been put down to a "supersonic boom'' by the Environment Ministry.

Permanent secretary for the Ministry Dr. James Burnett-Herkes, who heard the rumbling, said that after talking to technical officers, his best guess was that it had been caused by a supersonic aircraft flying over the Island.

However, a spokesperson from the US Naval Air Station said the base was not aware of any supersonic craft in the area when the tremor was felt.

Dr. Burnett-Herkes ruled out thunder or any kind of explosion as the cause of the tremor, because its force seemed to have been the same from Smith's to Somerset.

"It seemed to cover too wide an area for thunder or anything man-made,'' he said, adding the US Geographical Survey and National Earthquake Information Centre had no recording of any seismographic activity in the area.

Supersonic boom Police and the media received dozens of calls around 3.30 p.m. on Sunday from people saying they heard the earth move and heard loud rumblings. No calls were received from St. George's residents.

Mr. Miles Mayall, who operates a Bermuda College-funded seismograph station beneath Harbour Radio at Fort St. George, also ruled out an earthquake.

Although something did register on his seismograph, Mr. Mayall did not think it was consistent with an earth tremor. He also thought the tremor came from an airplane, saying it was probably a US Navy craft.

A Harbour Radio spokesman explained the seismograph would pick up any shake in Bermuda, man-made or natural.

However, the station -- once funded by the US Earthquake Information Centre -- is to close down at the end of the month as the College has withdrawn its funding.

Dr. Martin Brewer, a former Bermuda College geology professor who has been tracing the history of earthquakes in Bermuda -- though he works for the Immigration Department, said the Island usually gets slight tremors every three-four years. The Island has had some big quakes, like the one in 1925 which cracked water tanks and roofs.

According to Dr. Brewer's charts, the last clump of tremors was in 1988, while just one was felt last summer.

He believes the "random phenomena'' are caused by strain as the thick Bermuda Ridge, a large lens of volcanic rock, settles deeper into the Earth's mantle.