WorldWide Drilling Resource

25 WorldWide Drilling Resource ® MARCH 2015 Scientific Drilling into the Alpine Fault Begins Adapted from Information by GNS Science An international team of scientists have started drilling a borehole over 4250 feet into theAlpine Fault in New Zealand’s South Island to learn more about the nature of the fault and the earthquakes it produces. The project will enable scientists to install monitoring equipment deep inside the fault to record small earthquakes and measure temperature, pressure, and chemical conditions close to where earth- quakes are generated. Other major faults around the world have been drilled the same way; however, it has always been after a big earthquake. This is the first time a major fault has been drilled before it ruptures. The team of up to 100 scientists and engineers will be working in shifts around the clock while drilling and sampling are underway. The project is being jointly led by GNS Science, Victoria University of Wellington, and the University of Otago, and involves scientists from other New Zealand organizations and from the United States, United Kingdom, Germany, Canada, France, Italy, Japan, Australia, China, and Taiwan. “We really don’t know what we will find once we get deep into the fault zone. No one has ever drilled this deep into a major New Zealand fault,” said project coleader Rupert Sutherland of GNS Science. “Similar projects overseas have shown that a huge amount of information can be extracted from samples retrieved from the heart of the fault zone.” Hopes are, the study and ongoing monitoring of conditions within the fault zone will ultimately lead to a better under- standing of how faults slip and generate seismic waves during large earthquakes. Another project coleader, Virginia Toy of the University of Otago, said it was always a challenge to get the fragile rock samples to the surface, but this project is doing everything possible to ensure good rates of sample retrieval from the bore- hole. “Rock and fluid samples from inside the fault will be shared among the science team with some analyzed in New Zealand and the rest sent to more than a dozen overseas laboratories for analysis,” Dr. Toy stated. TheAlpine Fault, which is visible from space, extends for over 400 miles, and is similar in character to the San Andreas Fault in the U.S. and the North Anatolian Fault in Turkey. It is among the more active plate boundary faults in the world Photo of the drill site near Whataroa Valley by Nicolas Barth. and one of the most scientifically-appeal- ing faults to study because of its size, fast rate of movement, and accessibility. Earthquakes of around magnitude 8.0 occur on the fault about every 200- 400 years, with the average gap between large earthquakes being about 330 years. The last rupture was 297 years ago in 1717; scientists estimate it has a 28% possibility of rupturing in the next 50 years. In 2011, scientists drilled two bore- holes into the fault to about 500 feet at Gaunt Creek. One of the main findings of the 2011 project was the existence of a finely-ground impermeable layer of rock in the center of the fault zone, holding back large amounts of fluid on the upper east side of the fault. The Alpine Fault appears to save up all its energy for one big eruption every few hundred years. In between the big ruptures, it seems to stay locked and produce mostly minor earthquakes, but what controls this timing behavior isn’t clear. The knowledge gained from this project would benefit earthquake sci- ence globally and enable New Zealand to better prepare for a future large earth- quake on the Alpine Fault.