When an earthquake occurs, people tend to think solely about the damage caused by shaking, tsunamis and other common side effects. This lesson will discuss a lesser-known effect: liquefaction.
What Is Liquefaction?
During an earthquake, especially a big one, people rarely worry about the consistency of the ground beneath their feet. They are more interested in finding a safe place. They’re trying to get out of buildings, moving away from structures that may break and fall, and generally avoiding anything that may hurt them. During an earthquake, however, there are several effects that may be damaging, other than what happens when the ground shakes. One of these effects, liquefaction, is particularly bizarre to experience.During an earthquake, the shaking ground may become much less solid as soil and groundwater combine to form a material that acts like a liquid. This process is called liquefaction.
In many ways, the ground becomes something like the quicksand found in children’s books and particularly thrilling action movies. Instead of being solid, the ground below your feet, or more dangerously, the ground beneath a building or road, becomes a semi-solid, capable of allowing objects and people to sink into it. Generally speaking, though, liquefaction does not cause the ground to swallow people up. Damage is typically caused as the foundation of buildings is weakened.
How Liquefaction Occurs
The ground beneath your feet is made up of multiple layers of soil. In all but the driest areas on Earth, there is also a fair amount of water that is held in many of those layers. During an earthquake, the soil layers are shaken, which causes them to behave differently than when they are still. The water that is absorbed into the soil layers begins to travel through the layers and is distributed evenly. The water also tends to travel toward the top, because it is slightly less dense than most soil types.
This redistribution of soil and water is what causes the soil to turn into a semi-solid material. Liquefaction beneath roads can cause extensive damage. In this image, a van has driven into an area of road that has sunk down due to the ground beneath it turning to a semi-solid material.
Liquefaction in Action
Liquefaction can occur during virtually any high-magnitude earthquake. All that is really needed is soil that’s unconsolidated (basically, just not solid rock) and enough water in the ground. In 1964, the area near Niigata, Japan, suffered a high-magnitude earthquake, around magnitude 7.
5 or 7.6, that caused extensive amounts of liquefaction. Entire portions of the city of Niigata suffered damage due to semi-solid surface conditions that caused building foundations to break down.
Entire buildings sunk into the earth (just a little; this isn’t a Hollywood movie, after all) and became unusable. Since this earthquake, scientists have had a better idea of what causes liquefaction and have designed buildings to withstand this type of damage, to a degree.
Earthquakes have many effects that can be both damaging and deadly. One of these effects, liquefaction, occurs when soil and water mix into a semi-solid material that can act like a liquid. An effect of the ground shaking, liquefaction can cause roads and buildings to sink, leading to untold amounts of damage.
Scientists have used recent large earthquakes to study this phenomenon and are continuously trying to design structures to withstand this problem.