Deep within the Earth's lower mantle, scientists have discovered mysterious zones known as ultra-low velocity zones (ULVZs) that have the ability to significantly slow down seismic waves by up to 50%. These enigmatic structures, resembling figurative black holes, have puzzled experts as their composition and function remain unknown.
Traditionally found near hotspots in the mantle where hot rock rises to form volcanic island chains like Hawaii, ULVZs are now believed to be more widespread than previously thought. Some researchers speculate that ULVZs could be remnants of ancient impactors from a time when Earth was bombarded by meteors. However, recent findings suggest that these structures may still be actively forming today.
Geophysicists suspect that ULVZs could be composed of basalt, a type of volcanic rock that forms at mid-ocean ridges and later gets pulled into the mantle through subduction. This molten basalt could create pockets within the mantle where seismic waves slow down, leading to the observed effects of ULVZs on seismic activity.
Researchers analyzing seismic waves from large earthquakes, known as PKP waves, discovered signatures of ULVZs across various regions worldwide, including North America, North Africa, East Asia, Papua New Guinea, the Pacific Northwest, and the western Pacific. The presence of ULVZs in these diverse locations highlights the global reach and impact of these mysterious structures.
Understanding the nature and function of ULVZs could provide valuable insights into volcanic hotspots and the dynamics of the Earth's mantle. Despite ongoing research efforts, many questions surrounding ULVZs remain unanswered, emphasizing the need for further exploration and study in this fascinating area of geophysics.
