Scattering-based focusing for imaging in highly complex media from band-limited, multicomponent data

Abstract

Reconstructing the details of subsurface structures deep beneath complex overburden structures, such as subsalt, remains a challenge for seismic imaging. Over the past few years, the Marchenko redatuming approach has proven to reliably retrieve full-wavefield information in the presence of complex overburden effects. When used for redatuming, current practical Marchenko schemes cannot make use of a priori subsurface models with sharp contrasts because of their requirements regarding initial focusing functions, which for sufficiently complex media can result in redatumed fields with significant waveform inaccuracies. Using a scattering framework, we evaluate an alternative form of the Marchenko representation that aims at retrieving only the unknown perturbations to focusing functions and redatumed fields. From this framework, we have developed a two-step practical focusing-based redatuming scheme that first solves an inverse problem for the background focusing functions, which are then used to estimate the perturbations to focusing functions and redatumed fields. In our scheme, initial focusing functions are significantly different from previous approaches because they contain complex waveforms encoding the full transmission response of the a priori model. Our goal is the handling of not only highly complex media but also realistic data — band-limited, unevenly sampled, free-surface-multiple contaminated data. To that end, we combine the versatility of Rayleigh-Marchenko redatuming with our scattering-based scheme allowing an extended version of the method able to handle single-sided band-limited multicomponent data. This scattering-Rayleigh-Marchenko strategy accurately retrieves wavefields while requiring minimum preprocessing of the data. In support of the new methods, we evaluate a comprehensive set of numerical tests using a complex 2D subsalt model. Our numerical results indicate that the scattering approaches retrieve accurate redatumed fields that appropriately account for the complexity of the a priori model. We find that the improvements in wavefield retrieval translate into measurable improvements in our subsalt images.