A ubiquitous low-velocity layer at the base of the mantle transition zone

摘要: Global stacks of receiver functions clearly exhibit the upper mantle stratification. Besides most prominent seismic discontinuities, such as Moho and 410 660 km a negative discontinuity is detected at depth ~600 km, indicating low-velocity layer base transition zone. The slant-slack technique helps to identify primary conversions from multiple reverberations. Presence 600 km underneath both continent ocean island stations, where crustal thickness significantly differs, also precludes possible cause We conclude that could be global feature, possibly resulted accumulation ancient subducted oceanic crust. X-discontinuity ~300 km observed in our stacks, which can explained by coesite-stishovite phase transformation.