An earthquake which shook parts of the UK on Saturday is the sort of event which happens only once "every two or three years", experts have said.
The British Geographical Survey (BGS) said the epicentre was 20km (12 miles) north of Swansea, with a 4.4 magnitude at a depth of 7.4km (4.6m).
A BGS tweet added: "Events of this magnitude only happen in the UK every 2-3 years."
People across south Wales and south west England said they felt what they thought was an earthquake this afternoon.
James Leonard wrote on Twitter: "Wow was that an earthquake in Swansea my house just shook #earthquake earthquake."
Mark Wyatt, a third year student at Cardiff University, was entering his house in the city centre when he heard a "weird, deep rumbling sound" around 2.30pm.
The 21-year-old said: "We heard the noises before we felt the rumble, and then the house shook for a couple of seconds before it stopped."
Tremors were felt across the Bristol Channel into England too.
Seth Piper wrote on Twitter: "OK pretty sure I just experienced my first ever earthquake ... in Bristol, UK?"