Major utilities may be as prepared as can be for Alpine Fault quake, but expect extensive damage

Friday, 23 April 2021

The massive Alpine Fault is due for another big earthquake and scientists have been drawing up a scenario of what the devastation would look like. (First published May 2018)

Some major roads could be put out of action for months when there is a major earthquake on the Alpine Fault, the NZ Transport Agency (NZTA) says.

But phone and power companies appear hopeful of a fast recovery.

Scientists led by Victoria University last week dramatically upped their estimate of the fault rupturing within the next 47 years, now estimating the chances at 75 per cent rather than 30 per cent.

There is a very high chance the next rupture would generate at least a magnitude 8 earthquake, the researchers forecast.

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The Treasury has not done any estimates specifically of the likely cost of an Alpine Fault earthquake, but the new research is expected to trigger new economic studies.

Pete Connors, NZTA's system manager for the West Coast and Canterbury, said it met regularly with South Island councils and emergency responders through a group known as AF8 to prepare for quake of that size on the fault.

“Exact predictions of the effects of an Alpine Fault earthquake on transport networks are difficult to make, given there are so many potential variables,” he said.

“One fault can trigger other faults, and new faults can be uncovered, as was the case for Kaikōura.”

Bailey bridges can be a quick option to restore access if road bridges are damaged, but the Transport Agency warns hazards that would flow from an Alpine Fault quake are not to be underestimated.

But State Highway 6 between Haast and Westport and SH73 running through Arthur’s Pass were the two highways likely to be severely affected after a rupture, he said.

Roads could be impassable for months at a time, he said.

There has been speculation SH6 might prove impossible to salvage.

The agency believed SH7, though Lewis Pass, would be reopened faster than the Arthur’s Pass route and that might be a priority after the next quake “to reconnect lifelines to the West Coast and Buller”.

.A union-backed report says the country’s three majority state-owned power firms have engaged in asset-stripping.

The agency stored parts in Christchurch to assemble “bailey bridges” that could potentially be used as temporary crossings.

Bailey bridges were developed by the British Army during World War II.

The hazards that would be posed by rockfalls, major slips, and river and creek bed avulsion were “not to be underestimated” with the potential for rivers to dam up and change direction, Connors said.

“Bridges, which tend to be at narrow river and creek crossing points, are particularly vulnerable in this scenario.”

Meridian Energy said a 10-year study undertaken by engineering company URS and GNS had given it confidence its hydro schemes could withstand extreme seismic events without an “uncontrolled release of water”.

But it expected electricity generation would be reduced as it fixed any damage.

Transpower manager Geoff Wishart said it designed key equipment on the national grid for an extreme, “one in 2500 year” event, and had reviewed the likely impact of an Alpine Fault quake.

“Naturally there will be some localised impacts, like lines straddling faults, that might need repair.

“But generally transmission lines can be repaired in a reasonable time,” he said.

“We understand that the major South Island generation stations would be to similar design standards as ours, and provided they’re up and available we envisage the main South Island grid could be up and going reasonably quickly,” he said.

Vodafone infrastructure director Tony Baird said it would do everything possible to continue coverage for customers if a natural disaster struck.

“We have a number of back-ups in place, such as fibre routes running down both sides of the country, and two undersea cables between the North and South islands, plus both fixed-line and mobile networks to provide different access types, with satellite technology in extreme circumstances.”

Telecommunications firms had a track record of working well together after disasters, he said.

“We reciprocally share our networks when needed. For instance during the Kaikōura earthquake, Spark and Chorus utilised the Vodafone Kaikōura fibre after other fibres were severed into the town.”

The West Coast had “unique infrastructure challenges”, but a new Chorus fibre line that was being built would greatly improve connections to that part of New Zealand, he said.

Spark spokeswoman Althea Lovell said it was not currently planning specifically for the increased risk of the Alpine Fault generating a major quake, but it built its networks to be resilient.

“Although we can't plan for every single scenario, risks such as earthquakes and their impacts on our infrastructure are evaluated regularly,” she said.