According to reports, Geoscience Australia (GA) recorded a ‘regular’ monthly blast conducted on 9 January at Boral’s Dunnstown quarry – located east of Ballarat – as a 1.8 magnitude earthquake and published the results on its earthquake webpage.
{{quote-a:r-w:300-I:2-Q:"A small seismic event may not be immediately or easily linked to an individual mine or quarry"-WHO:Jonathan Bathgate, GA senior seismologist}}However, seismologists later reviewed the information before advising that the seismic activity was in fact caused by the blast at the quarry, GA senior seismologist Jonathan Bathgate confirmed.
“GA monitors, analyses and reports on seismic data from more than 100 permanent stations across Australia, and in excess of 300 stations worldwide in near real time, 24 hours a day, seven days a week,” Bathgate told Quarry.
“Discriminating naturally occurring earthquakes from man-made seismic events is not always straightforward. Small seismic events that are located within GA’s permanent network will often have an error ellipse of tens of kilometres as a product of the seismic monitoring network density.
“Therefore, a small seismic event may not be immediately or easily linked to an individual mine or quarry,” he added.
A spokesperson for Boral added that the blasting – which had “similar intensity” to previous months – was “in line with the strict regulatory provisions followed by Boral”.
Blasts versus Earthquakes
When asked how the organisation ensured quarrying and mining activities did not ‘contaminate’ its earthquake records, Bathgate offered the following comments.
“GA undertakes to characterise all seismic activity it detects, whether earthquake or other source. When our analysis indicates an event is anthropogenic [caused or influenced by humans], we make a concerted effort to verify this by contacting potential sources such as mines or quarries near the epicentre,” he explained.
“From time to time, we’re unable to obtain all necessary information until several hours or days following the event. Consequently, the event may be published on our earthquakes webpage in the shorter term.”
Bathgate added that regardless, all records were categorised according to their source, whether that be earthquake or quarry blast.
“In this way, we ensure that the earthquake catalogue maintained by GA can be used to inform the Australian national seismic hazard assessment,” he added.
According to the organisation, more than 600 earthquakes are detected across Australia each year, with most commonly occurring in south-west Western Australia and south-east Victoria.
Dunnstown quarry – which supplies basalt aggregates – provides approximately 650,000 tonnes of material per year for building, road and rail construction projects in and around Ballarat, Central and Western Victoria.
The quarry is Boral's largest operation in regional Victoria.
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