Background With the comprehensive advancement in intelligent coal mine construction, creating high-precision, transparent geological models of coal seams and their surrounding strata has emerged as a prerequisite for intelligent coal mining. The accurate identification of concealed geological anomalies, such as folds and faults, within coal seams represents a key challenge in safe coal mining. In-seam seismic exploration has become an important approach to detecting underground concealed structures owing to its advantages, including a considerable detection distance along coal seams, high precision, pronounced frequency dispersion effects, and facilitating the identification of waveform signatures. However, conventional methods for seam wave simulation are prone to errors when used to characterize undulating coal seam interfaces, producing negative impacts on the accurate identification of structures such as folds and faults.

Objectives and Methods  To investigate the propagation patterns and frequency dispersion characteristics of seam waves in complex coal seams more effectively, this study conducted 3D forward modeling of channel waves using the finite difference method on curvilinear grids. Based on the accurate characterization of the undulating coal seam interfaces using body-fitted grids, the spatial and temporal partial derivative terms were approximated using the DRP/opt MacCormack scheme and the fourth-order Runge-Kutta algorithm, respectively. Finally, the dispersion curves of the Rayleigh- and Love-type seam waves were extracted using the phase-shift method and were then compared with theoretical dispersion curves.

Results and Conclusions  Test results on the curved coal seam models bearing a fold or a fault demonstrate that, compared to the conventional finite difference method on regular grids, the finite difference method on curvilinear grids yielded seam waves with more continuous waveforms in simulation. Furthermore, the proposed method effectively suppressed the spurious scattering induced by the staircase approximation of undulating interfaces. All these enhanced the accuracy of the simulation results. Comparison indicates that the dispersion energy from simulation using curvilinear grids agreed better with theoretical dispersion curves and exhibited more continuous morphologies and smaller oscillations compared to that from simulation using Cartesian grids. These characteristics facilitate the accurate picking of dispersion curves. The finite difference method on curvilinear grids can significantly enhance the simulation accuracy of seam waves in undulating coal seams, providing a reliable foundation for forward modelling in practical in-seam seismic exploration.