3D acoustic frequency-domain full waveform tomography (FWT): application to the SEG/EAGE Overthrust model

We present a massively parallel frequency-domain full-waveform tomography (FWT) algorithm for imaging 3D acoustic media. FWT refers to imaging method based on the complete solution of the two-way wave equation for the forward problem and on inverse problem theory for the imaging problem (Tarantola, 1987). A model is built by minimization of the misfit between the recorded data and that computed in a starting model. The frequency-domain (FD) formulation of FWT was originally developed for 2D cross-hole acquisition surveys which involve wide-aperture propagations (Pratt and Worthington, 1990). Only few discrete frequencies are required to develop a reliable image of the medium thanks to the wavenumber redundancy provided by multifold wide-aperture geometries. Full wave propagation modeling is a critical issue in FWT methods since it is the most computationally expensive task in the processing flow. In the frequency domain, the forward problem reduces to the resolution of a large sparse system of linear equations for each frequency to be considered. Therefore, a 3D optimal finite-difference stencil was designed by Operto et al. (2007) that leads to 4 grid points per wavelength. Aim of this work is to provide some insights on the feasibility and relevance of 3D frequency-domain FWT for building high-resolution velocity models of isotropic acoustic media. Indeed, we present application of FWT to two targets of the SEG/EAGE Overthrust model.