Adelaide, Australia
People across South Australia have reported being awoken by mysterious tremors that rattled windows and sent pets into a frenzy - but authorities say there was no earthquake.

The tremors and loud rumbles were heard between 2am and 2.30am on Saturday, prompting people to turn to Facebook and Twitter to look for answers and share what they felt and heard.

The Geoscience Australia website initially reported a 1.4 magnitude quake around Mount Compass but the notice was removed from the website after further investigations.

The agency subsequently advised instead that the event was caused by thunder and that no quake had been detected.

Some people reported feeling at least two minor shakes, while others reported hearing rumbles that woke them up. Geoscience Australia says it has received over 600 reports from Adelaide residents.

David Love, Seismologist with the Seismological Association of Australia, said the tremors remained a mystery. "We are investigating," Mr Love said.

"I can confirm that is definitely not an earthquake; exactly what it is, I don't know but we have recorded it on quite a lot of our instruments". He said very sensitive instruments had detected the tremors between Hamley Bridge and the Hindmarsh Valley. "So that covers the whole of Adelaide".

He said the strongest signal was detected at Morphett Vale. He was reluctant to speculate about what might have caused the tremors, except to say it was possibly "something occurring in the atmosphere".

Sky News Meteorologist Tristan Meyers tweeted that the tremors were "actually due to a temperature inversion, amplifying the sound of thunder in a storm! There was a large temperature inversion in the atmosphere- the sound waves refracted back towards the ground amplifying the sound of thunder," he said.

Comment: In an area covering just over 1,200 square miles?

Commenting on, CJ said: "Yep. Definitely heard it. Woke first at 2am, 2nd not long after. Was a strange rumbling noise with shaking windows. Cat went crazy. Never heard anything like it before. Freaked me out!!!"

Susan Stewart tweeted "Woken up by the windows rattling, and then a low frequency rumble-not much noise. (Colonel Light Gardens). Different to usual thunder."

Tom Roze tweeted: "Windows rattled and thought some one was breaking in".