Earthquakes are sudden tremors or vibrations that occur in the Earth’s crust. When tectonic plates are colliding or trying to slide past each other there is a build-up of pressure between the two plates in the Earth’s crust along what is called a fault line. This pressure is then suddenly released when the plates move at the fault line and cause a violent shaking of the earth’s surface in the form of an earthquake.


The point within the earth’s crust where the earthquake begins is called the focus. The focus can be tens of kilometres deep and it emits powerful shockwaves or tremors that shake the earth’s crust. As the shockwaves travel through the earth’s crust they spread out and become less powerful in much the same way as ripples in a pool spread out after a stone is thrown into the water.


The point on the earth’s surface directly above the focus is called the epicentre. The epicentre suffers the most powerful shockwaves and damage from an earthquake. Aftershocks are smaller tremors that occur after the main earthquake and can often cause weakened buildings to collapse.


Seismology is the scientific study of earthquakes. The ‘father of seismology’ was an Irishman from Dublin called Robert Mallet. He carried out scientific studies on seismology in the mid 1800’s using dynamite on Killiney Beach and is credited with inventing the words seismology and epicentre. Seismographs are instruments that are used for measuring the exact strength of an earthquake. For more on Robert Mallet and our National Seismic Network see the Dublin Institute for Advanced Studies website.

Richter Scale

The Richter Scale is used to show the strength of an earthquake and ranges from 1 to 12. Each unit on the Richter Scale is ten times more powerful than the previous one so an earthquake measuring 7 on the Richter Scale in ten times more powerful than one measuring 6.  

For more on earthquakes and real time monitoring see the Geofon Global Map