Don't stop now, says Brownlee

PAUL GORMAN

Last updated 05:00 24/06/2011

The threat of more large earthquakes cannot be allowed to stymie the recovery process, Earthquake Recovery Minister Gerry Brownlee says.

Scientific advice given to the Government was that Canterbury was only part-way through a major seismic event and there was no way of knowing how long that would last. Christchurch and the broader region could not sit paralysed until it was certain it was all over, he said.

Including the magnitude-7.1 quake that started it all on September 4, there have now been 28 quakes of more than magnitude 5.0.

Brownlee said any future major aftershocks could have more impact on the newly designated orange residential zone than on the red or green zones.

Further assessment was needed before decisions could be made on whether homes and land in the orange zone became part of the red or green zones. Some land had suffered new damage in the big aftershocks on June 13.

About 9000 properties in the Christchurch City Council area and about 1500 in the Waimakariri District are in the orange zone.

Brownlee said it was unclear "where we are at now as far as this [quake] event goes".

"We got advice on September 4 that over the next 12 months you could expect residual shaking of the ground to continue before it peters out. Now they are saying it is a seismic process, with a lot of seismic activity in a lot of different places," he said. "But from our perspective, we were able to comfortably conclude these [zones]. You have all those areas that are now orange. Most of those, I suspect, will turn green.

"What gives us comfort around the green zone is there are vast acreages of land there where properties may have suffered shaking damage but not land damage at any stage."

At yesterday's announcement, Tonkin & Taylor geotechnical specialist Nick Rogers said the February 22 quake had caused huge problems for the land investigations.

"It wasn't one step forward and one step back; it was more like one step forward and 10 steps back."

He outlined the engineering research on which the Government based its decisions.

Surveying of benchmarks by Land Information New Zealand after the September quake showed Christchurch had rotated clockwise, a motion pronounced in the western half of the city.

After the February quake, the benchmarks showed the city had moved southeast, with large vertical movement, some parts dropping down and other parts rising.