MARSDEN FUND IN THE NEWS | 2020
NEW INSIGHT ON ALPINE FAULT RISK Original article by Jamie Morton published on 11 January 2021 in Whanganui Chronicle. Republished with permission of the author.
‘Scratch marks’ point to epicentres of earthquakes. A discovery made in the wake of 2016’s Kaikoura Earthquake could help scientists better understand how the big-risk Alpine Fault may unravel. The Alpine Fault, which runs about 600km up the western side of the South Island between Milford Sound and Marlborough, poses one of the biggest natural threats to New Zealand. It has a clear geologic record of rupturing around every three centuries – and 2017 marked the 300th anniversary of what is thought to have been a magnitude 8 quake that moved one side of the fault by about 8m in a matter of seconds. Recent studies have suggested a big quake could block South Island highways in more than 120 places, leave 10,000 people cut off, and cost the economy about $10 billion. Now, a project led by GNS Science’s Dr Russ Van Dissen will dig into the hidden system and another large South Island fault the Wairau Fault – to work out which way they’ll rupture in the future.
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Van Dissen said the direction of rupture propagation, called unzipping, had a major influence on where seismic energy was focused. Because the 7.8 Kaikoura earthquake ruptured from south to north, it sent a pulse of energy northwards that was sharply felt across the lower North Island – especially in Wellington. For scientists trying to calculate potential levels of ground shaking in a given area, they typically looked at where, when, how strongly, and in which direction past ruptures had unfolded. But the last of those four factors remained tricky to quantify. “A lot of people have carried out modelling and found that, if we knew which way the Alpine Fault would actually rupture, this would be the sort of energy and ground motions it might send to the north, or to the south, and so on,” he said.
