GNS seismologist Dr Jason Ristau says today's earthquakes are some of the biggest to hit New Zealand in a long time.
Dr Ristau says, "There's two earthquakes which kind of totalled a magnitude of 7.5 of earthquakes and if we head around south to nearer Kaikoura is what we call a reverse faulting earthquake so we've got one side of the ground going up relative to the other and then to the north nearer towards Seddon where there are strike slips faulting, so kind of faults that go past one another like that and this is some of the biggest earthquakes that we've had in New Zealand in quite a long time."
Not long after midnight a magnitude 7.5 earthquake struck North Canterbury, near Hanmer Springs, causing extensive damage to areas in the South Island and many aftershocks have been felt since the quake.
He says, "One thing to be aware of, of course is the ongoing aftershock sequence we've had geo significant aftershocks really that have been at least magnitude 6 and there's the possibility of even more large aftershocks happening and an even lower probability but still a reasonable probability that this could trigger another larger magnitude 7 sizer earthquake. It's highly unlikely but still possible."
Dr Ristau describes the events as being the result of the Australian and Pacific tectonic plates crashing together.
"It's a result of New Zealand sitting on top of these tectonic plates the Australian plate to the west and the Pacific plate to the east and as these plates crash together and slide past one another it creates all these faults. So this earthquake is a result of these two plates colliding so it looks like we have the one fault which is an onshore one and what's actually going on off-shore we're not really too sure yet because this becomes a lot more difficult. We can't actually see anything."