What is liquefaction in earthquakes?

Answer 1

Liquefaction is the name given to the process that converts a solid soil mass into a liquid.

Liquefaction occurs in cohesionless soils (typically those with a higher content of larger grains such as sand sized clasts) which have water in the pore spaces, and are poorly drained.

When the seismic waves from the earthquake pass through the soil, the vibrations cause the individual grains in the soil to move around and re-adjust their positions. This ultimately results in a decrease in volume of the soil mass as the grains pack more tightly together (a reduction in porosity).

The pore water which was originally in those spaces becomes compressed. Water is relatively incompressible and as such it pushes back against the soil grains (more correctly this is described as an increase in pore water pressure). The pore pressure becomes so high, that the soil grains become almost buoyant causing a significant drop in the shear strength of the soil to a very low value.

When this occurs the soil loses it's ability to support loads (technically described as a loss of bearing capacity) which can cause subsidence of building foundations.

Answer 2

"liquefaction" means turning into liquid.

In architecture and civil engineering, "liquefaction" often is used to describe the effects of earthquakes on certain kinds of soil, making them act (at least temporarily during the earthquake) more like a liquid.
During the earthquake, buildings on top of that soil sink down; petrol tanks buried in such soil float up; the soil itself pours downhill, etc.

In the energy industry, "liquefaction" often is used to describe the process of taking natural gas and converting it into a liquid, called liquified natural gas (LNG).

Answer 3

Liquefaction normally occurs during earthquakes. It is when the ground shakes and the water trapped under the rocks also shake. The vibrations cause the water to rise and soften the rock. The surface will now be very soft and buildings and cars might sink ino the ground, as it becomes somtwhat like quicksand.