Christchurch's 'miracle' earthquake explained

Christchurch earthquake damage. Photo / NZPA

The magnitude 7.1 earthquake turned some buildings into rubble, sent brick chimneys through house roofs and knocked homes off their foundations - but no-one died.

Why? We asked four leaders their views.

University of Canterbury lecturer in active tectonics Mark Quigley said the Christchurch earthquake was similar to the one that hit Haiti in January. The reason why 230,000 people died in Haiti and none in Christchurch is a "feat of engineering".

"It's got nothing to do with the earthquake. The earthquake was big, and close, and shallow," Mr Quigley said.

He said while many Canterbury buildings were retro-fitted to survive earthquakes, Haiti buildings were not.

Police Commissioner Howard Broad also praised town planners and engineers.

"There are several generations of engineers, planners and inspectors who have built a city capable of withstanding an earthquake on this scale.

"They are to be commended, as are those who have kept working through the recent days despite themselves facing difficult circumstances."

Christchurch mayor Bob Parker also praised the engineers and the building code.

"Modern buildings in Christchurch and New Zealand have the building code and building standards behind them for a country that is subject to a number of potentially violent natural interventions - either wind and storms, or indeed earthquakes," Mr Parker said.

He said New Zealand learned lessons after the 7.8 Napier earthquake in 1931 which wiped out large parts of the city and killed 256 people.

"Secondly, many of the older masonry buildings that failed... were built pre 1930s but they also tended to be studios, or small businesses, and in a number of cases were dairies and they're not buildings that tend to be occupied in the early hours of the morning," Mr Parker said.

He said brick walls tended to fall on to the street and the city was lucky that the quake did not happen when people were out shopping on those streets.

St John Ambulance regional operation manager Chris Haines also put the low casualty rate down to the a time of day when most Cantabrians were tucked up in bed.

"When we look around the damage, the most affected area was the central business area and also the central commercial area of Riccarton but there was no one in those buildings which was really fortunate," Mr Haines said.

He said if the quake had happened in the middle of the day than there would have been "significant casualties".