurring on the Hikurangi subduction zone, New Zealand provides an ideal natural laboratory to deploy these instruments," said Professor Spahr Webb of Columbia University.

The expedition formed part of a wider international programme, which has already involved establishing two sub-seafloor earthquake observatories - making New Zealand only the fourth country in the world to have such capabilities.

The technology could help pave the way for offshore instrumentation needed for earthquake and tsunami early warning systems.