Liquefaction is the process of loose soil acting like a liquid during an earthquake.
Most of the time, buildings and homes are built upon solid bedrock. However, building also happens on what seems like solid ground. But underneath a solid layer of compact sediment, there is lurking a loose layer of sandy soil or soil that has been saturated with water. During the shaking of a powerful earthquake, this loose soil will act like quicksand. When liquefaction occurs, the homes and buildings atop this soil can sink or fall over when their foundations loosen or break apart. The surface of the ground will become very uneven and unstable. Crevices and gaps open up. Roads and sidewalks break into pieces and become hazardous.
These are not the only effects of liquefaction. Loose, sandy soil, or the water saturated soil underneath the compact layer of sediment can make its way up to the surface. The columns of rising sandy soil are called sand dikes. When the sand emerges on the surface it is called a sand boil. The results of this liquefaction phenomenon are often seen after high magnitude earthquakes. Street pavement will break apart, and sand boils can be seen on roadways and other areas. Sewer channels underneath streets can rise up during liquefaction. As a result, the manhole cover you see everyday on your way to school could be several inches to a couple of feet higher than the surface of the road. This is a common side effect of liquefaction. Other underground structures can break also; important things like gas and water lines.
Many geological studies have been or are currently being conducted to find the places that are most prone to liquefaction during earthquakes. You can go online and find a number of different maps that show where liquefaction is most likely to occur.
Some hazardous side effects of liquefaction.
Sand boils that emerged during a quake.
An earthquake caused this road to split right down the middle.