In an elastic medium, reverse time migration (RTM) uses the velocity-stress method for the wavefield propagation and a numerical seismic source to create shot and receiver wavefields required in the imaging conditions. This essay discusses different ways to introduce a seismic source in the elastic modeling process. The seismic source in the elastic reverse time migration/RTM is normally expressed by a combination of wavelet functions in spatial and time dimensions. In most occasions, pure P/S wave sources are preferred. This paper shows that the typical way to introduce the source in RTM is not a pure P/S wave source. A better approach to approximate pure P/S modes is to use a plane source. In this paper, we use elastic modeling process to generate P&S shot records. Then we use acoustic RTM and least squares RTM to migrate these elastic data, using P and S velocities in different experiments. In both cases, the reflectivity models obtained from RTM are very poorly defined, but the LSRTM produces a clean image because of its capability to filter out events that can not be properly predicted by the modeling operator.
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