SONIC EVENT: LEICESTERSHIRE TO WILTSHIRE 12 APRIL 2012 17:17/17:18 UTC (18:17/18:18 BST)
On the evening of 12 April 2012, from around 18:30 BST (17:30 UTC), the BGS began to receive information from the media, the police and several residents in towns and villages in and around Leicestershire, the West Midlands, Warwickshire, Oxfordshire and Wiltshire, who reported that they felt what many had thought to have been an earthquake at sometime around 17:15 BST (18:15 UTC). Reports described "we heard a loud boom ", "it felt like some kind of explosion", "felt and heard a loud, low, deep bang which lasted a few seconds" and "there was a loud, deep rumble and all the birds flew from the trees". Reports were received over an elongated area for a distance of approximately 120 km.
Data from the BGS seismic networks in the region were examined and signals consistent with a sonic origin were recorded at around 17:17/17:18 UTC on several stations in the area. The observations received are similar to those which have been received previously for sonic booms. RAF Kinloss were contacted and have advised that at the stated time there were military jets on exercise in the area.
The Ministry of Defence have since confirmed the sonic boom was caused by a Typhoon fighter aircraft.
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.