基于多震相的阿拉斯加地区D″结构不均匀性及核幔边界地形起伏研究

The properties of D″ layer and topography of core–mantle boundary (CMB) not only put direct constraints on the core–mantle coupling, mantle convection and the physical properties of inner core, but also play important role on the study of Earth evolution. Since there is trade-off between 3D D″ layer structure and topography variation of CMB, it is difficult to resolve the ambiguity between 3D tomography and CMB topography using a single phase. Researchers have been focused on the study of core mantle boundary layer beneath Alaska in the past decade, due to the complex structure, dramatic geodynamic processes and better study condition. This study intends to analyze the travel time, amplitude, polarization, frequency and waveform of PKPab, PKPbc, PKPdf, PcP, ScP phases which sample the core mantle boundary region beneath Alaska, and plans to develop a ray theory method to calculate short period core phases synthetic seismograms for a series 3D tomography and CMB topography models. By comparing the observations with synthetic seismograms, we will obtain a heterogeneity of D" layer and topography of CMB model beneath Alaska. Then we will propose a hypothesis in explaining the possible origin of such model. In summary, the knowledge of core mantle boundary layer beneath Alaska can provide key information for the modeling of mantle convection, core–mantle coupling and geo-dynamo，can also influence the study of inner core anisotropy and differential rotation.

研究D″层结构不均匀性和核幔边界地形起伏不仅为追溯地球演化提供重要信息，也为阐明现今地幔对流和核幔耦合、内核物理性质等重大前沿科学问题提供关键证据。由于地幔底部结构横向不均匀性与核幔边界地形起伏相互耦合并相互影响，单一震相一般难以准确约束。鉴于阿拉斯加地区核幔边界区域有高度的结构不均匀性、复杂的动力学过程及良好的研究条件。本研究拟分析采样该区域核幔边界附近的PKPab、PKPbc，PKPdf、PcP、ScP等多种震相的走时、振幅、偏振、频率及波形等特征。发展适应三维结构不均匀性和核幔边界起伏的射线理论正演算法，用合成波形拟合观测数据给出最优拟合模型，并结合地球动力学和矿物物理学成果，探讨上述地震学模型特征的可能成因。总之，厘清阿拉斯加地区核幔边界边界层复杂性可为地幔对流、核幔耦合、地磁场发电机等动力学模拟提供关键信息，也能为内核各向异性及旋转变化研究奠定重要基础。

研究D″层结构不均匀性、核幔边界地形起伏、下地幔温度状态等不仅为追溯地球演化提供重要信息，也为阐明现今地幔对流和核幔耦合、内核物理性质等重大前沿科学问题提供关键证据。本研究分析采样到核幔边界附近的PKPab、PKPbc，PKPdf、PKKP、PcP、ScP等多种震相的走时、振幅、偏振、频率及波形等特征。基于正演算法构建下地幔速度结构不均匀性、下地幔衰减结构、内核各向异性等模型，并结合地球动力学和矿物物理学成果，探讨上述地震学模型特征的可能成因。发现西半球局部地区内核各向异性的分层特征；约束了中国东北下地幔的衰减结构，估算了其现今的温度状态；厘清了PKPPKP 180s前驱波的非对称路径传播机理，否认了其下地幔界面处的对称性路径传播理论；构建了PKKP三重震相数据库，发现PKKPab衍射波传播距离远超理论截至震中距，并通过计算PKKPab衍射波互相关到时敏感核函数，定量研究了其对核幔边界上方低速层的敏感性；上述研究成果为地幔对流、核幔耦合、地磁场发电机等动力学模拟提供关键信息，也能为内核各向异性及旋转变化研究奠定重要基础。