Multipath acoustic arrivals on fixed receivers from a moving source in an underwater waveguide include wide-angle bottom reflections that are affected by sediment properties. Hence, one can use them as input data for seabed geoacoustic parameter estimation. In this study, the effects of seabed properties on such measurements are theoretically analyzed. The result shows that one can utilize time delays and source distances at the critical angle points of multipath arrivals to determine the sediment sound speed. The effect of sediment attenuation is also discussed, and the proposed method is demonstrated with experimental data.