"We need to live somewhere. But some of the older houses, where people built very close to the slope edge or very close to the slope bottom, those kind of areas aren't particularly great.
"When you look at what happened for the Kaikoura earthquake, and the Port Hills in Christchurch.
"Those at the very bottom of slopes or cliff edges, the houses were cracked, and then at the cliff bottoms people's homes were impacted by debris falling into the homes."
GNS is one year into a three-year project to investigate slope stability in Wellington, and develop strategies for dealing with unstable parts.
Massey is the project leader.
He said the problems caused by this year's wet winter showed how bad it could be in an earthquake.
"Especially if we had a big earthquake after a period of prolonged wet weather, like now. Because the slopes are falling down without any earthquake right now, just after bits of rain.
"We haven't had any large earthquakes in Wellington since 1855.
"Earthquakes like Kaikoura only triggered relatively low levels of shaking in Wellington. Not like the levels of shaking you would expect from a Wellington fault earthquake."
Massey said the slips which blocked arterial routes through the Ngauranga Gorge and Ngaio Gorge showed steep, man-made slopes were particularly vulnerable.
"They were cut in the 1940s and 50s, and there's been several periods of road widening."
The slip on Ngaio Gorge Rd in July. Photo / GNS Science
Wellington City Council spokesperson Richard MacLean said the slips this winter had left them with a hefty bill.
"I think it's time we started conceding that yes, it's been a wet winter, and it's probably the worst in the past 10 years.
"It's just been very, very wet, relentless rain, and it's come frequently enough. And it's taken its toll on steep slopes.
"It's probably heading north of a million dollars [in clean-up costs] now, because the Ngaio Gorge slip especially required a heck of a lot of effort, machinery and man hours.
"There's probably still more work to go into the Ngaio Gorge area, stabilising the bluff and things like that."
MacLean said they expected the final cost to be in the low millions.
That only applies to Wellington City itself, with other local councils taking care of wet weather damage in places such as Hutt City.
MacLean said Wellington drivers should be cautious particularly if they were driving at night, as a lot of the ground was still soggy and could slip again.
The GNS project on Wellington slope stability is investigating how different hillsides perform in earthquakes or heavy rain.
It's particularly focused on slopes that have been changed by urban development, and how construction methods have an impact.
The first borehole has just been drilled to 53m near St Gerard's Monastery, with seismometers to be placed at the top and bottom of the hole to measure differences in shaking during earthquakes.
A statement from GNS said the borehole was one of several sites that would be investigated.
"The scale of the problem and the level of risk to critical infrastructure and nationally significant infrastructure are not well known.
"By drilling at these sites, scientists are not suggesting that they are unstable and likely to fall down.
"The project will select a range of sites that are characteristic of those typically found in Wellington to investigate how these slopes might perform in future large rain events and strong ground shaking.
"GNS Science and Aurecon will use the findings from this project to fine tune engineering practice to help reduce the incidence of slope failure in urban areas."
Wellington City Council, Wellington Water, and the NZ Transport Agency are expected to use the results of the GNS research.
