What is Earthquake Engineering?
One of the deadliest natural disasters that can occur are earthquakes. Their impact on infrastructure is devastating for the socio-economic and environmental state of a country. The energy released from earthquakes can lead to buildings to collapsing whilst trapping people amongst the rubble, resulting in a lack of secure and safe shelter. This promotes unhygienic conditions which can lead to the spread of diseases. Moreover, damage to transport routes such as highways and airports can limit the number of safe routes for rescue workers to deliver aid, and also impact the delivery of foreign aid. Not to mention that the cost of rebuilding structures and the livelihoods of citizens can take billions of pounds and decades.
So how do countries located in tectonically active regions withstand the continuous threat of earthquakes and the consequences that will follow? How can countries such as Japan build bustling cities and skyscrapers even with the large amounts of earthquakes, they experience every year?
To initially answer these questions I must dispel the common misconception that earthquakes are the primary cause of the loss of human life. In fact, it is the collapsing of man-made structures that result in a high number of deaths.
Earthquake engineering is a field ‘devoted’ to designing and building structures to mitigate earthquake hazards. Infrastructure that is able to withstand the force of seismic waves released from the centre of an earthquake means buildings are less likely to collapse. In this post, I will discuss some of the techniques employed by engineers to build earthquake proof structures.
Below I shall list three popular techniques used by earthquake engineers and describe the engineering behind them.
1) Base Isolators
Base Isolator image from Pinterest
Base isolators are a structures placed at the bottom of a building separating the base of the building from the ground, therefore isolating the building from the Earth’s surface. By doing this, less energy is transferred from the earthquake to the building. The base isolators absorb and dissipate most of the seismic waves away from the building, so it sustains less damage.
So how do these base isolators work? They are built with a lead centre surrounded by alternating layers of steel plates and high-density rubber. During an earthquake, the lead softens and absorbs energy from the seismic waves. Therefore, less seismic wave energy is transferred to the building itself, which minimises the building's shaking, which allows it to reach a more stable position in a shorter time.
New Zealand employs this technique on buildings such as the House of Parliament and Parliamentary Library to withstand seismic waves. Earthquakes are commonplace New Zealand, as the country lies on two tectonic plates, resulting in pressure buildups at plate boundaries. Therefore, New Zealand must ensure that its buildings are adequately protected.
2) Pendulum tuned mass damper
Like the name suggests, the tuned pendulum damper is a pendulum located inside skyscrapers, where the pendulum hangs from the ceiling of the building. During an earthquake, the building will begin to sway, and so will the pendulum. When the structure starts to vibrate the pendulum will create a force [to] counter against the motion of the structure. When the building sways to the right, the pendulum will offset this force by swinging to the left. This results in the building reaching stability within a shorter time since the energy from the seismic waves will is dissipated by the pendulum damper.
This technique is visible in the Tapei Tower in Japan. Japan is a country which lies on 3 tectonic plates and is located in the Ring of Fire, the most tectonically active region in the world. Thus, Japan experiences many earthquakes each year; approximately 5000 minor earthquakes and 60 earthquakes with magnitude 5 or higher. Therefore every building in Japan is carefully engineered; techniques such as the tuned pendulum damper allows engineers to build skyscrapers without fearing the risk of their collapse.
3) Seismic Invisibility Cloak
The seismic invisibility cloak works much like Harry Potter's invisibility cloak, as it makes the structure appear invisible to the seismic waves. As odd as this sounds, it is done through some clever engineering that works to manipulate the seismic waves. Cylindrical pits are dug underneath the building in an ordered fashion. These pits work to scatter the incoming seismic waves, therefore forcing them to interfere and cancel each other out. This ultimately means that less will waves hit the building itself.
However, this method isn’t always successful, since earthquakes produce very long wavelengths that could bypass the cylindrical pits without ever interacting with it. Continued research into the topic has brought forward the idea of metamaterials, which are materials designed to interact with electromagnetic radiation to produce a desired response. Natural metamaterials such as trees can be used, since trees act as resonators. In the correct arrangement, the interactions of resonating trees can redirect the energy of seismic waves deep into the soil, thus reducing the energy hitting the buildings.
The engineering techniques that I have discussed above are very efficient, however they are expensive to implement and require professionals to complete the process. Low income developing countries lack professionals, income and the resources needed to build structures such as these with ease. Furthermore, many buildings in rural areas of developing countries are built by the homeowners themselves without adhering to any building regulations. As a result, many of these structures are weak and are unable to withstand the force of earthquakes, which makes them more susceptible to collapsing.
Therefore, developing countries often use different techniques which are more affordable and easier to implement, such as the few listed below:
In this process, existing buildings, most commonly homes, are strengthened using wire mesh within the internal structure of the building. This reduces the chances of homes being displaced from their internal infrastructure. It also provides a safer place for individuals to take shelter during earthquakes as their homes are more likely to stay intact and not collapse around them.
This method is very useful in low-income countries due to its inexpensive nature.
2) Open Fields
Collapsing buildings is one of the main reasons for deaths during earthquakes. Therefore, in developing countries, sine it is difficult to engineer more efficient buildings, areas of open space can be used instead. Open fields provide a place for people to evacuate to and gather away from any falling structures. This process also requires no extra cost to implement.
3) Seismic invisibility cloaks
As mentioned before, seismic invisibly cloaks with the use of metamaterials can be easily implemented in low-income countries. The technique would only require the planting of trees in a specific formation around structures to help dissipate incoming seismic waves.
Below, I've attached an interesting map showcasing earthquakes within the last 30 days displayed on ArcGIS. As you can see, there is a ring around the Pacific Ocean in which a large number of earthquakes occur. This is the Ring of the Fire, where about 90% of the worlds earthquakes occur. There is, of course, no surprise that Japan and New Zealand are on this Ring of Fire.
Advancements in engineering allow us to mitigate the impact of earthquakes, which can help protect the livelihoods of many people. I hope that you have learned a bit about engineering techniques commonly used, and the ongoing research within the field of earthquake engineering.