Effect of Magnitude and Type of Damping on Soil Amplification

Soil Amplification studies conducted to obtain site specific seismic motions at the free surface of a soil deposit or at any other elevation (convolution process), or to determine compatible base motions at a given depth for soil structure interaction analyses (deconvolution) assume, when performed in the frequency domain simulating nonlinear soil behavior through an iterative linear analysis, that the internal soil damping is of a linear hysteretic nature. This tends to filter out excessively the high frequency components of motion for convolution studies and leads to eventual instability of the solution at a given depth (function of the soil properties) when performing deconvolution. In this paper, the results obtained using constant frequency independent, linear proportional and inverse proportional damping in the iterative solution are compared to those provided by true nonlinear analyses using consistent soil models