[imagesource:imageflare]

People living on the Danish island of Bornholm contacted the Geological Survey of Denmark and Greenland (GEUS) on Saturday, 13 May, to report several tremors that were making their island shake.

Residents described a deep rumbling, shaking, and change of pressure in their ears when the tremors hit.

One would expect the authorities to confirm some sort of earthquake, but even though GEUS reported the tremors to be a magnitude of 2.3, seismologists confirmed that no earthquake activity had taken place.

Instead, they believe the tremors were caused by ”acoustic pressure waves from an unknown source”.

A possible cause for these acoustic pressure waves’ was a military exercise that was conducted about 140km away in Poland, however, that, along with earthquakes, was ruled out soon after.

“The seismologists can report that it is unlikely that the tremors originate from a controlled explosion in Poland, which was carried out shortly before the first reports of tremors on Bornholm.”

According to The Guardian, GEUS seems to be as puzzled as the inhabitants of Bornholm, and to date, no cause for the tremors has been determined, so we are left with ‘possibilities’. One of those is a likely sonic boom from a military aircraft passing through the sound barrier.

“What usually happens when we receive reports of rumbling and shaking is almost always that the air force has passed through the sound barrier at sea, and the atmospheric conditions have been such that the sound bang rolled in over land.”

In certain weather conditions, the sonic boom can create the feeling of a tremor as the pressure waves buffet our bodies and buildings. A similar incident happened in 2022 when a British Typhoon jet broke the sound barrier and sent tremors running through towns in the northwest of England.

Aircraft have however also been ruled out by now, so the cause of these ‘pressure waves from an event in the atmosphere’ over Bornholm is still unexplained.

[source:guardian&ifls]