Damage caused to the Wellington waterfront by the 2016 Kaikoura earthquake. Scientists say that event may have carried implications for major earthquakes in the future.
Damage caused to the Wellington waterfront by the 2016 Kaikoura earthquake. Scientists say that event may have carried implications for major earthquakes in the future.
Scientists have warned of the rising risk of a mammoth earthquake on New Zealand’s plate boundary – but what comes after the Big One?
That’s the key question of a new $12.6 million study investigating whether such an event could leave a decades-long legacy of large quakes for Wellington and central New Zealand.
The Alpine Fault had a record of rupturing around every three centuries - 2017 marked the 300th anniversary of its last big shake – and the next one could block South Island highways in more than 120 places, leave 10,000 people cut off and cost the economy about $10 billion.
At the same time, scientists have projected a 25 per cent probability of a major quake within the next half-century in what poses New Zealand’s single largest natural hazard: the Hikurangi Subduction Zone.
Lying off the North Island’s East Coast, it marks the boundary where the Pacific plate plunges beneath the Australian plate, and is thought capable of generating powerful, tsunami-triggering “megathrust” earthquakes.
Yet little is understood about how these two giant fault systems interact – and particularly, whether an event like an 8.0 Alpine Fault cataclysm could kick off further big events in the complex “transition zone” sitting between them.
New Zealand sits on the boundary of two tectonic plates, which is marked in the north by the Hikurangi Subduction Zone, and in the south by the Alpine Fault. Scientists are studying how these two zones interact in the "transition zone" in central New Zealand.
“We think a shake of this size could significantly change the state of stress in the transition zone, potentially triggering decades of more large quakes,” said the study’s leader, Victoria University geologist Associate Professor Jamie Howarth.
Within the zone’s geological record lie hints of such sequences: a trio of quakes larger than 7.0 struck in the zone between 1848 and 1868, and there were similar clues after past Alpine Fault and southern Hikurangi margin ruptures.
But this record isn’t clear or long enough for scientists to reliably tell how often they occurred, or to forecast future activity - posing a huge question for the potential vulnerability of centres like Wellington.
The case for answering it has been made more pressing by 2016′s 7.8 Kaikōura earthquake, which ruptured numerous faults in the transition zone and piled more stress on others nearby – including the Hikurangi Subduction Zone.
“Indeed, the 2016 Kaikōura earthquake may mark the starting point for a multi-decade sequence of large earthquakes.”
To build a better picture, the researchers will draw on lake and wetland sediment records – as had been recently used to develop new forecasts for the Alpine Fault – which could take them back up to 10,000 years in time.
The Alpine Fault runs several hundred kilometres from near Milford Sound all the way to Nelson Lakes National Park. Photo / North and South
“This data will help inform computer simulations of earthquake processes, dramatically improving our ability to forecast future quake sequences and understand the hazard they present to people and communities.”
The study, dubbed Ngā Ngaru Wakapuke, will also explore scenarios, co-designed with communities and iwi, of how society might respond to long periods of disruption.
Project co-researcher and GNS Science marine geophysicist Dr Dan Bassett expects the work to boost preparedness and resilience, while also helping to “stress-test” infrastructure investments.
“By giving us better information about the likelihood of future quakes,” added Otago University’s Associate Professor Caroline Orchiston, “this project will reduce the uncertainty in hazard estimates and help inform decision-making so we can minimise costs from these events, potentially saving billions of dollars”.
Later, insights from the research might also be applied elsewhere.
“The dynamic hazard, risk and economic modelling approaches developed by the programme will be transferable to other seismically active regions of New Zealand and globally,” Howarth said.
“They will also open the way for exploring potential impacts of other temporally sequenced natural hazard events.”
The project, which also brings together experts from Canterbury and Massey universities, along with Niwa and consultancy Market Economics, is supported by MBIE’s Endeavour Fund and begins next month.
