Melbourne earthquake 2023: are they becoming more common? A seismology expert explains

By Dee Ninis, Monash University

Last night at 11:41pm local time, the greater Melbourne region was shaken by a magnitude 4.0 earthquake – as calculated by the Seismology Research Centre – centred near Sunbury, approximately 30km north of the CBD.

Geoscience Australia have so far received more than 25,000 reports from people who felt this earthquake, some as far as Hobart, which is 620km away from the epicentre.

In the Melbourne region, the earthquake reportedly produced shaking which lasted roughly 10–20 seconds, according to witness reports on social media. It was followed two minutes later by a magnitude 2.8 aftershock, which was reported by some people in the epicentral region between Sunbury and Cragieburn.

Are earthquakes becoming more common in Melbourne?

In September 2021, a magnitude 5.8 earthquake rattled Melbourne, its epicentre being at Woods Point to the east of the city. This earthquake was felt as far away as Brisbane and Adelaide.

Last night’s earthquake follows a magnitude 2.5 earthquake near Ferntree Gully, to the east of Melbourne, two weeks ago on May 16. Another one with a magnitude of 2.0 was felt by about 1,300 people in roughly the same region on May 22, according to Geoscience Australia.

Although this means some Melbournians have experienced two or even three earthquakes in the last two weeks, earthquakes are not becoming more common in Melbourne. It is not unexpected for there to be 10–12 felt earthquakes a year somewhere in the greater Melbourne region – these need not occur at regular intervals.

Earthquakes in Australia occur as a result of stresses at our surrounding tectonic plate boundaries – where different plates collide, grind past one another, or are being forced apart. These stresses make their way towards the middle of the plate, too.

In southeast Australia, the forces at the Pacific-Australian plate boundary to the east of us – the same plate boundary which passes through Aotearoa New Zealand – produce a buildup of strain. This is eventually released in the form of earthquake ruptures at weak zones or “faults” in the crust.

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