TWO-DIMENSIONAL VELOCITY ANOMALY RECONSTRUCTION BY SEISMIC TOMOGRAPHY (SIRT)

Computerized tomography is a process which allows us to reconstruct the spatial variation of a field without having to sample it directly. The reconstructed image is produced from measuremens of the field's affect on energy transmitted across it. Computerized tomography can faithfully reconstruct complex fields. It can also detect subtle variations in the reconstructed field. Conventional seismic techniques experience considerable difficulty in interpreting complex geologic structures and detecting subtle variations in the velocity structure.; A computerized tomography algorithm for seismic applications is presented. It is based upon the SIRT algorithms first described Gilbert. A reconstruction of the velocity field is obtained from travel time information by iteratively adjusting an estimate of the field. Iteration of the estimate is terminated once the difference between the observed data set and a similar set calculated across the reconstruction become sufficiently small. A ray trace is included in the algorithm. The performance of the new technique is demonstrated with a number of computer simulations.; The wide range of seismic imaging situations to which the technique may be applied is illustrated with four different types of data set.