How the Victoria Seismic Network tracks 400 earthquakes a year

In September last year, Victoria was hit by a 5.9-magnitude earthquake that shook buildings in the state and was felt (albeit subtly) as far away as Tasmania; It was the largest earthquake recorded in Victoria since European settlement.

Seven earthquakes struck in total, causing less damage than expected – only one building, Betty’s Burgers in a Melbourne suburb, was reported to be significantly damaged.

The quake was a mild albeit compelling reminder that Australians live on a geologically active continent, even though we’re nowhere near as close to the edge of the tectonic plate as the more dangerous places in Japan or New Zealand, for example.

The Victorian earthquake occurred on a fault line that had not been mapped before; Crack in the earth’s crust sitting idly but threatened under the case.

In fact, Southeast Australia has a lot of these fault lines; According to Januka Attanayake, a research fellow in seismology at the University of Melbourne, these fissures formed when the supercontinent Gondwana broke up 180 million years ago, pushing the Australian continent northward.

Earthquakes occur along these fault lines by breaking of the Indo-Australian continental plate into the Eurasian plate in the north and the Pacific plate in the east and southeast; All this pushing and pulling creates stresses on the plates, which can create earthquakes in these fault lines, even if they are hundreds of kilometers away.

Fortunately, Victoria has an incredibly developed seismic network operated by the University of Melbourne. In the past four years, it has doubled in size.

But how does the earthquake network work, and why exactly do we need it?

Micro-vibration measurement with seismographs

“When an earthquake occurs, it causes mechanical disturbances in the crust,” explains Atanayaki, one of the principal investigators helping to map the Gippsland region of Victoria, a particularly geologically active region. “Our goal is to record these disturbances that radiate far from the earthquake.”

But recording these disturbances isn’t always straightforward – most earthquakes that do occur are so subtle you’re unlikely to notice them.

“We need to put in place tools that can work with these relatively large amplitudes of disturbances, from those that you don’t feel all the way through to those that can shake buildings rather violently,” Atanayake says.

“So these are very sensitive instruments that can record these very small vibrations in the ground down to several centimeters of vibrations.”

The Victorian earthquake occurred on a fault line that had not been mapped before; Crack in the earth’s crust sitting idly but threatened under the case.

These instruments are called seismometers, and there are approximately 43 workers in the network that Attanayake oversees on any given day around the Gippsland area. The network contains different types of seismographs operating at different levels and types of locations – from those at or near the surface in wells 10 to 1,000 meters deep, to those on the ocean floor in Bass Strait.

The devices are on site and automatically send the data to the researchers, but a human analyzer is needed to review the signals.

“We record about 2 to 3 terabytes of data each year, and we’ve detected about 400 earthquakes a year since the end of 2017,” Atanayake says. That’s a lot of earthquakes. Before 2017, when the team installed more stations closer to smaller, previously undetectable events, they were logging just 150 per year.

Why do we need a seismic network?

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University of Melbourne seismologists first established a seismic network in Gippsland after the 2012 Thorbdale earthquake, when they set up six aftershock monitoring stations in the area. A 2019 study by Atanayaki and colleagues found that the series of earthquakes may have been triggered by one earthquake that stimulated another to a different fault—the first evidence of this type of interaction in the state.

If most of the earthquakes recorded in Victoria are so subtle that you would hardly notice them if you were sitting on top of their epicenter, why would we need such a grid?

“We know that there are these faults that have formed since the breakup of Gondwana, and some of these faults have been recorded in the Neotectonic database by Geoscience Australia,” Atanayake says. “But there may be many other flaws that have yet to be identified.”

The worst earthquake in Victoria’s post-settlement history didn’t cause much damage, it’s true, but Atanayake says that while serious events may be rare, the repercussions can be massive — and so far, we’ve been lucky.

“Just look at 1989 in Newcastle,” he says.

The 1989 Newcastle earthquake recorded 5.6 on the Richter scale. The devastating earthquake killed 13 people and injured more than 160; Total economic damage was calculated at A$4 billion ($8.5 billion today, adjusted for inflation), although Deloitte estimated the true cost of such an earthquake today would exceed A$18 billion.

“Because Australia is a very large continent but the population is concentrated in very small areas, we don’t experience earthquakes in urban centers all the time,” Atanayake says. But we know that these earthquakes happen. A powerful five-degree event happens in Victoria every seven years, and we’ve been lucky so far. We know that it is very difficult to predict the location of these, and we know that they occur.

“So, at some point in the future, one of these five Richter-scale earthquakes is going to hit an urban center. We know it’s going to happen, it’s just a matter of time.”

Preparing for an event like this is important: buildings must be designed appropriately, especially critical infrastructure such as hospitals and power supplies.

In fact, in 2016, a 6.0-magnitude earthquake struck the Petermann mountain range in central Australia, leaving a 21-kilometre scar in the desert. The earthquake was far away, but a similar event near an urban center could have disastrous consequences.

But to determine what kinds of building standards we need to live up to, we need to know how much traffic will be produced, and where – where the seismic network comes from.

The good news is that as the network is getting better than ever at detecting thinning earthquakes, we are able to fully understand the Victoria earthquakes, because there is a correlation between smaller and larger earthquakes.

“If you know the number of smaller events, you can actually predict how many larger events you can expect from a segment in a given period,” Atanayaki says. We call this the Gutenberg-Richter relationship [or law]. “

“If you take a place like Victoria, what we see is that for every earthquake of a given magnitude, there are about five to seven earthquakes of one smaller unit size,” he says. “So, for every five to seven earthquakes of magnitude four, there will be a magnitude five of the Richter scale at some point in the future.” Furthermore, seismologists can determine a stressful time period in which this larger earthquake will occur using statistical techniques.

And it’s not just about predicting the next catastrophe – small earthquakes that do so little damage to us above ground can wreak havoc on the infrastructure we depend on.

In fact, the University of Melbourne research team’s data is being used by the CarbonNet project in Victoria, a commercial scale carbon capture and storage (CCS) network being built in Gippsland.

Carbon capture and storage is a climate change mitigation strategy identified by the Intergovernmental Panel on Climate Change as a necessary component of a net-zero future if we are to keep the world below 1.5 to 2°C of warming—although the technologies needed to do so are imperfect, and not without controversy.

Carbon dioxide capture and storage involves sequestering the carbon dioxide produced, for example, from extracting natural gas, and you can do this in a variety of ways – but CarbonNet will sequester the carbon in cavities deep under the Bass Strait.

All stored carbon dioxide must be protected, including from natural disasters such as earthquakes: “Protecting these assets that will directly affect the well-being of the planet is critical,” Atanayake says.

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