Polarization-based wave-equation migration velocity analysis in acoustic media

Abstract

The source extrapolation step in wave-equation prestack reverse-time migration gives wavefield polarization information, which can be used to generate angle-domain common-image gathers (ADCIGs) from seismic reflection data from acoustic media. Concatenation of P-wave polarization segments gives wavefield propagation paths (“wavepaths”), which are similar to the raypaths in ray-based velocity tomography. The ADCIGs provide residual depth moveout (RMO) information, from which a system of linear equations is constructed for tomography to solve for the velocity ratio used for velocity updating. An empirical relation between the RMO data and the velocity ratio updates reduces the amount of computation, and is stabilized by the feedback provided by the iterative loop through prestack migration, to RMO, to velocity update, to prestack migration. Correcting the RMOs to flatten the ADGIGs is the convergence condition. Synthetic data for a layered model with a fault successfully illustrates the method.

Removing smearing-effect artifacts in angle-domain common-image gathers from reverse time migration

“…Reflection events in ADCIGs are flat when a correct velocity model is used for migration, curved up when the migration velocity model is slower, or curved down when the migration velocity model is faster than the correct model ( Figure 1). Velocity updates are related to the curvature of the events, as defined by picking residual depth moveouts (Xie and Yang, 2008b;Zhang and McMechan, 2013), or by differential semblance optimization (Shen and Symes, 2008).…”