A new study has shown for the first time how Australia’s rich geological history is reflected deep below the Earth’s surface.
Author of the study, Dr Caroline Eakin from The Australian National University (ANU), said the country’s land mass is made up of different building blocks that fused together over 1.3-billion years ago.
“Australia is an old, stable continent,” Dr Eakin explained. “Australia’s different building blocks are reflected on the Earth’s surface, but it’s been unclear to what depth these geological differences would be reflected below the Earth’s crust.”
Dr Eakin used observations of scattered surface waves – known as Quasi-Love waves – created by distant earthquakes to study Australia’s geological makeup.
Features are preserved for billions of years
“These Quasi-Love waves show boundaries deep within and surrounding the Australian continent that correspond to the same tectonic boundaries seen at the surface,” she said.
“This suggests these kinds of geological features are preserved for billions of years.”
According to Dr Eakin, this new information about what’s happening 100-200 kilometres below the Earth’s surface indicates the deeper part of our continent is just as geologically diverse as the crust.
It is the most detailed analysis of this kind of data in Australia to date, taking into account over 2,000 earthquake recordings made at seismometers across the continent.
The study has been published in the open-access journal Communications Earth & Environment.
A land of big geological contradictions
According to Geoscience Australia, which is part of the Federal Government, Australia is a land of geological contradictions with some of the oldest features in the world alongside rocks which are in the process of formation.
The continent is home to rocks dating from more than 3-billion years, while others are the result of volcanic activity which continued up to only a few thousand years ago.
Recently, scientists have been able to obtain a much clearer picture of Australia’s geological past through deep seismic surveys, which has provided new information about how the continent was formed, particularly around Broken Hill, Mount Isa, Iron Knob and West Arnhem Land.
Although the shape of Australia is due largely to tectonic Earth movements and long-term changes in sea level, most of its topography is a result of prolonged erosion by wind and water.