Australian city threatens to have devastating earthquake, seismic researchers discover
Geologists have made the alarming discovery that Adelaide is at risk of being hit by a devastating 7.2 magnitude earthquake.
They say the discovery means Adelaide could be exposed to an earthquake much stronger than the earthquake that shook Christchurch in 2011.
Scientists discovered the Willunga Fault – 40 km south of the city – looking for the scars of old earthquakes when they found the new vulnerability to the region home to 1.3 million people.
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“What we were trying to establish is how often earthquakes have occurred on this fault in the past, how big they were, and what this could mean for the people of Adelaide today,” said earthquake geologist Dr. Dan Clark of Geoscience Australia.
“We calculated that this fault’s 55 km active length could potentially trigger a magnitude 7.2 earthquake.
“An earthquake of this magnitude would release about 30 times as much energy as the earthquake that devastated Christchurch in New Zealand in 2011.”
Australia has never recorded an earthquake of that magnitude.
The Christchurch earthquake was declared the highest possible regional disaster category, with 6,659 serious injuries and 185 confirmed fatalities, including one Australian.
Geoscience Australia, earthquake geologist Dr. Dan Clark, examines the trench on the Willunga Fault. Credit: Geoscience Australia
“As with Christchurch, Adelaide’s building stock includes many historic buildings that would be vulnerable to strong ground shaking from an earthquake of this magnitude,” Clark said.
Adelaide was hit by an earthquake measuring 5.4 on the Richter scale in 1954, damaging 3,000 buildings and more than 30,000 insurance claims for subsequent damage, such as collapsed and cracked walls, broken windows, and collapsed chimneys.
The new findings will advise future updates to Geoscience Australia’s National Seismic Hazard Assessment (NSHA), which decision-makers use to consider insurance premiums, infrastructure investment risk areas, and communities in the said areas.
The NSHA also informs the Australian Government Building Codes Board.
Digging up the evidence
To expose the flaw, two large trenches were dug by scientists from Geoscience Australia and researchers and students from the University of Melbourne and the Seismology Research Center.
“In Australia, researchers have identified more than 350 fault lines — the landscape features caused by large earthquakes — mostly through desktop studies using digital elevation data,” Clark said.
The team looked for “offset stratigraphy” in the trench — layers of sediment displaced when an earthquake ruptured the fault. These layers can be dated to estimate when the earthquake occurred.
They also measured the amount of surface rock and soil displacement associated with the earthquake to determine its magnitude.
“While the techniques are not new in plate margin settings like California or New Zealand, few errors in Australia have been studied this way,” Clark said.
Earthquakes in Australia
The slow build-up of stress causes earthquakes in Australia in the continent’s interior, Geoscience says, produced when the Australian tectonic plate moves about 7cm to the northeast each year.
The tension in these tectonic plates is released during this movement as an earthquake.
Ten earthquakes have been greater than magnitude three within 150 km of Adelaide in the last ten years.
The largest in the past decade was the 3.7 magnitude earthquake that struck Mount Barker on March 5, 2022.
The largest recorded earthquake in Australia occurred in 1988 at Tennant Creek in the Northern Territory, with an estimated magnitude of 6.6.