Seismic evidence indicates the existence of two prominent seismically low-velocity anomalies in the Earth?s lower mantle, namely the Pacific Anomaly and the African Anomaly. It is now recognized that these two prominent anomalies may directly be related to the early differentiation, evolution and dynamics of the Earth?s mantle. Thus, resolving the detailed structural and velocity features of these two anomalies is important to further our understanding of the Earth?s internal processes that lead to the geological events and tectonic activities at the Earth?s surface.
This proposal intends to resolve the outstanding issues related to the Pacific Anomaly based on extensive waveform modeling and travel time analysis, and to study detailed 3D anisotropy, structural feature and velocity structure in several particular regions of the mantle, including a) anisotropic structure near the edge of the African Anomaly, and b) structural feature and velocity structure of the southeastern edge of the African Anomaly and the western edge of the high-velocity anomaly beneath the Cocos plate. The important outstanding issues related to the Pacific Anomaly to be addressed include: the exact geographic extent of the Anomaly at the core-mantle boundary; the structural and velocity features of the Anomaly in other cross sections; the detailed transitional structures from the Pacific Anomaly to the surrounding mantle in various directions; and the lateral variations of structural feature, length-scale and velocity reductions of small-scale anomalies at the base of the Anomaly.
The proposed approaches include development of a hybrid anisotropic method; collection and identification of high-quality anomalous seismic data; and waveform and travel time modeling of the seismic data with a scientific goal of mapping detailed structural features and velocity structures of the three prominent velocity anomalies in the lower mantle. Besides training a graduate student and providing the community computer source code for a hybrid method, the proposal would further our understanding of the thermal evolution of the Earth, thermal-chemical convection in the mantle, thermal-chemical mantle plume, and relationship of mantle seismic heterogeneities to early differentiations of the Earth, the characteristics of the hotspot motions, and the unique geochemical signatures including the DUPAL anomaly and the South Pacific Isotopic and Thermal Anomaly.
