Ground-breaking new research has created a million-year catalogue of ‘synthetic’ earthquakes that could shape future earthquake and tsunami hazard models for Aotearoa New Zealand.
“The full cycle of New Zealand’s earthquake activity spans thousands of years,” explains Dr Bill Fry of GNS Science, co-leader of the research programme. “Modern observations and data only cover the last few decades, and this combined with the incompleteness of geological information means we can’t capture the entire range of possible natural earthquakes, especially the largest, most devastating events.”
A research team led by Dr Fry and Prof Andy Nicol (University of Canterbury) as part of the Resilience to Nature’s Challenges National Science Challenge are using physics to create computational models of hundreds of thousands of years of earthquakes.
The team starts with a 3D model of Aotearoa New Zealand and its faults, then uses computer calculations to simulate forces that cause earthquakes. When the forces acting on a fault overcome its strength, this triggers a ‘synthetic’ earthquake. Researchers can then see how the synthetic earthquake redistributes stress onto other faults and leads to other earthquakes.
Dr Fry says the new research could help gain a better understanding of what will happen after large earthquakes, such as Friday’s M7.2 off the east coast, and the M7.4 and M8.1 that followed soon after in the Kermadecs.
“One of the big challenges on Friday was complexity in modelling tsunamis. There’s already a lot of complexity in modelling tsunamis from a single earthquake. When you have tsunamis from two or more large earthquakes happening so close together, the uncertainties balloon.”
“The new synthetic catalogue will help us get a better understanding of the frequency of these earthquakes that happen within hours of each other. It will also help reduce uncertainties in forecasting the likely impacts of these compound events.”
Dr Fry says they have used the new catalogue to test the effectiveness of the recently deployed New Zealand DART tsunami buoy array, which formed an essential part of the tsunami warning system following Friday’s earthquakes.
“We’ve also started work looking at how major earthquakes might change our rivers and groundwater systems.”
Dr Fry says there are many other potential applications for the computer-modelled catalogues. “The big prize is to use the catalogue to underpin future earthquake and tsunami hazard models, but there are less obvious opportunities too. For example, we plan to use it to better understand the way New Zealand’s landscape intensifies earthquake shaking, causing landslides and damage to buildings.”
“Another key application is to improve our understanding of the way one earthquake triggers another,” says Dr Fry. “We hope this work will help explain why the 2016 Kaikōura earthquake happened and what it means for the future of earthquakes in central Aotearoa New Zealand.”
“Every time we get a big earthquake, we learn something new. Our ultimate goal is to ensure this new knowledge helps us be much better prepared for the next big, complex earthquake.”