At 7:08PM on Wednesday night, Melbourne, Australia was hit by an earthquake.
Hundreds of residents in the city’s eastern suburbs reported hearing a loud rumbling and feeling their houses shake as the tremor—later confirmed by Geoscience Australia as a Magnitude 2.5 earthquake occurring about seven kilometres beneath the surface—struck near Pakenham, about 60 kilometres south-east of the CBD.
Geoscience Australia—the government’s “pre-eminent public sector geoscience organisation”—received more than 500 reports from people who experienced the quake, many of who described it as a bang, a blast, or a rumble, followed by palpable vibrations.
"It sounded like a loud rumble rolling in from the distance, almost train-like," a man from Boronia, about 35 kilometres from the epicentre, told the ABC. "The windows started shaking and then the couch started to shake too."
That "blasting noise" is fairly common during earthquakes, according to senior seismologist Trevor Allen, who suggested that “it may be a noise that's resulting from the rocks actually breaking beneath the surface, and that transmits to the surface of the earth as soundwaves.”
What exactly triggered the earthquake remains uncertain, although Dr Allen further noted that Magnitude 2 tremors are typically identified in the Pakenham area about once a year. Southeast Victoria has multiple known active earthquake areas, he added—despite Australia being located in the centre of a tectonic plate.
Speaking to VICE News over email, Dr Allen explained that although the vast majority of earthquakes occur at the boundaries of tectonic plates—often when the edges of two plates become locked together, building up stress as they move until the fault breaks and releases seismic energy—it’s not uncommon for similar phenomena to occur elsewhere.
“While we don’t experience nearly as many earthquakes in the middle of tectonic plates, such as the Australian continent, the same tectonic forces strain the rocks beneath the continent,” he said. “Over much longer periods of time (perhaps thousands to hundreds of thousands of years), these forces stress the Australian continent until the rocks break along a zone of weakness, or fault.”
So what are the chances of Australia being hit by a more devastating earthquake in the future? Not all that slim, according to Dr Allen.
“Australia experiences about one to two earthquakes of Magnitude 5 every year, and perhaps one earthquake of Magnitude 6 or larger every ten years,” he said. For reference, a Magnitude 6.4 in Albania last year killed 51 people; a Magnitude 5.6 in Pakistan killed 40.
“Most of the time we are fortunate that large earthquakes in Australia mostly occur in relatively remote regions and don’t have significant societal impact—for example, a Magnitude 6.6 that occurred about 200 kilometres off the coast of Broome in July last year,” Dr Allen added. “Sometimes, however, a significant earthquake does occur closer to a population centre.”
Earthquakes aren’t the only tectonic phenomena occurring in and around Melbourne, either. More than 400 active volcanoes are littered throughout south-eastern Australia as part of a 15,000 square kilometre volcanic field known as the Newer Volcanics Province, and at least three of those are sleeping beneath Australia’s second-largest city. One volcano is sitting beneath the metropolitan centre; one in the western suburbs; while a third is located underneath Tullamarine International Airport.