Seismic waves can be danger

THE 4.4 magnitude earthquake may have come as a shock, but how do earthquakes happen in the first place?

Movements within the Earth’s crust cause stress to build up at points of weakness.

When the stress exceeds the strength of the rock, the rock fractures and the stored energy is suddenly released like a spring.

Intense vibrations or seismic waves spread out from the initial point of rupture, the focus, like ripples on a pond. These waves are what makes the ground shake and can travel large distances in all directions.

Near the epicentre, the waves can be very large, making them extremely destructive if there is enough energy released.

Wales is crossed by several major faults but there are hundreds of lesser ones.

It is difficult to tell which fault produces a particular earthquake because a geological map show what faults are visible at the surface.

The UK’s largest onshore earthquake occurred in July 1984 on the Llyn Peninsula.

The magnitude 5.4 quake hit 14 miles below the crust and hundreds of aftershocks were registered.

The last major earthquake to hit the UK was 10 years ago, in Market Rasen, Lincolnshire.

The 5.2 magnitude earthquake struck in February 2008.

According to the British Geological Survey, around 3,000 events of this size happen in the world every year, with events of this magnitude happening in the UK every three to five years.