The strong aftershicks and secondary quakes go on for months after the main quake occurs. We're seeing this in Japan, and in New Zealand, and it was the case in the other earthquakes in the past decade, such as the Great Tsunami earthquake at Christmas 2004, and the earthquake a few years ago that generated deadly tsunami in Samoa, Chile, and China.
The Japanese have been luckier than the folks in Christchurch, that is for sure. The city centre and neighborhoods that haves shown to be quite unstable are not going to be rebuilt, those areas are being bought out and turned into greenbelts/ That's a smart move.