What are earthquakes, how are they caused and what can we do to minimise the threat they pose? Here we explore the issues.
In the UK, earthquakes are usually something that happens to other people. And while the UK does experience very minor tremors from time to time, the more devastating effects are visited upon countries further afield than our small island in the North Sea. Here we look into why they occur and what countries can do to mitigate the worst of the effects.
What is an earthquake?
Earthquakes are the most extreme kind of geological event. They can inflict enormous loss of life and near-incalculable economic harm. For all of recorded history, earthquakes have been present. You might read a lot of references to them in religious texts, where they’re usually attributed to divine intervention. The Book of Samuel, for example, mentions the earth shaking because God was angry.
It’s only relatively recently that we’ve obtained a more scientific understanding of what earthquakes are what can be done about them. For a detailed dive into the nature of earthquakes, join our Extreme Geological Events course and learn how they have transformed Earth over centuries.
What causes earthquakes?
The surface of the Earth is not composed of a single fixed mass, but rather 17 large bodies (called tectonic plates) which float upon a mass of molten rock called the mantle. Since these bodies are floating, they can occasionally bump and grind into one another.
If you want to impress an environmental scientist, you might refer to these plates collectively as the ‘lithosphere’, which is a bit like the atmosphere and stratosphere, except it’s made of solid rock. Learn more about complex environmental issues in our A Beginner’s Guide to Environmental Science course by Central Queensland University.
While we might think of solid rock as something that’s incredibly hard, the truth is that it provides a certain degree of elasticity, especially when there’s a lot of it. So, when the plates strike one another, they give way a little bit. But sometimes, the pressure becomes greater than the friction, and the plates will suddenly slip past one another.
This event sends out shockwaves that radiate out through the surrounding earth, eventually arriving at the surface. So where do earthquakes strike?
Where do earthquakes occur
Earthquakes occur, almost by definition, along geological faults. If you look at a map of the world’s recent earthquakes, you’ll find them concentrated along fault lines. Why do earthquakes occur at plate boundaries? Because that’s where the slipping occurs. It’s possible for another event, like a meteor strike or a volcanic eruption, to cause the ground to shake. But these aren’t technically classed as earthquakes.
Volcanoes and earthquakes
What’s the relationship between volcanoes and earthquakes, you may ask? If you look along the average fault line, you might spot plenty of mountain ranges formed by the two plates smashing into one another, pushing each other upward. You might also spot plenty of volcanoes. This is because anywhere that the crust is thin is prone to occasionally release magma from beneath.
Volcanoes can trigger earthquakes (albeit indirectly), and earthquakes can accelerate volcanic eruptions. Events in the lithosphere have a habit of influencing one another since they’re all related — just like weather events in the atmosphere.
Facts about earthquakes
When you’re discussing earthquakes, or you’re seeing them discussed on the news, you might hear a few special terms used. It’s easy to assume that we know what these mean, but many of them are quite particular.
What is the epicentre of an earthquake?
For example, what is meant by the ‘epicentre’ of an earthquake? Isn’t it the centre of the earthquake, where the actual shock is coming from? Wrong. The epicentre is actually a point on the surface of the earth, vertically straight up from where the movement is coming from. The location from which the earthquake actually originates underground is called the focus, or ‘point of origin’, or ‘hypocenter’ if you’re in the US.
What is the magnitude of an earthquake?
Not all earthquakes are alike. If there’s a little bit of movement under the earth, then you get a small earthquake. If there’s a lot of movement, then you get a big earthquake. The term ‘magnitude’ describes the amount of energy released by the event.
This is distinct from the term ‘intensity’ which describes the extent to which the ground shakes on the surface. Researchers from Cardiff University also note that the relationship between magnitude and deadliness is not always straightforward: sometimes smaller quakes can be more deadly than larger ones.
How are earthquakes measured?
Magnitude can be measured using a whole range of different scales. The most famous and widely used of these is the Richter Scale, developed by seismologist Charles Richter in the 1930s. The Richter Scale is a bit like the decibel scale for sound volume, in that it is logarithmic. For every point on the Richter Scale, you get a tenfold increase in energy.
This is great for quickly conveying information about big and small earthquakes without having to resort to really big and confusing numbers. It’s less great for communicating the threat to the public. Once we understand that a magnitude eight earthquake is a thousand times the severity of a magnitude five earthquake, we can start to get a handle on things.
Usually, an earthquake that’s more than around an eight is considered a ‘megaquake’, according to Cardiff University. The authors acknowledge, however, that this boundary is a little bit arbitrary and prone to interpretation.
While the Richter Scale is undoubtedly the best-known means of measuring an earthquake’s magnitude, there are a few problems that leave it outdated. When Richter developed his scale, seismology was still a new field, and not a lot was really known about the underlying mechanisms that caused earthquakes to happen.
It was developed through the study of relatively shallow earthquakes that occurred in quite a narrow band of amplitude. Consequently, it’s not very good at judging very large, small, deep or shallow quakes.
This leads to a problem called saturation. Since we’re judging quakes from the surface, we might be fooled into thinking a quake is weaker when the focus is in fact just deeper. As the waves radiate upward through the crust, they get absorbed — meaning that we can’t accurately measure them.
A more modern alternative comes in the form of the ‘Moment Magnitude Scale’, or MMS. This more directly looks at the power of the quake, rather than its impact on the surface.
The term ‘Richter Scale’ is embedded into popular culture, now, and it’s often used interchangeably with more modern scales (a little bit like how ‘Hoover’ became synonymous with all kinds of vacuum cleaners).
In 2008, Lincolnshire was struck by a widely felt earthquake measuring 5.2 on the Richter Scale, which amounted to the biggest earthquake felt in the UK in recent times.
For comparison, the underwater Tōhoku earthquake that caused the 2011 Tsunami in Japan was an incredible 9.2 on the Richter scale. This is an increase of four on the Richter Scale, which effectively means we’re multiplying the earthquake’s amplitude by 10,000.
If you’d like to understand the regional differences in the risk of earthquakes around the globe, you can refer to something called a risk map, or to something slightly different called a hazard map.
The dinosaur-annihilating asteroid that impacted the Yucatán Peninsula 65 million years ago, incidentally, was the equivalent to 12 on the Richter scale. But since the focus was actually on the surface of the earth rather than beneath it, it’s difficult to compare precisely.
Effects of earthquakes
Earthquakes pose hazards of several kinds. Some are direct, others, less so.
Primary effects of earthquakes
The first and most obvious effect of an earthquake is that the ground shakes. In practice, it’s a bit more complicated than that. The ground might also split apart, causing an enormous fissure into which people, vehicles, buildings and just about anything can fall. If the earthquake happens underwater, then a tsunami might result.
A tsunami is an enormous wave that sweeps across a coastline, causing huge devastation. There’s also something called liquefaction to consider. This will be familiar to fans of the 2021 ‘Dune’ adaptation — it’s when solid matter behaves like a liquid. When this happens to soil it causes the earth to lose cohesion, which is bad news in the same way as the ground splitting apart is.
Secondary effects of earthquakes
When an earthquake has passed, there is a whole range of secondary phenomena that we need to deal with. Of these, the deadliest are fires, which can often rage unchecked, with no emergency services available to deal with them. When a fire exceeds the fire service’s ability to cope with it, it can escalate rapidly.
Then there are interruptions to power and other utilities, and damage to transport infrastructure. While we might think of immediate consequences (like people dying) as much more important than economic ones (like a business going under), in the long term these are not so easily disentangled.
For example, a study published in Nature concluded that for every one person who died because of the 2011 Great East Japan Earthquake and Tsunami, just under three died in the ensuing 38-month period due to the knock-on effects.
How to prepare for an earthquake
Knowing the origins of an earthquake is one thing. Knowing what it’s going to do is another. And knowing how you’re going to respond to it is something else entirely! Let’s examine some of the earthquake-management strategies.
Earthquake safety information
When we know in advance how severe an earthquake will be, and where the epicentre is, we take more effective measures against this. Of course, this information has to be quickly conveyed to the public too.
In Japan, there are more than four thousand seismometers spread around the country. There is also a system that automatically analyses the information and determines the epicentre, before issuing a warning.
The warnings, via national television, public loudspeakers and just about everyone’s phone, consist of two distinctive chimes, and advice to stop whatever people are doing because an earthquake is imminent. You can see it in action here.
In parts of the world where extreme events occur fairly often, there’s a kind of cultural resilience against them. If you, or some older relative, can remember the last big earthquake, then you’re more likely to prepare for the threat.
Preparing these communities for a big, extreme event is, therefore, more of a technical challenge than one of persuasion. If you want to learn how to help your community before, throughout and after such a disaster, join our Humanitarian Action, Response and Relief course by Coventry University.
Earthquake preparedness plan
Preparing for an earthquake allows earthquake-prone countries to minimise the impact of a quake on human life and well-being. This often involves conducting drills. Much like people in other parts of the world might practice what to do in the event of a fire, people in earthquake-prone countries drill for earthquakes.
Some kinds of facility might contend not only with the earthquake itself but with the aftermath. A hospital, for example, is likely to be inundated with new patients immediately after a quake. Having an effective process of triage is critical to ensuring that the medical infrastructure can cope with the sudden strain.
Allocating resources like beds and doctors to the people who need them most urgently is crucial to preserving life. The same goes for emergency first-responders, who need to deal with the damage, and for the police, who need to get to grips with a chaotic situation.
Of course, it’s not only individuals and organisations that need to prepare but also governments. Experts are brought in to analyse previous earthquakes and try to learn lessons about what can be done in response to future disasters.
Fatality rates from natural disasters, in general, have fallen dramatically over the last century, despite a massive increase in population over the same period, and the increase in extreme weather that’s been linked to climate change. Earthquakes, however, are still quite deadly.
We might attribute this to the unpredictable nature of earthquakes. While a drought or a storm can be predicted and anticipated, earthquakes strike suddenly and often without warning. While our tools, like seismometers and satellite observation, have become better — we’re still some way from an ideal level of preparedness. Learn more about how satellites can predict weather in our Understanding Climate Change using Satellite Data course.
Earthquake preparedness kit
An earthquake preparedness kit should include everything required to cope with an event of this kind. You might construct a kit yourself, or you might buy one ready made to store in your house for when emergency conditions arrive. Earthquake preparedness kits aren’t just good for earthquakes, they contain items that might be useful in just about every kind of natural disaster.
Non-perishable food and several days’ worth of water, a torch, a whistle, extra batteries and first aid kits are all essential components of a preparedness kit. You might also throw in things like dust masks since an earthquake in a major urban area can cause an enormous amount of dust to be thrown up into the air.
Earthquake proof buildings
Designing buildings so that they resist earthquakes is an art that’s been around for millennia. Japanese pagodas, for example, consist of tiers that are structurally unattached to one another. These are bound by complex joinery that resists snapping, and which comes with wide eaves that have superior balance and resist toppling.
Modern buildings take advantage of similar principles. The idea is that a building should be free to change shape during a quake, rather than try to maintain a fixed shape (which will usually result in the building breaking apart or falling over).
Elastic shock absorbers built into the foundations help the building to lean and then return to its original posture. Similarly, steel frames can be created that twist and warp rather than snap into pieces.
Earthquakes are a hazard that’s not likely to go away. While there might be some ambitious efforts to prevent earthquakes from occurring in the first place, a more plausible strategy is for us to get better at predicting quakes, and to develop better humanitarian responses to them, preventing damage to property and people.
Through the study of humanitarian logistics, we can get better at responding effectively, ahead of time. In the long term, it’s more expensive not to take precautions — especially if you’re running a country on a fault line. For more information, join our Introduction to Humanitarian Aid course by Deakin University.
While we might one day take a trip to other, more stable worlds, for the time being we’ve only got one planet. Learning to cope with whatever it throws at us is the only way forward…for now!