Efficient 3-D Seismic Wave Simulation in the Presence of Topography Using an Overset Virieux-Lebedev Grid FDTD Scheme

Summary Sufficiently accurate 3-D seismic wave modelling in the presence of topography remains computationally demanding, particularly when curvilinear discretizations are applied throughout the full domain. We develop an overset Virieux-Lebedev finite-difference framework that confines the curvilinear Lebedev-grid (LG) discretization to a near-surface patch and couples it to a standard staggered-grid (SSG) scheme in the deeper region through wavefield exchange across an overlap zone. The approach aims to reproduce traction-free free-surface effects and topographic scattering while reducing the cost associated with domain-wide curvilinear LG finite-difference operators. We first verify the underlying mimetic finite-difference implementation using homogeneous half-space benchmarks with both flat and Gaussian topographic free surfaces by comparison with reference solutions. We then assess the overset coupling using a series of verification tests, including a homogeneous Cartesian benchmark,a layered model with topography and impedance-contrast interfaces, and a modified GO_3D_OBS crustal model. Across these experiments, the receiver seismograms and wavefield snapshots exhibit no discernible artefacts attributable to the overset coupling interface, and the time-frequency envelope and phase misfit measures indicate close waveform agreement. Runtime profiling further indicates substantial efficiency gains when the LG overset thickness is held fixed, and a representative GO_3D_OBS experiment achieves a marked reduction in wall-clock time relative to a full-domain LG simulation. These results demonstrate that the proposed overset strategy enables efficient and sufficiently accurate 3-D wave propagation modelling for complex topographic settings relevant to waveform-based imaging and inversion.