An earthquake in Sunbury on Melbourne's western fringe shook thousands of Victorians awake on Sunday night.
The quake, which Geoscience Australia gave a preliminary magnitude of 3.8, caused a social media storm but luckily no reported damage.
Geoscience Australia says more than 25,000 people reported feeling the tremors in the 10 hours after the quake was recorded at 11:41pm, as most Melburnians were sleeping.
It's far from the 43,072 reports after Victoria's biggest earthquake in 2021.
That magnitude-5.9 quake was centred near the town of Rawson and was felt from Sydney to Hobart, west to Adelaide and, of course, in Melbourne.
But what was unusual about Sunday night how shallow the quake was, and how close it was to Melbourne.
Here's what we know.
How common are earthquakes in Victoria?
Earthquakes are measured in magnitude, which signifies the amount of energy released by the quake.
Geoscience Australia says Australia records about 100 earthquakes above magnitude-3 each year.
It says Australia's tectonic plate is the fastest-moving continental land mass on Earth and is colliding with the Pacific and Eurasian plates, generating compressive stress in the interior of Australia.
Earthquakes occur when there is a sudden release of that stress, breaking rocks along fault lines deep underground.
Geoscience Australia seismologist Hugh Glanville says smaller tremors are a regular occurrence in Victoria.
"We have had 29 in the past 10 years, so there's averaging nearly three small earthquakes a year in this local area," Mr Glanville says.
Why did so many people feel the Sunbury quake?
Most of Australia's earthquakes occur at a depth of around 10 kilometres. Geoscience Australia says the Sunbury quake happened at an estimated depth of less than 3 kilometres underground.
"It's quite shallow and possibly the reason people felt this strongly as they did and as widely as they did," Mr Glanville says.
"The source of the shaking is much closer to the people, so they're feeling it more strongly."
Another reason why it caused such a stir was the time it struck.
Hazard seismologist at the Seismology Research Centre, Elodie Borleis, says most people were in a quiet house and many were in bed, meaning it was louder and more noticeable.
"It might sound like a truck passing by or train," she says.
Some callers to ABC Radio Melbourne have described hearing what sounded like a small explosion.
"It's the waveforms of the earthquake travelling through the earth and then coming up and creating that boom sound as it comes to the surface," Ms Borleis says.
How destructive are Victorian earthquakes?
Geoscience Australia says nationally, there is an earthquake above magnitude 5 every one to two years.
Potentially damaging earthquakes of magnitude 6.0 or above happen about every 10 years.
Mr Glanville says earthquakes of the strength recorded at Sunbury can cause strong shaking, but generally only cause minor damage, such as cracks in plaster.
"It's not until 4.5 and even magnitude 5 that you start getting damage to walls and buildings themselves," he says.
The 2021 Rawson quake caused significant structural damage to several locally heritage-listed buildings in Melbourne's Chapel Street, including a century-old building housing a burger chain.
"Of course, that one in 2021 was the largest we've ever instrumentally recorded in Victoria so that was a very large exception in terms of earthquakes," Mr Glanville says.
Federation University geology lecturer Stephen Carey says the Sunbury quake is typical of tremors recorded in Victoria.
But it is more towards the upper end of the strength usually experienced close to Melbourne.
"Because Victoria's a fair way from the edge of the continental plate that we're on, the Australian Tectonic Plate, we don't tend to get many earthquakes and the earthquakes that we get are generally fairly small," Dr Carey says.
He says it is more common to record tremors in South Gippsland, which is closer to fault lines.
"You'll get a shake that might rattle the windows or glasses in a cabinet, but generally that's about as damaging as they get," he says.
Are quakes becoming more frequent?
There were two minor tremors recorded in Croydon, in Melbourne's east, this month.
But the Seismology Research Centre's Elodie Borleis says they are not becoming more frequent.
"It's not unusual," she says.
"A lot of them are so small that people won't feel them, especially if it's during work hours.
"We don't report all the earthquakes that happen just because they're so small so people don't really realise that they're happening all the time."
Will there be aftershocks?
Ms Borleis says some aftershocks have already occurred.
"We did have an aftershock about two minutes after the main shock that everyone felt," she says.
"It was magnitude-2.8."
She says there may be small tremors recorded over the following days.
How safe are you during a tremor or quake?
Just seconds before the Sunbury quake rattled Melbourne, thousands of Android phone users received an emergency alert warning of them about what was about to happen.
Point Cook resident and ABC Radio Melbourne caller Wally says he was one of them.
"It was quite weird," he says.
"I was sitting there sort of watching YouTube and stuff on the phone and just as it was about to happen, like about two or three seconds before, the phone comes up with this alert just saying that there's an earthquake coming.
"It was only three seconds then bang, bang, bang and it happened."
He says the message included advice on what action to take to keep safe.
iPhones do not provide earthquake warnings.
Dr Carey says the phone alert technology is in use around the world, including Japan where his son recently received a warning just seconds before a quake.
"The earthquake has happened, there's been a virtually instantaneous message sent and it's reached the recipients as the earthquake has travelled towards them," he says.
"Those digital signals are really responsive to the earthquake so they're sending a message very quickly which is quite impressive."
Dr Carey says Australia's written records of earthquakes only date back to the early 1900s.
He says the Australian building codes have substantially improved since the 1989 magnitude-5.6 earthquake in Newcastle, which killed 13 people in New South Wales.
"On a world scale, it wasn't a big earthquake but I guess it illustrates the point that our history is a pretty limited one and most of the earthquakes that we've had have been pretty small … so our building codes didn't take earthquakes into account," Dr Carey says.
"But that Newcastle earthquake over 30 years ago now did cause planners to look again – or probably for the first time – at earthquake risk in Australia."
That may explain why the 2021 Rawson quake, which was stronger, was not as destructive.
"There was a bit of damage in the one in 2021 but that was to I think it was a 19th-century building," he says.
What if you didn't feel it?
Well, you're in good company.
Dr Carey has devoted the last 30 years of his career to studying earthquakes and earth sciences.
And he has never felt an earthquake.
He did not feel the Sunbury tremor and even once slept through two magnitude-6 quakes on consecutive nights while leading a study tour in Taiwan.
