Widespread Ultra-Low Velocity Zones in Earth’s Mantle could be more common than previously thought. New research reveals that these mysterious zones, which slow down seismic waves, might be scattered throughout the mantle, challenging existing theories and offering new insights into Earth’s geology.

Widespread Ultra-Low Velocity Zones in Earth’s Mantle: A Groundbreaking Discovery

Introduction to ULVZs

Widespread Ultra-Low Velocity Zones in Earth’s Mantle have recently captured the attention of geologists and geophysicists alike. These enigmatic regions, located deep within the Earth’s mantle, have long been known to slow down seismic waves. Traditionally, they were thought to be confined to specific areas such as volcanic hotspots. However, recent research suggests that these ultra-low velocity zones (ULVZs) might be far more prevalent throughout the mantle than previously imagined.

The Mystery of ULVZs

To understand the significance of this discovery, it’s essential to first grasp what ULVZs are. These zones are characterized by their ability to dramatically reduce the speed of seismic waves—up to 50% slower than in surrounding mantle material. This unique property makes ULVZs one of the most intriguing features within the Earth’s interior. Michael Thorne, a geologist and geophysicist at the University of Utah, described them as “one of the most extreme features that we see anywhere inside the planet.” Despite their dramatic effects on seismic waves, their exact nature and origin remain elusive.

Research Unveiling Widespread ULVZs

The latest research, led by Thorne and his team, sheds new light on the distribution of ULVZs. The study, published in the journal AGU Advances on August 10, 2024, originally aimed to explore a different mantle mystery. The focus was on large earthquakes, particularly those occurring at subduction zones where one tectonic plate slides beneath another. These massive quakes generate powerful seismic waves known as PKP waves. Some of these waves traverse the Earth’s mantle, outer core, and mantle again, traveling across the planet from their origin.

Interestingly, the researchers noticed a peculiar type of wave called a precursor PKP wave. These waves appear before the main seismic wave, scattering off mysterious features in the lower mantle. To uncover these features, Thorne’s team modeled PKP waves using a computer simulation of the Earth’s mantle. They introduced areas within the model that altered the velocity of the waves, looking for patterns in how the waves changed speed.

Findings from Earthquake Data

Armed with this model, the researchers analyzed real earthquake data. They focused on 58 deep earthquakes with magnitudes exceeding 5.8 that occurred near New Guinea between 2008 and 2022. The seismic waves from these quakes traveled through the core and reached North America, where they were recorded by EarthScope—a project that deployed portable seismic monitors across the U.S. between 2003 and 2018.

The analysis revealed that something was significantly slowing down the seismic waves, causing them to scatter. The two primary suspects were valleys and ridges along the core-mantle boundary or the presence of ULVZs. While the core-mantle boundary under the western Pacific, where the waves passed, was thought to be smooth, previous research had identified a large ULVZ in the same region, east of the Philippines. The new study found additional evidence suggesting the presence of ULVZs under North America and other locations, including North Africa, East Asia, Papua New Guinea, and the Pacific Northwest.

Possible Origins and Implications

The widespread nature of these ULVZs raises intriguing questions about their origins. Some researchers speculate that ULVZs might be remnants of massive impacts from Earth’s early history when meteor bombardments were common. However, if ULVZs are indeed widespread, it suggests that they might be actively forming today. Thorne proposes that these zones could be associated with volcanic rock basalt from mid-ocean ridges. When this basalt is subducted into the mantle, it melts more easily, potentially forming pockets where seismic waves slow down. These pockets could then be transported around the mantle by other slabs of subducting crust.

The Importance of Understanding ULVZs

Understanding the widespread Ultra-Low Velocity Zones in Earth’s Mantle could significantly enhance our knowledge of various geological processes. For instance, it could improve our understanding of volcanic hotspots, which are regions where hot rock rises from the mantle to create volcanic island chains like Hawaii. Additionally, a better grasp of ULVZs could shed light on how the mantle moves and how tectonic plates interact with each other.

Despite these advancements, many questions about ULVZs remain unanswered. Researchers are still working to determine their precise composition, formation processes, and role within the Earth’s mantle. As science continues to unravel the mysteries of these fascinating zones, they offer a window into the dynamic and complex nature of our planet’s interior.

Conclusion

The discovery of widespread Ultra-Low Velocity Zones in Earth’s Mantle marks a significant breakthrough in geoscience. These mysterious zones, which dramatically alter the speed of seismic waves, are not as isolated as once thought. Instead, they may be scattered throughout the mantle, challenging existing theories and providing new insights into Earth’s geology. As researchers continue to explore these enigmatic features, they pave the way for a deeper understanding of our planet’s inner workings.

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