The Cross-Borehole-Seismic Tomography is a seismic method most used for the determination of subsurface structure of the land. This method involves placing in a borehole the seismic wave generating sources, and in another borehole the receiver as waves detector. The tomographic image reconstructed from Cross-Borehole-Seismic Tomography is obtained by considering a parameter called slowness which is reverse speed with which the seismic waves travel, slowness S varies depending on the geological structure. We consider direct waves traveling from one borehole to another and we obtain an approximation of the following linear system as MS = T , where M is a matrix and is related to the discretization domain, S is the vector formed by the slowness of each discretized domain element and T is the arrival time of the first wave coming from source to detector. For the evaluation of the algorithms ...