Canberrans have reported feeling tremors on Wednesday morning after an earthquake struck north-east of Melbourne.
The initial 5.8-magnitude earthquake hit Mansfield, Victoria at 9.15am with a depth of 10 kilometres, according to Geoscience Australia.
It was followed about 15 minutes later with a magnitude four aftershock and another magnitude 3.2 aftershock hit shortly before 10am.
Geoscience Australia seismologist Spiro Spiliopoulos said it was very unusual for Australia to experience earthquakes of this magnitude.
"When we look at the statistics of earthquakes in Australia, magnitude six occurs every roughly every 10 years, eight to 10 years, so these are very unusual," he said.
Mr Spiliopoulos said there were two 5.0-magnitude earthquakes within 100 kilometres of this location in 2012.
He said aftershocks were expected to continue.
"Typically we say you can get aftershocks up to a magnitude one below the initial one. So we may get after shocks up to a magnitude 5, but we can't predict when they occur, we just know they will occur."
Dr Michelle Salmon, a seismology research officer at the Australian National University, said today's earthquake was the largest onshore earthquake since the 5.7-magnitude Lake Muir earthquake in in Western Australia in 2018.
Dr Salmon said she had heard reports of the quake as far north as Newcastle, but some areas felt the tremors more than others.
"Within Canberra, I didn't feel it, but it will depend on what you're standing on at the time, some areas of the ground will shake more than others. Specifically, areas that sort of have very soft soil tend to shake more than if you're standing on rock," she said.
"The high rise apartments can tend to sway and so you will feel more at the top floors than you would on the ground floors."
She said aftershocks could continue for weeks afterwards getting smaller over time.
The Australian building code takes into account the possibility of earthquakes, but depending on the location, foundations and age of a structure there could be some damage caused by a magnitude-6 quake.
Social media footage has shown some damage to buildings on Chapel Street in Melbourne.
Mr Spiliopoulos said some Canberrans in high-rise apartments felt the earthquake, while others didn't feel a thing.
"People in high-rise buildings tend to feel these things more because they sway a little bit as the earthquake waves pass through the building," he said.
ACT Chief Minister Andrew Barr said the earthquake was felt in the Legislative Assembly building in Civic and confirmed ACT ESA was responding to calls across Canberra.
However, there have been no reports of damage in the ACT.
"Our ACTESA Emergency triple zero (000) call centre has received a number of calls from concerned community members who have felt the tremors," an ESA spokesperson said.
"At this stage, we have no reports of damage within the ACT. Please be assured that the ACTESA is ready to respond to any incident that occurs within the territory."
The initial earthquake was felt as far away as northern Tasmania and Sydney.
Residents in Wagga Wagga and throughout the Riverina region have also reported feeling the tremors.
GeoScience Australia said the epicentre of the earthquake was in Gaffneys Creek, Mansfield Victoria.
The shaking and shuddering was felt in the Albury Wodonga area at about 9.16am and was also felt in Melbourne.
A second earthquake was measured 15 minutes later at the same location, this time at a magnitude of four.
A Canberra Times reader from Phillip Island reported initially thinking someone was breaking into his home, upon seeing and hearing his screen door handle shake and rattle for almost a minute.
He heard the earthquake while outside his home about 9.15am.
"It was errey [sic] like imagining an unseen force shaking the screen door as if wanting to get in."
Macgregor resident Dan Sanguineti said he felt a mild tremor which was enough to alert his senses.
"It felt a bit like a big truck going past for a couple of seconds," he said.
Other Canberrans noticed drinks spilling or curtains swaying. Some buildings were evacuated, including the Department of Finance building at One Canberra Avenue in Forrest.
Canberra Times reporter Harley Dennett, who was in the Department of Finance building, said it felt like someone walking on the roof of the building. The few occupants of the building had to leave the building for about two hours while it was checked for damage.
Earthquakes occur when stress in the Earth's continental plates builds up and is suddenly released.
"The Australian continent is in the middle of a plate, and that plate is moving across the surface of the Earth - and that generates stresses within the plate because it's running into other plates," Mr Spiliopoulos said.
"And that builds up the stresses within the Australian Plate and wherever there are weaknesses in the plate and there are faults, you get these get this energy released, the stress released, and that's what causes earthquakes."
A large number of faults are located near Mansfield, Victoria, making it more prone to earthquakes.
An average of 100 earthquakes of magnitude 3.0 or more are recorded each year. The destructive Newcastle earthquake in 1989 was a magnitude 5.6.
In Canberra there is a seismometer in the basement of Parliament House, one at Melrose High School, one at Daramalan College, two on Mount Stromlo and one at Kowen Forest.
Dr Salmon manages the schools program and said there was usually an uptick in interest in seismology following earthquake, especially in areas which felt the tremors.
"Actually, the first thing I knew about this earthquake was a teacher in Griffith who sent me an email to say that they've felt an earthquake," she said.
She encouraged anyone who felt today's earthquake to fill out the form on Geoscience Australia's website to report their experiences.
"It gives them a really good idea of how the shaking occurred around the country, and that gives us good information for earthquake hazard modelling in the future."
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