Geoscientists identify seismic activity in Southern Australia including the  Flinders Ranges

Earthquake Hazzard Map of Australia

Australia is not as geologically stable as many think. Despite popular belief, Australia is a geologically active continent with moving fault-lines, regular seismic activity, and a long history of mountain making, said internationally respected geologist, Associate Professor Malcolm Wallace from the School of Earth Sciences at the University of Melbourne.

We have discovered substantial evidence of ancient and current mountain building on this continent, and seismic activity which commenced 10 million years ago and continues to this day,”  Associate Professor Wallace said.

“Two separate geological studies have concluded that an area from Adelaide to south-east Victoria is seismically active and the next ‘big one’ could endanger lives and infrastructure”.

“There are numerous young faultlines weaving their way across southern Australia, including one that goes right around the perimeter of Adelaide.  There are also young faultlines running through the Mornington Peninsula outside Melbourne, the Strzelecki Ranges in Victoria and the Flinders Ranges in South Australia.

Fault Lines Located in Australia Map data source courtesy : Geoscience Australia

Fault Lines Located in Australia Map data source courtesy : Geoscience Australia

The University of Melbourne geologists have uncovered evidence that parts of  South-eastern Australia recently stirred from their geological slumber and are in an active mountain building phase. These mountains are being shaped by earthquakes, some reaching greater than 6 on the Richter scale.

Submission: Seismic hazards SA
[The area between Quorn and Leigh Creek has the highest number of seismic events (considered to be related to zones of crustal weakness)]

SA earthquake hazard map of region surrounding location marked by the black square. The yellow, brown, and red dots represent earthquakes (Geoscience Australia)

“Their seismic activity is generated by tectonic plates pushing up against each other on a daily basis, so it is critically important that scientists and emergency management agencies know of their whereabouts and the potential risks they pose – this is where geoscientists play a crucial role.”

“Some faults around Adelaide have moved slabs of the continent up to 30 metres in the last one million years,” says ARC Professorial Fellow, Mike Sandiford.

“When these big quakes reoccur, they have the potential to cause catastrophic damage to cities such as Melbourne, Adelaide, and the La Trobe Valley area, which straddle some of these major faults lines,” says Professor Mike Sandiford also from the School of Earth Sciences at the University of Melbourne, who conducted one of the studies.

Possibly, the most dramatic indication of this geological stirring, which the studies estimate began suddenly about ten million years ago, can be found in the landscape of the Mount Lofty Ranges near Adelaide.

“A typical earthquake of magnitude 6.0 might produce a displacement of about one metre. Thirty metres is equivalent to 30-50 big earthquakes in the last million years,” he says.

Other areas of intense mountain building have been around Victoria’s Otway Ranges, Mornington Peninsula and Strzeleckis. In some of these areas, similar uplift and erosion over the last 10 million years have thrust chunks of Australia upwards in the order of one kilometre.

The big earthquake still building South East Australia Epicentres of Australian earthquakes in the period 1859 to 1992 with magnitudes of ML4 or greater.(Illustration courtesy AGSO)

Tectonic movements have pushed the Otways 250 metres higher in the last three million years, and The Selwyn fault, which runs from Mt Martha, on Victoria’s Mornington Peninsula, east to the Dandenong Ranges has possibly produced six metres of uplift in the last 100,000 years.

“This is potentially six big earthquakes,” says Sandiford.  “We are still trying to determine the slip rates along these fault lines, but our evidence so far suggests that we  should expect, on any one of the major faults, a large earthquake every 10-20,000 years. The estimated return period of a quake greater than 6.0 in south-east Australia is about 30 years, but none have been recorded in the last 100 years,” he says.

Associate Professor Malcolm Wallace has undertaken significant research on the environmental and climatic evolution of the southern Australian margin. His research on greenhouse/icehouse climate and environmental evolution of Victoria for the last 80 million years has formed an important geological analogue for future climate change in Victoria.

Associate Professor Wallace was the recipient of the prestigious Geological Society of Australia (Victoria Division) Selwyn Medal for 2008.  The Medal, named in honour of Sir Alfred Selwyn, an eminent Victorian pioneering geologist and founder of the Geological Survey of Victoria. recognises significant ongoing or former contributions of high calibre to any field of Victorian geology.

Induced seismicity – Wikipedia

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