Built to shake: how Aotearoa designs for earthquakes

Aotearoa sits on the boundary between two giant tectonic plates, the Pacific Plate and the Australian Plate. They grind past each other, and every year thousands of earthquakes shake the country. Most are too small to feel. Some are big enough to damage buildings, roads and bridges. So New Zealand engineers have had to become experts in one tricky question: how do you build something that survives being shaken?

Stiff or flexible?

A very stiff building can crack when the ground moves suddenly. A building that is too floppy can sway so far it falls. Good earthquake design finds the middle: strong enough to carry its weight, flexible enough to move a little, and able to soak up the shaking's energy.

A Kiwi invention in the tearoom

In the 1970s, scientist Bill Robinson was working at a government research lab near Wellington. He had an idea: a bearing made of layers of rubber and steel with a plug of lead in the middle. The rubber lets the building slide sideways. The steel layers keep it strong. The soft lead core squashes and turns some of the earthquake's energy into heat. He invented the lead rubber bearing in 1974.

Te Papa on 152 bearings

Te Papa, the national museum in Wellington, sits on 152 of these base isolators. The whole building rests on them like a tray on rollers, with a gap around the base so it has room to move. In the 2016 Kaikōura earthquake, the building slid gently while its taonga stayed safe inside. Today these bearings protect buildings and bridges in Japan, the United States and many other countries.

Other ways to beat the shake

Your turn

On a home-made shake table, you can test a tower with and without your own base isolation. Film it in slow motion. Where does it bend most? That is where a real engineer would add strength.