Quaking in our boots: How prepared is Dunedin?

The Christchurch earthquake has raised the obvious question of whether Dunedin is likely to be similarly struck, and how prepared the city is to cope. Mark Price and Kim Dungey report.

If earthquakes were as regular as clockwork, then a "big one" of magnitude 8 affecting Otago is 43 years overdue.

The South Island's major fault line, the "Alpine Fault", which is responsible for the Southern Alps, last moved in a big way about 1717, 293 years ago.

But, the geological record shows four major earthquakes there over the past 1000 years - or one every 250 years on average.

University of Otago geophysicist Dr Andrew Gorman does not believe it is scaremongering to suggest we are overdue for a big one.

• City stands ready

"There is a 50% chance over the next 50 years that there will be a magnitude 8 earthquake on the alpine fault.

"Using statistics, that's sort of the best answer we can give."

He says the gaps between quakes on the alpine fault have varied between 400 years and 112 years.

"So, it's not a precise clock that's ticking.

"But certainly the longer that gap is, the more likely there is going to be one."

And, although all the many fault lines of the South Island are interlinked, Dr Gorman does not expect the Canterbury earthquake has reduced the odds.

"It's certainly reducing the pressure but it basically comes down to statistics, and statistics can bite you sometimes.

"You can end up having another one that's really close in time and it could be just bad luck.

"The other thing that's been found, just looking at earthquakes in other parts of the world, is that sometimes earthquakes will happen in clusters.

"So you will get one earthquake that will happen and then another one will happen that's related to it - maybe not even in the same location.