Victoria’s biggest earthquake on record
23 September 2021
Geoscience Australia says more aftershocks may be felt across Victoria, after the largest onshore earthquake for the state was recorded on Wednesday.
At 9.15 AM on Wednesday 22 September, a magnitude 5.9 earthquake hit near the town of Rawson in Victoria.
This is the biggest earthquake to hit Victoria in the modern instrumental era (post 1900), and probably since European settlement. This event can be classified as the mainshock followed by a series of aftershocks, Geoscience Australia senior seismologist Dr Hadi Ghasemi said.
“Geoscience Australia recorded nine aftershocks in the 24 hours following the main quake, and there may be more in the coming weeks and even months,” Dr Ghasemi said.
Aftershocks are smaller than the mainshock, and generally become less frequent with time. “However it is important to note that it is not possible to predict precisely when or how large these earthquakes may be, or when the sequence will diminish to a point where they are no longer detectable.”
While earthquakes of this size are less common in Australia, no area is completely immune from earthquakes.
“Moderate to large earthquakes can occur anywhere across the continent, and without warning. On average, Australia experiences an earthquake of this size once every year or two,” Dr Ghasemi said.
“The Australian plate is the fastest moving continental land mass on Earth and is colliding into the Pacific plate to the north and east, and the Eurasian Plate to the northwest.
“This generates compressive stress in the interior of the Australian continent. Earthquakes are caused by the sudden release of this stress when rocks deep underground break and move along a fault line."
The Rawson earthquake occurred in Australia’s South-East Highlands region, which has a relatively high level of seismic activity and was felt across four states.
Geoscience Australia received more than 40,000 reports from people reporting that they felt the earthquake: a record since the agency started collecting felt reports.
The size of the quake, combined with the geology of the area where it happened, means that the earthquake was felt hundreds of kilometres away from the epicentre: from Sydney to Hobart and west to Adelaide.
“Geoscience Australia’s scientists are moving fast to get more data about this earthquake. The closest seismic station to the earthquake was over 70 kilometres from the epicentre, which means estimates of the earthquake’s depth are uncertain,” Dr Ghasemi said.
“We have sent Rapid Deployment Kits to the area that will remain in the field for several months to measure seismic signals from aftershocks. We will also be analysing satellite data to see if there has been ground surface movement since the earthquake.
“All of this information helps our scientists to better define the source of the earthquake, including the active fault and depth of the main event. This data can be used to improve hazard estimates and guide building design, helping to make our community safer.”
To protect yourself during an earthquake, the best advice is to drop, cover and hold on. First, drop to your hands and knees, bend over to protect your vital organs, and protect your head and neck with your hands. If you can, find something sturdy to shelter under, such as a desk or table, and hold on by gripping a table leg or other part of your sturdy shelter.
Earthquakes can and do occur anywhere and at any time. Geoscience Australia works with governments, industry and communities to help reduce the impact of disasters on our country, and to help build more resilient communities now and in the future.
If you felt the earthquake, please complete a felt report at https://earthquakes.ga.gov.au.
On average, Australia experiences an earthquake of this size once every 1-2 years.
- The 2018 Lake Muir earthquakes were magnitude 5.2 and 5.3
- The 1989 Newcastle earthquake was magnitude 5.4.
About every ten years or so, Australia experiences a potentially damaging earthquake of magnitude 6.0 or more.
- The 1968 Meckering earthquake was magnitude 6.5
- The 1988 Tennant Creek earthquake was Australia’s biggest on record, at magnitude 6.6