Strong seismic scatterers near the core-mantle boundary north of the Pacific Anomaly

Tomographic images have shown that there are clear high-velocity heterogeneities to the north of the Pacific Anomaly near the core-mantle boundary (CMB), but the detailed structure and origin of these heterogeneities are poorly known. In this study, we analyze PKP precursors from earthquakes in the Aleutian Islands and Kamchatka Peninsula recorded by seismic arrays in Antarctica, and find that these heterogeneities extend similar to 400 km above the CMB and are distributed between 30 degrees and 45 degrees N in latitude. The scatterers show the largest P-wave velocity perturbation of 1.0-1.2% in the center (160-180 degrees E) and similar to 0.5% to the west and east (140-160 degrees E, 180-200 degrees E). ScS-S differential travel-time residuals reveal similar features. We suggest that these seismic scatterers are the remnants of ancient subducted slab material. The lateral variations may be caused either by different slabs, or by variations in slab composition resulting from their segregation process. (C) 2016 Elsevier B.V. All rights reserved.