Denmark’s Mystery Tremors Caused by Acoustic Waves From Unknown Source, Officials Say

Denmark’s Mystery Tremors Caused by Acoustic Waves From Unknown Source, Officials Say
The shore near the city of Ronne on the Danish island of Bornholm in the Baltic Sea on Feb. 5, 2012. Jonathan Nackstrand/AFP via Getty Images
The Associated Press
Updated:

COPENHAGEN, Denmark—A series of minor tremors recorded on the Danish Baltic island of Bornholm Saturday has puzzled scientists, who now say they were caused by ”acoustic pressure waves from an unknown source.”

At first the tremors were thought to have been caused by earthquakes. Then, seismologists theorized that they originated from controlled explosions in Poland, more than 140 kilometers (nearly 90 miles) to the south.