Study Of First Break Tomographic Inversion And Static Corrections In Surface Model

Drastic topographic relief and sharp variations of velocity in near-surface always adds to the difficulties of geologic prospecting. For engineering geophysics and environmental geophysics, near-surface is our object. But for seismic survey, it will lead static correction. This paper presents an approach that derives the LVZ velocity and static correction values by using tomography technology.First, we introduce two ray tracing method—total iterative ray-tracing method and linear/nonlinear traveltime interpolation(LTI) ray-tracing method. The ray-tracing of reflected waves and transmitted waves can be obtained by a positive tridiagonal matrix equation in total iterative ray-tracing method. First break including direct path waves, refracted waves and diffracted waves can be derived by interpolation in linear/nonlinear traveltime interpolation. In LTI method, this paper presents a new approach to obtain the first break traveltime. The numerical tests show that it is accurate enough and fit for near-surface with complex conditions.Second, we introduce the principium and process of tomography inversion and deduct the linear matrix of inversion. Nonlinear traveltime interpolation ray-tracing is used in the forward step and simultaneous iterative reconstruction technique (SIRT) in the inversion step. Theoretical model show that effects of the inversion is remarkable and is suitable for inversion in complex surface model that the velocity can vary arbitrarily.Last, we put forward the formula of static correction values according to near-surface model that resulted from tomography inversion. Having analysed the localization of several methods for static correction, the author considers that tomography inversion method for static corrections is the new direction in static correction.