Scientists to drill into the edge of the world

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An international consortium of scientists is preparing to drill into a crack in the edge of the world – the South Island's Alpine Fault.

The researchers want to drill over 5km deep in the Mt Cook National Park, west of Lilybank, in a cutting-edge experiment which will give a look at changes within the fault, which is expected to eventually destroy large areas of the South Island in a magnitude 8 quake.

By drilling a hole into a fault in the Earth's mid-crust, the scientists will get a close look at changes in the underlying rock, and whether the fault is being "lubricated" by fluids under huge pressures or even talc associated with layers of serpentinite under the Southern Alps.

Average slip rates in the fault's central region are about 30mm a year, very fast by global standards.

"We can take advantage of a rare window into the physical character of the seismologically expressed brittle-ductile transition zone in a fault that is active today and which can be geophysically monitored in the coming decades," the researchers in the International Continental Scientific Drilling Programme (ICDP) say on their website.

A principal investigator is Victoria University geophysicist and Earthquake Commission fellow in seismic studies, John Townend, who proposed the "ambitious, technically challenging" drillhole.

"Establishment of a fault-hosted observatory will allow continuous observation of a fault that is late in its earthquake cycle," he said.

The Alpine Fault is thought to fail in magnitude 8 quakes at intervals between 100 and 400 years. most recently 291 years ago, in 1717.

The 1717 quake appears to have involved a rupture along nearly 400km of the southern two thirds of the fault, and some researchers have said a similar earthquake could happen at any time as the interval since 1717 is longer than between the earlier events.

Dr Townend said the drillhole also offers "the exciting possibility" of recording data before and during a future large earthquake.

And samples from the drilling will be able to be compared with young rock now on the surface, about 7km above the fault, which some scientists believe has been particularly brittle under extreme pressures when it was underground, and to have be exposed to big pressure changes exerted by fluid deep in the earth.

The ICDP has proposed hold a five-day international workshop in early 2009 to plan the drilling.

The Alpine Fault has some similarities to a Californian fault where researchers at the San Andreas Fault Observatory at Depth (Safod) recently used a similarly deep drillhole to observe 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.

A drillhole allows the measurement of stress, the pressure of fluids, the temperature, the heat flow, the chemistry of the fluids, the rocks and any gases in the fault zone.

 - NZPA