A groundbreaking PhD: earthquake data is the key to exploring the Earth’s interior

Dr Thuany Costa de Lima remembers the day that a geophysics professor came to her high school in Brazil and gave a presentation which changed the course of her life. 

The presentation revealed a whole new world to 16-year-old Thuany: one that rumbles on deep beneath our feet.

“I’ve always had a passion for physics, and the idea of applying that knowledge to understand how the Earth works was incredibly exciting,” she says.

After completing an undergraduate science degree then Masters in geophysics in her home country of Brazil and working in hydrocarbon exploration, Costa de Lima moved to Canberra to begin a PhD at the ANU Research School of Earth Sciences. Here, she shifted her focus to seismology: the study of earthquakes and their seismic waves.

Costa de Lima’s PhD investigated the (literally) groundbreaking topic of the deepest component of Earth: the inner core, which is buried more than 5000 kilometres beneath the surface.

“The inner core is the deepest region of our planet, and there’s so much about it that we don’t know,” she says. “My goal was to develop new sophisticated tools to investigate the inner core structure and better understand its influence on Earth’s evolution and dynamics.”

She was charting an unknown course developing pioneering methodologies alongside the rest of the ANU seismology research group, led by Professor Hrvoje Tkalčić.

“We cannot drill into the inner core,” she says. “So, to investigate its structure we use numerical modeling of seismic waves that travel through its body.”

Measuring the seismic waves from large earthquakes around the globe, Costa de Lima pieced together data to simulate the Earth’s interior utilising high-performance computing resources at ANU. The propagation and directional variation of the seismic waves provide crucial information about the properties of the inner core.

Costa de Lima and the team found a new line of evidence for the make-up of the Earth’s innermost inner core, and confirmed that while the inner core is solid, it is softer than we thought. This work was published in Nature Communications in 2023.

This helps scientists to understand the evolution and the history of how Earth’s inner core has solidified over time.

“People might think the inner core has little relevance to our lives,” Costa de Lima says. “But in fact, it is part of this big powerful engine beneath the surface driving fundamental geodynamic processes that shape the Earth.”

As part of her research, Costa de Lima has travelled to the far-reaches of the planet for field work. She installed seismic stations in outback Northern Territory and even deployed ocean-bottom seismometers off the coast of Macquarie Island, near Antarctica.

Costa de Lima also relished the trips to many international conferences across the course of her PhD to present her research and connect with the scientific community.

She compares the experience to meeting Hollywood stars from your favourite movie.

“Going to a conference is so nice because you get to meet all these scientists who wrote papers that you’ve read, and it’s like, ‘Wow, this is incredible.’” She mimics the wide-eyed awe that comes with meeting these legends in real life.

“Then you talk to them, discuss science, and realise how inspiring these interactions are. They foster collaborations for future research.”

Completing her PhD at the end of 2024, Costa de Lima now works as a seismologist at Geoscience Australia. All her experience in seismic modelling from her PhD research comes into play in this job.

“I’m looking into much shallower parts of the Earth. I am now focusing on how earthquakes affect ground motion, their impact on communities across Australia and nearby countries, and the broader implications for public safety.”

Not only did her PhD set her up for a successful career, but it must be amazing to know she’s played a vital part in expanding the scientific understanding of the Earth’s interior.

“It’s incredibly rewarding to know my work contributes towards something so big,” she agrees.

“On a personal level, I feel very happy, and proud. And curious. There’s just so much that we still need to explore.”

This article first appeared at ANU College of Science.