Full-wavefield Redatuming of Perturbed Fields with the Marchenko Method

Wavefield extrapolation, or redatuming, is a critical step for imaging. It is particularly challenging in areas such as subsalt or under complex overburdens. The framework of Marchenko redatuming allows for the retrieval of up- and downgoing fields at chosen locations in the subsurface that contain primary arrivals and internal multiples, while requiring relatively little knowledge of the subsurface model. In this paper, we present a new form of the Marchenko system for perturbed fields. Based on this system, we present a new iterative scheme that explicitly reconstructs only the unknown perturbations to the Marchenko focusing functions, and by consequence only the perturbed/scattered up- and downgoing Green’s functions. This new scheme departs from previous versions of the method in that it requires additional inputs, which include an extra initial focusing operator and perturbations to the surface reflection data. We validate our method with numerical tests, showing that it is particularly well-suited to properly handle complex models with large/sharp constrasts such as salt boundaries. We foresee this new approach to be of use not only in general imaging applications, but also for time-lapse studies as it can directly redatum time-lapse changes.