The British Geological Survey says there was a magnitude 5.4 earthquake in the area in 1984.
It describes that year's event as "significant".
More top news
Women speak to ITV Wales about the chronic pain they are suffering after having surgical mesh as fresh calls are made for it to be banned
Welsh drivers have incurred nearly half a million penalty points from speeding, new analysis has found.
A windy day with a mixture of blustery showers and some sunny spells.