Earthquakes

When the Earth moves
Earthquakes are caused by the motion of tectonic plates - individual sections that make up the Earth's surface like panels on a football. Immense strain accumulates along fault lines where adjacent plates meet. When the rock separating the plates give way, sudden seismic ground-shaking movement occurs.

Of course, if we want to know why earthquakes happen, we need to dig a little deeper.



Centre of the Earth
The Earth is made up of three main layers:
# The core is at the centre of the Earth
# The mantle is a mobile semi-molten layer around the core
# The outer-shell of the Earth is called the crust. Scientists call this the lithosphere - it's the part we're on now

The crust is made up of 12 individual tectonic plates. Below the sea, they can measure three to six miles (4km-9.6km) thick and under land this increases to 20-44 miles (32km-70.8km). Below the crust, radiation from the Earth's core heats the semi-molten mantle to temperatures of over 5000°C.

All fluids when heated - even molten rock - are affected by a process called convection. The makes hot liquid rise to displace cooler liquid, creating a current. Tectonic plates effectively float on the mantle, like croutons in a bowl of super-heated soup. But these plates and constantly moving due to the convection current.

Of course, they creep along very slowly - roughly the same speed your fingernails grow. Even at this sub snail-pace, the effects can be devastating. The combined annual force of earthquakes is equal to 100,000 times the power of the atomic bombs that flattened Hiroshima.




The point where the seismic activity occurs is the epicentre, where the earthquake is strongest. But it doesn't always end there, seismic waves travel out from the epicentre, sometimes creating widespread destruction as they pass.


Earthquakes hit Britain on a fairly regular basis. In fact, there can be as many as three in a week. Luckily, the geology beneath us is stable, and these tremors usually go unnoticed.