Google Earth maps the surface, but new tech lets us map Earth’s insides too

Luke Dormehl

Google Maps may have done an impressive job of mapping the world’s surface, but geoscientists at the University of Texas at Dallas are going deeper with a new piece of research. Literally deeper. Using 10 years’ worth of data from 480 earthquakes that was processed using supercomputers, they have generated high-resolution 3D images of what is going on far below the Earth’s outermost layer — in this case, a subduction region under Central America and the Caribbean Sea.

Using a technique called full waveform inversion (FWI), this is the first time that seismologists, people who study earthquakes, have been able to record images this way. It means that they are able to see, in three dimensions, the kind of seismic activity happening deep in the Earth and the depths that it is occurring at.

“Conventional techniques have difficulties to decide the depth distribution of seismic anisotropy,” Hejun Zhu, assistant professor of geosciences at UT Dallas, told Digital Trends.

Seismic anisotropy is a term used in the study of earthquakes to describe a technique for measuring the difference in how quickly waves created by earthquakes travel in different directions inside our planet. It can help reveal how the mantle — the thickest part of the planet, between the Earth’s thin outer layer and its super-heated core — moves around inside the Earth. While the mantle, which makes up around 84% of the Earth’s total volume, appears to be solid rock, over millions of years it shifts around more like the flow of a viscous fluid such as lava.

Under Earth surface

“In our study, we [were] able to simultaneously constrain 3D distributions of wave speeds and anisotropy,” Zhu explained. “Jointly interpreting these features allows us to not only constrain the geometry of subducting slabs, but also to investigate induced mantle flows. Comparing to conventional seismic imaging techniques, this [full waveform inversion technique] takes advantage of high-performance computers and high-quality seismic waveform records to better constrain physical properties of our planet.”

Zhu said that the team next plans to use this technique to image other subduction systems, the boundaries that mark collisions between two of Earth’s tectonic plates. “The Middle American Subduction Zone just provides us one end member with an intermediate trench retreat rate,” Zhu explained. “In the future, we would like to use this technique to [also] study other subduction systems with different kinematic and dynamic characteristics, such as the Tonga and Japan Subduction Systems. By synthesizing their differences and similarities, we are able to provide the full spectrum information for subduction-induced mantle flows.”

A paper describing the research was recently published in the journal Nature Communications.