Researchers to bore major fault

The Apline Fault stretches 650km along the spine of the south island from Marlborough to Fiordland.

Global team to explore causes of deadly quakes by drilling 1.3km into Alpine Fault which is due to rupture

The world is turning to New Zealand's most threatening fault to better understand the levers that cause catastrophic earthquakes.

Scientists from a dozen countries plan to drill 1.3km into the Alpine Fault, spanning the spine of the South Island, in what will be one of the first attempts to probe inside a major fault before it ruptures.

The huge fault poses the country's biggest earthquake risk - it has the potential to cause an estimated 10,000 casualties and kill at least 1000 - and is expected to rupture again in coming decades, causing a magnitude 8 quake.

A major quake would most likely also prove the catalyst for a large-scale, near-shore tsunami.

Dr Rupert Sutherland, of GNS Science, said the fault tended to save its energy for "one big showdown" every few hundred years, producing only minor quakes and tremors the rest of the time.

One of the more active plate boundary faults in the world, it is seen as a key fault to study because of its size, fast rate of movement, and accessibility.

The major drilling project is planned to begin in October at a site near Whataroa, north Franz Josef.

"The question that has been pressing for the international science community has been, what does a fault look like before it ruptures in an earthquake," Dr Sutherland told the Herald.

As part of a lead-up to this year's project, a smaller group of scientists drilled two boreholes about 150m into the fault in early 2011.

One of the main findings was the existence of a finely-ground impermeable layer of rock in the centre of the fault zone, holding back large amounts of fluid on the upper east side of the fault.

Scientists hope the proposed 1.3km-deep borehole would shed more light on the relationship between fluid pressure, the internal structure of the fault zone, and the mechanics of earthquakes.

Their aim in October is to intersect the fault at about 1km depth and drill a further 300m into the underlying Australian tectonic plate.

They will take rock samples from the borehole for analysis.

Big shakes not linked: scientist

Two big quakes, two hemispheres, an hour and a half apart.

Despite the scales of the 7.2 and 7.9 quakes that respectively struck yesterday near the Kermadec Islands, north of New Zealand, and near Alaska's Aleutian Islands, there was no direct link.

GNS Science duty seismologist Caroline Holden said when the Alaskan quake came at 8.53am NZT, after a 7.19am quake that rattled several Department of Conservation staff on Raoul Island, she thought they may have been connected.

"If you get a decent level of shaking, you can trigger a pretty decent event," she said. "But these ones were too far apart - we're talking thousands of kilometres."

But both quakes, which caused no deaths or injuries, were part of the Pacific Ring of Fire, an arc of earthquake and volcanic activity around the rim of the Pacific.

Dr Holden said quakes like the Raoul Island one were relatively common for the area - a 7.6 tremor was recorded in April near the Solomon Islands.