New Zealand fault hole revealing secrets of earth's crust

An international team of scientists drilling a 1.3-km deep hole into the Alpine Fault in New Zealand's South Island say they are already gaining valuable insights into the earth's crust less than a quarter of the way down.

The New Zealand-led team had drilled 240 metres, already the deepest borehole ever attempted in the fault, through gravel-laden sediments north of the Franz Josef Glacier and hit schist bedrock, according to a joint statement issued Monday.

"We have discovered that temperatures increase quite rapidly with depth, which tells us a lot about how fluids that once fell on the Southern Alps as rain circulate and warm up next to the Alpine Fault," project co-leader Virginia Toy of the University of Otago, said in the statement.

"These measurements are important scientific findings in their own right and also allow us to predict what we will encounter as we drill deeper."

The borehole would provide the scientific data required to improve understanding of the largest seismic hazard in the South Island, another project co-leader, John Townend of Victoria University, said in the statement, according to Xinhua.

"It's also very important to the international scientific community in terms of understanding how large faults work mechanically, which is why so many scientists from around the world are working with us to extract maximum information from the borehole," he said.

The Alpine Fault, the on-land boundary between the Pacific and Australian tectonic plates, moved about 27 metres horizontally every 1,000 years, in three or four separate large ruptures.

Scientists had evidence that it had ruptured 24 times in the past 8,000 years at an average interval of 330 years, although individual intervals ranged from 140 to 500 years.

The fault last ruptured 297 years ago in 1717 and scientists estimated it had a 28 percent probability of rupturing in the next 50 years, which was high by global standards.

By comparing rocks retrieved by drilling with the rocks on the surface, the research team hoped to discover how the earth's crust deformed during earthquakes, and learn about chemical and physical changes occurring at various depths inside the fault zone.

Other major faults around the world had been drilled in this way after a big earthquake, but this was the first time a major fault had been drilled before it ruptured.

Scientists and engineers from New Zealand, the US, Britain, Germany, Canada, France, Italy, Japan, Australia and China are working on the project.