1. Social
August 13, 2014updated 16 Jul 2021 10:36am

Some engineers simulated an earthquake by blowing up a New Zealand suburb

By Barbara Speed

Last October, Martin Howman, a 70-year-old resident of Avondale, New Zealand, pressed a button, and detonated 400kg of gelignite under his neighbours’ homes.

The area had, thankfully, been abandoned months before: Howman was not some kind of crazed, anti-suburban psychopath. In fact, he was helping the New Zealand Earthquake Commission with a research project. In an interview with NextCity, the Commission’s boss Hugh Cowan described the trials as the “largest and most sophisticated of their kind ever undertaken”.

Two and half years earlier, in February 2011, the city of Christchurch was hit by an earthquake. It measured 6.3 on the Richter scale; 185 people died. After the quake, several of the city’s neighbourhoods, Avondale among them, were largely abandoned. Some residents left because their homes had collapsed. Others, though, left because of a side effect, which had caused flooding and left foundations impossibly damaged.

The phenomenon is called “soil liquefaction”. The land beneath Christchurch has a hard upper layer, with softer materials underneath. But the earthquake had loosened that lower layer, making it more fluid; the pressure exerted by the ground above then caused sludge to ooze its way to the top.

An analogy is probably useful here. Imagine what would happen if you dropped a piece of chocolate onto the surface of some yoghurt. Now imagine that chocolate is your driveway.

Soil liquefaction can have some pretty nasty effects. Here’s what it did to another New Zealand suburb. Those grey patches are the water and silt which has been forced to the surface.

Content from our partners
The key role of heat network integration in creating one of London’s most sustainable buildings
The role of green bonds in financing the urban energy transition
The need to grow London's EV infrastructure at speed and scale

Image: New Zealand Defence Force on Flickr, re-used under creative commons.

This effect was making it hard, if not impossible, for parts of Christchurch to recover from the disaster. So researchers at the New Zealand Earthquake Commission came up with a way of strengthening the affected land: by inserting concrete columns into the earth, they’d make the softer layer more rigid.

But before putting the plan into action, they needed to test it. So, they chose Avondale as the site of a new, manmade earthquake. By then, most of the area’s residents had given up shovelling silt from their land and left, leaving Martin Howman as the only man left on his street. That’s why, after inserting concrete columns and planting explosives beneath the earth, the Commission gave him the honour of blowing up his own neighbourhood.

An Avondale road after the 2011 earthquake. Image: Martin Luff at Flickr, reused under creative commons.

Pre-detonation, cameras were set up in and around the nearby houses; during the explosions, they recorded film of falling furniture and slates sliding off roofs. Footage from above, published on a local news site, shows the ground rippling. But the houses themselves seemed to be stable; and after the tremor, liquefaction was less intense.

So the research team now believe they may have found a way to limit the damage of this process: that could help to convince insurers and construction companies that it’s time to start rebuilding.  Similar methods could even be used to pre-empt earthquake damage.

Liquefaction is a problem in many places prone to earthquakes. Seattle, Vancouver, parts of Chile, and other places on the Pacific Rim have all been victims; Urayasu, a city in Japan, was almost entirely taken over by sludge after a quake in 2011. So Martin Howman and the NZ earthquake commission may have started a chain reaction that could help earthquake victims all over the world.

For now, though, Howman has moved away from Avondale to live near his family – that was probably enough excitement for one year.

This article is from the CityMetric archive: some formatting and images may not be present.
Topics in this article :
Websites in our network