Mysterious tremors felt on Denmark's Baltic Sea island of Bornholm on Saturday were not caused by an earthquake, according to experts investigating the phenomenon.
Instead, an explosion in Poland was the possible cause, Trine Dahl-Jensen, a geophysicist with the Geological Survey of Denmark and Greenland, told dpa on Sunday.
"We have received nearly 70 reports from people on Bornholm that they experienced all kinds of pressure waves, loud, low rumbling noise and windows rattling," Dahl-Jensen said.
The aberrations were felt between about 3 and 4 pm (1300-1400 GMT) and were definitely exceptional in nature, she added: "We have never received so many reports from Bornholm."
However, a seismic event was not detected on the island. The scientist assumed that the sensations felt on Bornholm were sound waves and said an explosion in northern Poland coincided with the reports.
That blast occurred on land and was registered by several measuring stations shortly before 3 pm. Whether there is a connection with the perceptions on Bornholm, however, has not been clarified.
"I don't know whether sound from an explosion in Poland can spread so far," said Dahl-Jensen, who did not want to speculate on other possible causes such as supersonic aircraft.
Detonations in themselves are nothing unusual, she stressed. "We register explosions in our neighbouring countries every day." These could occur in mining, for example. Moreover, the shock wave in Poland had not been particularly strong.
Police on Bornholm said on Saturday that they had received several reports of earthquake-like tremors - mainly in the east of the island. A spokesman was unable to give further details a day later but said the investigation by Danish authorities was continuing.
