COMPARISON AMONG IMPLEMENTATIONS OF FREE-SURFACE BOUNDARY IN ELASTIC WAVE SIMULATION USING THE FINITE-DIFFERENCE METHOD

Representation of free-surface boundary condition in numerical calculations is an important aspect for seismic wave simulation. The effectiveness of numerical representation directly relates to whether the wave field can represent the true response of free-surface medium characteristics. Five common implementations of free-surface boundary used in the staggered-grid finite-difference method were evaluated, including the direct method, the stress image method, the improved stress image method, the transversely isotropic medium approach and the acoustic-elastic boundary approach, and a comparison with the finite-element method was also conducted. Simulation results of the transversely isotropic medium approach and the finite-element method are consistent best in visual comparison of waveform curve and quantitative comparison of amplitude ratio and correlation coefficient. Further numerical simulation results of elastic wave in layered medium model show that the transversely isotropic medium approach is the most accurate and reliable one which could represent seismic wave propagation in free-surface medium.