Deformation of New Zealand

Reasonably steady deformation - squashing, stretching, rotation and twisting - is occurring in the plate boundary zone all the time, even during the time periods between major earthquakes.


These deformations, which amount to less than 1 millimetre per kilometre each year, are very small. But over tens or hundreds of years, and over distances of tens or hundreds of kilometres, they build up to amplitudes of many metres. It is generally when the deformation has built up to large levels that the rocks of the Earth's crust can't stand the strain any more, and the rocks break as earthquakes along geological faults.

View New Zealand’s deformation

Velocity model (Deformation map)

The New Zealand Velocity Model (or Deformation Map) shows the motion as if the Australian plate is stationary. It is the motion that would be seen by a giant standing on the Australian plate and looking down on New Zealand.

Each arrow in the model represents the velocity at which that point on the ground is moving. It shows how far the point moves relative to the Australian plate in 1 year. Points near Auckland move hardly at all. Points near Christchurch move southwest at about 40 millimetres each year.

NZ Deformation Map Movie


This Deformation Map Movie shows a picture of how New Zealand would change over the next 4 million years if it continued to deform in exactly the same way it has been deforming over the past 8 to 10 years.

The movie contains the same information as the velocity model.

Some of the important features that show up in the movie are:

  • Extension across the Taupo Volcanic Zone
  • Strong contraction (or squashing) in the lower North Island and northern South Island
  • Strong shearing (or sideways sliding) motion along the Southern Alps

Remember, this movie is only a way of visualising the deformation that has actually occurred over the past 8 to 10 years.

It is not a prediction of the future because:

(1) we have ignored the effect of future earthquakes - these will change the details of deformation within the country though they will not change the overall picture;

(2) we have ignored the role of erosion and sedimentation - in reality shorelines will be eroded away by the sea in some places, while in other places rocks eroded from the mountains will be washed out to the coast to form new land.

Strain-Rate Maps

Strain-rate maps are derived from the velocity model, but show more directly how much stretching, squashing and shearing is taking place in different parts of the country.

Instead of showing the velocity itself, the strain-rate maps show the difference in velocity from place to place. Where the velocity changes slowly from place to place (as in Northland or the south-eastern South Island) there is little deformation occurring. Where the velocity changes rapidly from place to place (as across the Southern Alps or the Taupo Volcanic Zone) there is a lot of deformation occurring.

Shear strain map


Maximum shear strain map shows the rate at which shearing or sideways deformation is taking place. The red areas are those that are undergoing the most shear strain. The units on the scale bar are ppm/yr or parts per million per year.

A shear strain of 1 ppm/yr means that if a perfect square with sides of length 1 km were drawn on the ground, then


after 1 year the square would be slightly distorted into a diamond shape, as shown in the (exaggerated) diagram.

The region with highest shear strain rate is the Southern Alps along the west coast of the South Island. But the high shear strains continue south into Fiordland and north through Marlborough, the southern North Island, and the Taupo Volcanic region.

Areal strain map


The areal strain map shows the rate at which the ground surface is expanding or contracting. The areas that are expanding are red, while those that are contracting are blue. An areal strain of 1 ppm/yr means that over a one year period the 1 km square will expand by half-a-millimetre in each direction.

The areal strain rates are smaller than the shear strain rates, and show a less clear pattern. There is expansion in the Taupo Volcanic region, and contraction in the southern North Island and north-western South Island. There are also bands of contraction running along the east coasts of both islands. The small region of expansion near East Cape (in the far north-east) may be associated with non-uniform rates of subduction of the Pacific plate beneath New Zealand.

Uncertainty Map


This map indicates the uncertainty in the first two maps. Where this map is dark, the first two maps have precise estimates of strain rate; where the map is lighter the estimates of strain rate are less precise.

One use of these maps is to assist in estimating future earthquake hazards. In general, regions with higher shearing rates are more likely to experience earthquakes in the future. However, there are many other aspects to be considered in earthquake hazard modelling and the maps shown here only tell part of the story. Find out more about earthquake hazard modelling.