Isotropic angle-domain elastic reverse-time migration

Imaging with scalar and vector potentials

Consider the images (Figures 6) obtained using the imaging conditionfrom equation  applied to the data (Figures 4a and 4b) from the preceding example. Because we used an explosive source for our simulation, the source wavefield contains mostly P-wave energy, while the receiver wavefield contains P- and S-wave mode energy. Helmholtz decomposition after extrapolation but prior to imaging isolates P and S wavefield components. Therefore, migration produces images of reflectivity corresponding to PP and PS reflections, Figures 6a and 6b, but not reflectivity corresponding to SP or SS reflections, Figures 6c and 6d. The illumination regions are different between PP and PS images, due to different illumination angles of the two propagation modes for the given acquisition geometry. The PS image, Figure 6b, also shows the usual polarity reversal for positive and negative angles of incidence measured relative to the reflector normal. By comparing Figures 6a and 6b with Figures 5a and 5b, it is apparent that the crosstalk in the images obtained from displacement-based imaging condition is more prominent than the one obtained from potential-based imaging conditions, especially in Figure 5a. Furthermore, the polarity in Figure 5b, normally taken as the PS image, does not reverse polarity at normal incidence, which is not correct either.

Isotropic angle-domain elastic reverse-time migration