New earthquake research project compares Hikurangi fault to Japanese quake

Friday, 22 November 2019

A look at the Hikurangi subduction zone, the big faultline off the east coast of the North Island.

A new earthquake research project will be a step towards better understanding New Zealand's largest and most active fault.

The project comparing Japanese and New Zealand faults will shed light on the types of earthquakes expected from the Hikurangi subduction zone off the East Coast.

Stretching from the seafloor north of Gisborne and down to Marlborough, the Hikurangi fault is the country's largest subduction zone, capable of producing devastating earthquakes and tsunamis.

In the zone, two tectonic plates have met and one - the Pacific plate - is diving under the other, the Australian plate.

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Geophysicist Dr Brook Tozer will lead a research team at GNS Science to compare earthquakes between New Zealand and Japan.

Led by geophysicist Dr Brook Tozer, researchers at GNS Science hope to uncover more clues about future earthquake activity in the fault, by comparing its seismic recordings and data to similar data from the magnitude 9 'megathrust'' earthquake that hit Japan in 2011.

'This study will focus specifically on imaging the internal structure beneath Cook Strait region as well as the Tohoku region of Northeast Japan,' Tozer said.

Recent GNS research discovered evidence for a structural boundary under Cook Strait which could be similar to one that played a key part in determining the magnitude and rupture point of the Tohoku earthquake, which claimed more than 20,000 lives.

Tozer said the study would look at where the Hikurangi fault could rupture and the amount of slip (movement) that could occur.

Previously, the best data to draw on came from older evidence preserved in the geological record, which stretched back thousands of years, while the amount of slip that could occur during a megathrust quake was 'even more poorly understood'.

Maximum water surface elevation for the 8.9 Hikurangi earthquake scenario.The colour scale is limited so that water heights above 5m appear as 5m1

The amount of slip that happened during the 2011 event reached much further offshore than expected and the amount of slip was 70 per cent larger than had ever been recorded for a megathrust earthquake.

'By comparing and contrasting [Tohoku] with the Southern Hikurangi megathrust, we hope to help identify whether or not our fault is also capable of slipping by such an enormous amount in a single event.'

Tozer will draw on two decades of seismic data and compare the properties of both subduction zones, including the rock type, their physical properties and relationships with observed slip behaviour.

He and the team will also produce high-resolution 3D models - similar to a CAT scan - of the two different region's subsurface structure to study.

Earlier this year, Hikurangi Response Plan Project Lead Natasha Goldring said it's not if there's an earthquake, but when.

Civil Defence Emergency Management groups around the North Island have already been working on an emergency response plan for a magnitude 8.9 earthquake and tsunami scenario.