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The mystery of the massive "boom" that shook parts of southern Perth has been solved.
Multiple people reported what they described as a "deep bang" about 11.30am followed by a "shock wave" or "deep earth shake", which rattled their homes.
"It was really strange. It was like it was loud, but it was far away at the same time," Baldivis mother Krystal Brown told 9News.
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Speculation ran rife throughout the day before the cause of the sound – heard as far south as Mandurah and Fremantle – was revealed to be a sonic boom from Republic of Singapore Air Force F-15 fighter jets training off the Western Australia coast.
"By going supersonic, they've broken the sound barrier and it gives a loud, sharp crack," aviation expert Geoff Thomas told 9News.
The fighters, which were training off Rockingham, should only go supersonic above water, not land, experts say, because of the potentially dangerous effects on residents.
"[It was] just a massive boom," Parmelia resident Hazel Williams said.
"Very, very loud. Very intense. Very quick.
"I grabbed the cat and I thought, 'I'm getting out of here'."
9News understands the fighters were 30 nautical miles off the coast and going twice the speed of sound.
It was simply a perfect storm of weather conditions that amplified the noise, which was heard at Garden Island in the west, as far east as Wandering in the wheat belt, and as far south as Boddington.
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People in suburbs including East Fremantle, South Guilford, Jandakot, Hilbert, Spearwood and Bull Creek also experienced it.
The Royal Australian Air Force is hosting an extended fighter aircraft detachment from the Republic of Singapore Air Force, it says online.
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They are based at RAAF Base Pearce in Bullsbrook, WA.
"Additional to the Pilatus PC-21, and Hawk-127 Lead-in Fighter aircraft which are currently based out of RAAF Base Pearce, the base will host small detachments of F-15SG and F-16C/D/+ aircraft from the Republic of Singapore Air Force," it said.
Geoscience Australia said it had not detected any seismic activity indicating an earthquake.
9News has contacted the Defence Force.
