基于谱元-简正振型耦合方法的核幔边界D″区地震波波形模拟方法研究

A coupled method of spectral element and normal mode:an powerful tool of modeling the seismic waves propagation in anisotropic D″region

本文拓展了一种模拟地震波在地球核幔边界D″区各向异性介质中传播的数值方法:谱元-简正振型耦合方法(CSEM).该方法通过在球对称各向同性介质空间采用简正振型方法,在各向异性的D″区采用谱元方法,并在两种介质的边界采用"DtN"算子耦合的策略计算一维模型PREM(见文献[1])或修改后的D″区横向各向同性VTI-PREM模型的理论地震图.模拟所得数值解结果与采用简正振型方法得到的解析解结果进行对比以验证方法的精度.在中国科学院地球深部结构重点实验室高性能计算机上使用128个CPU计算得到的结果显示,在10-5～0.125Hz的频率范围内谱元简正振型法得到的波形与简正振型方法能很好拟合.此外,对于VTI介质结构模型,谱元简正振型法能够准确模拟S波分裂现象,从而验证了谱元简正振型耦合方法对各向异性介质中地震波传播数值模拟是一种有效的方法.

We extended a coupled mode/spectral element method （CSEM hereafter）, which can efficiently modeling the seismic waves propagation in the anisotropic D＂ region. Using the original PREM and a modified transverse isotropic PREM model in D＂ region, we calculated synthetic seismograms with a new PC cluster with 128 CPUs and 160GB memory in the Key Laboratory of Earth Deep Interior. The numerical solution was compared with the analytical solution by normal mode method in order to verify the accuracy of CSEM. Comparison shows that in a broad frequency band （10^-5-0. 125 Hz） the results of the two methods match very well. Besides, thesynthetic seismograms of the transverse isotropic PREM model show obvious arrival time differences between SH and SV components. This proved the capability of CSEM to modeling S wave splitting caused by anisotropic media.