Tomographic Static-correction with Ray Multi-retracing and Constrained SIRT Technique

As for complex near surface, because of its lateral variation of thickness and rapid velocity changement,seismic tomography becomes an effective way for determining wave velocities for static correlation. Here we put forward an improved tomographic static-correction method with ray multi-retracing and constrained SIRT technique. Our method is composed of two main parts. One is high precision ray tracing with multi-retracing technique, and the other is constrained simultaneous iterative reconstruction technique (CSIRT) with double grid strategy. Our ray tracing method uses Fermat’s principle. In complex near surface situation ray tracing could not be precise with only one direction search, here ray tracing is performed from source to receiver and from receiver to source several times, we call this as multi-retracing technique. In order to get unique solution, some constraint conditions were added to SIRT and formed CSIRT inversion method. In order to reduce the dimension of the null space of travel time matrix, we use two kinds of grid of different size, small grid for ray tracing and big grid for travel time inversion. Processing results demonstrate validity of our method.