Bulldozing the core-mantle boundary: Localized seismic scatterers beneath the Caribbean Sea

Images of the scattering field near the core-mantle boundary (CMB) beneath the Caribbean were obtained from migration processing of PKIKP precursors recorded by a broadband seismic array in the southern Caribbean from earthquakes in the Western Pacific. Strong seismic scatterers were found to be concentrated near the CMB north of Colombia and are surrounded by high velocity anomalies associated with the subducted Farallon plate. The relative location between the imaged scatterers and the surrounding high velocity anomalies leads us to speculate that the observed seismic scatterers are remnants of the subducted slab. As the Farallon plate penetrated into the lower mantle, segregation allowed its basaltic crust to descend more quickly and to pool in front of the major portion of the subducting slab. The ponding oceanic crustal material could be further collected (or bulldozed) by the residual motion of the subducting plate, forming a localized region with strong seismic scatterers.