On Saturday, May 13, more than 60 people contacted the Danish and Greenland Geological Survey (GEUS) to report the tremors on the Danish Baltic island of Bornholm.
According to the news of AP News, residents of the region said that they felt a deep rumble, shaking and pressure change in their ears along with the tremors, while GEUS reported that 2.3 magnitude tremors were recorded. It was initially assumed that these tremors were an earthquake, but this was dismissed by GEUS seismologists.
Instead, they stated that they believed the tremors were caused by “acoustic pressure waves from an unknown source.” Also, another possible source of these unexplained tremors could be military exercises in Poland, more than 140 kilometers to the south. However, this possibility, like earthquakes, does not seem correct. In a statement seen by AP News, GEUS said, “Seismologists have reported that the tremors are unlikely to be caused by a controlled eruption in Poland, which took place shortly before the initial reports of tremors in Bornholm.”
No injuries were reported, although tremors were reported to crack the walls of a house. Although GEUS cannot give a clear answer as to the source of the pressure waves, several different possibilities are mentioned.
“When we get reports of rumble and shaking, we usually find that the air force almost always crosses the sound barrier at sea and that the atmospheric conditions are suitable for the propagation of sound on land,” said Björn Lund, Associate Professor of Earth Sciences at Uppsala University, in a conversation with Swedish newspaper Dagens Nyheter.
Lund added that under certain weather conditions the sonic boom may appear to be coming from the land.
Similar reports of earthquakes had come from residents in the northwest of England in 2022, which were later determined to be caused by a Typhoon warplane breaking through the sound barrier off the coast. For now, however, the exact cause of the tremors felt in Bornholm is unknown.
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