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Possible Sonic Events - Grampian Area - 22 May 2012 19:00-23:30 UTC

On the night of 22 May 2012, from around 19:00 UTC, the BGS began to receive information from the media, the police and many residents in predominantly coastal towns and villages in the Grampian area, who reported that they felt what many had thought to have been several earthquakes at times between 19:00 and 23:30 UTC.

Data from the BGS seismograph network in the region were examined and no earthquakes or signals consistent with a sonic origin were recorded. However, the reports received are consistent with historical observations received for previous events with a sonic origin.

RAF flying complaints were contacted but were unable to confirm if aircraft were operational at the time.

The extent of the effects of the possible sonic events were felt over a distance of approximately 65 km, stretching from near Ellon, in the north, to Laurencekirk in the south. Inland, one report was received from close to Aboyne, approximately 35 km from the coast. Reports described "A very loud rumbling sound like thunder but from the ground", "felt like a compression wave, and saw the curtains move and window flex twice with each sound. Trembling could be felt through the floor", "whole summer house shook", "velux window moved while open" and "roof timbers vibrated ".

A sonic boom is the sound associated with the shock waves created when an object, such as an aircraft, breaks the sound barrier. An aircraft travelling slower than the speed of sound (~760 mph) creates a series of audible pressure waves that spread out in front and behind it. These waves travel at the speed of sound. As the speed of the aircraft increases these waves get closer together and at the speed of sound they merge into a single shock wave that starts at the nose and ends at the tail of the aircraft.

The boom is created by the sudden increase in pressure at the nose and also as the pressure returns to normal at the tail as the aircraft passes. This can lead to a distinctive "double boom". The shock wave or boom continues to be generated for as long as the aircraft is supersonic, which is why they are typically observed along a long strip along the flight path of the aircraft.

 

Map showing the distribution of felt reports. CLICK FOR A LARGER VERSION

 

The moment a sonic boom occurs. CLICK FOR A LARGER VERSION.