f OBTAINING VELOCITY MODELS FROM SYNTHETIC FIRST-ARRIVAL TRAVEL TIMES USING REFRACTION TOMOGRAPHY METHODS

The possibility to apply different approaches to first-arrival time analysis of seismic data was examined using a sample synthetic first-arrival data set calculated initially from an unknown velocity model. This model was intentionally created for the purposes of a blind test and it was designed to represent a realistic near-surface target. Using the provided synthetic first-arrival data set various velocity models were estimated based on the understanding of the wide range of possible solution that can exist when dealing with the inverse refraction-traveltime problem (IRTP). Solutions to the IRTP were obtained using the refraction-tomography inversion technique. Comparison with the synthetic velocity model showed that none of the obtained models was accurate enough. Next, efforts were applied to find out what inversion parameters, such as initial model, types and degrees of regularization, etc., are required that would obtain solutions that match closely the synthetic model. Other possible models demonstrating possible nonuniqueness will be provided for comparison, as well. Such a comparison is expected to provide more evidence about the possible degrees of nonuniqueness of the IRTP for this particular model and the key inversion parameters for finding this true synthetic model.