A group of 65 scientists from seven countries has started refining plans for a long-term project to drill into the South Island's largest and most dangerous quake zone - the Alpine Fault.
They have laid out a research programme that will eventually culminate in the drilling of a bore hole 4km or 5km deep, into rocks which will give new clues about what happens in the lead-up to a major quake.
The Government was told late last year that there was a 20 percent chance of a big quake on the fault in the next 20 years, compared with a 15 percent chance of a major one affecting Wellington over the next 50 years.
Massive pressures build up on the Alpine Fault. It has moved at an average of 27mm a year over the past 50,000 years - but this has included catastrophic quakes in which it has moved 8m in seconds.
The Alpine Fault runs for more than 650km from south of Fiordland, along the spine of the South Island into Marlborough, and is part of the boundary between the Pacific and Australian tectonic plates.
It ruptures every 200 to 400 years, producing earthquakes of about magnitude 8.
It last ruptured in 1717 along nearly 400km of the southern two thirds of the fault.
The geophysicists hope it may enable them to monitor a major quake, from within the quake zone, while it happens.
"We're interested in getting down to where the seismic action is," said United States Geological Survey (USGS) geophysicist Bill Ellsworth, who is one of three scientists visiting New Zealand from a similar project at Parkfield on California's San Andreas Fault.
Their $US25 million ($NZ44.2 million) San Andreas Fault Observatory at Depth (SAFOD) borehole has equipment inserted 3km deep and has been observing geophysical changes underground two to 10 hours before small earthquakes occurred.
The seeds of SAFOD were sown by earthquake experts in the 1980s, when researchers said they would have to dig to the very heart of earthquake zones to find out what drives the engine of quakes.
At major plate boundary faults in most other parts of the world, the earthquake-generating zone is deep and largely beyond the reach of present drilling technology, and Dr Ellsworth said drilling into the Alpine Fault would also be a "world class" project which could attract international funding.
It would be a landmark in New Zealand in terms of its scale and for the potential significance of its findings.
Geophysicists John Townend, of Victoria University, and Rupert Sutherland of GNS Science proposed the "ambitious, technically challenging" drillhole to allow continuous observation of a fault that is late in its earthquake cycle.
The possibility of recording data before and during a future large earthquake was "exciting", Dr Townend told NZPA.
The five-day planning workshop just completed at Franz Joseph - funded by the International Continental Scientific Drilling Programme (ICDP) - expects the drillhole to allow the measurement of stress, pressure and temperature conditions in the quake zone, the role of underground fluids, and how large faults evolve.
Research will start with a series of surface studies, followed by initial drill holes to retrieve unweathered rock samples and measure temperatures and fluids at depth.
Studies being done by academics have suggested there are bodies of fluid 4km deep inside the fault, raising questions about their role in quakes.
The work could not only indicate the strength of ground-shaking from the next big quake on the Alpine Fault, but could show how large faults work around the world.
