Probing the Earth's Core and Lowermost Mantle

地核在地球的形成和化学分化、全球地球动力学和地球自转以及磁场的产生中起着重要的作用。这个项目集中在三个相关的目标上，涉及内部核心的结构和自转的地震成像以及最低地幔的非均质性。(1)使用固定的地震台路径来约束内核自转，以减少未建模的地幔不均一性和震源错位造成的偏差。该项目将寻找PKP(BC)-PKP(DF)差分时间和PKP(CD)-PKP(DF)差分时间的时间相关性。还将作出相当大的努力来解决在确定内核自转方面的不确定性，特别是潜在的系统性事件错位造成的误差。(2)利用PKP波形和差分时间对三维各向异性岩心结构进行建模和反演。该项目将检验最近提出的一个明显的最内核层的建议，并考察从相对各向同性的上核心区到下核心区强各向异性的核心区过渡带的锐度和横向变化。(3)利用南美洲和东亚地区地震台站丰富的PKP资料，绘制出最低地幔的不均一性，特别是中太平洋核幔边界异常。

The Earth's core plays an important role in the formation andchemical differentiation of our planet, in global earth dynamicsand earth rotation, and in the generation of the magnetic field.This project focuses on three related objectives, concerning theseismic imaging of the structure and rotation of the inner core andthe heterogeneity of the the lowermost mantle. (1) To constrain theinner core rotation using fixed earthquake-station paths, which reducesbiases from unmodeled mantle heterogeneities and source mislocation.The project will search for time-dependence of PKP(BC)-PKP(DF) differentialtimes and PKP(CD)-PKP(DF) differential times. Considerable effortwill also be made to address uncertainties in determining innercore rotation, in particular errors from potential systematicevent mislocation. (2) To model and invert for 3D anisotropicinner core structure using PKP waveforms and differential times.The project will test the recent proposal of a distinct innermostinner core and examine the sharpness and lateral variation of the innercore transition zone from the relatively isotropic upper inner coreto strong anisotropy in the lower inner core. (3) To map theheterogeneity of the lowermost mantle from the PKP data collected,in particular, the Central Pacific core-mantle boundary anomalyusing abundant PKP samples from the earthquakes andstations in South America and east Asia.