THE LARGEST earthquake to hit the Hunter in two decades was recorded at a coal mine on Friday afternoon, injuring some workers.
Geoscience Australia said the 4.8 magnitude event, 10 kilometres deep, was followed by at least two aftershocks within 15 minutes, with magnitudes of 3.3 and 2.9.
Thousands of people across the region, and as far away as Wollongong, Dubbo and Tamworth, felt the earth rumble beneath them or buildings shake around them.
Schools and courthouses were evacuated, businesses closed and more than 2500 people were without power in Muswellbrook.
Items fell, desks moved, windows rattled and people were left shaken.
Emergency services were prepared to respond but thankfully the earthquakes caused no major damage.
The epicentres of the initial quake and at least two aftershocks appeared to be at BHP's Mt Arthur Coal mine in Muswellbrook.
A BHP spokesperson told the Newcastle Herald that "a few" team members from the mine site required first aid for minor injuries suffered when items fell.
"Thankfully, no one was seriously hurt," the spokesperson said.
Inspections are being carried out at the site before operations can safely resume and BHP is working with Muswellbrook Shire Council on Friday.
Geoscience Australia's senior seismologist Dr Hadi Ghasemi said the organisation was flooded with more than 1600 field reports of a tremor within just a couple of hours, some from hundreds of kilometres away.
"It is not unusual for the earthquakes to occur close to the mines, because the mines are actually located close to the fault lines," Dr Ghasemi said.
"There is always a possibility that the aftershocks will continue for the weeks to come, but as a general rule of thumb, the larger aftershocks tend to occur at the earlier stages."
He confirmed the 4.8 magnitude earthquake recorded at 12.01pm on August 23 was the most significant seismic event within 100 kilometres of the epicentres in the past 20 years.
In that time, more than 150 earthquakes have been recorded in that area, he said.
UNSW Sydney associate professor Stuart Clark is a geophysicist from the School of Civil and Environmental Engineering and an expert in earth physics and plate tectonics.
He said the geology around Muswellbrook acted as a funnel for the earthquake, channelling its power towards the town.
"Basically the way the geology is structured is there is a long sinkline acting as a telegraph to transport the signal northward," Professor Clark said.
"That's propagating it from the epicentre to that location along the geological structure and concentrating in that direction."
Bridge Street businesses at Muswellbrook were taking stock Friday afternoon after scattered but minor damage was sustained during the earthquake.
Local workers described feeling like a car or truck was about to burst through the walls as a chimney was felled on the historic Edward Higgens, Parkinson real estate building.
Amanda Sharp lives two minutes from the centre of Denman and told the Newcastle Herald she heard the earthquake coming before she felt it.
"It actually sounded like a huge wind tunnel coming up, it sounded like massive wind but there was no wind, and then the whole entire house just started shaking," she said.
"We have things on the top of our kitchen and they all fell off, we had glasses on top of our kitchen shelf and they've fallen down."
She said her horses were stirred up and agitated, and she still couldn't coax her dog out from under the bed and hour after the rattle.
Muswellbrook's Eatons Hotel licensee Khalifa Askar said it was "a little bit scary there for a moment".
"It was shaking for about 10 to 15 seconds... a bunch of stuff fell off my fridge," Mr Askar said.
Layla Moss was working at Denman's Royal Hotel when she felt the tremor.
"It shook everything inside," she said.
"All our wine glasses are hanging up over the bar and they shook a lot, but there was no damage, nothing falling over."
Over at the Denman Hotel Jack Buckley said the only causality was a runaway wine bottle.
"We did feel it, it was just a bit of shake and we had a few bottles rolling around on the shelf," he said.
One Hamilton resident reported feeling their whole house shake when the quake hit.
"It felt like there was something under the house," they said.
"I was very confused."
A Department of Education spokesperson confirmed Muswellbrook High School and Muswellbrook South Public School students went home after an earth tremor at about 12.30pm on Friday as a precaution.
"Signs of damage have been reported in a number of places across the two sites," they said.
Hunter Water completed a visual inspection of the Grahamstown and Chichester Dams, as required by its earthquake safety protocols, and the SES was working with private dam owners.
