Kaikoura quake ‘astonishingly complex’
The Kaikoura earthquake shunted parts of the South Island 5 metres closer to the North Island in a rupture so unusual it could forever change the way experts think about earthquake hazards.
Scientists analysing data 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 today 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 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 worldwide.
Hazard models measure the likely characteristics of future earthquakes, such as the recurrence period, maximum magnitude and type of ground shaking. They are used by authorities for building codes.
The Kaikoura earthquake showed that paleoseismic studies – the analysis of earthquakes long ago, which are frequently used for hazard models – may not account for more complex ruptures.
‘‘We’re starting to see these earthquakes that seem to defy what we thought,’’ Hamling said.
‘‘If [the Kaikoura earthquake] had happened 1000 years ago . . . if you were to look at it with current paleoseismic methods . . . you would see it as separate individual events. You would never consider it as a single rupture.
‘‘It may be in fact that past earthquakes which were considered as smaller, individual ruptures potentially could have been one big rupture. That feeds into long-term hazards, in which you can end up with larger events than you might expect.’’
Scientists are continuing to pore over the data collected following the earthquake, which was one of the best-recorded quakes anywhere in the world.
Much of the information came via advanced radar technology on satellites circling the Earth.
The European and Japanese space agencies both re-tasked their satellites immediately after the earthquake to help with research.
At least 10 research papers on the earthquake involving GNS Science staff are in progress, with more likely from national and international institutions.