AN EXPLICIT SPECTRAL-ELEMENT APPROACH TO FLUID-SOLID COUPLING PROBLEMS IN SEISMIC WAVE PROPAGATION

Fluid-solid coupling seismic wave motion problems are aimed at investigating the characteristics and laws of seismic wave propagation in the complex system composed of fluid and solid media. In traditional simulation methods, numerical solutions of acoustic and elastic wave equations are generally used to describe the waves in ideal fluid and elastic solid respectively, and the coupling between the two media with different properties is dealt with in real time. Consequently, traditional methods suffer from complex numerical schemes, relatively low numerical simulation accuracy and computational efficiency. Based on spectral element method and multi-transmitting formula artificial boundary condition, a high order explicit numerical method for fluid-solid coupling seismic wave motion problems is developed in this paper. This method uses a unified computational framework, in which Biot’s equations for saturated porous media can degenerate to acoustic and elastic wave equations for ideal fluid and elastic solid respectively. Three numerical examples of ideal fluid-saturated porous medium-elastic solid system are given: the horizontal layered site model with vertical incidence of P wave, the irregular layered interface model under obliquely incident P wave and arbitrary shape interface model under obliquely incident P wave. The accuracy and efficiency of the proposed method are verified in comparison with the results of transfer matrix method and lumped mass finite element method. The numerical simulation results show that compared with the traditional finite element method, this method can obtain higher numerical accuracy with much less nodes, and can reliably simulate the dynamic response of fluid-solid coupling problems in a wider frequency range. The proposed method fully represents the characteristics of high precision, high efficiency and flexibility to handle complex sites.