Movement in a fault line that runs through the Hunter Valley is the most likely explanation for a series of earthquakes that have rocked the Upper Hunter over the past week.
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The fault, known as the Hunter-Mooki Thrust, forms the boundary between the Sydney Basin Rocks and the New England Fold Belt to the north.
A Geoscience Australia spokeswoman said the fault may have been reactivated due to a build-up of pressure.
“While this feature has not been the subject of detailed earthquake study, it is favourably oriented for reactivation in the current stress field,” she said.
“A possible continuation of the thrust offshore Newcastle shows significant earthquake-related uplift across it.”
Geoscience Australia recorded seven earthquakes near Muswellbrook ranging from 2.1 to 3.5 on the Richter Scale between last Thursday and Monday.
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The spokeswoman said seismic activity in the Hunter was not surprising, with 90 earthquakes recorded in the region over the past decade.
They include 19 earthquakes that have occurred within 50 kilometres of Muswellbrook since last January.
The director of Australian Centre for Astrobiology at the University of NSW, Martin Van Kranendonk, said it was unlikely the recent earthquakes were the result of mining activity.
“Earthquakes are much more likely to be the result of movement in the crystalline structures of the earth,” Professor Van Kranendonk said.
“If it was a mining-related earthquake it would almost certainly be a one-off event. You might get a little bit of uplift but that would be it,” he said.
Professor Van Kranendonk said it was common for rich ore seams to be found along geological fault lines.
The Geoscience spokeswoman said mine sites were not monitored for seismic activity.
“The National Earthquake Alerts Centre monitors earthquakes across Australia using a national network of seismometers,” the spokeswoman said.
“Monitoring of individual mine sites for low levels of seismicity is not an activity that Geoscience Australia is engaged in.”
Warkworth resident John Krey said it was difficult to distinguish between an earth tremor and a mining blast.
“If it’s a blast then you are kind of relieved that it’s done for the day,” he said.
NSW Minerals Council chief executive Stephen Galilee said the number of coal mines operating in the Hunter had fallen by a quarter since 2012.
“All mine blasting in the Hunter is conducted under strict regulation and with public safety as the first priority,” he said.