The study of rock stresses and their changes is of great importance for safety in mines. To detect dangerous stress accumulations in coal mines an empirical method, Jahn's drilling test, is generally used. An experimental survey to solve the same problem by geophysical measurements was undertaken in a Hungarian coal mine. The basic idea was to determine the easily measurable seismic velocities instead of the more difficult to measure stresses in the rocks, since there is a monotonic relation between them. During the survey seismic transmission‐type measurements were carried out in the fore‐field of longwall faces between the top and tail roads. The seismic velocity data obtained were processed using an iterative algebraic reconstruction technique to determine the ‘velocity field’, i.e., the seismic velocity distribution, of the area covered by the ray paths. By periodically repeating the measurements in the same area, it was possible to follow the changes in the stress conditions caused by mining operations.

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It is frequently occurring problem that existing buildings are located at filled up onetime open pit mining area or at recultivated waste deposit sites. Many times the quality of refiuing is not appropnate for bearing the bad, moreover, the foundation also has not been built properly. Recent and present damages (subsidences, cracks of houses) cail the attention for this problem and for the need of investigation of building foundations using some non destructive geophysical methods. Figure 1 shows the subsurface condition of a present built up urban area. Note that nursery also present at this site, the other buildings are multi-storied blocks of flats. The lines with numbers indicates the proflles of geophysical measurements. The underground conditions of this map was reconstructed on the basis of a one-time mining map. A refihled celiar also exists at this site.Several types of geophysical measurements were carried Out along the marked lines in order to get an image about the geology of the site and to qua1if r the bad bearing capacity of the subsurface material. Geoelectrics, georadar and seismics were applied. Seismics proved to give the best resuits but only using special measuring and processing procedures.One of these special methods is the diving wave tomography resulting a velocity-depth section shown like in Figure 2. The initial model is originated from the refraction ifit was reached but from the diving waves ifrefractor did not exist or was not reached On the basis of this section the geological model of the one-time mining area could be reconstructed. This is also shown in Figure 2 below. 451

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