Parts of north Wales were hit by a Valentine's Day earth tremor recorded at 3.1 on the Richter scale.
The Menai Straits lies on a geological fault line
Police had scores of calls after loud noises and violent shaking lasted more than 10 seconds. Some minor damage was reported but no injuries.
The tremor struck at about 1845 GMT on Monday and affected properties from Dolgellau to Bangor and Conwy.
The British Geological Survey said the quake was small by global standards but "quite significant" for the UK.
The area around the Menai Straits lies on a geological fault and people living in the area have experienced tremors in the past.
The biggest tremor in recent times was a 5.4 quake which had Nefyn as its epicentre in July, 1984.
Monday's disturbance was described by some as a vibrating rumble, similar to the sound of a heavy lorry passing.
Trevor Taylor, of Llanfairfechan, said one of the windows of his flat cracked, and his bookshelf fell over.
"This rumbling came past and I thought it was a big lorry," he said.
"The lights went out for a few seconds and the rumbling just got louder and louder and then my vases and pots and pans fell on the floor, my bookshelves fell over and my parrots went absolutely nuts.
Trevor Taylor's home shook and sustained minor damage
"It had to be some kind of an earth tremor because it vibrated the whole building, the whole place just shook."
Davie Galloway of the British Geological Survey said about three earthquakes of such a size affected the UK every year.
"A lot of people have phoned to say that they felt it," said Mr Galloway.
North Wales Police Inspector Jason Higgins said the tremor was felt 40 miles inland and along a 10-mile stretch of coast.
"It affected areas both on the coast and inland," he said. "People heard a loud bang and some movement and shaking of buildings.
A second police spokesman added: "We got multiple calls earlier this evening - the switchboard fairly lit up with calls from people saying there had been a tremor.
"People came out of their houses to see what was happening and told how things were shaking about."
Cenin Eision, 18, from Penisarwaen, near Caernarfon, was in choir practice with friends when the quake hit.
"It was terrifying," said the Bangor University agriculture student.
"I could quite literally feel the earth move beneath my feet.
"I couldn't hear any rumbling but it felt like being on a roller coaster. You could feel the vibrations through your whole body.
"There was this shaking everywhere. It was like a shiver went through the building.
"I think everyone was frightened. I have never felt anything like that before."
Part-time barman Andrew Roberts, 18, of Bangor, was working in the Ship Inn at the time.
"I was just standing at the bar when I felt it," he said. "At first I had no idea what was happening.
"It lasted for around three to four seconds and the entire bar just shook. I could hear the glasses rattling on the bar top and all the trays were moving.
"I would have run but I was just too shocked. By the time I thought of moving, it was all over."