Elastic wave reverse time migration based on vector wavefield seperation

Key words:  elastic wave reverse time migration  polarity reversal  wavefield decomposition  inner product imaging condition

Abstract:

With the advances of seismic acquisition, seismic imaging has migrated from using single-component data alone to multi-component elastic wave imaging. Because of its high precision imaging ability, reverse-time migration (RTM) has been widely applied to complex structure imaging. However, S-mode polarization changes via incident direction, which will cause polarity reversal, and this polarity reversal will seriously damage the continuity of reflection events in conventional PS imaging as well as SP imaging after stacking over multiple shots. In the conventional elastic RTM, Helmholtz decomposition is used to obtain the scalar potential (P-wave) and the vector potential (S-wave). In this paper, we introduce gradient and curl operators to the scalar potential and the vector potential, respectively. Consequently, we can obtain vector P-waves and S-waves. As for the vector wavefield, we introduce an inner product imaging condition to the elastic RTM, which can avoid using extra polarity correction. Wavefield analyses show that this method is applicable not only to primary imaging (PP and SS) but also to converted wave imaging (PS and SP).The effectiveness and feasibility of our new imaging method in simple and complex models are illustrated in numerical examples using synthetic data.