The much smaller February 22 Christchurch aftershock was so disastrous, not just because of its vertical acceleration, but its location under Christchurch and its timing on a week-day lunchtime. The same sensitivity could apply to Wellington. We also know now that structural damage is only part of the story.
The February Christchurch earthquake showed that soil liquefaction can also cause land damage that is highly problematic for buildings and underground infrastructure. Given that most private insurance does not cover this, it presents major problems for rebuild. This is further exacerbated by land-slips. Both liquefaction in valleys and reclaimed land, and slips on higher ground could cause major economic complications in Wellington.