Investigations were carried out for three soft-sediment filled basins in the Ottawa, Canada region to examine the contributions of 2 and 3D site effects on ground motions due to weak motion earthquakes. In order for a 1D ground motion modelling software program to produce transfer functions approaching the frequency peaks obtained from soil-to-rock ratios of local earthquake recordings, a detailed soil profile, local modulus reduction and damping ratio curves, and local earthquake recordings are required as input. However, soil-to-rock amplifications and spectral curves varied from the predicted 1D output, suggesting the influenced of 2 and 3D effects. Horizontal particle motions on the soil sites do not match the orientations recorded on the rock site, with the direction of the motions depending on the frequencies examined.