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A groundbreaking study by geophysicists from ETH Zurich and the California Institute of Technology has uncovered unexpected anomalies in the Earth’s lower mantle beneath the Pacific Ocean. Using advanced high-resolution models, researchers have identified zones where seismic waves behave differently, suggesting the presence of previously unknown materials. This discovery challenges long-standing theories of plate tectonics and opens up a new chapter in understanding Earth’s internal dynamics.

Hidden Anomalies in the Earth’s Mantle

The research, published in Scientific Reports, highlights areas under the western Pacific where seismic waves travel at varying speeds, indicating differences in rock composition or temperature. These zones, which appear as regions where waves either slow down (red) or speed up (blue), were previously undetected. Notably, a large blue zone in the western Pacific presents a significant mystery, as it contradicts existing models of plate tectonics.

The Role of Seismic Waves

Seismic waves are crucial tools for geophysicists to investigate Earth’s interior. When an earthquake occurs, these waves propagate through the Earth, providing valuable data on the planet’s internal structure. The speed and behavior of these waves depend on the material they traverse, allowing scientists to infer the composition and characteristics of subsurface layers.

Unexpected Findings

Traditionally, geophysicists have mapped subducted tectonic plates in expected regions, such as subduction zones where one plate sinks beneath another. However, the new model reveals plate-like anomalies in locations far from any known subduction zones, such as under vast oceans and within continental interiors. These findings defy current geological theories, which do not account for subducted material in these regions.

Potential Explanations and Implications

The anomalies might represent ancient, silica-rich material from the early formation of Earth’s mantle or zones where iron-rich rocks have accumulated over billions of years. These possibilities suggest a more complex and dynamic Earth than previously understood.

According to Thomas Schouten, the study’s lead author, “We believe these anomalies in the lower mantle have diverse origins. They could be remnants of ancient materials or result from mantle convection processes over billions of years.”

The Need for Advanced Models

The researchers emphasize the necessity for even more refined models to further explore these anomalies. Current seismic wave data primarily reveal wave speeds, but deeper analysis of material properties is required to fully understand the nature of these zones. Andreas Fichtner, an ETH professor, notes, “With better examination tools, we can uncover more details, just like a doctor discovering unexpected arteries with advanced imaging technology.”

Future Directions

This discovery sets the stage for further research into Earth’s interior. By enhancing models and incorporating diverse wave types, geophysicists aim to unravel the mysteries of these anomalous zones and their implications for Earth’s geological history and dynamics.

Reference

Schouten TLA, Gebraad L, Noe S et al. Full-waveform inversion reveals diverse origins of lower mantle positive wave speed anomalies. Sci Rep 14, 26708 (2024). DOI: external page10.1038/s41598-024-77399-2