Scientists investigate ruptures along high-risk Alpine Fault

Scientists will investigate intriguing "barriers" capable of influencing earthquakes along one of New Zealand's most dangerous faults.

The fault, which runs about 500km up the western side of the South Island between Milford Sound and Marlborough, poses one of the country's biggest natural threats, making it of intense interest to scientists and civil defence planners.

It has a clear geographic record of rupturing around every three centuries - and last year marked the 300th anniversary since an 8.1 quake that shunted the fault's southern side eight metres further south in a matter of seconds.

A new project, just awarded a $300,000 Marsden Fund grant, will focus on finding out what controls how much of the Alpine Fault ruptures in a particular earthquake.

Scientists have observed from geological records of previous Alpine Fault earthquakes that some places on the West Coast frequently act as barriers to rupture.

Project leader and seismologist, Emily Warren-Smith, said the aim of her team was to find out why some locations were so influential in putting the brakes on ruptures.

"To do this, we will acquire and analyse recordings of small earthquakes occurring close to two of the most persistent rupture barriers," she said.

This would enable scientists to build a high-resolution three-dimensional image of the physical properties of these complex rupture barrier regions.

They would use this information to build computer models that will simulated a range of rupture scenarios on the Alpine Fault, giving scientists a clearer picture of the length and style of rupture that could unfold in the future.

The new project follows a series of recent scientific papers focused on the fault.

One suggested a large event could strand some 10,000 people living in affected areas, along with several thousand tourists.

Roads would likely be blocked at State Highway 6 just south of Franz Josef, 20km northeast of Haast and 10km east of Haast, and at State Highway 94 just south of Milford Sound and State Highway 73 just north of Arthurs Pass.

If these sections were cut off, reaching the West Coast would only be possible via State Highway 7 - and with access only to 50km south of Hokitika.

The study pointed out that 1.3 million travellers visited the West Coast each year, with enough capacity for 4000 visitors each night in the popular Franz Josef area.

The Milford Sound area alone attracted 650,000 visitors each year - equating to 1700 each day - and in the event of a quake, hundreds could be spread out in the region and on foot.

Authorities have responded to the threat with a collaborative programme dubbed Project AF8.

The project had developed scenarios so South Island communities can plan how they might respond to impacts such as road closures, power losses, fatalities, injuries, and social dislocation.

Based on the first seven days of emergency response, AF8's planning covered such things as the shelter and care of displaced people including the potential for tens of thousands of tourists, an immediate medical response and the restoration of priority telecommunications.

A Tier 4 national Civil Defence exercise was planned to be held in 2020 to build awareness and resilience and to test the planning and national response capability.