Ground Deformation

Deformation in the boundary zone between tectonic plates is the fundamental cause of earthquakes in New Zealand.

How do we know what deformation is taking place?

New Zealand ground deformation vectors.

New Zealand ground deformation vectors.

New Zealand is being squeezed and deformed within the Australian-Pacific plate boundary zone.

Up to the mid 1980s, scientists had analysed many repeated survey measurements taken over the previous 100 years. This gave an average picture of the ground deformation over the last century.

New technology has revolutionized surveying and geophysics. Global positioning system (GPS) equipment measures where and by how much the Earth’s crust is undergoing slow deformation. With high quality GPS receivers it is possible to measure the distance between two points 40 kilometres apart with an accuracy of 1-2 millimetres.

We now have quite a detailed picture of the average deformation that has occurred in New Zealand over the last 8 to 10 years. Many readings need to be taken at the same place in order to determine in which direction the ground is moving.

Continuous GPS is used to give near real-time data that can show abrupt deformation of the crust caused by individual earthquakes, as well as slow continuous movements.