Scientists digging into new part of South Island's Alpine Fault
JOANNE CARROLL
Last updated 13:34, January 24 2016
Scientists drill into the Alpine Fault in 2014 as part of ongoing research to learn more about how the fault might act in the future.
Geologists will dig two trenches across the Alpine Fault to study how it has ruptured in the past and what kind of earthquake might happen in the future.
Five geologists will arrive in Springs Junction, near the Lewis Pass on the West Coast, on Monday and spend a week exploring the fault to find out exactly how big the last three or four earthquakes were and when they happened.
Project leader Dr Rob Langridge, of GNS Science, said they hoped to identify and date the last few ruptures on the fault.
The Alpine Fault runs across the South Island.
"This will provide a pointer to the size and style of earthquake that can be expected in the future."
The 20 metre-long and 2m-deep trenches at Springs Junction, next to the Maruia River, would allow geologists to take photos and make detailed drawings of the layers.
They would also collect organic material for radiocarbon dating.
Langridge expected the last three or four earthquakes triggered by the fault would have happened within the last 1200 years.
The geologists hoped to get a clearer picture of the earthquake potential of the northern part of the Alpine Fault, he said.
"The southern and central portions of the fault have been reasonably well studied over the past decade, and now we are including the northern section as the knowledge of its rupture history is fairly sketchy."
Previous studies found the old river terraces at Springs Junction had moved 11m horizontally and about 2m vertically as a result of earthquakes.
Langridge said the trench studies would reveal how many earthquakes produced the movement.
The northern end of the Alpine Fault moved about 10 millimetres a year, compared to 28mm further south in Westland.
Langridge said the fault featured at least three distinct sections, each with different characteristics.
North of Hokitika, it splintered into several large faults that ran northeast to southwest through Marlborough.
Aerial images obtained late last year revealed the Alpine Fault was several hundred metres away from where the fault had appeared on maps, Langridge said.
"[These] images have helped to revolutionise the study of active faults."
The trenches would be filled in and the land returned to its previous state when the investigation was finished.
The project had the approval of the Department of Conservation, which owned the land, and was funded by the Natural Hazard Research Platform.
The study's findings were expected to be published in 2017.
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