A research trench dug by Tim Little and Russ Van Dissen on the Kekerengu Fault is now in two halves - about nine metres apart.

Scientists investigating North Canterbury's Kekerengu Fault received a graphic example of its destructive power when a trench they had dug was ripped in half during the magnitude-7.8 Kaikoura Earthquake.

Following the November 14 quake, one half of the trench is now nine metres away from the other half.

Victoria University structural geologist Tim Little and GNS Science earthquake geologist Russ Van Dissen dug three trenches in February across the fault, looking for evidence of past large earthquakes.

GNS SCIENCE An example of the energy unleashed in the Kekerengu Fault rupture.

They found evidence of at least three large quakes in the past 1250 years, GNS scientist Ursula Cochran wrote in a GNS blog.

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Initial results confirmed the Kekerengu Fault was capable of producing large earthquakes frequently - on average every 300 or 400 years.

"Then, two weeks ago, as if to say, 'Don't underestimate me!' the fault ruptured right through those same trenches," Cochran wrote.

Map published by GNS Science shows the current understanding of surface fault rupture during the Kaikoura Earthquake.

While scientists had known about the fault and even that it could rupture jointly with other faults, even more faults were involved in the Kaikoura Earthquake than expected.

"Currently we have evidence for seven faults rupturing in the M7.8 Kaikoura Earthquake so work on the Kekerengu Fault is just a small part of the earthquake geology response," Cochran said.

Teams from the universities of Otago, Canterbury, Auckland and Victoria, as well as from Niwa and GNS Science, along with volunteers from overseas, were mapping and measuring the faults that moved in the quake. The work would help them understand what happened in the quake, and what it meant for future events.

Little and Van Dissen were interested in the Kekerengu Fault because it had been identified as likely to be the fastest slipping fault within 100km of Wellington, 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," Cochran said.