New earthquake fault off New Zealand coast

New Zealand new earthquake fault ‘similar to Alpine’ fault

An Otago geologist's draft manuscript suggests there's a tectonic fault system off the South Island's east coast potentially comparable in size to the Alpine Fault.

Stuff,

2 August, 2013

University of Otago geologist Phil Ford has privately written a draft proposal, as yet unpublished, detailing the possibility of the major South Island intra-plate fault, with possible seismic and tsunami hazard implications.

His draft uses previous research that identified beach deposits on the coast east of Milton as potential evidence of tsunami relating to the Akatore fault, or another, hitherto unidentified, offshore system.

Proposing to name it as the Indiania Fault System (IFS), he says it appears to run for most of the offshore length of the South Island, similar in size to the Alpine Fault.

Using New Zealand Institute of Water and Atmospheric Research bathymetric charts, some portions of a fault parallel with the coast were apparent, the paper says.

"It is immediately apparent that portions of the suggested system must be covered by South Island river run-off sediment, at least in places, just as the active and earthquake-related fault in the Christchurch area is covered in gravels and other... sediments onshore."

East of Canterbury and Otago the seafloor feature runs south off southeast Southland and down towards northwest of the Auckland Islands.

"A strike length of greater than 1000km is clear, more than comparable with the Alpine Fault at about 800km south-southwest of the South Island.

"Both the southern IFS elements and southern Alpine Fault offshore continuations are clear and readily visible on seafloor bathymetry displays."

He said the potential of that suggested system warranted immediate research and if shown to be an active fault system then the scale must be "very significant" given a potential overall length of 1600km.

"If the proposed system is accepted by the New Zealand geological fraternity then early notice of serious tsunami vulnerability needs to be passed to governing authorities and civil defence organisations."

GNS Science engineering geologist David Barrell said he was not aware of the proposal but scientists recognised a system of faults off the southeast coast.

The faults, many apparently inactive or remnants of geological activity from the formation of New Zealand, were parallel to the coast and associated with, for example, the Great South Basin or the Waipounamu fault zone.

"It's a fault system that has a history that starts back not long after New Zealand parted company from Australia and Antarctica more than 100 million years ago.

"It's got more of the appearance of a fossil fault rather than anything we would regard as major relating to the present tectonic setting of New Zealand."

Unpublished manuscripts needed peer review and publication in a reputable journal before being accepted as official, he said.

University of Otago geophysicist Dr Andrew Gorman said he would want much more data before making such an assertion and there were other theories.

"I still think the major worry in Otago and Southland is the Alpine Fault itself, and also from the sorts of smaller faults through the South Island."