A range of methods in which the subsurface is divided into a box-grid whose elements are illuminated by seismic rays and the physical character of each element computed. The results are displayed as colour-coded contour maps of subsurface planes. In borehole tomography, two holes are used; a source is moved up one while detectors record along the length of the other. By using a succession of shot positions, most of the box elements in the plane linking the two boreholes are illuminated satisfactorily. Seismic tomography is used to study geologic structures in detail. It has been extended to investigate the mantle and, increasingly, the effectiveness of extraction techniques in hydrocarbon reservoirs.
Subjects: Earth Sciences and Geography.