## 3 Methods and Materials
### Gravity Data Characterizations  
The results provided independent data carrying information on the structural variability related to changes in the density contrasts of rock formations [6; 9; 17; 35; 36; 37]. The characterization of the physical phenomena, which are essential for this geophysical methodology results in its high sensitivity in the near-surface zone but also in a decrease in sensitivity with increasing depth [32; 34]. This is a classic phenomenon of geophysical data analysis based on the potential fields. It is associated with a decrease in the resolution of this methods with depth. However, the published results of analyses demonstrated that this limitation did not adversely affect the validation of VID models [1; 2; 9; 30]. The analysis of previous publications and unpublished reports enabled the researchers to conclude that the specificity of the gravity field distribution in both the western and the eastern regions of the Polish Carpathians was diverse [6; 32; 34; 35; 36]. The most complicated was the Bouguer anomaly pattern for the eastern region. The gravity survey carried out in the Carpathian area revealed a number of local anomalies of irregular shapes [6; 33; 35; 36] (Figure 5A). These anomalies indicated the presence of geological structures composed of rocks with different densities [6; 33; 35; 36; 37]. The analysis of the gravity field pattern, combined with the varying density of particular lithological units [16; 35; 36], showed that relatively negative anomalies were caused by various formations. Disturbances of Bouguer anomaly distribution were caused by a strong regional gravity field generated by a deep-seated basement. As a result, anomalies of lower amplitudes and local ranges, which represent structural elements or lithological units of lower order, became less visible. In order to separate and highlight the gravity effects generated by these structures (or units), regional gravity anomalies were calculated (Figure 5A). In order to illustrate the influence of the basement, distributions of the regional component of the recorded gravity field were determined. The transformation parameters were selected in such a way that extraction was possible of disturbing bodies in the particular depth intervals. Therefore, the filters were tested suitable for the generation of regional maps. The results are presented in Figure 5. On their basis, the residual values were determined and used to carry out the inversion tests. At this stage of the project, the aim was to filter out the effects of the deep basement and the isostatic movements related to the lithosphere/asthenosphere boundary [35]. Taking into account the fact that the analysis included also the basement structures, it became necessary to ensure that the gravity effect generated by differences in the density of basement formations is included in the data input into the SJI. The results of the tests enabled the researchers to select Option No. 1 of residual Bouguer anomalies (Figure 5B) for inversion calculations. Data analyses published earlier demonstrated that the values of residual anomalies calculated for various depth intervals increased with the increasing depths of measurements [6; 33; 35; 36; 37], as illustrated in Figure 5. Variability analysis of residual anomalies with the depth of measurements allowed us to conclude that the source of the Carpathian gravity depression [36] (Figure 5A,B anomaly I) is the mass deficiency occurring within a significant depth interval, from flysch formations to deep crystalline basement. This deficiency determines both the shape and the amplitude of regional gravity anomaly. The anomalous decrease in the value of the gravity field in the Carpathian foreland reflects the diverse depth of the sub-Tertiary basement covered by less dense Miocene molasses although [PERSON] et al. [35] proposed alternatively the isostatic effects as a factor modifying the gravity field in that area.