Christchurch was rattled by further aftershocks on Tuesday.
Centred within 5 km of Christchurch, the 4.0 quake at 9.13am was felt strongly in the central business district.
It was followed by a 3.1 quake at 11:36 am.
In all, three aftershocks occurred before midday Tuesday that were strong enough to register on the GeoNet website. Four occured on Monday.
Last week GNS Science said Canterbury residents should prepare for a sizeable aftershock about every four to six weeks.
The main quake was of magnitude 7.1 at 4.35am on 4 September 2010.
