New Zealand's economy could take a $16.7 billion hit following a large earthquake on the Wellington Fault, new research shows.

Wellington's commuter rail network would be out of action for almost three years following a major earthquake, even after a proposed $100 million upgrade.

A Wellington Lifelines report estimated it would take two years and nine months for the region's passenger network to be fully restored should a 7.5-magnitude earthquake occur on the Wellington Fault.

And that's after a proposed $100m upgrade of structures and slopes along the North Island Main Trunk (NIMT), Hutt Valley and Wairarapa lines to improve the network's resilience.

The upgrade was recommended as part of the $5.3 billion Wellington Lifelines Regional Resilience Project, aimed at reducing the impact of a major earthquake on New Zealand's economy.

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ROSA WOODS/STUFF Wellington's rail passenger network would be affected for almost three years should a 7.5-magnitude earthquake occur on the Wellington Fault. (File photo)

It estimated the region's passenger network would not be fully restored for up to 3½ years should things remain as they are, and for two years and nine months should the upgrade happen.

Entrances to the Rimutaka Tunnel would be heavily affected, and there was no timeframe on when the Rimutaka Hill Rd on State Highway 2 would be able to reopen to motorists.

KiwiRail chief operating officer for capital projects and asset development David Gordon said the timeframes used in the Lifelines Group report were high-level estimates, and averaged out across the region.

Some lines could be affected more than others depending on the nature of the earthquake, he said.



ROSA WOODS/STUFF The network would not return to full service for two years and nine months, even after a proposed $100m upgrade, according to the report. (File photo)

"For example, if the Wellington fault ruptures all the way up the Hutt Valley, then we would expect it would take longer for the railway to be repaired on the Hutt line than on the Kāpiti line.



"Similar to recovery of the railway line after the [2016] Kaikōura earthquake, and depending on the damage and reinstatement works required, we would expect that rail services will be reintroduced in stages."

That meant a small number of diesel-fuelled trains could resume first, with more added as railway lines were gradually repaired.

Electric-powered trains would probably resume in stages as sections of the overhead power network were restored.



ILLYA MCLELLAN/STUFF The report recommended a $100m upgrade along the Wairarapa line (pictured), the Hutt Valley line and the North Island Main Truck (NIMT) line. (File photo)

Gordon expected the Rimutaka Tunnel would hold up well in a major earthquake, and that anyone in there at the time would be easily able to get out.



"Although there may be slippages on the steep hillsides leading up to the tunnels, we would not expect them to completely block the tunnel.



"An escape route would be available either on foot or by light vehicle, even if the tunnel was impassable to trains."

KiwiRail, which is a Lifelines Group member, was also looking at options to improve shipping emergency response times as part of an ongoing ferry and terminal replacement, Gordon said.

It was also looking at terminal and wharf options that would enable transport links to be quickly re-established.

MONIQUE FORD/STUFF Transport Minister Phil Twyford announced a $193m upgrade for the region's rail network last year. (File photo)

Transport Minister Phil Twyford announced last year the government would pump $193m into the region's rail network to upgrade ageing tracks and infrastructure and increase safety.

Gordon said some of that money could be used for the proposed resilience work, but most of it was intended for protection against weather events rather than earthquakes.

THE LONG WALK HOME

Wellington City-based commuters are being invited to take part in Wellington's annual long-distance walking event, The Long Walk Home, on Friday.

The walk was organised to acknowledge that if a large earthquake struck Wellington on a weekday, many of the city's 80,000 daily commuters would probably be forced to walk home.

The 30-kilometre walk, organised by Rotary Clubs of the Hutt Valley and Wellington Region Emergency Management Office (Wremo), will take place between 1pm and 7pm. It will start at Westpac Stadium and end at County Lane in Silverstream.