Wave-equation migration velocity analysis in the common-offset domain to avoid cycle-skipping for FWI

Abstract

Full waveform inversion (FWI) has been used successfully to build high-resolution acoustic velocity models for imaging but can fail when the starting model is far from accurate because the absence of low frequency information can lead to conversion to local minima. Wave-equation based migration velocity analysis (WEMVA), is an iterative method that has successfully been used to provide low-frequency starting models for full waveform inversion (FWI) and avoid cycle-skipping. In this work, we extend WEMVA to the common-offset domain by minimizing an image residual in the common-offset domain, which can be formed after either reverse-time migration (RTM) or least-squares migration (LSM). Although very expensive in comparison to RTM, LSM has an increased amplitude fidelity that helps to ensure that the image residual used in WEMVA is largely a function of moveout instead of errors in amplitude, thus increasing the likelihood of converging to a global minimum. We demonstrate the method, theory and results on three synthetic models of increasing complexity.