Why Aotearoa shakes: plates, liquefaction and tsunami

People sometimes call New Zealand the Shaky Isles. GeoNet, the team that watches our ground, records thousands of earthquakes every year. Most are too small to feel, but a few are big enough to change the land for ever.

Two plates meeting

The Earth's outer shell is broken into huge pieces called plates, which move a few centimetres a year, about as fast as your fingernails grow. Aotearoa sits right on the boundary between the Pacific Plate and the Australian Plate.

When the ground turns to liquid

In some places the ground is loose sand with water between the grains. Strong shaking pushes the grains apart, and for a short time the ground behaves like a thick liquid. This is liquefaction. Heavy things sink, pipes break, and grey silt bubbles up through cracks. It happened across the eastern suburbs of Christchurch in 2010 and 2011.

Waves from the sea floor

A big earthquake under the sea can lift the sea floor and push up a series of waves called a tsunami. Near the coast, the rule is simple: if an earthquake is long (more than a minute) or strong (hard to stand up), get gone. Move to high ground or inland straight away. Do not wait for an official warning.

Rūaumoko and GeoNet

In Māori tradition, Rūaumoko is the atua of earthquakes and volcanoes, the child of Papatūānuku still moving within her. Today scientists also use hundreds of instruments across the country to measure shaking, and they share the data freely online. Nobody can predict the day an earthquake will happen, but they can say how likely one is, so we can get ready.