Seismic imagingImproving Aotearoa New Zealand’s earthquake resilience

Overview

The deep structure of the Northeast Japan subduction zone is being compared with that of Southern Hikurangi to investigate how the geology of the overriding plates affect where slips occur on these faults.

GNS Science’s Brook Tozer has been awarded a prestigious Rutherford Foundation postdoctoral fellowship to research Hikurangi. The project will strengthen links with Japanese and US scientists while working on some of the best crustal-scale seismic data ever recorded across two subduction megathrust faults.

The project aims to

• understand the potential extent and slip of a future Hikurangi megathrust earthquake by:
  • investigating how closely the Japanese megathrust and Te Moana-o-Raukawa Cook Strait resemble each other to learn how Hikurangi might behave
  • improving our ability to assess the hazard posed by the Hikurangi megathrust fault and understanding of megathrusts globally

The project

Preparing for the greatest quakes on Earth

Megathrust faults produce the largest earthquakes on Earth. These faults form where two tectonic plates converge and one plate dives down, or subducts, beneath the other. One such megathrust fault – the Hikurangi megathrust – occurs along the east coast of the North Island, where the Pacific plate dives beneath the Australian plate.

Earthquake magnitude is primarily controlled by the area of the fault that ruptures, and how much movement, or slip, occurs during an event. Hikurangi last moved about 500–600 years ago. This means scientists can only make very approximate estimates of future megathrust earthquakes.

Looking globally to learn locally

A natural analogue to Hikurangi is the NE Japan megathrust which produced the 2011 magnitude 9 Tohoku earthquake. This well-recorded event provided invaluable data for understanding the underlying processes that lead to such a large earthquake.

In New Zealand, ongoing research by GNS Science has revealed that the Te Moana-o-Raukawa Cook Strait region bears many similarities to that of Tohoku. This project is investigating how closely the two regions resemble each other, to understand the potential extent and slip of a future Hikurangi megathrust earthquake.

High-resolution 3D imaging

Addressing this question requires a detailed comparison of the rock types, their physical properties and 3D distribution to examine and compare their slip behaviour. It uses the geological equivalent of medical CAT scanning. By analysing seismic waves that have travelled through the crust, high-resolution 3D models of the subsurface structure of each region can be generated. This will produce the most detailed pictures to date of the Japanese and Hikurangi megathrust faults, revealing far more about them than was previously possible.