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A joint expedition of international scientists aiming to provide more information about New Zealand’s largest earthquake and tsunami hazard started over the weekend.
Tagged as an “ambitious mission,” it sees a team of scientists spending the next eight weeks aboard the scientific drilling ship, JOIDES Resolution, to lower two sub-seafloor observatories into the Hikurangi subduction zone east of the North Island to study New Zealand’s largest fault.
The project was led by scientists from GNS Science and Pennsylvania State University. It was funded by the International Ocean Discovery Program (IODP) and the US National Science Foundation.
The Hikurangi subduction zone off the east coast of the North Island is part of the Pacific Ring of Fire where the Pacific tectonic plate dives beneath the Australian plate.
According to GNS Science, the scientists believe the Hikurangi subduction zone 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,” GNS Science expedition co-leader Dr. Laura Wallace explained. “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.
The Kaikōura earthquake of 2016 triggered a large slow-slip event off the east coast covering an area of more than 15,000km2. 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.
Investigating why and where slow-slip events happen is a key missing link in understanding how faults work. Slow-slip events also have great potential to improve our ability to forecast earthquakes, Wallace added.
James Allan, National Science Foundation’s Division of Ocean Sciences program director, meanwhile, said: “This expedition will yield information that’s key to understanding why destructive tsunamis happen after shallow earthquakes at plate subduction zones and underwater landslides.”
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 Australia and New Zealand IODP Consortium (ANZIC) is supporting the participation of New Zealand scientists and outreach officers on both expeditions.
