Three-dimensional seismic responses of two-dimensional topographies are studied by means of the indirect boundary element method (IBEM). The IBEM yields, in the presented form, very accurate results and has the advantage of low computational cost. In IBEM, diffracted waves are constructed in terms of single-layer boundary souces. The appropriate Green's functions used are those of a harmonic point foce moving along the axis of the topography in a full space. Obtained reults are compared against those published by other authors. Examples of simulations are presented for different geometries, for different types of incident wave fields, and in particular, for different arrival angles to the topography to quantitatively study three-dimensional effects of the scattering. The accuracy of the results makes it possible to analyze them in both the time and drequency domaisn. Frequency-space representations allow identification of difraction and interference patterns in the seismic response of the topography. Synthetic seismograms are obtained by Fourier analysis. Using timespace domain representations, the nature of each of the scattered waves are identified in terms of, for example, creeping waves and reflected compressional waves.