A big quake could leave Wellington cut off from the rest of the North Island for four months, new disaster predictions show.
It could take 40 days to restore the capital's water supply to even a basic level, while road access could take up to 120 days, according to "worst case" predictions presented to the region's Civil Defence Emergency Management Group.
That could leave Wellington residents or trapped commuters unable to leave the city for months, and dependent on water rations being distributed by authorities for about six weeks.
The predictions relate to a quake of magnitude 7.5 or worse, and come as people throughout the region were shaken by a magnitude 7 earthquake off the Taranaki coast on Tuesday night.
The long, rolling quake, at 230 kilometres deep, was felt throughout the lower North Island and upper South Island, and rail services had to be suspended while tracks were inspected for damage.
The new timeframes for recovery are revealed in a report presented to the emergency management group last week.
It looks at how long it will take to restore "lifeline" services – road access, water and power.
Wellington's hilly topography means it will take longer to restore services to a "survival level" than it did in a flatter city such as Christchurch, it says. Water would be restored more quickly in Petone and the Hutt Valley.
For water, survival level is defined as a limited supply that still required boiling. Before that, it would have to be distributed from reservoirs and storage sites – probably rationed to 20 litres a person a day – and there would be no road access or power.
Services such as water are generally buried, and are likely to be restored only as each leak or break in the network is identified.
After the Christchurch quake in February last year, it took about two weeks to restore water to about 85 per cent of homes, but "boil water" notices remained in place until April.
Survival level road access is defined as one lane with speed restrictions. The Manawatu Gorge slip, which closed the state highway for months, shows how long large slips can take to clear, the report says.
The timeframes are "indicative only and not definitive", it says, and regional emergency management group co-ordinator Bruce Pepperell stressed they were for the "worst case scenario".
But understanding how long it could take to restore services meant strategies to speed up those processes could be devised, he said.
"You need to look at that in a lot more depth.
"We can put in place some plans to overcome some of this."
Access was an important difference between Wellington and Christchurch.
There were 30 routes in and out of Christchurch compared to Wellington's two, which were both regularly affected by slips.
The timelines highlighted the importance of people being prepared and having good systems in place – as was emphasised by Tuesday night's quake, he said.
"While it was a really significant shake, it was deep, so it didn't have the same twist in the tail that we sometimes get.
"It is a timely reminder that we do live on the Shaky Isles – so to speak – and we need to be prepared."
Civil Defence Emergency Management Group chairwoman and Kapiti Coast Mayor Jenny Rowan said the "single most important message" from the report's findings was for people to prepare themselves.
Those who lived in outer areas of the region and travelled to central Wellington for work could be cut off for a long time. "You could be in a situation where you're needing to look after yourself ... you could be trapped in that city with no way of getting out other than by foot."
The water timeframe also emphasised the need for people to have good stocks of stored water, she said.
The timeframes, developed with input from utility providers, would be enhanced.
- © Fairfax NZ News
Why are fewer teens learning to drive?Related story: Teen non-drivers lazy 'narcissists'