Drilling into New Zealand s Most Dangerous Fault |Discovery Geology

The Alpine Fault is the largest source of seismic hazard, earthquake hazard, in the South Island. We think that the Alpine Fault fails in magnitude 8 earthquakes approximately every 330 years. The last event occurred, we think, in 1717 AD, so around about 300 years ago. So we're pretty sure that the Alpine Fault is at the end of what we would call its seismic cycle. So it's due to have another earthquake. We have a detailed record of Alpine Fault earthquakes during the last 8,000 years. If you do the statistics on the Alpine Fault earthquakes, the record of earthquakes, the probability of an Alpine Fault earthquake occurring in the next 50 years is about 28%. So that's a very high probability by global standards. Earthquakes happen when movement occurs on a geological fault. And scientists are trying to understand how that rupture occurs. Scientific drilling projects have investigated faults which have recently ruptured in earthquakes, in California near Parkfield, in Fenshuan in China, after the Kobe earthquake in Japan, and after the Chi-Chi earthquake in Taiwan, for example. They provided us with some fantastic insights into the state of the geological fault that recently ruptured. So the international science community has this question. What does a fault look like before an earthquake? That's where our project comes in. The Alpine Fault is probably the best example worldwide of a fault that we know could fail in a magnitude 8 earthquake and hasn't in the last 300 years. So the Alpine Fault, it runs the entire length of South Island. And it runs all the way up through Nelson Lakes and merges with a complex set of faults in Marlborough. And on one side of the fault, there's some big mountains, the Southern Alps, because one side of the fault is being pushed up. And on the other side, you've got the coastal plain of Westland. If we were to go and look deep into the Earth, we would see that the Alpine Fault is not a vertical fault. It's quite steeply dipping in some places, but in the central Alps, it dips at about 45 degrees. We can trace that fault in the central South Island down to about 30 kilometres depth. So we can trace it through the brittle part of the crust, the uppermost 8 to 10 kilometres, where earthquakes happen, and into the ductile regime, where we can see its geophysical signature, but its only real signs of life are small amounts of tremor that you can record on seismometers. There are a range of different things that we need to know. We need to know what will happen in an Alpine Fault earthquake. And that's going to inform us. That's going to help us to plan. It's going to help us to build the right buildings, and it's going to help us to build infrastructure, or at least predict what will happen to infrastructure, like roads, bridges, etc. We also would like to know if the probability of an Alpine Fault rupture varies from day to day. And at the moment, we don't know, but it's possible that we will be able to make forecasts in the future. And finally, if an Alpine Fault earthquake happens, it's such a large event, it may go for hundreds of kilometres, that we may actually be able to make a warning system, and give people a few tens of seconds, maybe a minute of warning, which would be potentially very, very useful if you were, say, driving a fast vehicle, or you were controlling a power station. So we aim to drill to about just over one kilometre's depth, and collect samples from the fault. So the materials will help us to understand what the fault is made of. They will go off to laboratories and be analysed. But we'll also put instruments down the borehole to make observations in place, geophysical observations, to measure its physical properties in place, and to measure the ambient conditions within the crust. And then finally, we will install equipment within the borehole, an observatory, a fault zone observatory, that will monitor natural phenomena that are going on, and help us to understand the types of phenomena that go on around that fault, and may, in the future, may, one day, be the basis for a forecasting or a warning system.