Australian Earthquake Cracks Offer Clues to Future Seismic Activity

Cracks in the ground in outback Australia caused by a recent magnitude-5.5 earthquake could help researchers predict future seismic activity.

Amata, a remote community in the Anangu Pitjantjatjara Yankunytjatjara (APY) Lands near the border of South Australia and the Northern Territory, felt the earthquake at the start of April.

Shortly after, University of Melbourne researchers attended the scene and were met by a several-kilometre-long rupture in the ground.

"The rocks on the western side have been lifted up about half a metre or so relative to the rocks on the eastern side," University of Melbourne professor Mark Quigley told ABC North & West Breakfast's Tom Mann.

Professor Quigley said the obvious rupture was "maybe 3 or 4 kilometres long", with more subtle cracking also visible.

"It's extended right through areas of bedrock into areas of younger sediment on either side of the bedrock knob," he said.

"It allows us to do detailed geological analyses of the ground surface rupture … to understand how the geology influences the patterns of earthquake damage."

Geoscience Australia senior seismologist Jonathan Bathgate said that on April 5, the agency had received about 30 reports from people who felt the quake that morning.

He said the magnitude was equivalent to the devastating 1989 Newcastle earthquake that killed and injured dozens, and created a $4 billion damage bill.

"It's the same size earthquake, it just happens to be in quite a remote part of the country rather than near a populated centre," he said.

Lessons from the land

Surface-rupturing earthquakes are relatively rare, with 11 known to have occurred in Australia in the 50 years to 2018, according to Professor Quigley's research.

The surrounding landscape after these types of earthquakes can provide important insight.

"What we're able to do here is go out immediately after the earthquake and look at, for example, the way rockfalls have occurred, or individual rock fragments have flown in the air."

The rupture from this earthquake has now become the topic of ongoing research from the University of Melbourne, in collaboration with Geoscience Australia.

Observations from the ground have already proven interesting for Professor Quigley.

"There's this really distinct and interesting characteristic of the earthquake that tells us the motions were dominated by motions perpendicular to the fault, which is quite cool," he said.

"In other words, for a roughly north-south striking fault, the predominant motions are more east-west. The rocks were moving towards and away from the fault."

The research into this quake should provide lessons that could then be applied to the same type of fault mapped elsewhere, Professor Quigley said.

"Including proximal to urban centres like in Adelaide, for example, to try to understand … what the patterns of shaking might look like and therefore what potential impacts they might have on infrastructure," he said.