Sky Tower can take big jolts

Photo / Brett Phibbs

As buildings crumble and fall in Christchurch after Saturday's 7.1-magnitude earthquake and aftershocks, the question has to be asked - how would Auckland fare in such an event?

In particular, how would our most famous corporate landmark, the Sky Tower, come through?

The answer is - rather well.

Analysis shows that an earthquake measuring 7 on the Richter scale and centred 40km away would leave the Sky Tower practically undamaged.

An 8-magnitude earthquake, which is more than 30 times greater than a 7-magnitude quake in terms of energy released, might damage the tower but not cause it to collapse.

However, a shake of magnitude 9 - the size of the one that hit the Indian Ocean region on December 26, 2004, setting off the Boxing Day tsunami - would almost certainly bring down the Sky Tower.

Weather events are more likely to threaten the tower.

The Sky Tower has been closed more than once during storms, but this was for visitor comfort, rather than for any safety issues.

In November 2006, the tower began to sway noticeably as winds gusted up to 150km/h. In fact, the visitors would have been perfectly safe inside, as the Sky Tower was built to withstand winds of up to 210km/h, when side-to-side movement at the top of the concrete shaft could be up to 1m.

This occurrence is expected about once every 1000 years.

Other older, well-known buildings in Auckland would be likely to withstand an earthquake of the size that struck Christchurch, with only moderate or little damage, said Dr Charles Clifton, associate professor of civil engineering at Auckland University.

Another factor that protects Auckland is the distance between the city and the nearest fault line.

The plate boundary closest to the city is south of the Taupo volcanic area, which would have the effect of limiting any damage.

There are very few faults under the city that are known to be historically active, so a period of 30,000-50,000 years before we get a big shake would not be unreasonable.

STAND OR FALL

How the Sky Tower is likely to be affected by an earthquake

* 7.1 magnitude: no damage
* 8.0 magnitude: some damage
* 9.0 magnitude: likely collapse