ELVES: Earthquakes and Locking inVEstigation of Subduction

Introduction

A team of New Zealand and Canadian scientists are working to reveal how the tectonic plates may be ‘stuck’ (or ‘locked’) along the southern part of the Hikurangi Subduction Zone. This will help understand the potential for a major earthquake and tsunami offshore southern Te Ika-a-Māui/North Island.

Long-duration GPS studies have shown that the southern part of the Hikurangi Subduction Zone is ‘locked’, building up forces, or stress, to be released in a future major earthquake (see Figure 1), which would also likely lead to a tsunami. This locked zone is of great interest to seismologists and hazard scientists because it lies beneath Wellington and the southern North Island, posing significant seismic hazard for the region.

Project scientists aim to investigate whether the ‘locked’ zone is producing any small-scale earthquake activity and use these signals to paint a clearer picture of the structure and potential for the subduction zone to cause major earthquakes.

Detecting small earthquake signals on the offshore fault is very difficult using land-based instruments alone; scientists require instruments close to the earthquake source to “listen” for any activity. This is especially important because the stuck nature of the fault means it won’t be moving very much, if at all. 

Figure 1.

By placing sensitive, ocean-bottom seismometers (OBS) on the seafloor, the team will record and analyse any signals of small earthquakes occurring in the locked zone. Twenty OBS will be deployed in late-2023 from the NIWA Research Vessel Tangaroa and sit on the seafloor for one year.

“Even if we find very few earthquake signals in the locked zone, this is still a significant discovery – it helps confirm that our land-based observations have been right and that there is significant stress build-up occurring offshore. Mapping the extent of the locked region ultimately helps us build better tsunami and earthquake forecasting models” says cruise leader and project team member Dr Emily Warren-Smith (GNS Science).

The locked zone behaves differently to other parts of the subduction zone, where regular slow slip events (SSEs) occur as slow-motion earthquakes, partially relieving the stress building up from tectonic plate motions. Previous projects (e.g. PULSE, HOBITSS) have studied these slow slip zones in detail, but no focused study has looked for earthquakes occurring in the locked zone.

The ELVES project is a collaboration between Victoria University of Wellington/Te Herenga Waka and GNS Science/Te Pu Ao alongside the University of Ottawa and Dalhousie University in Canada. The project is funded by a Toka Tū Ake/EQC biennial grant, SSIF funding to GNS Science and Canadian funding from the University of Ottawa. 

Ocean floor view to give clearer picture of subduction zone earthquakes :: Toka Tū Ake EQC