The seismic response of a two-dimensional sedimentary basin is studied with the indirect boundary element method (IBEM) and compared with the results of a hybrid technique that combines modal summation and the finite-difference technique. To perform this numerical experiment we used the “observed” ground motion at the edge of the basin, computed independently with the hybrid technique. This ground motion is used to estimate the apparent incoming wave field. The estimation is based on a simplified polarization analysis that led us to select time windows for various incident plane-wave types. The numerical simulations with IBEM gave results in the time and frequency domain that compare well with those of the hybrid approach. It suggests that a realistic simulation of strong ground motion is possible using two-dimensional wave propagation modeling together with an estimate of the incident wavefield. This estimate can be obtained with a polarization analysis of observed ground motion at a station located on bedrock, as long as the different wave types can be separated in time and frequency.