Abstract

Estimation of velocity during processing of seismic data in thrust belt areas are difficult as the CMP gathers may not show consistent coherency function from one gather to another. The lack of coherency is mainly due to steeply dipping reflectors, strong lateral variation in velocity and rough topography. In such cases, either the velocity picking should be made at finer intervals or an independent guide for velocity picking should be made available. In this paper, effort is made to estimate velocity-depth model using travel-time inversion to be used for processing of seismic data from thrust belts. In this study, the seismic first arrivals are picked in shot domain at a regular interval after making corrections for polarity of the data. The elevation and other co-ordinate details were also the input. With all these and a broad velocity function / model as input, travel time inversion of the first arrivals were carried out using the algorithm of Zelt and Smith (1992 hereafter referred as ZS 92) for obtaining a velocity-depth model along the seismic profile. Repeated runs of travel-time inversion were performed until the results were within the permissible limits.