Christchurch Volcanic Eruption Looms

Aftershocks Aftershocks have generally been occurring at the expected rate following a main shock of this size.[23] GNS Science has not ruled out an aftershock as large as magnitude 6 but suspect that the largest aftershock (a 5.6 magnitude quake 20 minutes after the main one) has already happened.[24][25][26]

As of 20 January 2011 (2011 -01-20)

Important Topic Updates
, over 4400 aftershocks of magnitude 2 or more have been recorded, including three of 5.4 magnitude,[27] and some have caused further damage to buildings in the central business district, and been felt as far away as Dunedin.[28][29][30][31]

On 8 September 2010, there was a large 5.1 magnitude aftershock with an epicentre just 7 km from the city centre.[32]

On 19 October 2010 a magnitude 5.0 aftershock with a depth of just 9 km which caused surface shaking reported at the time to be the worst since the original earthquake.

On 26 December 2010, a swarm of more than 32 shallow aftershocks,[27] many centred directly under the city,[33] occurred throughout the day beginning with a 4.2 jolt at 2:07am. The largest of these, with a magnitude of 4.9, at a depth of 12 km below Opawa[34] was felt very strongly and caused further damage to at least 20 buildings, the closure of the central city,[35] and cut power to more than 40,000 for some time.[36]

On 20 January 2011 a magnitude 5.1 aftershock with a depth of 10 kilometres (6.2 mi) struck at 6:03am, waking many residents. The shock caused some minor damage and was felt as far away as the West Coast and Oamaru