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
The Wales Deaf Rugby team take on England today at the Cardiff Arms Park
A shopper has received a community order after he admitted uploading an explicit image to an iPad at a Tesco supermarket in Swansea.
Wintry showers this morning, particularly in the west. Turning drier and brighter this afternoon but still some sleet or snow showers.