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Kaikoura quake shakes up science models

NZ Newswire logoNZ Newswire 23/03/2017

The Kaikoura earthquake was so complex and unusual that it's likely to change the way scientists think about quake models internationally, a GNS Science-led study says.

The magnitude-7.8 tremor on November 14 was also one of the best recorded in the world, enabling analysis in unprecedented detail.

The paper, published in the journal Science, involved input from 29 co-authors from 11 international and international institutes.

The authors say the quake has underlined the importance of re-evaluating how rupture scenarios are defined for seismic hazard models in plate boundary zones worldwide.

The study shows parts of the South Island were moved more than five metres closer to the North Island, in addition to being uplifted by up to eight metres.

The quake ruptured at least 12 major crustal faults plus another nine lesser faults.

The rupture started in North Canterbury and propagated northward for more than 170km along some well-known and some previously unknown faults.

The largest movement occurred on the Kekerengu Fault, where pieces of the Earth's crust were displaced relative to each other up by to 25 metres at a depth of about 15km.

The maximum rupture at the surface was measured at 12 metres of horizontal displacement.

GNS Science geodesy specialist Dr Ian Hamling, the paper's lead author, says the earthquake has underlined that conventional seismic hazard models are too simple and restrictive.

"The message from Kaikoura is that earthquake science should be more open to a wider range of possibilities when rupture propagation models are being developed," he said.

However, Dr Hamling noted that insights from several large, complex earthquakes worldwide during the past decade were helping to relax some of the existing assumptions about how multi-fault ruptures can occur.

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