Another aftershock in Canterbury

11:06 am on 20 January 2011

Another strong aftershock occurred in Canterbury on Thursday morning.

The quake measured 5.1 on the Richter scale at 6.03am. It was centred 10km southwest of Christchurch. It was 10km deep.

GNS Science says there have been about 700 reports of people feeling the quake, including from far away as Greymouth and Dunedin.

It was followed by an aftershock measuring magnitude 3.2 at 6.28am.

Three smaller quakes occurred between 8m and 8.15am: magnitude 3.4 at 8.02am, magnitude 4.0 at 8.06am and magnitude 3.2 at 8.14am.

Christchurch City Council says there are no obvious signs of damage to infrastructure, such as waste water equipment. Police have reported no incidents.

Orion says power supply has not been affected. Chief executive Roger Sutton says back-up equipment kicked in and no homes should be without power.

The shock was larger than any of the aftershocks which hit the city on Boxing Day, when at least 16 aftershocks were recorded from 2am onwards.

The strongest was magnitude 4.9 at 10.30am, at a depth of 12km.

The main quake was magnitude 7.1 at 4.35am on 4 September. The epicentre was 40 km west of Christchurch at a depth of 10km.

GNS Science says Canterbury residents should prepare for a sizeable aftershock about every four to six weeks.

Seismologist John Ristau told Summer Report that it's likely aftershocks of this strength will continue for up to a year.