Our shaky isles

Today will bring fresh disclosures of the extent of the damage to Christchurch and its surrounding towns and villages following Saturday's earthquake.

It is certain to be more substantial than early examination has shown, certain to require much prioritising of repairs which will take months to complete, and certain to cost more than preliminary estimates.

No earthquake in our developed history may have caused more damage on a more widespread scale to a larger urban area: Christchurch is our second largest city, sprawling not far short of the 40km distant from Cathedral Square to the earthquake's epicentre at Darfield.

The catastrophe in Hawkes Bay in 1931 was the most destructive of life, killing 256 people, and the most destructive, at 7.9 on the Richter scale, largely destroying Napier and Hastings.

Saturday's event, at 7.1 on the scale, miraculously seems to have caused no loss of life but very severely damaged at least 500 buildings and wrecked much underground infrastructure.

That there was no loss of life is truly something at which to marvel. Fortunately, most people were in their beds when the earthquake occurred, at 4.36am.

The Hawkes Bay event occurred at 10.47am on a Tuesday, when people were about their normal daily business; it lasted for an extremely damaging two and a-half minutes and was centred just 15km from Napier.

Though comparable in terms of damage and strength, the Christchurch earthquake appears to have had several unusual features.

Christchurch has not had a popular reputation for severe earthquakes, being some distance from the New Zealand Alpine Fault and lying on an alluvial plain.

Although scientists have long been mapping active faults under the plain and in the foothills, this earthquake appears to have occurred along an unknown fault line, and may have been a close combination of several movements.

It will certainly belie any complacency in the country that some regions are less prone to such events than others.

In this regard, much praise is due to the Civil Defence and emergency services in Christchurch, which appear to have functioned with skill and good organisation from the moment the emergency began.