New science sheds light on Australia’s potential risk for earthquakes

Geoscience Australia has released the first update to the National Seismic Hazard Assessment since 2018, identifying Darwin and the eastern highlands through into Latrobe Valley as areas where there is a higher risk of strong ground shaking.

The National Seismic Hazard Assessment defines the level of earthquake ground shaking across Australia that has a given chance of being exceeded in a specific time period. Knowing how the ground shaking hazard varies across Australia allows emergency managers, government agencies and the engineering sector to prepare for, and respond to, earthquakes in Australia.

Senior Seismologist Dr Trevor Allen said the new assessment is based on updated data, models, and insights, collected from field surveys and earthquake catalogues, as well as from people who have felt an earthquake.

“We have a large body of information that helps us understand the physical characteristics of earthquakes in Australia and how they impact the landscape around us,” Dr Allen said.

“Consistent with previous assessments, most areas around Australia are at low to moderate risk of experiencing strong ground shaking. However, our understanding has changed for some regions, such as Darwin and the Victorian high country.”

Dr Allen emphasised that this change in the assessment of risk doesn’t mean earthquakes will happen more often.

“We aren’t getting more earthquakes or stronger earthquakes all of a sudden,” Dr Allen said.

“What has changed is how we understand and interpret the risk of earthquakes occurring and their consequent ground motions.

“The new assessment simply clarifies and improves our understanding of the risks that can be associated with this hazard.”

Darwin at higher risk of strong ground shaking

“We now know the level of risk in Darwin is higher than previously understood, because we have a much better understanding of how earthquakes in the Banda Sea - which are felt quite strongly in the area - affect the hazard,” Dr Allen said.

“The shaking energy from Banda Sea earthquakes travels much more efficiently to Northern Australia than it does to other places, even places that are much closer to the epicentre.”

Slight rise in seismic hazard in Victoria’s high country

Dr Allen added that data from recent earthquakes in areas such as Victoria’s high country have been incorporated into the assessment, leading to a slight rise in the level of seismic hazard in the area.

“The recent earthquake activity in Victoria’s high country tells us a lot about the potential risk for future earthquakes in the region,” Dr Allen said.

“Each earthquake is unique and provides us with more information that can be used to understand the likelihood and physical consequences of earthquakes in Australia.

“This information is then used to improve the accuracy of models and algorithms that underpin our hazard calculations.”

Protecting older buildings against earthquakes

Australia’s seismic hazard profile is low compared to nearby nations such as New Zealand, Indonesia and Papua New Guinea. However, a large proportion of the built environment is vulnerable to earthquake ground shaking –especially masonry buildings that were built before the enforcement of modern earthquake loading standards.

To help manage the impacts of earthquake risk, Geoscience Australia has recently released resources that guide retrofitting older unreinforced masonry buildings to resist earthquake damage.

The National Seismic Hazard Assessment is publicly available on the Geoscience Australia website.