Alpine fault quake likely to block off lifelines to West Coast

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An earthquake on the alpine fault is likely to close all the Southern Alp road and rail passes, possibly for months, blocking critical lifelines to the West Coast, a researcher says.

Dr Tom Robinson, a geological sciences researcher from University of Canterbury, studied the impact of an alpine fault quake for his doctoral thesis.

He said recovery from such a quake would need to focus on rapidly rebuilding the road and rail links to sustain the South Island economy.

"This will primarily require restoration of the Arthur's, Lewis and Haast Passes as well as the railway line," he said.

"Given the extent of landsliding anticipated, it is estimated that Lewis Pass will require at least six weeks to fully restore, while Arthur's Pass, the rail line and Haast Pass could need more than six months."

Dr Robinson said the alpine fault was one of the largest earthquake hazards facing New Zealand.

Quakes on the fault would be expected to create widespread landslides throughout the Southern Alps.

"The State Highway network is particularly exposed, with Lewis Pass, Arthur's Pass, and SH6 between Hokitika and Wanaka all anticipated to be blocked by multiple large landslides," he said.

"A route between Nelson and Hokitika via Inangahua, Reefton and Greymouth is identified as having limited exposure to landsliding, and is therefore considered the most critical link in the network.

"If bridges and other structures along this route can withstand the strong ground shaking they are exposed to, direct access to 30,000 people who would otherwise be completely isolated, will be possible."

Dr Robinson's study recommends reinforcing the section of road, and using Nelson and Blenheim as primary staging posts for a disaster response to the West Coast.

"This will allow Christchurch and Dunedin, which are not expected to be badly affected, to be used as staging posts to focus response on badly-affected inland areas of Canterbury and Otago."

He said planning for the expected impact of earthquakes can allow better emergency responses and long-term recovery plans.

Dr Robinson's PhD thesis was supervised by hazard research experts Professor Tim Davies and Dr Tom Wilson.