2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/123773We consider a linearized inverse problem, arising in offshore seismic exploration, for an isotropic wave equation with sound speed assumed to be a small, singular perturbation of a smooth background. Under an assumption of at most fold caustics for the background, we identify the geometry of the canonical relation underlying the linearization, F, which is a Fourier integral operator, and establish a composition calculus sufficient to describe the normal operator F^*F. The resulting artifacts are 1/2 derivative smoother than in the case of a single-source seismic experiment.Revised; 35 pages; to appear in Comm. in P.D.EAnalysis of PDEs35S30, 58J40 ; 35R30text