The biggest aftershock from the magnitude-7.1 Canterbury earthquake has probably already happened, the Institute of Geological and Nuclear Sciences says.
A 4.4 aftershock was recorded near Christchurch shortly after midnight on Sunday - the first to hit the region since Saturday night.
GNS Science senior seismologist Warwick Smith told Morning Report that a 5.6 aftershock about 20 minutes after the main earthquake on 4 September is likely to have been the main aftershock.
He says he cannot rule out the possibility of an aftershock of about magnitude 6.0, but that is now looking less likely.
