An optimized scheme of dispersion suppression for elastic-wave variable-order rotated staggered-grid forward modeling

Numerical simulations of seismic waves are effective ways to analyze wave propagation in subsurface geological structures. Finite-difference forward modeling based on elastic-wave equations is one of the numerical simulation methods, which can effectively depict elastic-wave propagation. In elastic-wave finite-difference forward modeling, the numerical dispersion of wavefield is one of the most serious problems, which could contaminate the expected wavefield signals in seismic records. The variable-order rotated staggered-grid method (VRSM) has been developed by applying the variable-order method to the rotated staggered-grid method (RSM), which solves the numerical dispersion problem of the RSM in low-velocity regions. In this paper, the norm modified method (NMM) is introduced. The NMM can offer different finite-difference coefficients under different threshold constraint conditions to optimize the Taylor series expansion method (TSM) in suppressing numerical dispersion error and increasing the accuracy of numerical simulation. The optimized norm modified method (ONMM) is developed by combining the advantages of the NMM and the TSM to increase the accuracy of numerical simulation of the NMM. We apply the ONMM to further improve the precision and suppression of the numerical dispersion error of the VRSM, and name it the optimized variable-order rotated staggered-grid method (OVRSM). In the numerical experiments, we evaluate the finite-difference order distribution both from waveform characteristics and numerical dispersion analysis by OVRSM. The results of experiments demonstrate that the new order distribution is reasonable and the OVRSM is effective in numerical dispersion suppression.