COPENHAGEN, Denmark (AP) — A series of minor tremors on the Danish Baltic island of Bornholm on Saturday has baffled scientists, who now say they were caused by “acoustic pressure waves from an unknown source.”
The tremors were initially thought to have been caused by earthquakes. Seismologists then theorized that they originated from controlled explosions in Poland, more than 140 kilometers (nearly 90 miles) to the south.
On Monday, the Geological Survey of Denmark and Greenland, an official body that monitors the subsurface, said the tremors “were not caused by earthquakes, but by pressure waves from an event in the atmosphere.” However, they came from “an unknown source”.
“Seismologists can report that the tremors are unlikely to originate from a controlled explosion in Poland, which took place shortly before the first reports of tremors on Bornholm,” the body known as GEUS said in a statement.
On Saturday, GEUS said it had received “more than 60” notices from people on Bornholm that “earthquake-like tremors”, described as deep rumbling, shaking and rattling, changing pressure in the ear, had been reported in afternoon on Bornholm. .
Nobody was hurt. Police said they, too, were contacted by members of the public about the tremor in the eastern part of the island. Danish media reported that the tremors caused a crack in the wall of a house.
GEUS said the seismic tremors were measured at magnitude 2.3.
Polish authorities have said that there was intense activity during the Anakonda23 exercise in Ustka in northern Poland, involving fighter jets and live firing of artillery ammunition.
GEUS, an independent research and advisory institution within Denmark’s Ministry of Climate, Energy and Utilities, said it had two seismographs on Bornholm that collect data around the clock.
Bornholm, home to almost 40,000 people, is a rocky island in the Baltic Sea, south of Sweden, north-east of Germany and north of Poland.