A Modified Viscous Boundary LIU Jia-hua (Jinji Lake Hotel Project Preparatory Department, Suzhou 215021, China)In modern design for aseismatic structures, viscous boundaries have to be introduced to take account of the soil-structure interaction.In the boundary model, the standard or modified viscous dampr are imposed at the bottom boundary while the lateral boundaries are tied together. In this case,the standard viscous boundary conditions are easy to be imposed on some artifitial truncated boundary.The modified viscous boundary is proposed here to deal with the non-plane wave behaviour near the boundary.The modified viscous boundary is reasonable.modern design for aseismatic structures; soil-structure interaction; standard viscous boundary conditions; modified viscous boundary conditions