![]() ![]() She’s part of an international team that arrived days after the quake to help out. Above him, PhD student Alex Hatem from the University of Southern California locates the site using a super-accurate GPS reading. Russ Van Dissen from GNS investigates a chasm opened by the rupture on the Kekerengu Fault. Marlborough is scrunched in the middle-and its complex network of faults carries the plate-boundary movement from the Alps through to Cook Strait at around three centimetres per year. The Australian Plate dives beneath the Pacific Plate off Fiordland, collides with and crunches past it through the Alpine Fault, then rides over the Pacific Plate off the North Island’s east coast, forcing it down into the molten mantle. This country is crumpled by the shoving, straining might of two great sections of the Earth’s outer shell: these islands are the result of their meeting. The poet was thinking of gold, but the answer could equally be plate tectonics, the great unifying theory of geological science that rose to prominence a decade after Glover published his poem sequence about the old prospector. “What unknown affinity / Lies between mountain and sea / In country crumpled like an unmade bed,” asked Denis Glover in his 1953 poem Arawata Bill. Now, though, it is split clean down the middle by a scar of tortured soil, the far side ripped sideways along the hill, the two halves nine metres apart. Though they had filled in their survey trench, a faint rectangular outline remained in the grassy paddock. “Our study found it was a very active fault by New Zealand standards-but we couldn’t have told you it was going to move in a few months’ time!” Van Dissen says. Less than a year after Van Dissen and Little dug across where they thought the fault would be, the Kekerengu came to life-one of at least nine faults ignited in the magnitude 7.8 Kaikōura Earthquake on November 14. The results confirmed their suspicions-the Kekerengu Fault had a very fast slip rate, and had ruptured three times in the past 1200 years… Make that four. They use both radiocarbon and ‘optically stimulated luminescence’ techniques, which can detect how long ago a mineral particle last saw sunlight. In February, the geologists sent the samples taken from the trench for dating. “Globally speaking, that’s huge,” he says. Parts of the Kekerengu slipped by as much as 12 metres. “This is a fast-moving fault that makes earthquakes quite frequently, every 300 years or so,” says Van Dissen. The land shifted both sideways and vertically each side of the rupture, the changing topography forming a brand new wetland that’s already attracting waterbirds. This formerly flat, straight railway line illustrates the massive displacement caused when the Kekerengu Fault split to the sea. New Zealand’s historical record is short-we’ve had only a handful of really large earthquakes since records began in the 1800s-so figuring out their patterns relies on this kind of ‘palaeo-seismic’ research. ![]() They have both spent their professional lives trying to understand a handful of connected faults that score Marlborough and North Canterbury’s farms and river valleys to infer from faint echoes left in the landscape what happens when they detonate in sudden movement. Though Van Dissen works for GNS Science and Little for Victoria University, they’ve been best friends since they met while making a similar trench on the Awatere Fault two decades ago, sharing a taste for beer and music around the campfire at the end of a day’s work (Van Dissen on guitar, Little on harmonica). ![]() They cut down through the earth in a series of steps, taking soil samples from the walls, until they were four metres below the surface in a muddy hole at the heart of the fault. Their team spent several weeks in the field, tracing the fault’s story into the past. Last summer, earthquake geologists Russ Van Dissen and Tim Little dug a 15-metre-long trench across a paddock on North Canterbury’s Kekerengu Fault, hoping to answer a question that had long eluded scientists: how often did it rupture, and how far did it slide when it did? They suspected it was one of the fastest-moving faults in the country, and new dating techniques gave them a chance to find out for sure. “Instead of it being Russian roulette, you can wear a helmet.” “To be able to predict an earthquake you’d need to know a whole lot more than we do now about how these processes work.” So is anywhere in New Zealand safe? Not really, he says, but there are things everyone can do to prepare. Could we have seen it coming? Science is still a long way from being able to forecast earthquakes, says GNS earthquake geologist Russ Van Dissen. Roads and hillsides subsided without warning in those few minutes in the middle of the night. Written by Kate Evans Photographed by Rob Suisted ![]()
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