Denmark’s mystery tremors caused by acoustic waves from unknown source, officials say

COPENHAGEN, Denmark (AP) — Scientists are puzzled by a series of minor tremors that were recorded on the Danish Baltic island of Bornholm on Saturday. Officials said Monday that they were caused by ”acoustic pressure waves from an unknown source.” At first, scientists thought the tremors had been caused by earthquakes, then from controlled explosions in Poland, about 140 kilometers (nearly 90 miles) to the south. However, the seismologists later said the tremors were “not caused by earthquakes, but by pressure waves from an event in the atmosphere.” On Saturday, there were more than 60 reports about the minor tremors, but no injuries.