Earthquake Impacts on the Environment
When you see earthquake costs reported in the media, one of the most common quotes is how many millions of dollars of damage has been done. This is often worked out as a function of how much it will cost to bring the affected neighbourhoods back into the same condition as they were before the earthquake struck. With the focus on homes and buildings, an earthquake with a deep epicenter will cause more financial damage as it will affect the foundations of each structure as well as the ground at the surface.
However, when calculated as a percentage of total land usage in British Columbia, man-made buildings and structures actually take up a very small amount of space. The impact of an earthquake on the natural environment can also have devastating effects; not just for humans, but for local plants and wildlife who form part of the vital food chain.
Earthquake Environmental Effects
To understand the main earthquake impacts on the environment, it’s important to learn about some of the ways that earthquakes impact the ground:
Soil liquefaction – this is one of the most terrifying consequences of an earthquake as it effectively turns what looks like solid dirt into a liquid mess. It happens when the ground is saturated with rainwater (or at least 75% saturated) and the stress of the earthquake tremors cause the bonds between solid matter to soften and lose strength. The sudden change from solid to liquid can be devastating to anything that uses the soil as foundation.
Landslides – another intimidating earthquake environmental effect are landslides, where significant portions of sloped land suddenly break off and slip down the hill. Landslides caused by earthquakes typically happen in places where the soil is either saturated, which makes it automatically weaker as the bonds between solid matter are broken up by water), or where the solid matter is in larger chunks such as stones or boulders. The effect of having the ground shake and oscillate underneath the hill dislodges enough matter and gravity takes care of the rest, pulling tons of rock, dirt and rubble down the hillside.
Surface faulting – a fault occurs where the ground actually splits apart under the force of the seismic shocks. This tends to happen in dryer locations and those locations that have a certain rock type and formation close to the surface. It’s important to note here that the Hollywood movie vision of the earth cracking open wide enough to swallow cars and people is massively overstated and is solely intended for dramatic purposes. A typical surface fault is likely to be less than 30 cm wide and definitely less than a metre deep.
The scientific community has groups these earthquake environmental effects (which they shorten to EEE in the literature) into two classes: primary and secondary effects. Primary effects are those which are as a direct result of the earthquake’s seismic shock waves and include surface faulting and subsidence (where gaps and holes below the earth’s surface occur, causing the land above it to sink or collapse). Secondary effects are those which happen as a direct result of the primary earthquake environmental effects. These include tsunamis, soil liquefaction and landslides. It is often the secondary effects that cause the greatest devastation and that are more visible in the post-earthquake media coverage.
Earthquake Impacts on the Environment
All of these earthquake environmental impacts are devastating to human lives and interests when they happen in built up urban areas. However, each of them also directly impacts the natural environment, often in ways that have long lasting consequences:
Destruction of habitats – the biggest and most obvious impact of an earthquake on the natural environment is the destruction of animal habitats. For example, a landslide in a wooded hillside can cause trees to fall, ruining nests and tree based homes. This will cause a squeeze on local animal populations as the displaced creatures will need to have somewhere to go. In the case of soil liquefaction, the most saturated land tends to be found in rural areas, meaning that wild animal habitats are at risk from subsidence.
Changing soil composition – larger earthquakes have the potential to completely alter the pH balance of the soil. For example, in a subsidence scenario, gaps and holes are formed deep under the earth’s surface, which get filled in by looser top soil. The sunken areas will slowly get filled in as the wind blows dirt and seeds around, but there’s no guarantee that the pH will be the same in the new top soil. This can affect the types of plants that grow in an area, which in turn can affect the entire local ecosystem.
Disruption of the water cycle – finally, earthquake environmental effects such as ground faults and soil liquefaction can instantly change the course of rivers and streams, as well as adding unknown impurities into the water cycle. In urban and suburban areas, it’s also possible for ground faults to crack water and sewage pipes, which can alter the local water supply and make it harder for all creatures, including humans, to get access to clean, fresh water.
While these are all longer term impacts of an earthquake on the natural environment, the weakening of the underground structures can be a hidden time bomb waiting for the next big quake. Seismologists can identify the possible earthquake impacts on rock structures and soil solidity based on the strength of the seismic waves, but there’s no way to accurately assess the ongoing stress that frequent earthquakes put on the earth’s crust until they finally give way.
Is there any way to mitigate against these environmental disasters? As noted, it’s almost impossible to predict when a big earthquake will come, and even harder to assess the current state of damage underground. However, humans can take steps by monitoring land that is at risk of subsidence and landslides, and providing preventative measures through placing natural foundations to support the weakened ground. Water and sewage pipes can also be made out of a more flexible material to help them move and sway with the underground shakes, which should reduce their chances of breaking under pressure.