What Is Liquefaction?
Liquefaction is a secondary effect of earthquakes. It is more common in developing areas that do not have resilient infrastructure. It can be very costly for countries to fix damage caused by liquefaction and so many are investing in preventing it from happening.
So what is it?
Liquefaction is caused by seismic shaking that occurs during earthquake events. It occurs when partially or fully saturated soil loses its strength and bonding due to the shaking caused by P, S and L waves. During the shaking, water pressure increases. This causes the sand particles to lose contact with each other resulting in the soils starting to flow like a liquid. When the shaking stops, the water pressure decreases again. The soil becomes solid again. Liquefaction can occur in both wet and dry soil but it has a more devastating effect in areas that have a higher water content in their soil.
What impacts does liquefaction have?
Liquefaction can cause the foundations of buildings and other infrastructure such as bridges to sink. The lower levels of the buildings will sink beneath the surface. They are often beyond repair.
Underground pipes, gas lines and electricity cables may break due to liquefaction. This can cause significant flooding and fires to break out.
The water pushes upwards and can enter buildings through service vents. The interior of the building then floods and causes significant water damage.
Most dangerously, the ground affected by liquefaction can open, crack and fissure meaning all structures on the surface will sink into the space and there is a risk to human life.
This video is very good at showing how the particles losing contact has a huge impact on the buildings and infrastructure in the area:
Let’s look at a real life example of liquefaction:
San Francisco lies in an area that is very prone to earthquakes. There have been multiple violent earthquakes in the area over the last 200 years. The 1989 earthquake led to lots of liquefaction. In the Marina District, many buildings collapsed and gas and water pipelines ruptured.
As the district lies on saturated soil the damage was a lot more extensive than it would’ve been if it lay on solid bedrock. The ruptured gas lines caused fires in the city.
Recap:
Liquefaction happens due to seismic shaking during an earthquake. It can happen during or after the event and is caused by water pressure changes in the soil. It can have devastating impacts for a country or city’s infrastructure and can even risk human life.
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