Converted Phase Elastic Migration Velocity Analysis

Abstract

Multi-component elastic seismic data collected at large offsets have the potential to be used in seismic imaging and velocity analysis. In this study, we present an approach for converted-phase elastic-transmission migration velocity analysis with an application for VSP and micro-seismic studies. Our approach is based on the cross-correlation between converted-phase P- and S-waves propagated backward in time, and is formulated as an inverse problem with a differential semblance criterium objective function for the simultaneous update of both P- and S-wave velocity models. The merit of this approach is that it is fully data-driven and requires only one elastic backward propagation to form an image rather than the two (one forward and one backward) acoustic propagations needed for standard RTM. Moreover, as the method does not require forward propagation, it does not suffer from migration operator source aliasing when a small number of shots are used. We present a derivation of the method and test it with the synthetic Marmousi model. We also show the differences between the standard reflection offset domain common image gathers and the converted-phase image gathers that we use for model updates.