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

Tuesday, 16 December 2014
Xinlei Sun1, Xiaolong Ma1, Doulgas A Wiens2, Lianxing Wen3, Andrew Nyblade4, Sridhar Anandakrishnan5, Richard C Aster6, Audrey D Huerta7 and Terry J Wilson8, (1)GIG Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, State Key Laboratory of Isotope Geochemistry, Guangzhou, China, (2)Washington University in St Louis, Department of Earth and Planetary Sciences, St. Louis, MO, United States, (3)Stony Brook University, Stony Brook, NY, United States, (4)Penn St Univ, University Park, PA, United States, (5)Pennsylvania State University Main Campus, University Park, PA, United States, (6)Colorado State University, Geosciences Department, Fort Collins, CO, United States, (7)Central Washington University, Ellensburg, WA, United States, (8)Ohio State Univ, Department of Geological Sciences, Columbus, OH, United States
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.