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14/3/2018 — Education, Science and Technology
Hikurangi quest to expand slow-slip understanding

GNS Science has provided an update on the quest to improve understanding New Zealand’s largest fault, the Hikurangi subduction zone, east of the North Island

A team of Kiwi and international scientists will lower two sub-seafloor observatories into the Hikurangi subduction.

The expedition is jointly led by scientists from GNS Science and Pennsylvania State University and funded by the International Ocean Discovery Programme (IODP) and the US National Science Foundation.

The project will see a team of international scientists spending the next eight weeks aboard the scientific drilling ship, JOIDES Resolution, probing the seafloor east of Gisborne to find out more about New Zealand’s largest earthquake and tsunami hazard.

The Hikurangi subduction zone is part of the Pacific Ring of Fire where the Pacific tectonic plate dives beneath the Australian plate.

Scientists believe this plate boundary fault is capable of generating earthquakes of more than magnitude 8. Subduction zone earthquakes can produce large tsunamis because there are large and rapid displacements of the seafloor during the earthquakes.

The voyage team will collect and analyse cores from below the seabed to understand the rock properties and conditions where slow-slip events occur.

Expedition co-leader, Dr Laura Wallace of GNS Science said: “Slow-slip events or slow-slip earthquakes are similar to earthquakes, because they involve more rapid than normal movement along a fault.

“However, during a slow-slip event it takes weeks to months for this fault movement to occur. This is very different from an earthquake, where fault movement occurs over a matter of seconds releasing energy suddenly.”

Slow-slip events occur at intervals of 12 to 24 months near Gisborne, at a relatively shallow depth beneath the seabed – making this region one of the best places in the world for scientists to study them.

“Slow-slip events are enigmatic because we don't yet understand the physical processes that cause faults to behave in such a way, and we don’t know very much about their relationship to large subduction zone earthquakes,” said expedition co-leader Dr Demian Saffer, of Pennsylvania State University.

The Kaikōura earthquake of 2016 triggered a large slow-slip event off the east coast covering an area of more than 15,000 square kilometres.

The slow-slip event started in the region of the planned drilling east of Gisborne, so the results from this research should shed new light on why this occurred.

GNS Science said investigating why and where slow-slip events happen is a key missing link in understanding how faults work.

Dr Wallace believes that “slow-slip events also have great potential to improve our ability to forecast earthquakes.”

A major aim of the voyage is installing two borehole observatories into pre-drilled holes 500m below the seabed. This will be the first time such observatories have been installed in NZ waters.

It brings brand new monitoring capability to New Zealand, which may help pave the way for offshore instrumentation needed for earthquake and tsunami early warning systems.

The observatories contain high-tech measuring and monitoring equipment inside their steel casing and will remain under the seafloor for five to 10 years. They will collect information on how the rocks are strained during slow-slip events, as well as changes in temperature and also fingerprint the fluids released in fault zones during tectonic activity.

One observatory will be placed into the Australian tectonic plate above the area where slow-slip events occur, and the other will be placed directly into the fault zone where the two plates meet and slide past each other.

GNS Science said information gathered by the observatories will give scientists important new insights into the behaviour of slow-slip events and their relationship to great earthquakes along the subduction plate boundary.

Understanding the linkages between slow-slip events and devastating earthquakes and tsunamis will allow for better risk modelling and ultimately, better hazard preparation for our coastal communities.

New Zealand participates in IODP through a consortium of research organisations and universities in Australia and NZ, including GNS Science, NIWA, The University of Auckland, Victoria University of Wellington, and University of Otago. The Australia and NZ IODP Consortium (ANZIC) is supporting participation of Kiwi scientists and outreach officers on both expeditions.

The scientific drilling vessel JOIDES Resolution is funded by the US National Science Foundation.

Source: gns.cri.nz

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