Unidentified acoustic waves cause mystery tremors in Denmark's Baltic island.

Scientists in Denmark have said that a series of minor tremors recorded on the Baltic island of Bornholm were caused by "acoustic pressure waves from an unknown source." The Geological Survey of Denmark and Greenland said the tremors were "not caused by earthquakes, but by pressure waves from an event in the atmosphere." The source of the waves is still unknown, but they were not caused by controlled explosions in Poland, as previously thought. No one was hurt during the tremors.