Strong Seismic Scatterers Near the Core-Mantle Boundary North of Pacific Anomaly From PKP Precursors Recorded by Antarctica Arrays

The arrival times and amplitudes of PKP precursors can provide valuable information on the location, geometry, velocity and density variations of small-scale heterogeneities near the CMB, making it a very useful tool to study the nature of CMB region. We observed PKP precursors from earthquakes in Aleutian Islands and Kamchatka Peninsula recorded by seismic arrays in Antarctica (GAMSEIS and POLENET/ANET) from distance 134-142o. By comparing the CMB entry and exit points of the two sets of earthquakes, we suggest that the precursors are generated by scatterers near the source side entry point. We further analyze the arrival times of PKP precursors and forward model the precursor envelopes. Our preliminary results show that the scatterers are located near the north side of Pacific anomaly, in latitude 30-50°N, and within ~400 km above CMB. Furthermore, the scatterers can be divided into three regions, with 2-3% variation in the middle (160-180°E) and ~1% variation in the other two sides (140-160°E,160-180°W). By further analyzing ScS-S differential traveltime residuals sampling these regions, we argue that the heterogeneous scatterers are probably the remnants of ancient subducted slab.