Scientists puzzled by mysterious tremors on Danish island.

Scientists are puzzled by a series of minor tremors that were recorded on the Danish Baltic island of Bornholm on Saturday. The Geological Survey of Denmark and Greenland has now said that the tremors were caused by "acoustic pressure waves from an unknown source." The tremors were initially thought to have been caused by earthquakes or controlled explosions in Poland, but seismologists have ruled out both possibilities. The source of the pressure waves remains unknown.