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
Showers overnight will make way for heavy rain tomorrow! The Met Office has issued a warning to be aware!
Dermatology services in west Wales are at breaking point say top skin experts in Wales. Hywel Dda currently has no consultant dermatologist.
Sara Garbutt of Rhyl robbed a vulnerable pensioner and stood by while he was beaten up. She's now been jailed for eight years.