Effect of the Upper Part of the Soil Profile on the Site Response

The effect of the upper part of a layered profile on calculated seismic hazard parameters is analyzed. The behavior of the soil profile is studied as part of equivalent linear modeling with the example of six seismogeological models. Peak ground acceleration of the input signal varies from 0.1 to 0.6 g. It is shown that the character of the dependence of physicomechanical properties in the layer on the strain value leads to variations in the amplitudes of the response spectrum on the free surface and displacement of the maximum of the frequency spectrum. An increase in the thickness of the upper layer significantly influences the shape of the response spectra. Variations in the PGA values, damping coefficients, strain values with depth are calculated, as well as the velocity profiles for different soil layers with respect to the degradation curves. It is demonstrated that restricting the upper limit of the damping coefficient to 15% does not lead to noticeable changes in the shape of the response spectra on the free surface. The soil column begins to decrease the peak value of the input signal when its level exceeds 0.3 g.