Virtual Green's Functions Using Seismic Interferometry and Marchenko Redatuming

We compare several redatuming approaches for the estimation of virtual Green's functions in the subsurface, including seismic interferometry, Marchenko redatuming, and extended source-receiver Marchenko redatuming, in which each of these approaches accounts for internal multiple scattering. One application of redatuming is to reduce the distorting effects of overburden structures for better imaging of subsurface structures at depth. Classic seismic interferometry allows for the reconstruction of the Green's function between two receivers in the subsurface but needs illumination along the surrounding boundary. In contrast, Marchenko redatuming only requires one-sided illumination; however, a smooth estimate of the velocity model is needed to convert the focusing times to depth. We test interferometric and Marchenko redatuming approaches using synthetic data in a ID medium for the estimation of a virtual source beneath a heterogeneous layer. For Marchenko redatuming, upgoing and downgoing components of the virtual Green's function can be estimated, and from the deconvolution of these at a series of depths, an inversion for subsurface reflectivity can be obtained. Extended source-receiver Marchenko redatuming allows for the reconstruction of the Green's function at depth where there are no physical sources or receivers in the subsurface. Extended source-receiver Marchenko redatuming can also be utilized to reconstruct the wavefield from a virtual source along an arbitrarily sampled virtual array of receivers in the subsurface. Marchenko redatuming, using one-sided illumination, may prove useful for the estimation of shallow Earth structure and also by reciprocity for deeper structure, using earthquake sources.