Gnat sez, "A resident of Christchurch, New Zealand, cleverly demonstrates the liquifaction that caused so much trouble in the recent earthquakes. The ground is soil and water, usually stable. When shaken, the soil clumps and water separates out: liquifaction. The result is damaged houses, fallen buildings, and a city of death and mess."
Christchurch Earthquake Showing the sand liquefaction process with vibration