Validating a GPU elastodynamic solver for anisotropic seismic wave propagation: application to a Swiss earthquake, explosion and collapse sources

SUMMARY We present and validate an efficient GPU-accelerated solver for seismic wave propagation in 3-D elastic media. The solver achieves up to a 372$\times$ speedup relative to a CPU implementation and supports forward simulations on grids ranging from 100 million to 1 billion cells. It is based on a velocity-stress, first-order formulation of the elastodynamic wave equation and supports kilometre-scale models with layered isotropic and anisotropic structure. We validate the solver by comparing synthetic seismograms to analytical solutions from a propagator matrix method in axisymmetric media. Simulations include moment-tensor sources for a 2017 nuclear explosion and collapse in North Korea, and a magnitude $\sim$4 earthquake near Linthal, Switzerland (2017 March 6). Anisotropic effects for the Swiss event are modelled using rotated orthorhombic stiffness tensors derived from laboratory measurements of gneiss. Projection onto orthorhombic symmetry enables solver compatibility. We find that anisotropy changes waveform polarity, amplitude and phase at near-source stations. Unscaled laboratory values produce polarity reversals, while velocity-rescaled tensors correct them. These results demonstrate the impact of anisotropy on waveform modelling and indicate that simplified 1-D isotropic models may be insufficient for complex crustal settings. We review how structural effects, including anisotropy and 3-D heterogeneity, contribute to transverse-component energy in the 2017 DPRK explosion and discuss implications for seismic source classification.