THE Hunter Valley is a seismic hot zone, with data showing earthquakes have become more frequent in recent decades.
While there is no conclusive link, some believe the impact of open-cut mining has destabilised millions of tonnes of pressure in the earth’s crust.
Geoscience Australia records show there were 94 earthquakes in the Hunter Region between 1996 and 2016, compared with 65 between 1976 and 1996.
“It is important to keep in mind that Australia’s seismic monitoring has improved over time with technology and additional seismic monitoring stations,” a spokeswoman said.
Upper Hunter residents have already experienced the earth move 31 times over the past decade, including several times this year.
A 3.1 magnitude earthquake was recorded at Denman on September 16, a 2.5 magnitude earthquake was recorded at Muswellbrook on September 15.
Dozens of residents from Lochinvar, Greta and Branxton and Kurri reported what they suspected was an earth tremor on Sunday November 20.
“There were about three big bangs about two minutes apart. The windows rattled; the whole house shook,” Branxton resident Catherine Duffey said.
“It didn’t feel like an earthquake but the earth was definitely moving.”
The Geoscience Australia spokeswoman said that while the incident was recorded at seismic stations at Newcastle and Mangrove Mountain, the characteristics of the signal were not consistent with seismic activity.
“Geoscience Australia cannot confirm the cause of these reports, however, explosions or atmospheric sonic booms from aircraft or objects passing through the atmosphere, such as meteors, could also explain the noises and shaking that the residents reported,” the spokeswoman said.
“In cases of confirmed seismic activity, it can be difficult to differentiate between earthquakes and man-made seismicity, such as mining blasts, depending on the location, size and other factors.”
Bulga resident John Krey, whose property is surrounded by open-cut mining, said his experience of mine blasting led him to believe there was a clear relationship between mining and seismic activity.
“There are about 3000 blasts a year in Hunter Valley. Warkworth mine blasts every second or third day. When you have that many blasts there has to be some impact on the surface tension of the surrounding area,” Mr Krey said.
While Bulga and surrounding residents had learned to live with the effects of mine blasting, Mr Krey said a powerful blast recorded earlier this year was particularly memorable.
“It was recorded at 4.8 millimeters a second and detected at a seismic station 150 kilometres away in the Blue Mountains,” he said.
“The Department of Planning and the EPA said they were looking into it but we haven’t heard anything back.”
Mr Krey and other residents have called for more research into the relationship between seismic activity and mining.
NSW Minerals Council chief executive Stephen Galilee said the number of coal mines operating in the Hunter had fallen by a third over the past four years.
“Further, all mine blasting is conducted under strict regulation and with public safety as the first priority,” he said.
Writing in The Conversation in 2012, Christian Klose, an adjunct research scientist at US-based Northwest Research Associates, referred to the Upper Hunter as part of the “Newcastle Triangle Seismic Hazard Zone.”
Earthquakes with a magnitude of greater than 5 on the Richter scale occur, on average, every 40 years in this area. Other areas of the sate experience such seismic events, on average, every 170 years.
Dr Klose, an expert on natural hazards and human security, argued that tectonic plates deep beneath the earth’s surface reacted to the mass removal of pressure through mining.
He said the risks associated with human-made earthquakes need to be addressed when large-scale geoengineering projects were planned.
“Ensuring sustainable geoengineering practices is especially important in the regions of high population densities. This is, in particular, important for deep geothermal power generation or carbon sequestration as hot spots for earthquakes crafted by human action,” he wrote.