Scalar reverse-time depth migration of prestack elastic seismic data

Abstract Reflected P-to-P and P-to-S converted seismic waves in a two-component elastic common-source gather generated with a P-wave source in a two-dimensional model can be imaged by two independent scalar reverse-time depth migrations. The inputs to migration are pure P- and S-waves that are extracted by divergence and curl calculations during (shallow) extrapolation of the elastic data recorded at the earth's surface. For both P-to-P and P-to-S converted reflected waves, the imaging time at each point is the P-wave traveltime from the source to that point. The extracted P-wave is reverse-time extrapolated and imaged with a P-velocity model, using a finite difference solution of the scalar wave equation. The extracted S-wave is reverse-time extrapolated and imaged similarly, but with an S-velocity model. Converted S-wave data requires a polarity correction prior to migration to ensure constructive interference between data from adjacent sources. Synthetic examples show that the algorithm gives satisfactory results for laterally inhomogeneous models.