David Galloway, a seismologist at the British Geological Survey in Edinburgh, said the earthquake was fairly small and went relatively unnoticed by residents because of the time of day it happened.
"We only had one person, who was already awake, report to us that they felt a slight rumbling," he said.
"Most people will have been asleep when this happened and we wouldn't expect it to wake anyone up. If it was during the day, and in an area of higher population, we would expect more reports of people having felt it.
"It is one of five or six recorded in the region within a 30km (19-mile) radius, and the largest since 1887. It is not a region that experiences many earthquakes."