Developers built on land that could turn into murky soup after an earthquake, despite legal opposition from the local council, says the Mayor of Christchurch.

Bob Parker said that for the past 30 years his council had insisted that Land Information reports record if homes were built on sandy soil deposits and subject to liquefaction.

Whole streets in Christchurch had been built on sandy soil deposits.

Shortly before Saturday's magnitude 7.1 quake, rains caused the soil to take in large amounts of water.

The soil was then turned to mush when the ground began to shake - a process known as liquefaction.

"With the benefit of hindsight, you would probably have to say that the nature of the foundations were not designed to cope in the end with the type of earthquake that we had," said Mr Parker.

"There are areas where council has indicated that it did not want residential development to go ahead.

"In a number of cases this has resulted in court cases and on some occasions the council has lost those court cases."

The mayor said there had also been some older areas of Christchurch which had suffered liquefaction damage but were developed long before the phenomenon was known about.

"But it is interesting to note that the new Deans Stand built in AMI Stadium was built on a liquefaction zone," Mr Parker said.

"There is not an iota of damage, settling, or shifting that has occurred in that massive structure. And the reason is that the foundations have been designed to cope with the ground situation."

Building was possible in liquefaction areas but the appropriate type of foundation was needed, he said.

Building requirements have been changed by the council as a result of the quake.

The council has pushed through an urgent change requiring earthquake-damaged buildings undergoing repairs to meet a higher standard of structural safety.

In an extraordinary meeting yesterday, the council resolved to adopt a policy whereby earthquake-prone buildings would have to aim for a goal of 67 per cent of building code levels rather than the existing 33 per cent.

The new standard would bring older buildings up from about 10 per cent of the strength of a brand new building to about 50 per cent.

"What we are trying to do is make sure buildings don't fall on people," said Christchurch City councillor Sue Wells.

"What we have learned through the last little while is that buildings which are strengthened to 33 per cent of the [building] code will not provide the security that we are needing."

Mayor Parker said the city had a "duty of care" to the people and the council had to react to the quake.