Over The Horizon

Strained Relations between Australia and New Zealand?

New Zealand and Australia are much closer than most people realise. The two countries actually rub up against each other in the South Island, but apart from some friction, not much else is known about this close contact. Geologists from Otago University are hoping to find out more about this.

The boundary between the Australian and Pacific tectonic plates crosses the South Island. These plates grind in opposite directions at the rate of 40mm a year, colliding along the Alpine Fault running up the western side of the island. A project led by Professor Richard Norris is finding out how important the faultline is, what effect this grinding has on the line, and whether it produces great earthquakes.

"Clearly some of the plate motion is spread across the island. This continuous movement may be accumulated as elastic strain within the Earth's crust and released during earthquakes of various sizes," Norris says.

The result is the growth of the Southern Alps and the development of many geological faults. Knowing how this affects the South Island is vital for correctly assessing and preparing for earthquakes. It is important also for properly understanding the origins of land forms in the South Island.

"On an international scale, the Southern Alps are a superb natural laboratory in which to study the processes of crustal deformation."

The project has discovered at least three big ground ruptures which occurred around Haast in the past 1,000 years. These and other investigations have led to a better understanding of the faultline and seismic behaviour. The northern part of the fault around Hokitika might behave differently from the section south of Haast, Norris says.

All this has implications for regional councils and Civil Defence authorities in the South Island. Norris and his researchers have given presentations and workshops to those authorities that will help them plan for the after-effects of quakes.