Geologists have located where the magnitude 7.1 earthquake on Saturday began.
Dr Mark Quigley of Canterbury University says an area of the fault plain in rural Canterbury ruptured and caused the quake.
He told Morning Report on Sunday that one side of the earth had basically lurched to the right, about 3.5 metres, breaking roads apart and snapping at least two houses in half.
Dr Quigley said no-one knew the fault was there before the quake occurred at a depth of 10km at 4.35am on Saturday, as there had been no physical sign on the surface.
He said that means it's either a new fault, or at least, the first time a quake has punched through to the surface.
He said faults like this provide an additional hazard that perhaps need to be considered more carefully in the future.
Dr Quigley said aftershocks in Christchurch may continue for months.