In this paper some simple algorithms are introduced which give added flexibility to the Aki et al. (1977) inversion technique of two-dimensional travel time data. The new options include, besides computational efficiency, a block equalization scheme which may be used for smoothing poorly sampled blocks, testing whether geological surface contours have a counterpart in the deeper lithosphere and also to restrict the anomalous volume to parts of the lithosphere only. This novel computational scheme is demonstrated on a large Norsar data set, and the main results were as follows. Even a single heterogeneous layer at a depth of round 170 km, i.e., a two-dimensional model, gives a not unreasonable fit to the observational data (explained variance of the order of 60--65%), dominant surface geological features have no counterparts in the deeper lithosphere, though a seismic counterpart of the Oslo graben (associated with a marked gravity high) is found in the crustal layer. Changes in the basic model parameters like number and thickness of layers affect only the secondary features of the final three-dimensional seismic image of parts of the lithosphere. Physical smoothing of the final results in terms of equalizing poorly sampling blocks (e.g., number of hits less than 6) to nearby ones is demonstrated to be a viable alternative to introducing specific smoothing kernels.