Reynir Bödvarsson at Uppsala University told TT on Thursday morning that the quake was localised in the western part of the city.
“We hardly noticed anything here in Uppsala. But this morning when I analysed the data I saw that it was an earthquake,” he said.
Bödvarsson told Swedish Radio that the earthquake measured “a little over two on the Richter scale”. The epicentre was located seven kilometres south east of Bromma.
Police thought at first that the quake was an explosion, as hundreds of panic-stricken residents called SOS Alarm. Nobody was injured.
“It was primarily in the vicinity of Alvik, the Essinge islands and Kungsholmen,” said Thomas Ibstedt, at Stockholm police.
A resident of Stora Essingen, Hans-Olov Zetterström, was one of those woken by the rumbling.
“It was as though there was rock-blasting being carried out on a building site,” he told The Local.
“But it was the middle of the night – and there’s no building site near here.”
Officers were sent to investigate the incident and a helicopter was called in to help find the cause of the noise.
The rarity of earth tremors in Stockholm meant that this explanation was not even considered by police, who speculated that it could have been an explosion set off by someone from a boat.
But Bödvarsson said that across Sweden these kinds of quakes are not unheard of.
“There are over ten earthquakes like this each year somewhere in Sweden. But when it happens in central Stockholm there are obviously many more people who experience it than when it happens somewhere in Lappland,” he said.
“An earthquake of this size can be usually felt within a radius of maybe five to ten kilometres from the epicentre.”
There is very little seismic activity in the Stockholm, Uppland and east coast regions. Around Vänern, Bottenviken and Lappland, earthquakes are more common.
Bödvarsson said there was very little risk of further disturbances in Stockholm.
“If there are aftershocks, they will probably be so small that nobody will notice them. That’s not to say that there can’t be another earthquake in Stockholm, but the probability is not increased because of this.”