M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)

Prospecting - SŐRÉS László: Geophysical measurements at the site of a Roman homestead at Balácapuszta

The material of the ruins is very resistive limestone covered with soil of low resistivity (30 to 50 Urn). Accordingly, the geophysical model of the buried buildings (walls) is a highly resistive "two-dimensional" prism, i.e. a prism of infinite length in a medium of low resistivity. Since this is a simplification of the real situation, the possible differences must be considered. The buildings are of finite extent, i.e. they are not two-, but three-dimensional bodies. As can also be seen from the ground plan of the already known buildings, the separation between the walls may be as small as 2—3 m, thus, their effects are superimposed, and they can be separated only to a certain extent. This gives rise to the question of the resolution of the measurements. Measuring results are also influenced by the state of the buried walls. It is possible that the completely destroyed walls, having become a mass of debris, increase the resistivity of the soil only to a very small extent. In some rooms of building no. I, mosaic flooring was excavated. In the case of measurements over such places of terrazzo flooring or other rooms of cement-, or possibly brick covering, the current cannot penetrate below the layer of high resistivity, and a situation corresponding to the model characterized by the two-layer basement of infinite resistivity develops. Resistivity increases rapidly with increasing electrode distance, which means - in the case we, are interested in - that a greater difference in the resistivity values of the profiles with a penetration of 1 and 1.5 m appears. This phenomenon is called deviation. Figure 1 also presents the areas showing deviation. Considering what has been discussed so far, let us examine what kind of anomalies can be expected. 1,4 1.3 -1,2 1.1 1.0 */?1 X Fig 3 Theoretical resistivity profile over an infinitely long cylinder. The parameters correspond to the case examined by us, where a = 1 m.