What is liquefaction and why is it so dangerous to buildings and their inhabitants?

During an earthquake, as most people may recall from grade school, sometimes a strange phenomenon occurs in sandy soils known as liquefaction. And it is exactly what it sounds like — the ground that is made up of solid particles (sand) suddenly behaves like a liquid.

Liquid is a poor support for a building’s foundation, so when the ground begin behaving as if it were a liquid, bad things happen. Science Alert posted a neat article with lots of great videos involving liquefaction.

The video below is a great way of demonstrating the physics behind liquefaction in a typical earthquake:

As the article explains:

The phenomenon occurs because of how loose and dense soils respond to sudden and repeated amounts of pressure – dense soils tend to expand and dilate, while loose soils tend to compress.

That compression might sound like a good thing if you want solid ground to strand on, but if the soil contains a lot of water, that liquid starts to move into the gaps that form between the soil grains – called pore spaces.

This causes the soil particles to lose contact with each other, significantly decreasing the overall strength of the ground, while at the same time, the water is responding to the increased pressure by trying to move up towards the surface.

When liquefaction occurs below the foundation of a building, the ground becomes destabilized and the entire building or portions of it may topple or even collapse.


Image of New Zealand earthquake 3D simulation courtesy Youtube