What are earthquakes?
An earthquake is the shaking and vibration of the ground due to energy released when two tectonic plates suddenly slip past each other.
On average there are around 15 major earthquakes every year around the world. It’s impossible to predict when or where an earthquake will happen.
As well as the damage caused directly by the tremor, quakes can trigger secondary catastrophes such as tsunamis, landslides and sinkholes.
They can also lead to fires and explosions if gas or electrical lines are affected. All of which increase the risk to life and property and the scale of business losses.
How do earthquakes happen?
Earthquakes occur when two tectonic plates slip past each other. There are three main theories on the cause of plate tectonic motion:
- Mantle convection currents: super-heated parts of the earth’s core cause the semi-molten mantle above them to rise by convection, pulling on the tectonic plates above.
- Ridge push: newer plates are less dense and float higher than older plates above the earth’s mantle, which pushes older plates away.
- Slab pull: denser older plates sink into the earth’s mantle, dragging the newer plates with them.
Where do earthquakes happen?
Earthquakes can happen almost anywhere depending on how the plates move. But the largest and most destructive are at the plate boundaries where there is most friction. There are three types of plate boundary that can create earthquakes, as shown below:
Three different types of plate boundary
| Boundary Type | Cause | Strength | Found in… |
|---|---|---|---|
| Convergent | Plates collide and push into or under/above each other | Strongest can exceed Mw 9 |
Chile, southern Europe, Asia-Pacific |
| Transform | Plates slide past each other in the same or different directions | Strong up to Mw 8.5 |
California, New Zealand, South East Asia |
| Divergent | Plates move away from each other | Least strong Typically less than Mw 8 |
Iceland, East Africa |
Where do earthquakes occur?
Earthquakes can occur anywhere in the world but areas at the highest risk are usually found along plate boundaries.
Coastal regions near to fault lines also experience tsunami risk.
Convergent plate boundaries produce the largest magnitude earthquakes.
