Jamie Morton is the NZ Herald's science reporter.

Dramatic earthquake pictures: The great wall of Waiau

Scientists working in North Canterbury have captured incredible images showing the fractures in the landscape wrought by this month's 7.8 Kaikoura earthquake.

Dr Kate Pedley, of University of Canterbury's Department of Geological Sciences, shared on Facebook some of the dramatic sights she and her colleagues have encountered as they've surveyed evidence of faulting in the countryside around Waiau, about 30km east of Hanmer Springs.

Pedley said the survey area covered a "complicated 3km wide zone" of numerous ruptures and associated structures.

"Thankfully, those south and west of Waiau generally got off lightly, but it very quickly got messy for infrastructure to the northeast," she wrote.

"The amount of associated rockfall, landslides and slumps were incredible."

Meanwhile, geologists Tim Little of Victoria University of Wellington and Russ Van Dissen of GNS Science have been investigating the area's Kekerengu Fault, which they'd previously found was likely to be the fastest slipping fault within 100km of Wellington city, apart from the Hikurangi subduction zone.

They knew this meant it posed a significant seismic hazard to the northeastern South Island and also to Wellington if linking faults in Cook Strait ruptured at the same time as the Kekerengu Fault.

In February this year, the pair excavated three trenches across the fault to look for evidence of past large earthquakes, with an aim of getting a deeper understanding of the seismic hazard it posed.

In these trenches, they found evidence of at least three past large earthquakes in the past 1250 years.

These initial results confirmed that the fault was capable of producing large earthquakes frequently - on average, every 300 to 400 years - and was likely to do so again.

"Then, two weeks ago, as if to say, 'Don't underestimate me' the fault ruptured right through those same trenches," GNS Science earthquake geologist Dr Ursula Cochran wrote in a blog post this week.

"Tim was awestruck. As a geologist working on active faults he said, 'I had often wondered what it would look like if a fault moved while we were working on a trench cut across it, but I had never expected this to happen to me'."

Its impacts on the landscape were dramatic, she said: one side of the fault had moved as much as 11m with respect to the other side.

"Tim did not expect quite this amount of slip on this fault during a single earthquake. Russ, though, was less surprised - he says it fits with the long-term slip rate calculated for the fault - but he is still amazed to see such fault movement in action."

- NZ Herald

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