I remember first hearing about this a long time ago and the examples given then were pretty much all in the British Isles (thank you for the link, btw). Still, Schoch was talking about glaciers disappearing so rapidly that earthquakes may have occurred - if something happened it must have been over a very wide area.
On the one hand if most of these forts are in Scotland, it could mean the plasma events were more common in that area or that there just was more of these forts in Scotland at the time.
It is also interesting to note that when the Sarmatian Dal Riada clan invaded Ireland, they claimed the Irish natives could control the weather, according to the surviving legends.