Abstract :
Until recently seismic refraction analysis has been limited to generalized reciprocal, dealy-time, or other techniques that require simplifying assumption such as constant velocity layers and lateral homogeneity within. The faster and more powerful computers available nowadays have led to the development of various seismic tomography routines. A new solutions based on tomographic inversion have been proposed for determination of the LVL structure and do not make the limited assumption mentioned above, it treats the first arrivals traveltimes as input, and represents the velocity structure with a grid model. Estimation of the grid s velocities is formulated as an iterative, regularized, linear least squares problem. The static corrections based on tomographic approach are named tomostatics. However the Purpose of this paper is to demonstrate the possibilities of recovering near surface velocity fields by means of tomographic inversion of first breaks on reflection seismics records, as well as analysis of the effect of different tomographic inversion parameters on results of imaging near surface velocity fields has been estimated. In addition to generating synthetics for various subsurface models, synthetics with different acquisition geometries are considered for the same models. The analysis has been based on synthetic records generated with the finite difference method in the acoustic variant. Constructed two simple velocity models of near surface medium have been considered, respectively as, gradient model containing local heterogeneities, either decreased or increased comparing to surroundings background velocity , and model of gradient layer over constant velocity basement. The modeling of theoretical wave pattern has been realized using procedure Finite Difference Modeling (FDM) in 2-D seismic data processing system ProMAX.
