A global team of 100 scientists and engineers has begun drilling a 1.3km-deep borehole into the South Island's Alpine Fault to gather information about the inner workings of the fault line.
The project, which was taking place near Whataroa, north of Franz Josef Glacier, would allow scientists to install monitoring equipment into the fault, where small earthquakes, temperature, pressure and chemical conditions could be studied.
The venture was being led by GNS Science, Victoria University and the University of Otago and involved a team of scientists from New Zealand, the United States, United Kingdom, Germany, Canada, France, Italy, Australia, China and Taiwan.
Project co-leader Rupert Sutherland from GNS said the fault, which was visible from space, stretched about 650km south of Fiordland alongside the spine of the Southern Alps and into Martinborough, and was of particular interest to scientists as it was one of the most active plate boundary faults in the world.
Dr Sutherland earlier said the fault was the country's biggest earthquake risk and had the potential to cause an estimated 10,000 casualties and kill at least 1000.
While other major faults had been drilled this way, it had previously only occurred following a big earthquake. This was the first time in history that a major fault had been drilled before it ruptured, he said.
He hoped the scientists would achieve a greater understanding of earthquake processes through the sampling and analysis of rock and fluid materials retrieved from deep within the fault, or what some scientists had dubbed "the earthquake machine".
Project co-leader John Townend [correct] of Victoria University said he hoped the monitoring of the conditions within the fault zone would ultimately lead to a better understanding of how faults slipped and generated seismic waves during large earthquakes.
"The Alpine Fault appears to save up all its energy for one big showdown every few hundred years. In between its big ruptures, it seems to stay locked and produce mostly minor earthquakes, but what controls this timing behaviour isn't clear."
New knowledge and understanding gained from the project would benefit earthquake science globally and enable New Zealand to better prepare for a future large-scale earthquake on the Alpine Fault. he said.
The fault, which last ruptured 297 years ago in 1717, had a 28 per cent probability of rupturing within the next 50 years, which was a high percentage by global standards.