Last night, a magnitude 4 earthquake struck Melbourne’s northwest. According to Geoscience Australia, this earthquake was felt and reported by over 25,000 people across Melbourne, with some reports from up north in Bendigo and down south in Hobart. This earthquake, which hit Sunbury at 11:41pm, had a shallow depth of just 3km, resulting in notable shakes and rumbles across households. This incident was not the first earthquake in Victoria, and it certainly won’t be the last. Just a couple of weeks ago, there was a magnitude 2.5 earthquake in Croydon. And, perhaps more memorably, there was the 5.9 earthquake of 2021, which had an epicentre north of Rawson, and sparked plenty of memes. So, are earthquakes a common occurrence in Melbourne? We spoke to Adam Pascale, chief scientist at the Seismology Research Centre, to find out more.
Earthquakes in Melbourne
While it might feel like we’ve been having more earthquakes than usual in Melbourne, according to Adam, this is simply because there’s an increase in awareness about earthquakes, rather than an increase in the quakes themselves.
The Seismology Research Centre has been operating since 1976, and has the greatest number of earthquake seismograph stations in the country. Every week, they release an earthquake map showing all of the incidents that have occurred in southeast Australia.
“We’re recording 30 to 40 earthquakes a week, sometimes more, sometimes less, but they’re always happening,” said Adam.
The ones that are being felt and reported, like the 2021 earthquake, just happen to occur closer to populated areas. Earthquakes that occur in the middle of nowhere, and that aren’t felt by anybody, don’t get as much attention.
“So it really is a coincidence of where those earthquakes are occurring exactly, when they’re close to populated areas,” said Adam.
The overall rate of earthquakes of a particular magnitude also isn’t changing. “We look at things on geological time frames, so to see a magnitude 4 every so often is not unusual,” said Adam. “We’ve had magnitude 4s where nobody’s felt them, and they don’t make the news so people don’t know about them.”
What is the likelihood for a big earthquake in Victoria?
The earthquake last night was the largest one within 40km of Melbourne CBD in 120 years. The last tremor to beat it took place in 1920, and reached a magnitude 4.5 in Port Phillip Bay.
If you look further out than 40km, you’ll find more examples of seismic activity. The magnitude 5.9 earthquake in 2021, for example, had its epicentre 180 km east of Melbourne. You can find the results of earthquakes in our mountain regions, like Mount Dandenong and the Yarra Ranges, which were formed by earthquake activity over millions of years.
Australia is sitting nicely in the centre of the Indo-Australian plate. While it’s not on a plate boundary, like New Zealand or Indonesia, there is the potential for an earthquake to occur anywhere in the country as high as magnitude 7.5. This is because our plate is under pressure from neighbouring plates, like the Pacific plate, and this pressure results in fault lines.
“We know that there are faults near enough to Melbourne that are large enough or long enough to host a magnitude 7 earthquake,” said Adam. “So it is possible. But unfortunately we can’t predict earthquakes, so we can’t say when it will happen.”
You can find a map of Australia’s neotectonic features, like faults and folds, here.
What should you do during an earthquake?
If you experience an earthquake in the future, and you’re indoors, remember to drop, cover and hold on. Drop down to the ground and find some cover under something that can protect you from falling objects, like a sturdy table or bed. Then, hold on until the shaking stops.
If you can’t find cover under something study, drop down to the ground and protect your head and neck with whatever you have available, like a book or a pillow. Stay away from glass, windows, outside doors and walls, and anything that could fall. Stay indoors until shaking stops, then exit the building, get somewhere safe and find help if you need it.
If you’re outdoors during an earthquake, stay where you are, and keep away from buildings, streetlights and utility wires. The greatest danger lies directly outside buildings, at exits and along exterior walls.
To learn more about what to do during an earthquake, read this guide from Victoria State Emergency Service.