North and South Islands 'creeping' closer together Geonet

  • 24/11/2018

The North and South Islands are moving closer together after the effects of the Kaikōura earthquake in 2016.

The magnitude 7.8 earthquake produced 25 fault ruptures, causing dramatic changes to the sea bed and land, and also brought the North and South Islands five meters closer together.

According to GNS Science geodetic scientist Dr Sigrun Hreinsdottir, the islands have continued to creep together over the last two years.

The most north-eastern tip of the South Island, Cape Campbell, has now moved 35cm closer to Wellington.

As for Kaikōura, it has moved 15cm east and Wellington has moved five centimetres northeast.

Scientists have yet to pinpoint which of the fault ruptures are responsible for the change in the islands, Dr Hreinsdottir told Stuff.

"In reality we are having all these creepings going on and the question is, which is the dominant factor? The idea there was a quite significant component on that plate interface was the surprising thing to us."

The Papatea Fault ruptured according to Geonet. The fault starts offshore and extends inland north of Kaikōura, and the rupture caused vertical displacement of around five metres and a horizontal displacement of many metres, causing a wall to form.

"Right after the earthquake, the fault formed a vertical wall," says Dr Rob Langridge, GNS Science Earthquake Geologist. "Two years later the wall has degraded away and collapsed. It has sort of dissolved before our eyes."

The biggest fault rupture of the 2016 quake was in Kekerengu which slipped 9 metres in length.


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