‘An explosion underneath the house’: Record-breaking earthquake strikes near mine

A record-breaking earthquake near a gold mine in NSW’s central west has rattled the ground as far away as Sydney and Batemans Bay.

The 4.5-magnitude quake hit about 35 kilometres south-west of Orange at 8.19pm on Tuesday.

Nearby residents reported 10 to 15 seconds of rumbling, and compared the sound to a jumbo jet. Those closest to the epicentre said it was like a bomb going off.

“It was like an explosion underneath the house,” said Bruce Reynolds, the mayor of Blayney Shire, who lives 12 kilometres from the epicentre.

Reynolds said it felt more violent and sudden than a 4.3 magnitude quake that struck in a similar location on Good Friday in 2017.

“This one was different,” he said. “This is possibly the biggest that we’ve seen in this local area in modern history, since the Richter scale was first used.”

Couches jumped in Mittagong, houses creaked in Lawson, windows rattled in Bathurst and cats acted up in Caringbah, people reported on social media.

The biggest concern was for miners working underground at the Cadia gold mine, close to the epicentre, who had to be evacuated.

In a statement, the operator of the mine, Newmont Cadia, confirmed its seismic sensors detected the quake and that its workforce was safe.

In some cases, mining, fracking, and other human activities such as wastewater injection can induce earth tremors, but it’s very difficult to draw a direct link between a mine and specific earthquake, senior seismologist at Geoscience Australia Dr Phil Cummins said.

“Mining can change the ‘stress field’ across the earth, and a change in the stress field can potentially trigger an earthquake,” he said. “The problem is that our network that we use to monitor earthquakes nationally is just too coarse to be able to determine that mechanism with any accuracy.”

Extracting and depositing large amounts of material underground – and moving water around – can change how tectonic stress is distributed and influence seismic activity, he said.

“Some papers have been able to correlate the change in seismic activity with changes in mining activity, particularly for things like fracking in particular, and draw a correlational relationship,” he said.

Dense, local monitoring of seismic activity over a long period of time would be required to better understand if specific mining activities trigger tremors or earthquakes.

Cummins said there had been four earthquakes above 3.5 magnitude in the immediate vicinity of the Cadia mine since 2017. The quake on Tuesday night was the largest ever felt in the area, he said.

Premier Chris Minns was asked on Wednesday morning if he had been briefed on a possible link between earthquakes and the mine.

“We don’t believe it’s linked, or I’ve been given no information that it has been linked. I was briefed about it late last night,” Minns said.

Earthquakes can happen across the continent due to forces exerted on the boundaries of the Australian tectonic plate. “Even though those boundaries are very far away, the stress is slowly building up in the Australian crust – so earthquakes can happen anywhere,” Cummins said.

More than 2000 people reported feeling the recent quake to Geoscience Australia.

“The weak shaking extends as far as Batemans Bay in the southeast, which is a couple of hundred kilometres at least,” Cummins said.

Two aftershocks, of magnitudes 2.4 and 2.2, hit the central west in the 30 minutes after the earthquake.

Police are not aware of injuries or damage. NSW Recovery Minister Janelle Saffin had been in touch to offer support, Reynolds said.

Because the Richter scale is logarithmic – meaning each number represents a 10-fold increase in severity – a 4.5-magnitude earthquake is about 1.6 times bigger than a 4.3-magnitude quake, but twice as strong in terms of energy released.

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