Residents in parts of north Wales were given a rude awakening on Tuesday after a small tremor was recorded.
Residents in Anglesey and Gwynedd were woken by the tremor
The shock wave measured 1.4 on the Richter scale at 0322 BST.
The British Geological Survey (BGS) said the tremor, which was centred around the south west corner of Anglesey, was very small.
Dozens of residents in Anglesey and Gwynedd reported hearing a "tremor-like" rumble.
Anglesey resident Robert Hesketh, of Llanfairpwll, said he was woken up by the rumble.
"It was a very loud but low rumble with a slight shudder," he said.
"It felt like tremors we have had before.
History of tremors in Wales
1984 - Llyn Peninsula, north Wales - 5.4 (Richter scale)
1991 - Bishop's Castle, Welsh borders - 5.1
2002 (February) - South Wales Valleys - 3.0
2002 (September) - north and south Wales - 4.8
2005 - north Wales - 3.1
"We get tremors during the night almost every year, though I've yet to feel one during the day but they might be mistaken for something else.
"I personally find them fascinating as they are a small taste of what nature can do and hope they never become as strong as you hear in other countries."
Glenn Ford from the BGS said the tremor was around 400 times smaller than one measured at 3.1 on the Richter scale from the same epicentral area in September 1999.
The tremor was one million times smaller than 5.4 quake felt in 1984
And it was a million times smaller than the 5.4 earthquake felt all over Wales and parts of UK in July 1984.
"Tuesday's tremor was right on the cusp of being felt," he said. "If the tremor had happened during the day or in a busier part of the world it is unlikely it would have been noticed," he said.
"The conditions were very favourable for the tremor to wake people up because it would have been very quiet and they would have been lying in bed."
Mr Ford said that north Wales was one of the most active regions in the UK for earthquakes.
The area around the Menai Straits lies on a geological fault and people living in the area have experienced tremors in the past.
North Wales Police received no calls about the earthquake.