South Island moved in earthquake

The Kaikoura earthquake shunted parts of the South Island more than 5 metres closer to the North Island, in a rupture so unusual it could forever change the way scientists think about earthquake hazards.

Scientists analysing data from the earthquake are learning more about its complexity, which was on a scale that may be globally unprecedented.

In the first major research derived from the earthquake, published on Friday in the high-profile Science journal, the 29 co-authors said the earthquake’s characteristics could not have been predicted by existing models.

It confirmed that at least 21 faults, some of them previously unknown, had ruptured across two active fault domains that were not known to be connected.

The rupture took about two minutes to travel from its starting point near Culverden to its end point north of Kaikoura, 180 kilometres away.

Where it peaked, on the Kekerengu fault north of Kaikoura, researchers found up to 12 metres of horizontal displacement on the surface, which would have happened nearly instantaneously.

The area was already known to have one of the most complicated plate boundaries in the world, but scientists were still shocked at how the earthquake played out.

‘‘The major takeaway is the sheer complexity of the event,’’ lead author Dr Ian Hamling, of GNS Science, said. ‘‘Some of the apparent jumps between faults I don’t think any seismic hazards model in the world would have considered a possible scenario.’’

The plate boundary ruptured across two fault domains: the North Canterbury system and the Marlborough system. Scientists did not know they were connected. Its complexity would have implications for seismic hazard models around the world. Scientists are continuing to pore over the data collected following the earthquake, which was one of the best-recorded earthquakes anywhere.