Abstract: The scattering and diffraction of plane P waves in circular alluvial valleys with soft soil deposits is studied in this paper with the deposits simulated by Biot dynamic theory for saturated porous mediam, and the half space assumed to be elastic single phase mediam. The Fourier Bessel series expansion technique is used to solve this problem. Numerical results are given to illustrate the influence of different interface condition and the saturation and porosity of the soil deposits on the surface motion.