Earth tremors reported by people living in north Wales and parts of north west England on Tuesday are believed to have been caused by a "sonic boom".
A Typhoon jet is reported to have been flying in the area
The first tremors were felt around midday on Anglesey, with further reports in Merseyside and Lancashire.
They were caused by a "sonic boom", which can be heard when an aircraft exceeds the speed of sound.
The British Geological Society says a Typhoon jet was on exercise over the Irish Sea at the time.
People rang BBC Wales to report a series of "tremors" on Tuesday lunchtime with reports of "loud explosions" being heard.
Hundreds of people all over Merseyside also felt the tremor.
Police, firefighters and the Met Office on Merseyside received calls from people from as far afield as Widnes, Southport, Birkenhead, St Helens.
Police in Lancashire received calls from a wide area including Poulton, Cleveleys and Blackpool.
But the British Geological Society in Edinburgh said British Aerospace in Preston confirmed that a Typhoon Eurofighter aircraft was on exercise over the Irish Sea at the time.
A spokesman said that there were at least four separate events between 1200 and 1230 GMT.
Reports described " heard a loud rumbling noise", "felt the ground shaking", "the whole house shook quite violently" and "all the windows rattled," said the spokesman.
In September workers at Powys Council HQ in Llandrindod Wells thought they has suffered similar earth tremors.
But the disturbance was later blamed on a sonic boom from low-flying aircraft as was another loud explosion heard in Conwy and Denbighshire a week later.