Highland earthquake was 'quite unusual', says expert
The British Geological Survey (BGS) reported a 2.2 magnitude earthquake just outside Roybridge, near Spean Bridge, in the Highlands on Friday around 9.30pm.
It was the second quake to hit the country in less than a week.
The earthquake, which had a depth of 7.5km, was described by Glenn Ford, the BGS seismic analyst on call at the time of the tremor, as "absolutely tiny" when compared with other quakes seen around the world.
But he said this one was unusual as only around 10% of earthquakes are felt at all.
Mr Ford said: “In UK terms, because we are a very low seismic area, we only perhaps get about 15 earthquakes a year of this size or greater, so it's quite unusual in that respect.
"We get about two to three hundred earthquakes every year somewhere in the United Kingdom area, so the fact that this one was actually felt was unusual because approximately 90% of them are so small nobody actually perceives them."
One person who did feel it was Iain MacDonald, who was staying in the village at the time of the tremor.
He said: "It was about 9.30pm and I felt the tremor, but I heard it much more. It was really quite loud, like a train rumbling past the house.
"To me it seemed like a train rumbling past. I knew what it was straight away, I have heard it before and felt the tremor before."
The quakes was 17 billion times smaller than the earthquake which devastated Japan in 2011, said Mr Ford.
He added: "You literally wouldn't look up from your coffee or your newspaper for an earthquake that size in California or Japan."
He added there were a number of factors as to why people felt earthquakes in the UK, including size and depth.
"The other type is time of day. Because people are not used to earthquakes in the UK, they put a small earthquake, because it could just be a small tremor, down to traffic noise, so if somebody is in a very remote area like this which occurred last night there is much better opportunity to actually feel it because they are nice and still, it was late at night, and probably in a sedentary position," Mr Ford said.
"Normally if the roads had been busy or you're near a motorway, you'd just put it down to traffic,” he added.
A 3.1 magnitude earthquake was reported by the United States Geological Survey (USGS) on Tuesday just before 2am, with its epicentre some 11 miles north-west of of Lochgilphead, 88 miles north-west of Glasgow.
More than 30 people reported to the USGS that they had felt the tremor, with reports coming from as far as Edinburgh and Ballycastle in Northern Ireland.
The agency said that quake happened 10km below the Earth's surface.
As for the recent quakes in Scotland, Mr Ford said there had "obviously been a little bit of stress built up in that area".
Data from the British Geological Survey shows between 200 and 300 earthquakes are detected in the UK every year, with tremors of between 3.0 and 3.9 magnitude occurring on the mainland once every three years on average.