Question

How does liquefaction occur and what dangers are associated with it?

Answer 1

Hint:Severe seismic activities result in numerous disturbance in the Earth surface which can lead to cracks or collapse of structures and cause fatalities. Constructions without proper testing of soil contribute to hazards of liquefaction. Building on or near loose soil like close to rivers, ponds, or lakes are prone to structural failures.

Complete answer:
 Liquefaction occurs when unconsolidated, waterlogged sediment on or near the soil surface loses its strength in response to severe soil disturbances. Liquefaction under buildings and other structures can cause significant damage during seismic events.
Earthquakes of high magnitude put pressure due to which the ground loses its strength, the gaps in the soil are filled by water, turning a firm sediment into a liquid. The pressure exerted on the liquified layer is increased by the pressure exerted by the soil above it. Construction close to lakes, ponds, rivers etc, are in a direct risk of soil liquefaction because soil near the water bodies are loose, and lack strength and rigidity.
The construction of buildings in the vicinity of water bodies uses retaining walls that hold the soils. When the ground is liquefied, the retaining wall collapses, potentially causing landslides.
The damages from soil liquefaction can be reduced by proper testing of the quality of soil and measures must be taken to improve their quality. Soil mapping must be made mandatory and construction on saturated soil must be avoided. Liquefaction proof structural systems can help in mitigating its fatal consequences.

Note: liquefaction occurs when unconsolidated, waterlogged sediment on or near the soil surface loses its strength in response to severe soil disturbances. Liquefaction under buildings and other structures can cause significant damage during seismic events. Proper measures like soil mapping must be taken to avoid the risk caused by seismic activities on which humans have no control.