A linear viscoporoelastic model is developed to describe the problem of reflection and transmission of an obliquely incident plane P-wave at the interface between an elastic solid and an unsaturated poroelastic medium,in which the solid matrix is filled with two weakly coupled fluids (liquid and gas).The expressions for the amplitude reflection coefficients and the amplitude transmission coefficients are derived by using the potential method.The present derivation is subsequently applied to study the energy conversions among the incident,reflected,and transmitted wave modes.It is found that the reflection and transmission coefficients in the forms of amplitude ratios and energy ratios are functions of the incident angle,the liquid saturation,the frequency of the incident wave,and the elastic constants of the upper and lower media.Numerical results are presented graphically.The effects of the incident angle,the frequency,and the liquid saturation on the amplitude and the energy reflection and transmission coefficients are discussed.It is verified that in the transmission process,there is no energy dissipation at the interface.