In this paper, an analytical, numerical and experimental approach for identifying soil profile characteristics by using system identification and free field records, is presented. First, a theoretical soil amplification function for two sites is defined and expressed in terms of the different parameters of the layers constituting the soil profiles (thickness, damping ratio, shear wave velocity and unit weight). Then, this function is smoothed with an analogous function obtained from experimental data by using the least squares minimization technique. The identification of the parameters is performed by solving, numerically, a non-linear optimisation problem. To demonstrate the numerical efficiency and the validity of this approach, two examples are treated. The first one consists in the identification of characteristics of a given uniform soil layer. The second example consists in the experimental validation of this approach with the data recorded within the Garner Valley Down Hole Array (GVDA). Finally, this approach is applied to identify, simultaneously, soil profile characteristics of sites from only a single soil acceleration record at free surface of each site. This procedure is utilised to identify soil profile characteristics of sites by using strong ground motions data recorded during the recent Boumerdes earthquake of May 21, 2003.
