Seismic Transmission Tomography

Seismic transmission tomography is a high-resolution method for characterizing<br>subterranean geology. By recording many seismograms with sources and<br>detectors located on the boundary of a rock mass (for example, along co-planar<br>boreholes, or on two levels of a mine, or around a rock pillar), information<br>is obtained which enables one to construct a cross-sectional map of seismic and<br>mechanical properties, In the most common form of seismic tomography, the acoustic<br>velocity (i.e., the speed of sound) is the physical property which is mapped.<br>One begins by measuring the time it takes for a seismic pulse to travel along a<br>path through the rock section under study. This measurement is repeated for<br>hundreds or even thousands of paths with as many different directions through<br>the rock section as possible, The travel times, the path lengths, and the source<br>and detector locations on the boundary of the section are then used to create a<br>detailed two-dimensional image of the acoustic velocity within the rock section.<br>Image creation is done using computer-assisted tomographic (CAT) techniques<br>similar to those first developed for radiological imaging in diagnostic medicine.<br>The final tomographic image is best displayed as a coloured-coded map on which<br>different acoustic velocities are represented by different colours.