New research shows a fault line in western Otago has the potential to create an earthquake similar in size to the 2010 Christchurch earthquake.
The 2010 earthquake, also known as the Darfield earthquake, hit the South Island on September 4. It was a magnitude 7.1 and was responsible for damaging aftershocks including the magnitude 6.3 earthquake which struck nearly six months later and killed 185 people.
The new research, funded by EQC, looked at the Nevis Fault in western Otago. It found despite being a low-seismicity area, it has the potential to create an earthquake similar in size to the 2010 quake.
"People in Otago and Southland usually only think about the Alpine Fault when they think about earthquakes, but we now know that there are major faults in low-seismicity areas that could produce a major event," says lead researcher Mark Stirling from the University of Otago.
Professor Stirling, Postdoctoral Scholar Dr Jack Williams and a team of staff dug two 25-metre long trenches high in the Upper Nevis Basin, south of Queenstown, to gain a better understanding of the Nevis Fault and greater Nevis-Cardrona fault system.
The combined fault system stretches for about 100km from Lake Wanaka to near Garston in Southland. The researchers say evidence of at least two major prehistoric events show it has the potential to produce an earthquake well into the magnitude 7 range.
"We found evidence of the sediment layers being broken up, warped and thrust over each other, which would have been produced by significant seismic events," says Stirling.
EQC research manager Natalie Balfour says the research is important because the Queenstown Lakes District is one of the fastest-growing areas in New Zealand, with a huge amount of new housing and infrastructure development.
"EQC supports this type of research because it is important for developers, local councils, and the public to understand and manage potential seismic hazards," says Balfour
The University of Otago team re-excavated near sites that had previously been investigated by New Zealand Geological Survey seismologists in the 1980s, before carbon dating technology allowed scientists to create timelines.
Stirling says knowing the timings of the prehistoric earthquakes will help scientists better understand the fault system, but warned they need more data before they will be able to forecast the timing of the next event.
"To create probability models to forecast the likelihood and timing of the next event, like can be done with the Alpine Fault, you would need a lot more than just two earthquakes," he says.
Stirling says faults in Otago and Southland generally have long time periods between earthquakes and can show great variability in behaviour over time.
But he said if the Nevis-Cardrona system were to rupture there would "most definitely" be a large earthquake felt by most of Otago and Southland.
"Everyone knows about the Alpine Fault, which is a rock star of faults and gets most of the publicity in the South Island, but people also need to be aware of local seismic hazards."
He says even low seismic areas can have earthquakes pointing to the Canterbury Plains, which were seismically quiet until 2010, as an example.
Stirling says he hopes more awareness of potential earthquakes will help Kiwis be better prepared than they were in 2010.
