Scientists seek quake trigger secrets from New Zealand fault hole

An international team of scientists hope to find out the precise trigger for a major earthquake by studying a borehole almost a kilometer deep on the west of New Zealand's South Island.

Researchers from Britain, Canada and Germany have joined local counterparts to build an image of the Alpine Fault through an 893-meter deep borehole.

Information obtained from the three-week project would be used to study the fault's geometry and structure below the valley, and help in determining where future scientific drill holes could be sited.

The drill hole, which was completed in January 2015, was thought to end 200 meters to 300 meters short of the actual fault interface, where the Australian and Pacific tectonic plates meet, team leader Associate Professor John Townend, of Victoria University of Wellington, said in a statement Friday.

For the past year, equipment installed inside the borehole has been measuring temperature and earthquake activity and scientists in many countries had been analysing data and samples collected during the drilling phase of the project.

The Alpine Fault produced large earthquakes about every 330 years, and last broke in 1717, Townend said.

"The seismic survey we're doing this month is part of a much larger project addressing the temperatures, pressures, and stresses in the core of the Alpine Fault as it is being primed for the next big earthquake," he said.

"As time goes by, the Alpine Fault is being loaded by motion between the Australian and Pacific tectonic plates. What we're trying to do is understand the processes that eventually break the camel's back and cause the fault to slip and the conditions under which that happens."

The site in the Whataroa Valley was recognized internationally as a key site for studying earthquake processes, and the study was part of the Deep Fault Drilling Project involving 120 scientists and technicians from more than a dozen countries.

A key finding from the drilling in 2014 was that the rocks beneath Whataroa Valley were very hot, increasing in temperature by about 140 degrees Celsius for every kilometer in depth.

Scientists involved in the project were working to understand the implications this had for temperature-controlled processes occurring in the earthquake generation zone deep inside the fault.

The plan was to build a two dimensional seismic image, similar to a medical X-ray or a CAT scan, of the valley sub-surface to a depth of about 1.5 km to get a clear picture of the Alpine Fault at depth.

To do this, the scientists would generate artificial seismic waves at known points on the surface and record them using a wide range of sensors.

The large amount of data produced during the project would be pooled so that all the participants are able to work collaboratively on different aspects of the subsurface image. Endit