Abstract: In recent years, the technology of Rayleigh-waveform inversion is highly valued by scholars, because the wave field is calculated and inverted directly without the calculation of conventional dispersion curves. In other words, the waveform inversion method is no longer limited by the theoretical assumption of horizontal layered media. Rayleigh waveform inversion requires repeated forward and inverse calculations of wave field; in addition, due to the small velocity of the shallow surface, the simulation requires a small grid space to avoid numerical dispersion, which undoubtedly greatly increases the forward modeling calculation amount. Based on the idea of message passing interface (MPI) method, we applied a parallel finite-difference algorithm to wave field simulation to improve the computation efficiency of the forward modeling. Firstly, the whole calculation region was decomposed into several sub-regions; and then, the wave field was computed for each sub-region; finally, the whole wave field was completed together by communicating among sub-regions. In this paper, the detailed implementation methods and steps of the parallel schemes, such as region decomposition, coordinate transformation, region communication, and wave field combination and so on, are given. The analyzing results of the different parallel schemes in elastic model, Kelvin and standard linear solid (SLS) viscoelastic model show that our parallel scheme is feasible and effective. The parallel computation results indicate that multiple processors can significantly reduce the computing time compared with a single processor; however, the communication time between different processors also increases. It is necessary to select the appropriate number of processors in the parallel process. For viscoelastic medium model, the parallel computation efficiency of SLS viscoelastic model is better than that of Kelvin viscoelastic model.

Key words: MPI, high-order staggered-grid, finite-difference, image-method, CPML, region decomposition