Liquefaction
http://ecan.govt.nz/advice/emergencies-and-hazard/earthquakes/pages/liquefaction-information.aspx
Liquefaction is the process that occurs during the shaking of an earthquake when certain soils (sandy or silty soils) behave more like a liquid than a solid. The seismic shaking causes the sand and silt particles to compact, compressing water filled spaces. This causes a build up of pressure until sand and silt particles “float” in the water, leading the soil to behave more like a liquid than a solid. This means it is no longer able to support the weight of what is above ground level, causing tilting and sinking of buildings, roads and powerpoles. The pressurised water is forced up to ground level through cracks in the ground and concrete, where it creates sand boils and water fountains. Following an earthquake, liquefaction causes settlement of susceptible ground at a level lower than it was previously. The severity of liquefaction depends on the strength and length of time the ground shook during the earthquake.