The discovery of seismic signals known as PKP precursors has long perplexed scientists due to their complex nature. These signals originate in Earth’s lower mantle, where incoming seismic waves scatter and return to the surface as PKP waves at varying speeds. While these precursor signals precede the main seismic waves that traverse Earth’s core, their exact source has remained elusive. However, groundbreaking research led by geophysicists at the University of Utah has shed new light on this mysterious seismic energy.
The study suggests that PKP precursors emanate from deep beneath North America and the western Pacific, potentially linked to “ultra-low velocity zones” in the mantle. These zones are thin layers where seismic waves experience a significant slowdown, presenting some of the most extreme features observed on Earth. Lead author Michael Thorne, a professor of geology and geophysics, highlights the association between these zones and hotspot volcanoes, such as those at Yellowstone, the Hawaiian Islands, and Samoa. The accumulation of these zones may give rise to mantle plumes responsible for long-lived volcanic activity.
Utilizing advanced seismic array techniques and theoretical modeling, the research team analyzed data from earthquakes around New Guinea recorded in North America. By pinpointing the scattering of seismic waves along the core-mantle boundary, located 2,900 kilometers below the Earth’s surface, the researchers identified the likely source of PKP precursors. These signals appear to originate from regions housing ultra-low velocity zones, possibly formed by interactions between subducted tectonic plates and the core-mantle boundary in oceanic crust.
The study unveils that ultra-low velocity zones are not confined to hotspot regions but extend across the core-mantle boundary beneath North America. Thorne speculates that these zones, ranging from 20 to 40 kilometers in thickness, are actively generated near subduction zones, where mid-ocean ridge basalts undergo melting processes. The dynamics of these zones drive them to accumulate under hotspot volcanoes and along the boundaries of Large Low Velocity Provinces beneath the Pacific and Africa.
While the findings offer valuable insights into the origins of PKP precursors and ultra-low velocity zones, many questions remain unanswered. The exact mechanisms behind the generation of these zones and their interactions with mantle dynamics warrant further investigation. Understanding the consequences of these processes on Earth’s geological evolution and volcanic activity presents an exciting avenue for future research in the field of seismology.
The research led by the University of Utah geophysicists represents a significant advancement in unraveling the mysteries of PKP precursors and ultra-low velocity zones in Earth’s mantle. By combining innovative seismic analysis techniques with theoretical modeling, the study provides a deeper understanding of seismic phenomena and their geological implications. As scientists continue to explore the complexities of Earth’s interior, new discoveries in seismology hold the promise of unlocking further secrets of our planet’s dynamic processes.
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