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
Parents in Wales are urged to be aware of the potential fire risks associated with children's fancy dress costumes this Halloween.
There have been several theories after video footage emerged apparently showing a dramatic fireball falling from the sky over Penarth Pier.
Sam Warburton will miss Friday night's Challenge Cup clash with Pau in Cardiff due to neck stiffness.