Numerical simulation of 2-D seismic wave propagation in the presence of a topographic fluid-solid interface at the sea bottom by the curvilinear grid finite-difference method

This study simulates seismic wave propagation across a 2-D topographic fluid (acoustic) and solid (elastic) interface at the sea bottom by the finite-difference method (FDM). In this method, seismic waves in sea water are governed by acoustic wave equations, whereas seismic waves in solid earth are governed by elastic wave equations. The fluid-solid interface condition is implemented on the interface. Body-conforming grids are used to fit the topographic fluid-solid interface which naturally avoids spurious diffractions due to staircase approximation. A collocated-grid MacCormack FDM is utilized to update the wavefields in the fluid and solid media. The fluid-solid interface condition is explicitly implemented by decomposing the velocity and stress components to the normal and tangential directions with respect to the interface within a fourth-order Runge-Kutta time-marching scheme. The algorithm solutions for both flat and topographic fluid-solid interface models are compared with analytical solutions and spectral element solutions to validate the proposed method. Results show a suitable agreement with the reference solutions and hence confirms the validity of this method. The proposed FDM enforces the numerical solutions to satisfy the exact interface condition and it is more accurate than the conventional FDM that uses effective media parameters to approximate the interface condition.