A Coupled Method of Spectral Element and Normal Mode: A Powerful Tool for Modeling the Seismic Waves Propagation in the Anisotropic D″ Region

Abstract

We extended the coupled mode/spectral element method (CSEM hereafter) to incorporate threedimensional, anisotropic media in the lowest 300 km above the core-mantle boundary, the D area. This extended method was applied to modeling of seismic waves propagation in earth models under the so-called "sandwich" structure, which uses a spherical shell of spectral elements between two modal solutions to represent the D area. Using a spherically symmetric reference model with modified anisotropic parameters in the spherical shell, the CSEM yields waveforms in excellent agreement with that of normal-mode. The two methods match very well for all body wave arrivals with periods greater than 8 s. Besides, the S, ScS, SKS, and SKKS phases in the synthetic seismograms of the transverse isotropic model show obvious arrival time differences between SH and SV components. This proves the capability of the extended CSEM code for modeling S wave splitting caused by the radial anisotropic media in the D area.