Abstract

Synthetic seismograms are used to study elastic wave propagation in multi-layered media for cross-borehole geometries. The calculations are done using the discrete wavenumber method. We compute the wavefield for a series of receiver arrays located at various offsets to follow the evolution of the wavefronts and the distribution of the seismic energy in space. The results show the complexity of the wavefield at large offsets. Trapped waves and conical waves perturb the identification of direct and primary reflected phases. The display of polarization diagrams of the guided waves shows elliptical prograde motions. The source position plays an important role in the energy distribution within the medium. In order to study this dependency, we compare the cases of sources located in relatively low and high-velocity layers. In the former case, most of the energy is trapped within the source layer and in the neighboring region and propagates horizontally. The S-converted waves generated at the interfaces bounding the source layer have larger amplitude than the direct P-wave. When the source is placed in a relatively high-velocity layer the energy of the P-wavefront spreads rapidly throughout the medium as the offset increases.

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