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基于傅里叶伪谱法(Fourier pseudospectral method,PSM),发展了模拟具有任意横向非均匀结构的全地球模型中SH波传播的算法.所采用的模型为通过地球大圆选取的一个二维全地球剖面,所求解的弹性波动方程定义在二维柱坐标系下.波动方程中空间微分的数值求解通过波数域的乘积运算实现,空间域与波数域之间的变换通过快速傅里叶变换(fast Fourier transformation,FFT)进行.由于PSM具有精度较高、计算速度较快的特点,所以对于非均匀结构可以近似为在垂直剖面方向上对称的模型,本算法能够较精确地计算较高频率的全球SH波场的理论地震图.和基于球坐标系二维全球模型的算法相比,本算法能够更方便地处理震源项.用该算法计算了PREM模型中全球SH波的传播,分析了各种震相的产生以及它们在各个界面上的反射、透射、绕射,并将其应用于包含核幔边界低速扰动结构的横向非均匀全球模型,讨论了他们对全球SH波传播的影响.
Based on the Fourier pseudospectral method (PSM), an algorithm to simulate the propagation of SH waves in an all-earth model with arbitrary lateral non-uniform structure is developed. The model adopted is a two-dimensional all-earth Section, the solution of the elastic wave equation is defined in a two-dimensional cylindrical coordinate system. The numerical solution of the spatial differential in the wave equation is achieved by the product of the wave number domain. The transformation between the spatial and wavenumber domains is performed by the Fast Fourier Transform Fourier transform (FFT) .Because PSM is characterized by high precision and fast calculation speed, PSM can be approximated as a model with symmetry in vertical cross-section for non-uniform structure. This algorithm can calculate higher-frequency global SH wavefield.Compared with the algorithm based on the two-dimensional global model of spherical coordinate system, this algorithm can handle the source term more conveniently.With this algorithm, the propagation of global SH wave in PREM model is calculated, The generation of seismic facies and their reflection, transmission and diffraction at various interfaces are applied to the lateral heterogeneity of low-perturbation structures including the boundary of the core-mantle Uniform global model to discuss their impact on global SH wave propagation.