Australia earthquakes: Aftershocks likely after Hunter’s ‘earthquake swarm’

Power has been restored to homes in NSW's Hunter region after its third earthquake in weeks, but seismologists warn more aftershocks are likely to follow. Photo / Geoscience Australia

One of Australia’s major wine and coal-producing regions has rattled through its third earthquake in just over two weeks, and experts say there could be more to come.

The 4.5-magnitude quake struck roughly 5km underground, 10km southwest of Muswellbrook in the NSW Hunter just before 6am on Saturday, knocking out power to around 2500 premises.

There have been more than 30 earthquakes in the Muswellbrook area, about 175km north of Sydney, since an initial quake on January 23 this year.

Geoscience Australia senior seismologist Trevor Allen defined Saturday’s event as moderate.

“What, we’ve seen over the last couple of weeks is perhaps what we would now define as an earthquake swarm,” Dr Allen told AAP.

“That is where we see a series of moderate-sized events, and each of those earthquakes tends to have its own aftershock sequence.”

No major damage has been reported from the quake, despite 1100 felt reports to Geoscience Australia.

Ausgrid has since returned power to all 2500 customers affected by outages.

Allen said the region had a slightly elevated risk of more earthquakes of similar magnitudes in the coming weeks.

“There’s a low chance that perhaps even a larger event could occur, relative to baseline conditions, but the stronger likelihood is that we will start to see a reduction in the number of earthquakes and hopefully a reduction in the magnitudes,” he said.

“We’ve detected an earthquake with a preliminary magnitude of 4.5 at 5.58am in Muswellbrook, NSW. If you need assistance in response to this earthquake, contact your local emergency services. Complete a felt report at earthquakes.ga.gov.au.”

We’ve detected an #earthquake with a preliminary magnitude of 4.5 at 5.58am in Muswellbrook, NSW. If you need assistance in response to this earthquake, contact your local emergency services. Complete a felt report at https://t.co/GbOFf4zc24 pic.twitter.com/bteGKWCRaB

— Geoscience Australia (@GeoscienceAus) September 6, 2024

The Hunter Valley is home to significant mining operations, which can be a contributing factor to earthquake activity.

Allen said the lack of historical seismic baseline data for the region made it difficult to quantify mining’s role in recent seismic events.

“When you’re removing large volumes of rock mass, you are changing those stress conditions around the area near the mine, and so that can trigger the earth to respond, and it does so by triggering earthquakes,” he said.

The Liddell power station near Muswellbrook has been suggested by the federal opposition as a potential site for a nuclear reactor and power station as part of the party’s energy transition plan.

Allen encouraged anyone who experienced an earthquake to log it on Geoscience Australia’s felt report system.

“If you do find yourself experiencing earthquake, ground shaking, the best advice we have is to drop, cover and hold on,” he said.

“And so that is to drop to the ground, cover your head and, if you can, move underneath a sturdy table or desk and wait until the shaking stops.”