Scientists say they have evidence nine faults ruptured in the Kaikōura earthquake, which explains the massive landslides over State Highway 1.
GNS geologist Rob Langridge said after a flight over the area the tally has risen from seven to include the Fidget and newly-named Uwerau faults.
He said the discovery joined the dots between the ruptures already identified to the south and north of the earthquake zone.
Mr Langridge said the earthquake was in the same league as the 1855 Wairarapa earthquake and the catastrophic 1906 San Francisco earthquake.
"We couldn't put our finger on what exactly was causing the huge landslides and the shaking in the Kaikōura area." - GNS Scientist Rob Langridge
Russ Van Dissen and Jamie Howarth take samples from a giant chasm created by the quake on a Ward farm. Photo: RNZ / Tracy Neal
He told Morning Report GNS found a rupture in the back of the Seaward Kaikōura range, which caused rock avalanches and landslides.
The landscape was "hammered", he said. A lot of material had already come down because the shaking was "so intense".
Pieces of slope near the large landslides could be "reactivated' if there was a major aftershock in the area.
"The probabilities of a magnitude 7 earthquake or aftershock happening are still around 30 percent in a month," he said.
He said scientists were puzzled as to why the Hope Fault, which linked the Alpine Fault to the faults they were looking at, hardly ruptured at all.
Mr Langridge said GNS scientists believed there could be three segments to the Hope Fault, which moved about 10cm at Half Moon Bay.
When asked if the Hope Fault rupturing significantly would increase the changes of the Alpine Fault rupture, he said, "there would be increased stress at the ends of the rupture".
GNS was in the process of building a map of the faults.
Read our full Kaikōura coverage here.