## 4 Research Results and Discussion  
According to the methodology presented by [PERSON] [1; 2], if the seismic sections after PreSDM meet predetermined quality standards, the extracted velocity model is regarded as final. Otherwise, the model should be modified with the iterative process of MVA or the procedure should be returned to the SJI stage but with changed parameters. However, in the described approach, this methodology was applied to correct and verify the velocity model developed with the parametric modeling. The SJI procedure performed on both the refraction data and the residual anomalies of the gravity field enabled the researchers to develop the VID model. Therefore, the VID model (PVM), which is based on parametric modeling, was validated. Unfortunately, the parametric model has some drawbacks resulting from the limited amount and irregular distribution of well logs as well as from the extrapolation of velocity values measured in wells to areas where no wells exist, thus, no local values are available. The results of quality analyses of obtained velocity fields are shown in Figure 7.  
Figure 7: Comparison of seismic wave velocity models: (**A**)—raw P-wave velocity model, (**B**)—result of refraction tomography for near and far offsets, (**C**)—result of simultaneous inversion of refraction and gravity data. Figure 7A presents the raw VID model constructed based on parametric modeling. After converting this model to density using Gardner Equation [49; 50], the gravity effect was calculated and shown as a red line in Figure 8. It can be observed from this graph that the model provides a similar gravitational response compared to the actual data. Relatively good agreement is visible on the sides of the area of interest (Carpathian region and marginal zone of the pre-Carpathian basin). However, discrepancies are evident within the Area of Interest (AoI). These observations necessitate the need to correct the P-wave velocity model to reduce its ambiguity. Despite the observed deviations, it still served as a good initial model for further analysis. Three zones marked with numbers \"1\" to \"3\" are indicated on the velocity cross-sections. These zones represent the main areas of changes introduced into the initial P-wave velocity model. Based on these zones, it can be observed that using tomography alone leads to a smoothing effect on the velocity distribution, which is not the desired outcome. The application of SJI with the same parameters as the seismic tomography provided a more stabilized solution and allowed for velocity corrections, especially in Zone \"1\". For additional verification, a Single Gravity Inversion (SGI) [30; 32] was performed, which means that only gravity data were used for inversion. As seen in Figure 8, a very good fit was achieved between the calculated and observed data. However, this approach has its limitations, as the inversion algorithm adjusts the model to converge the misfit error at the expense of obtaining a realistic final model [9; 30]. Therefore, this result is presented as an example of quality control. Consequently, the misfit error in the gravity data during SJI is larger (approximately 1 mGal). This is closely related to the structural constraints imposed by the CG during the joint inversion of refraction and gravity data [3; 9; 30]. This algorithm ensured the stabilization of the inversion solution and proper regularization for the employed models, as well as the resolution and sensitivity of the geophysical data used [30; 32; 34]. Figure 8: Comparison of modeled gravity responses with respect to the observed residual values (Option-1) adopted for gravity inversion. Modeled effects for SJI (Simultaneous Joint Inversion), Single Gravity Inversion (SGI), and the raw model based on parametric modeling (PVM) were compared. The analysis was presented in a regional context, and the area subjected to PreSDM migration was marked with a black square.