Seismic Wave Modeling with an Improved Sponge Boundary Condition Considering Viscoelastic Behavior

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Abstract
The sponge boundary condition (SBC), an absorbing boundary condition, has not been discussed considerably; additionally, it has not been commonly used owing to its low applicability. Although the SBC is similar to the equation describing intrinsic attenuation in viscoelastic media, its behavior differs from the viscoelastic case. Herein, we present a new form of the SBC, which shows similarities with intrinsic attenuation. We describe the characteristics of the conventional and new SBCs with some numerical examples. By comparing the SBCs with the perfectly matched layer (PML) boundary condition, we found that the SBCs required broader damping areas than the PML to suppress artificial reflections; however, the SBCs could compensate for this deficiency with computational efficiency. The new SBC allows using variable-sized grids for damping areas, which substantially improves the performance of the SBC to be comparable to the PML while partially preserving computational efficiency.

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