Earthquakes in Australia: How big do they get and how prepared are we?


Most of us tend to associate earthquakes with places like New Zealand, California or Japan.

These locations lie on the edges of tectonic plates, where the stress of plates pushing against each other causes rocks deep within the earth to suddenly break and slip past one another, resulting in an earthquake.

But what about earthquakes in Australia?

Well, they do happen, as evidenced by Wednesday’s 5.8-magnitude earthquake, felt in various parts of south-eastern Australia.

Trevor Allen is a seismologist with Geoscience Australia who works on determining the likelihood of catastrophic earthquakes affecting Australian communities.

As Australia sits in the centre of a tectonic plate, our earthquakes are a bit different to other places, he says.

Dr Allen uses a pavlova to describe why we have earthquakes in Australia.

“Imagine if you will, that a tectonic plate is analogous to a pavlova — with a thin brittle crust lying above a ductile, but mostly solid meringue mantle,” Dr Allen says.

“The Australian continent would sit in the middle of our pavlova.”

If you put your hands on the edge of the pavlova and start to squeeze, the crust around your hands will be the first to break, like those earthquakes at the boundaries of tectonic plates.

But if you continue to squeeze, eventually strain builds up in the centre of the crust, and cracks will begin to appear.

This is similar to how we get earthquakes in Australia.

“The same forces that drive earthquakes on tectonic plate boundaries are at play — they just take a lot longer to manifest in the middle of our pavlova,” Dr Allen says.

Australia is actually rocked by an earthquake about once per day, but the more damaging quakes — above magnitude-5 — are only typically seen about twice a year.

But Dr Allen says it’s extremely unlikely Australia would ever experience a magnitude-8 or 9 earthquake.

That’s because the forces necessary only occur at the plate boundaries, where plates can lock together and break apart with tremendous force.

“We don’t have faults that are large enough or active enough to have these really big earthquakes we see on the plate boundaries,” Dr Allen says.

“In general, the rates of earthquakes we see here in Australia and in other stable tectonic regions are roughly about a hundred times less than that of areas on plate boundaries.”

What big earthquakes have happened?

Australia experiences about 80 magnitude-3 and larger earthquakes a year, although the majority are small.

The largest recorded earthquake in Australia was a magnitude-6.6 at the sparsely populated Tennant Creek, NT in 1988. Two similar-sized earthquakes followed within 12 hours and aftershocks are still being recorded today.

A magnitude-6.5 earthquake hit the small WA wheatbelt town of Meckering in 1968, destroying the town with a 37-kilometre-long rupture and 2-3 metres of vertical deformation from one side of the fault to the other.

One of the most significant earthquakes to occur in Australia was the magnitude-5.6 Newcastle earthquake that took place on a December morning in 1989.

It wasn’t that big in terms of magnitude, but because it occurred close to the city, it caused significant destruction and injury, and the death of 13 people.

Nine of those people were killed in the collapse of the Newcastle Workers’ Club, which was due to have a concert that night with thousands of attendees.

“It doesn’t take much imagination to see that the consequences of that day could have been so much worse had the earthquake been just a few hours later,” Dr Allen says.

When will we get another one?

Even in high earthquake zones, there is no perfect tool to predict when an earthquake might occur.

Fault lines and historic events can help scientists identify likely sites of future earthquakes.

But an earthquake could also occur in an unexpected location on an undiscovered fault.

“In spite of our best forecasting efforts, no part of Australia is immune from strong earthquake ground shaking,” Dr Allen says.

Quite a few of Australia’s more active fault lines are close to major urban centres, particularly near Adelaide and Melbourne.

An earthquake at these locations could be catastrophic, and disrupt the lives and livelihoods of many Australians.

These events are exceedingly rare, but that doesn’t mean that they can’t happen in our lifetime.

How can we prepare for a big earthquake?

Given we can’t predict where the next large earthquake will hit, how prepared are we to cope if it was to occur in a heavily populated area of Australia?

Ensuring that structures are built to withstand earthquakes is an important step.

“The best defence against earthquakes are strong building codes, and compliance with those codes,” Dr Allen says.

Structural engineer Michael Griffith works on developing ways to make older buildings less susceptible to earthquake damage.

“Most of the mainstream buildings in Australia were … built before earthquake forces were required to be considered,” says Dr Griffith, a researcher with the Bushfire and Natural Hazards CRC.

In 1995, after the Newcastle earthquake, the Building Code of Australia introduced earthquake design requirements.

This means that any modern construction should have quite a bit of inherent resistance in it.

“They may be damaged beyond economic repair, but they shouldn’t collapse and kill anyone,” Dr Griffiths says.

The main risk, he says, are older, unreinforced brick buildings.

Many street fronts in our capital cities have two- to three-storey buildings with large ornate brick fronted facades.

“[They] are very attractive and really give a lot of atmosphere for the area, but those are the types of buildings that have been damaged so heavily in Christchurch after their recent earthquakes,” Dr Griffiths says.

Many of the fatalities from the Christchurch earthquakes in 2010-11 were people who were outdoors and hit by falling masonry.

Dr Griffiths would like to see more work put into strengthening existing buildings, so that in the event of an earthquake, there is minimal damage and loss of life.

“As decades go by, progressively more and more of those old buildings will be demolished and replaced with modern construction that will comply with modern codes” Dr Griffiths says.

“But at the moment, there’s quite a few buildings that are fairly vulnerable.”

How can people protect themselves?

If you do happen to find yourself in an earthquake like the one on Wednesday, Dr Allen has a few tips on what to do.

His best advice is to “drop, cover and hold on”.

Take cover under a sturdy table or desk if you can, and hold on until the shaking stops.

The aim is to protect yourself from any falling debris or toppling furniture.

“Don’t go to a doorway — the door will probably swing shut and break your nose,” he says.

“Don’t try to run out of the building — in a strong earthquake, you won’t be able to walk, let alone run!”

A great way to feel prepared is to participate in the GreatShakeOut, the world’s largest earthquake drill, on October 21.

And if you ever do feel any tremors, let Geoscience Australia know through a felt report.

This will help provide important information to emergency services and first responders in the event of a damaging earthquake anywhere in Australia., 22 September 2021