A series of minor tremors on the Danish Baltic island of Bornholm on Saturday puzzled scientists, who now say they were caused by "acoustic pressure waves from an unknown source".
This is reported by AP.
At first it was believed that the tremors were caused by an earthquake. At the time, seismologists assumed they were caused by controlled explosions in Poland, more than 140 kilometers to the south.
On Monday, the Geological Survey of Denmark and Greenland said the tremors were "not caused by earthquakes, but by pressure waves from an atmospheric event". However, they came from an "unknown source".
"Seismologists can report that it is unlikely that the tremors originated from a controlled explosion in Poland, which was carried out shortly before the first reports of aftershocks at Bornholm," the organization known as GEUS said in a statement.
On Saturday, GEUS said it had received more than 60 reports from people on Bornholm about tremors during the day, described as deep rumbling, shaking and ringing, and changes in pressure in the ear.
No one was hurt. Police said they were also contacted by members of the public about tremors in the eastern part of the island. Danish media reports that aftershocks caused a crack in the wall of the building.
GEUS reported that a 2.3-magnitude tremor was recorded.
Polish authorities said that during the Anakonda23 exercise in Ustka, in northern Poland, there was intense activity involving jet fighters and live firing of artillery ammunition.
GEUS, an independent research and advisory body within the Danish Ministry of Climate, Energy and Utilities, said it has two seismographs on Bornholm collecting data around the clock.
Bornholm, home to almost 40,000 people, is a rocky island in the Baltic Sea, south of Sweden, northeast of Germany and north of Poland.
