13 Dec 2023

Our Changing World – 3D mapping the Hikurangi subduction zone

From Afternoons, 3:35 pm on 13 December 2023
A model showing one layer of seafloor with a hill being pushed under another layer of seafloor, which is coloured with rainbow.

The seamount subducting under the Australian plate. Photo: GNS Science

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Off the North Island’s East Coast, the Pacific Plate dives under the Australian Plate in an area known as the Hikurangi subduction zone.  

Such subduction zones have been responsible for extremely large earthquakes around the Pacific Ring of Fire, says GNS scientist Dr Stuart Henrys, so he and others are keen to understand the Hikurangi area in as much detail as possible.  

A man in a black and white checked shirt and glasses smiles at the camera while sitting in front of orange cylinder devices.

Dr Stuart Henrys. Photo: GNS Science

GPS sensors revealed that in part of this zone, to the east of Gisborne, slow-slip earthquakes are occurring regularly – every two years or so. In slow-slip earthquakes, the movement is similar to a traditional earthquake, except it takes weeks to occur rather than seconds. The slip is so slow that no damaging shaking occurs.  

Internationally there’s been a lot of scientific interest in slow-slip earthquakes, in part because they occurred in advance of the extremely destructive 9.1 magnitude Tohoku earthquake in Japan in 2011.  

The slow-slip earthquakes observed off Gisborne are the shallowest in the world, so researchers from New Zealand, the US, the UK and Japan pooled resources to create a 3D map of part of this region in incredible detail.  

Having crunched the data for many years, Stuart tells Claire Concannon about the surprising findings he and his colleagues have uncovered.  

Approximately 50 large yellow devices, roughly spherical, with bright blue attachments, inside red square metal frames lined up.

Sensors for the 3D scan of the Hikurangi subduction zone. Photo: GNS Science

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