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Tapping into New Zealand’s sleeping giant - 04/05/2018

Stretching down the length of the North Island’s east coast lies a sleeping geological giant - the Hikurangi subduction zone. It is New Zealand’s largest and most active plate boundary, where the Pacific Plate subducts beneath the Australian Plate, giving rise to large earthquakes and tsunamis.

The northern part of the Hikurangi subduction zone also hosts the Earth’s best documented shallow slow-slip earthquakes. Known as ‘silent’ earthquakes, they last for days to weeks at a time, moving faults at a snail’s pace without ever being felt on the surface.

A scientific drilling expedition on the research ship JOIDES Resolution has just returned from a two-month mission to study the rumblings of this sub-seafloor giant, during which sensors were installed in two boreholes beneath the ocean floor to monitor slow-slip events and earthquakes. The expedition also collected more than 1 kilometre of sediment and rock cores from below the seafloor at four locations across the subduction zone.

Two drill sites were on a section of the plate boundary that is not subducted yet, including the top of a seamount (an extinct underwater volcano). Cores were also collected from inside one of the major faults accommodating the motion of the tectonic plates, and from the sediments directly above the area where the largest slow slip occurs. 

Study of these samples in the coming years will reveal how the sediment and rocks behave once they are subjected to the forces of the megathrust zone, shedding light on the mystery of why slow-slip events occur.

Expedition co-leader Laura Wallace of GNS Science said slow-slip earthquakes at subduction zones in New Zealand and around the world were perplexing because scientists did not  understand what causes them. 

The Hikurangi observatory team on board the research ship JOIDES Resolution with voyage leaders Dr Demian Saffer and Dr Laura Wallace at centre. Photo credit: Laura Wallace, GNS Science.

The Hikurangi observatory team on board the research ship JOIDES Resolution with voyage leaders Dr Demian Saffer and Dr Laura Wallace at centre. Photo credit: Laura Wallace, GNS Science.

“This voyage has given us our very first look at the material in the subduction zone and will help to tell us why faults behave in such a way,” Dr Wallace said. 

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The observatories allow detection of even the smallest movements on the subduction fault, and will yield unparalleled insight into what happens during slow-slip earthquakes. Installing these probes is an incredibly challenging scientific and engineering feat, so we were thrilled to accomplish it on our expedition

Dr Demian Saffer

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“Understanding the relationship between slow-slip events and large earthquakes is also a major aim of these studies and is very important for New Zealand’s hazard preparedness.”

In a first for New Zealand, two sub-seafloor observatories were installed at the slow-slip fault region. The ‘quake labs’ will collect temperature, pressure and chemical data for up to five years, recording changes as earthquakes and slow-slip events occur. The data will be collected in the future by a ship with a submersible ROV (remotely operated vehicle).

Expedition co-leader, Dr Demian Saffer of The Pennsylvania State University, explained “these technically complex observatories are two of only a handful of observatories at subduction zones in the world.

“The observatories allow detection of even the smallest movements on the subduction fault, and will yield unparalleled insight into what happens during slow-slip earthquakes. Installing these probes is an incredibly challenging scientific and engineering feat, so we were thrilled to accomplish it on our expedition,” Dr Saffer said.

The expedition involved approximately $NZ30 million of international investment, funded by the United States National Science Foundation and the International Ocean Discovery Program. The expedition involved 30 geoscientists from New Zealand, the United States, Europe, Japan, China, South Korea, and Brazil.

The International Ocean Discovery Program is an international research collaboration that conducts seagoing expeditions to study Earth’s history and dynamics recorded in sediments and rocks beneath the ocean floor. New Zealand participates in IODP through a consortium of research organisations and universities in Australia and New Zealand including GNS Science, NIWA, The University of Auckland, Victoria University of Wellington, and University of Otago.

The Australian and New Zealand IODP Consortium, which supports participation of New Zealand scientists and outreach officers on these voyages, is funded by the Australian Government through the Australian Research Council’s LIEF funding scheme and an Australian and New Zealand consortium of universities and government agencies.

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In brief

  • The voyages of the scientific research ship JOIDES Resolution represent a major step forward in improving the understanding of the Hikurangi subduction zone, which is New Zealand’s largest and fastest moving plate boundary fault and may be our largest source of earthquake and tsunami hazard.
  • The IODP missions to the East Coast region and allied scientific projects probing New Zealand’s subduction zone involve more than $NZ60 million of international investment over the next few years.
  • Scientists regard the region east of the North Island as one of the best places in the world to study plate boundary subduction processes, including slow-slip earthquakes. 
  • The JOIDES Resolution is the flagship vessel of the 23-nation IODP and is one of the top earth science research ships in the world.
  • Membership of IODP allows New Zealand science organisations to use scientific drilling ships to answer questions important to New Zealanders relating to geological hazards, climate change, and the largely submerged continent of Zealandia.