The Alpine Fault, which runs much of the length of New Zealand's South Island, has moved more in the last 25 million years than any other onland fault in the world, New Zealand scientists said Tuesday.
Their study showed that over this time the two sides of the South Island had shifted relative to each other by more than 700 kilometers along the Alpine Fault, dramatically changing the understanding of New Zealand's tectonic movements.
"It was widely accepted that the Alpine Fault had shifted 450 km over time, based on the offset of distinctive rocks either side of the fault. But according to evidence found in the nature of the ocean floor, we knew the shift should be much larger," Associate Professor Simon Lamb, of Victoria University, said in a statement.
It had been thought the answer might lie in the shape of the belts of rock that run across New Zealand, starting south of the southern city of Dunedin and curving up to the Alpine Fault, but nobody had been able to prove it.
"By simply looking at it another way, at geological maps of New Zealand together with studies of the direction of magnetization in the rocks, we discovered that the missing displacement was actually on the Alpine Fault itself," said Lamb.
At the time New Zealand was part of Antarctica and the prehistoric continent of Gondwana.
"I don't think anybody in their wildest dreams would have thought that displacements on the fault could be so large, and also change direction so dramatically through time," said Lamb.
"It's a great demonstration of the power of plate tectonics as it offers answers to a bigger puzzle about what happened in Antarctica over 65 million years ago, on the other side of an ocean from New Zealand and when dinosaurs roamed."
The Alpine Fault, the on-land boundary between the Pacific and Australian tectonic plates, moved about 27 meters horizontally every 1,000 years.
It last ruptured in 1717 and scientists estimate it has a 28 percent probability of rupturing in the next 50 years, which is high by global standards.
