Liquefaction

Liquefaction

"When sediments liquefy, they lose their structure and strength. During earthquake shaking, the individual grains of sand within a deposit collapse on each other. Anything built on them can sink or collapse. Picture a container of balls of slightly different sizes–baseballs, golfballs, marbles. If they were transported by water into the container and then deposited, they would settle with spaces between them. Some of the spaces would be filled with water, some with air. When you shake the container, the balls settle against each other, and the water and air are forced to the surface. That is exactly what happens in a sediment-filled valley. The valley is a large ‘container’ holding gazillions of ‘balls’ or grains of sand. Shaking the container simulates an earthquake" (Science Views).

Source: Science Views

This video shows how and why houses get damaged or collapse during an earthquake in a seemingly stable geologic environment.
The following observations were made:

• The water works its way to the surface, flooding the area around the houses,
• The "houses" start leaning over and sinking into the sand, and
• The volume of the sand decreases by a small amount.