One studies on SASSI-2000 frequency domain resolution procedures to obtain the so called free-field response for a site under seismic excitation, consideration made to the soil structure interaction. A stratified site model is considered formed by a series of six semi-infinite horizontal layers with equal height resting on a rigid viscoelastic half-space; the structure model is a 3D isosymmetric orthogonal frame made of equal beam elements with variable soil embedment. Different free-field wave compositions, including body and surface waves, are used with variable incidence angle to the vertical Z-axis. The behavior of the free-field solution is observed through the following parameters and selections: wave types, value of their incidence angle to the vertical of the control point on the half-space surface and their relative participation factors in the overall wave field; the structure to soil mass and stiffness ratios are kept constant. One focalizes the variation of the system natural frequency values, obtained from a series of suitably selected transfer functions on the control point vertical line, and their associated modal configurations. The run series is repeated with the structure presence under different soil embedment and the observation is extended to the soil kinematics variation outside the excavated soil. Conclusions include the understanding of the main behavior aspects and orientation is given about the more convenient attitudes and selections to be taken.