Alpine Fault drilling project put on hold
SARAH-JANE O'CONNOR
TOUGH TASK: A frustrated team faced one problem after another while drilling into the Alpine Fault.
A project set to drill 1.3 kilometres into the Alpine Fault has been called off 400 metres shy of its goal.
Since September, an international team of scientists has been based on the West Coast drilling into the Alpine Fault - the on-land boundary between the Pacific and Australian tectonic plates.
With up to 100 scientists and engineers working in shifts around the clock, they aimed to complete the project by Christmas. The fault was expected to be intersected at about 1000m deep by mid-November.
But the fault has been reluctant to give up its secrets and the project has ground to a halt just shy of 900m, tantalisingly close to the fault itself.
First, the glacial sediment around Whataroa, north of Franz Josef, proved slow to drill through. Then once they hit schist bedrock, technical issues plagued the drilling.
Calamity first struck just before Labour Weekend when the 7.4 tonne "bottom hole assembly" from the drill fell into the borehole. Intricate fishing work allowed it to be pulled out, only for a similar mishap to occur days after drilling resumed.
In early December, the team was drilling at a rate of nearly 3m an hour and the nature of the rock being drilled through indicated they were closing in on the fault.
At 893m deep the team started preparing the borehole for coring - to allow close inspection of the material surrounding the fault.
That was when a third calamity struck - a 25 tonne steel tube, along with 40 tonnes of cement, dropped into the borehole.
Shortly before Christmas, the team called it a day.
They will not continue drilling in the same borehole but instead will regroup for another shot at the project at a later date.
The deep fault drilling project has a budget of $4 million, including funding from the Royal Society of New Zealand's Marsden Fund, the International Continental Scientific Drilling Programme and the lead scientists' institutes: GNS Science, Victoria University and the University of Otago.
Their drill site at Whataroa was selected because beneath it the fault dips at a 45-degree angle. That allowed the team to drill straight down with the intention of intersecting the fault about 1km down.
After that they would have drilled another 300m into the Australian tectonic plate.
The Alpine Fault produces earthquakes of about magnitude 8.0 every 200 to 400 years. In between it appears to stay "locked" and the scientists hope to find out more about the mechanics of this behaviour.
Installing seismometers around the fault itself would allow them to measure the temperatures, pressures and stresses - perhaps even at the time of an earthquake.
In time, those instruments might provide something once thought impossible, Victoria University's Professor Rewi Newnham wrote in The Press last month - "an early-warning system that detects precursory signals before a big earthquake or the seismic waves produced as rupture gets underway."
Scientists estimate the Alpine Fault has a 28 per cent probability of rupturing in the next 50 years.
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