Earthquakes, originating on the edge of the Nullarbor on Saturday night and felt as far away as Perth, were the equivalent of an “atomic bomb blast” beneath the surface, a senior seismologist says.
The Goldfields was shaken four times either side of midnight on Saturday, including a magnitude 5.2 tremor, making it the biggest to hit the region in nearly 15 years.
A magnitude 4.9 earthquake with an epicentre 6km below the surface, 80km east-south-east of Norseman in the Dundas Nature Reserve, struck at 11.30pm.
It woke residents more than 200km away in Kalgoorlie-Boulder and as far south as Esperance.
A 5.2 magnitude earthquake — equalling the region’s previous record from October 2001 near Ravensthorpe — hit in roughly the same location but at a depth of 15km at 12.39am.
An aftershock in the same area with a preliminary reading of magnitude 3.2 was recorded at a depth of 10km at 1.44am.
Goldfields residents took to social media last night to report their experience.
One said: “I’m in south Kalgoorlie and it rumbled on for ages. Initially I thought a truck was going down a laneway then the lights started to sway.”
Another said: “OMG, I was laying on my sofa and it moved.”
One reader told The Kalgoorlie Miner that the larger quake shook the family’s transportable home in Nyabing, just east of Katanning and more than 400km from Norseman.
Ashli Zis said it was felt as far away as Perth. “Frasers Range Sheep Station outside of Norseman has definitely felt them, too dark though to check the buildings and surrounds for damage.”
Charmaine Camplin said: “Sitting on night shift at Norseman Gold and yes, did feel them.”
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Saturday’s tremors come barely a week after the biggest earthquake in nearly 20 years hit central Australia, with a 6.1 magnitude tremor recorded by Geoscience Australia near Uluru in the Northern Territory on March 22.
It is six years since the Goldfields was rocked by a 5.0 magnitude earthquake in April 2010 which caused widespread damage to heritage buildings in Boulder's historic Burt Street.
Geoscience Australia senior duty seismologist Dan Jaksa said the vast majority of earthquakes were caused by tectonic stress related to the Australian continent moving 7cm north-east every year.
“The energy being released into the Earth’s crust is the equivalent size of an atomic blast,” he said.
“When North Korea conducts nuclear tests we typically see readings like this.”
Mr Jaksa said the difference between magnitude 5.0 and 6.0 earthquakes was the equivalent of “32 atomic blasts in energy release”, or put another way, each single-digit increase represented an earthquake 32 times bigger.
By 1.30am, Geoscience Australia had received at least 100 online reports from people who felt the earthquakes, including some more than 600km away in Perth.
WA Police had received no reports of damage as of 2am.
The only underground mine in the immediate area is the $443 million Nova nickel-copper project, near Balladonia, which is being developed by Independence Group.
Nova has been working towards producing first concentrate in the December quarter and was acquired by Independence in its $1.8 billion takeover of Sirius Resources last year.
The Department of Mines and Petroleum said there had been no immediate reports of rock falls or damage at mines across the Goldfields as a result of the earthquakes, but will know more tomorrow.
The only underground mine in the immediate area of the epicentre is the $443 million Nova nickel-copper project, near Balladonia, which is being developed by Independence Group.
A spokesman for the Peter Bradford-led Independence said the company is today conducting a full inspection of the underground workings at Nova, where mining contractors Barminco have completed 3.2km of underground development.
He said there has been no damage observed so far and miners continued working throughout the night shift with most unaware of the earthquakes due to the noise associated with heavy machinery and drill rigs.
Commissioning at Nova is targeted for the December quarter and the first shipment of concentrate via Esperance Port is earmarked for January or February.
Investors will be breathing a sigh of relief after Nova was acquired by Independence in its $1.8 billion takeover of Sirius Resources last year.
Mr Jaksa said 105 earthquakes measuring above magnitude 5.0 had been recorded in WA in the past century.
He said underground mining was not to blame as mineral deposits typically occur along fault lines.
“There are obviously a number of mines in the Goldfields, but it it no coincidence that there is seismic activity near these faults where mineral deposits occur,” he said.
“These events occur much deeper than the deepest mines in Australia. Micro seismic activity can be caused by mining, but these larger events are caused by the release of tectonic stress.”
The biggest earthquake on record in WA measured magnitude 6.5 and destroyed the small Wheatbelt town of Meckering in just 40 seconds in October 1968.
The second-biggest on record is the magnitude 6.3 earthquake which hit Meeberrie Station in the Murchison in April 1941.
The Wheatbelt was hit again in June 1979 when the town of Cadoux recorded a magnitude 6.1 earthquake.
Mr Jaksa said most earthquakes in WA typically occur in the Earth’s upper crust and are considered “shallow”.
Seismic activity in the lower crust, at depths below about 50km, are rarer, he said.