Britain Gets Earthquakes, Ireland Doesn't - Why? 

Intriguing fact in the heading above. The illustration below shows the evidence - on the left - and the reason - on the right. This come from THIS ARTICLE and gives rise to an important observation - Moderate variations in plate thickness, occurring far from plate boundaries, can influence patterns of seismic activity within those regions.

The fact that the island of Great Britain has more earthquakes than the island of Ireland has long been known. The cause has only recently come to our understanding. And it is seismic tomography which has given us the answers. The part of the tectonic plate below Ireland (and the eastern side of Great Britain) is thicker (95 - 115km) than that below western Britain (75 - 85km). 

The parent article is HERE but you need to pay for access. I suspect that the simple numbers for thickness I give above are the result of a great deal of work. This only adds to their interest.