NCI is supporting world-leading researchers at The Australian National University in their efforts to use seismology to learn more about the centre of Earth.
Lead researcher Associate Professor Hrvoje Tkalčić recently published the world's first book about the mysterious inner core – The Earth's Inner Core: Revealed by Observational Seismology.
Professor Tkalčić collaborated with NCI's VizLab to create animations and 3-D images for the publication.
Using computational algorithms in a method he describes as "like having an internal telescope into the Earth", Professor Tkalčić and his team analyse readings of earthquake waves – or 'seismograms' – that have travelled through the inner core.
"There are many things you can do with seismograms, but among the most basic is you can analyse the travel times of the waves through the Earth," explains Professor Tkalčić.
"This is a similar principle to medical imaging; in a sense, the waves illuminate the internal structure of the Earth in the same way CAT scans reveal the internal structure of the human body."
By analysing thousands of seismograms, the team can make inferences about the properties of Earth's interior.
"The waves are reflected and refracted along the boundaries within the Earth; for example the boundary between the outer core and the inner core," says Professor Tkalčić.
"Then you can use physics and some basic relationships between what it actually means for the waves to be fast or slow and the properties of the material to infer something about the structures; for instance whether they are partially melted, mushy or more solidified."
Each line represents a seismic wave that has travelled through the inner core on its way to the receiver on the opposite side of Earth. In a similar method to CAT scanning, the team use these waves to illuminate the internal structure of the inner core. Image generated by Drew Whitehouse, NCI VizLab.
One of the group's aims is to map the surface of the inner core – information that Professor Tkalčić says would be "extremely helpful" for other scientists, such as geodynamicists or geomagneticists.
"As the inner core crystallises, latent heat is released at the surface, and that drives convection in the liquid outer core," he explains.
"And that convection is responsible for the generation of Earth's magnetic field, which keeps us all alive because it protects the Earth from cosmic radiation."
After working with NCI's VizLab team five years ago, Professor Tkalčić approached them again when he was asked by Cambridge University Press to write The Earth's Inner Core.
"My students and I had made a discovery that the rate by which the inner core spins relative to the rest of the planet changes with time," he explains.
"We needed a really good way to visualise that effectively to present the data not just to our colleagues but to journalists and the general public. The VizLab team was very good at taking my datasets and visualising them using the Houdini software suite.
"So when this book progressed, I included supplementary animations in my proposal."
Professor Tkalčić says 3-D visualisations enrich his research.
"Before, we used maps, cross sections and tomograms, but to really put those in perspective we needed three-dimensionality."
"It not only helps people who are visual learners, but also it helps me," he says.
"There are moments when you tend to forget about what you working with. You can't see the forest for the trees, so to speak; you only see the numbers.
"But, after all, this is a 3-D subject – it's like studying a planet with a planet – so we absolutely need a way to look at the data in 3-D.
"Before, we used maps, cross sections and tomograms, but to really put those in perspective we needed three-dimensionality."
View The Earth's Inner Core: Revealed by Observational Seismology on Amazon.
