NZ’s fault with a ‘maverick streak’

The closest active geological fault to Dunedin behaves strangely and may have a ‘‘maverick streak’’, Otago researchers say.

Assessing the potential earthquake hazard from the Akatore fault is hard to define and a worry when it comes to the risk to Dunedin residents and coastal Otago.

Researchers from the University of Otago’s Department of Geology and GNS Science, led by Professor Mark Stirling, studied the recent geological history and movements of the fault, which could extend as much as 60 kilometres south of Dunedin towards the Clutha River mouth.

They have found the Akatore fault may have a maverick streak, behaving strangely during the past 125,000 years or so.

A large-magnitude quake along the fault could rupture the ground by three metres vertically and ground-shaking could reach destructive intensities.

Akatore runs south of the Taieri Plains and offshore from Taieri Mouth. Seismologists think a 1974 Dunedin quake was caused by a rupture along a fault, or faults, par- allel and Fault.

Studies indicate the fault last ruptured in the recent geological past, between 1000 and 1200 years ago.

Stirling, student Briar TaylorSilva, and senior GNS scientist Dr Nicola Litchfield found signs of three significant earthquakes on the Akatore fault in the past 12,000 years, following a long quiet spell possibly stretching back about 125,000 years.

Taylor-Silva three recent close to the Akatore estimated quakes the had magnitudes of between 6.8 and 7.4, each quake rupturing the ground by up to two metres vertically.

‘‘More work is required to answer this [risk] question. However, I think we need to treat the Akatore fault as a serious hazard.

‘‘The episodic nature of the fault just makes it more difficult to estimate future earthquake hazards.

‘‘With faults that have periodic ruptures, we can estimate how often an earthquake may be likely to occur - say, every x years - but we can’t do that for the Akatore fault very well.

‘‘It’s quite worrying for assessing the hazard the fault poses because we can’t say there won’t be another earthquake in the near future, as we don’t really understand its behaviour,’’ she said.

The fault runs for about 20km onshore between Taieri Mouth and Toko Mouth and possibly more than 40km offshore north and south. Its precise length is not known. Taylor-Silva said fieldwork included digging a trench across the fault at Big Creek, east of Milton near the Akatore forest.

A second trench was dug across a stream near Toko Mouth.

Organic material from the trenches, the remnants of deposits in earthquakes, was carbon dated.

The first major Akatore quakes was sometime between 12,100 years ago and 1280 years ago.

‘‘We have been trying to understand whether the fault has slipped enough during those three events or whether we should expect more earthquakes in the immediate future,’’ Taylor-Silva said.

Lumsden book sale

A combined book sale, run by three Lumsden churches, will be held this weekend. Co-organiser Eric Swift said donated books were being sorted this week. ‘‘Books are arriving in great quantities at Lumsden Anglican Church.’’ The sale will run today from 4pm-8pm, tomorrow from 10am until 4pm and Sunday from 10am until noon at the Lumsden Memorial Hall. Proceeds would go towards a range of causes including the Southland Hospital Chaplaincy, Northern Southland Community Resource Centre Charitable Trust.

Koi boys coming

They were a hit sensation on The Voice Australia and now The Koi Boys are heading to Invercargill. Danny Faifai, Kevin Keepa and Ngahere Ngatai, will headline at the New World Cancer Society Gala Ball, to be staged at the Ascot Park Hotel on June 17. Organising committee member Lindsay Moffatt said they were thrilled to secure entertainers. ‘‘This really is quite a coup for little old Invercargill.’’ Since its inception in 2011, the biannual gala ball has raised more than $100,000 for the Southland Cancer Society.

Motorcyclist hurt

A motorcyclist has serious leg injuries after a crash with a car in Invercargill on Durham St, Waikiwi, about 7.15am yesterday. A police spokeswoman said the motorcyclist suffered serious leg injuries. A St John spokesman said a female in her 60s was taken to Southland Hospital with moderate injuries.

Assault in Gore

Southland police are seeking a man in relation to an incident where three people assaulted a man in Gore on Wednesday night. A police communications spokeswoman said an assault took place on Broughton St after 11.30pm. ‘‘Four people arrived at a Gore address and demanded a man a person come out of a house.’’ Two people were in police custody and police were seeking to arrest another man, she said. A male and female were expected to appear in Invercargill District Court yesterday facing charges of wounding with intent to cause grievous bodily harm.