Operations at BHP's Mount Arthur coal mine in the Hunter Valley stopped for a site-wide inspection after a 4.1 magnitude earthquake reverberated across the region near Muswellbrook on Tuesday afternoon.
Thousands of homes around the greater Muswellbrook area had the power cut, as hundreds of reports came in of people feeling the earth move around 1pm on November 12. Geoscience Australia, the body that measures and observes seismic activity around the country, estimated the quake's magnitude at 4.1, at an approximate depth of three kilometres below the surface, the latest in a swarm event that has rocked the region since August.
It was the most recent in a slew of seismic activity in the Hunter in recent months, beginning with a 4.8 magnitude event on Friday, August 23. It was the most significant seismic shake in 20 years.
More than 150 events have been recorded in the region since January.
After the August swarm, Geoscience Australia deployed six monitoring devices around the Muswellbrook area, as the similarity in magnitude and epicentre indicated that the series of tremors were connected.
"Unlike a typical main-shock-aftershock sequence, where we have a major earthquake followed by a series of smaller aftershocks, a swam consists of multiple earthquakes of similar magnitude," Geoscientist Hadi Ghasemi said.
Since the initial event earlier this year, there have been three subsequent quakes of a similar magnitude to the one felt on Tuesday, as well as several other smaller events. Dr Ghasemi said it was likely the swarm could continue for several months.
Geoscience Australia's nearest permanent monitoring station to Muswellbrook is more than 100 kilometres from the supposed epicentre of the quake near Mt Arthur, the distance of which necessarily leads to some uncertainty about the potential depth and proximity of the epicentre relative to the BHP mining operation.
Coal mining, among other human undertakings, has been linked to earthquake activity in other parts of Australia and worldwide. Still, experts broadly say that it is difficult to draw an unequivocal or direct link between the events over the past few months and mining.
Dr Ghasemi said the six remote monitoring devices around Muswellbrook provided important data that helped the seismic research body better understand the extent of the swarm.
Ausgrid was working to restore power to more than 2500 homes around Muswellbrook into the afternoon, as the mine reported no injuries or damage to the site caused by the quake.
The details of this report are developing. It may be updated.
