Big Science: What will the next decade of quakes look like?

The September 2010 earthquake at Darfield, Canterbury, was among a half-dozen quakes over the decade that reached over 7.0 in magnitude. Photo / NZ Herald

As part of five-part series on major new Kiwi research projects, science reporter Jamie Morton speaks with scientists attempting to gauge future seismic hazard.

In the decade New Zealand was rattled by more than 226,000 quakes big enough to be felt – including a half-dozen that topped a magnitude of 7.0.

Researchers now are investigating whether those big events, such as the 7.8 Kaikoura Earthquake in 2016, could leave a shaky legacy for the next 10 years.

Currently, there's no way to predict when and how earthquakes will happen in the future. Indeed one scientist told the Herald that the next "big one" would come as a crude surprise.

Looking at how past quakes might set up others to come has proven a particularly difficult puzzle fo researchers, who only have a narrow number of events, over a short geological timeframe, to calculate seismic hazard from.

While New Zealand boasts an impressively dense network of seismometers providing a constant feed of activity to researchers at GNS Science, that system has only been operating since 2001.

"Unfortunately, this means that our estimates of seismic hazards, or answers to questions like 'how likely is damaging earthquake shaking?' are based on very limited information," GNS seismologist Dr Bill Fry said.

"This results in big uncertainties in our estimates. It also means that we haven't previously seen what the impact of earthquakes like the 7.8 Kaikoura earthquake have on other New Zealand faults and future earthquakes that may happen on them."

A new project, led by Fry and University of Canterbury structural geologist Professor Andy Nicol, will attempt to overcome that challenge by taking our current understanding of earthquake physics and putting it into simulations of millions of quakes.

We know that earthquakes kick off, Fry explained, when the stresses acting on a fault became larger than the strength of the fault itself.

"Think about bending a wooden chopstick – you can bend it only so far before it breaks and the two halves snap back into straight pieces. The point at which the chopstick breaks is analogous to an earthquake."

Those "bending" forces in the earth mainly came from the moving of tectonic plates.

In their project, Fry and Nicol will start with a 3D model of New Zealand and its faults, and then use computer calculations to simulate the forces stemming from the Australian and Pacific plates.

"At some point, this means that the stresses on a fault will overcome its strength and a 'synthetic' earthquake will happen," Fry said.

"We then calculate the way this computer earthquake would redistribute the stresses it releases onto near faults. It is a pretty simple concept, but the devil is in the details."

The pair hope their project would offer fresh insight into the earthquake process – and also, more importantly, more clarity about what seismic hazard over the next few decades might look like.

"Ultimately, we hope that our study will be the groundwork for future generations of hazard models," Fry said.

"We also want to use our approach to understand how and why so many faults broke in the Kaikoura earthquake."

He added the study – supported by a $4.2m grant through Resilience to Nature's Challenges, one of New Zealand's 11 collaborative national science challenges – was a world-first in many respects.

"While the North Americans and Japanese are aggressively exploring this approach, we intend to take our project in directions that haven't previously been researched."