How has the earthquake warped New Zealand?

Scientists are trawling through data collected by hundreds of GPS markers scattered across the country to see how New Zealand has shifted following the latest quake.

GNS Science regularly draws data from around 900 marker sites across the country, with 150 markers also streaming GPS locations to GeoNet monitors.

GNS geodetic scientist Dr Sigrun Hreinsdottir expected to see widespread deformation across the country, ranging from millimetres to several metres of displacement.

One of the most dramatic readings had come in from a GPS station at Cape Campbell - more than 200km away from the epicentre at Culverden but near where many of the large aftershocks hit - showing that the site had shifted 2m.

Hreinsdottir said this could be expected in large quakes: in other events she'd looked at, land had shifted 3 or 4m.

"We are looking at the data currently, but we are expecting to see deformation over whole of New Zealand, from millimetres to metres," she said.

"As soon as we get the new data in, we'll re-measure our sites."

Because of the complex nature of what was happening to the Earth's crust, the observed displacement didn't move in any one direction.

Previous surveys had shown the country was moving by 4cm a year but, rather than shifting as a whole, tectonic forces were deforming the land surface - stretching, slimming and sliding it southward.

While the Bay of Plenty had been stretching apart by around 4cm each year, Wellington was being squeezed together by a similar amount.

Different regions were moving at different rates and in different directions - in some places this movement was increasing the stress in the earth's crust, while in other places it is releasing stress.

Scientists had been able to use the GPS data to simulate the country's distortion over a four-million-year period without allowing for earthquake impacts.

It projected much of the South Island and the lower North Island slimming into a skinnier tract of land, while the North Island rotates around and both islands grow closer together.