Cube2sph : A toolkit enabling flexible and accurate continental-scale seismic wave simulations using the SPECFEM3D_Cartesian package

To enable flexible and accurate seismic wave simulations at continental scales (10°−60°) based on the spectral-element method using the open-source SPECFEM3D_Cartesian package, we develop a toolkit, Cube2sph, that allows the generation of customized spherical meshes that account for the Earth's curvature. This toolkit enables the usage of the perfectly matched layer (PML) absorbing boundary condition even when the artificial boundaries do not align with the coordinate axes. A series of numerical experiments are presented to validate the effectiveness of this toolkit. From these numerical experiments, we conclude that (1) continental-scale seismic wave simulations, especially surface wave simulations, can be more efficiently performed without the loss of accuracy by truncating the mesh at an appropriate depth, (2) curvilinear-grid PML can be used to effectively suppress artificial reflections for seismic wave simulations at continental scales, and (3) the Earth's spherical geometry needs to be accurately meshed in order to obtain accurate simulation results for study regions larger than 8°.