New Zealand's 7.8m quake reveals new fault lines

Previously unknown faultlines have been discovered by geologists surveying which fault lines ruptured in Monday's devastating Kaikoura earthquake.

GNS Science geologists Nicola Litchfield and Pilar Villamor say several faults ruptured during this week's magnitude 7.8 tremor, and some were previously unknown.

They are calling the destructive quake a "very complex" tremor, which left the earth violently fractured along faultlines.

Ruptures in farmland around Conway near Kaikoura. Photo: SNPA / David Alexander
Ruptures in farmland around Conway near Kaikoura. Photo: SNPA / David Alexander

The geologists, who flew over the South Island's eastern coast, said the first rupture was the Kekerengu Fault, which they followed from the beach inland to Bluff Station.

"Here, the earthquake dislocated hills, fences, roads, buildings and the river bed, some by as much as 10m horizontally.

A house was also spectacularly moved off its foundations - the occupants were shaken up, but otherwise okay," they posted on the GNS website.

Further south, the road and railway line had shifted 1m at Waipapa Bay.

The road had been offset by a similar distance along the Hope Fault. Other scientists who had flown along the faultline earlier reported no other disturbance of the land.

When they surveyed the Hundalee, Emu Plains, and The Humps fault zone there was evidence the fault had disturbed State Highway 1 and the railway line as well as the beach south of Kaikoura.

As they approached the epicentre the geologists found the earth ruptured along new faults.

"We then flew to the epicentre area [The Humps fault zone and Emu Plains] and found fault ruptures on the north side of the Waiau River, some on previously unknown faults.

"It was less clear exactly how these faults had moved compared to the others further north, but it looked like some horizontal movement had occurred."

They said some of the fractured earth had affected small streams.

The pair said it was only possible to see where fault lines had broken through the surface.

It was likely other faults below the surface had also moved. Other investigations, including satellite images, would help show any further subsurface fault movements.