3-DIMENSIONAL SCATTERING BY 2-DIMENSIONAL TOPOGRAPHIES

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 sources. The appropriate Green's functions used are those of a harmonic point force moving along the axis of the topography in a full space. Obtained results 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 frequency domains. Frequency-space representations allow identification of diffraction and interference patterns in the seismic response of the topography. Synthetic seismograms are obtained by Fourier analysis. Using time-space domain representations, the nature of each of the scattered waves are identified in terms of, for example, creeping waves and reflected compressional waves.