Distributed iterative reweighted least squares algorithm for high-resolution finite-frequency traveltime velocity inversion using VSP data

Abstract

Seismic traveltime between a source-receiver pair is a finite-frequency phenomenon. The velocity information at all points inside the first Fresnel zone is contained inside the traveltime. Therefore, finite-frequency traveltime velocity inversion (FFTVI) is able to invert velocity with finer structures than that can be obtained by ray-based tomography. Since FFTVI is a global inversion, its cost is lower than full waveform inversion. The implementation in this paper mainly focuses on the numerical aspects of FFTVI. We analyze the characteristics of FFTVI from the computational point of view. A parallel version, Iterative Reweighted Least Squares (IRLS) is designed for solving a large linear system in the memories of computer clusters. This implementation not only yields the accurate inversion of velocity at arbitrary grids and with an arbitrary acquisition geometry, but also is able to mitigate the impacts of traveltime picks with large uncertainties. The proposed workflow and parallel algorithm are demonstrated on synthetic VSP examples designed from a land project.