The Christchurch situation (highly varied pockets of riverine silt interpsersed with gravel bars and peat) was very well known by the early 1990's: see for example this paper, where the uncomfortable conclusion was reached that (final para of Summary) "the draft code may underestimate shaking by a factor of 2 or more".
This makes the Bexley, Atlantis (yes, Virginia, one of the worst-affected streets was named just that...) etc. subdivisions all the more unexplicable.
An early (Waitaha) name for the area was 'Waima-iri-iri' - the place of many waters, and the early Black Maps show watercourses throughout the central city that later turned out to be areas of particular vulnerability.
Both the Regional and City Councils have never really acknowledged their compiicity in waving through much of the newer Red Zone subdivisions.....given the by then well-understood geotechnical vulnerabilities.
Hugh P lays the blame on the 1989 swathe of amalgamations, which wiped out much intimate local knowledge, diverted attention to organisation-building instead of community safeguarding, and introduced a quasi-corporate ethos which glorified 'growth'. The attendant surge in rates, staffing, empires, and organisational layers is something which has come to bite the current Council, which faces a $1.2 billion shortfall in funding, against a rates income of around the $370-450 million mark, and with its head up against a debt-funding ceiling.
Hindsight is always 20/20, but the sad conclusion is that the whole shebang lacked the back-bone, the balls, and the brains to have done something to mitigate the known hazards.
The one shining exception was the electrical-supply organisation, which promptly reinforced every single one of its substations, resulting in minimal damage to that infrastructure compared to (say) the three-waters administered by the Clueless Council.
So in the light of the above, one must ask, would things be much different now, even with a shiny new RMA???