Reports of earthquake-like shaking in Port Stephens on Wednesday morning has authorities just as baffled as to the cause of the event as residents.
A number of Tomaree Peninsula residents in Nelson Bay, Anna Bay, Shoal Bay and Boat Harbour took to social media about 10am to report a feeling of "shaking" at their homes, with some people stating this occurred up to three times, and hearing a bang or boom.
Residents also reported that domestic pets such as dogs went into "melt down" and reacted to the shaking and noise.
Geoscience Australia, the Australian government agency that reports on significant earthquakes for the nation, said that it had received "felt reports" from Port Stephens, Newcastle, North Western Sydney and Blue Mountains areas describing shaking between 10am and noon.
However, the department said: "We were unable to detect any earthquakes in these areas during that time."
It comes as Geoscience Australia measured a small earthquake near Muswellbrook in the early hours of Wednesday morning near a mine west of Lake Liddell.
The 2.8 magnitude quake was felt in the surrounding area around 5.26am, and was measured at a depth of 10 kilometres in the earth's surface.
We have received felt reports from Port Stephens, Newcastle and Northwestern Sydney/Blue Mountains areas describing shaking between 1000 and 1200 AEDT. We were unable to detect any earthquakes in these areas during that time.— EarthquakesGA (@EarthquakesGA) February 12, 2020
While some people discussing Wednesday morning's event on social media attributed the shaking in Port Stephens to the Muswellbrook earthquake, which has not been confirmed by authorities, others theorised the noise and shaking could have been caused by a 'sonic boom' created by RAAF fighter jets conducting flight training off the coast. This is also unconfirmed.
A sonic boom, as outlined on the Department of Defence's website, is created when aircraft travel at approximately 1225km/h at sea level and the temperature is 20C.
Sonic booms can travel some distance and the sound can be enhanced by certain weather conditions, such as high humidity and cloud cover. In some cases, sonic booms can damage property, especially glass such as windows.
"Supersonic flight is not permitted over land and is usually only practiced over the ocean, well away from the coast, however, noise from a sonic boom may travel and be heard over land areas," the Department of Defence said on its website outlining what sonic booms are.
According to the RAAF's air noise map, the only Air Force flight activities scheduled for the eastern training area and flying corridor - which takes in Port Stephens and NSW's east coast - today was 'frequent flying'. There were no training exercises listed.
Geoscience Australia is always interested in hearing from anyone who feels a tremor. To fill out a felt report, visit Geoscience Australia's website.