Slabs and shear wave reflectors in the midmantle

摘要: [1] An extensive analysis of multiple ScS reverberation data sets sampling regions active or recent subduction reveals evidence midmantle reflections apparently stemming from fragments subducted slabs the interaction between and surrounding mantle. Transition zone reflectors are detected beneath southwest Pacific Ocean Melanesia with mean depths ∼850 1100 km in majority source–receiver corridors crossing study area. The observations most spatially coherent Coral Tasman Seas. Coincident two along seismic suggests (but does not mandate) existence distinct rather than bimodal depth distribution a single reflector distributed scatterers. Beneath North America, at ∼1380 1530 seen midcontinent region; further east, shallower, near 940 1130 km. Unlike Pacific, paired any individual corridors. This variability indicate that (or reflectors) Americas is (are) fragmented west to east (transecting corridors). impedance contrasts these features rival 660-km discontinuity, suggesting reflecting surfaces must be relatively continuous flat north south (along corridors) maintain strong apparent contrast. both areas unlikely result interacting chemical boundary layer small-scale scatterers within midmantle. More likely pressure–temperature-dependent phase transition around subducting slabs.