‘Catastrophic’ earthquake predicted

Press, 27 September 1985, Page 4

‘Catastrophic’ earthquake predicted

The South island’s Alpine Fault has the potential to move soon and cause an earthquake that could have catastrophic results, according to the leader of the Geological Survey’s earth deformation section, Mr Kelvin Berryman.

“The fault will move again, there is no doubt about it. We cannot say precisely when but I would not be surprised if it moved within the next 100 years or so. In geological terms, that is very soon.” Mr Berryman said that damages caused by the earthquake would be widespread in the South Island when the fault moved. “Cities as far away as Christchurch and Nelson are likely to be severely affected as will many places on the West Coast.” Future fault movement could not be avoided, but it could be planned for so as to minimise damage, he said. About 200 km of the Alpine Fault's length could break in one movement, said Mr Berryman. At present the area along the fault from Haast to Hokitika had

few earthquakes and so this could be where the fault moved next.

The Alpine Fault marks the boundary between two of the huge mobile plates which make up the Earth’s crust. Off Fiordland, the Australian Plate is forcing its way beneath the Pacific Plate.

Stresses caused by this collision had made not only the Alpine Fault but the Southern Alps which were still growing at the rate of 10mm to 20mm a year in some parts, said Mr Berryman.

It is a long time since the Alpine Fault last moved. Although it is one of the most active faults in the world, it has not moved for at least 300 years.

Rocks in the fault zone have been taking the strain by stretching and bending. “But like a taut rubber band, sooner or later these rocks will reach the end of their strength.” Mr Berryman said that just before a big earthquake on the Alpine Fault the number of small earthquakes was likely to increase markedly.