## 6 Conclusions  
The amplitude gain is an important factor during the inverse Q-filtering procedure. A substantial value of gain may lead to generating false reflections. A substantial increase in the dominant frequency of the signal, in relation to the quality of the seismic data, can introduce a distortion of the vertical amplitude relationships, and the reliability of the additional reflections can be difficult to establish. As a result, such seismic images, although high-resolution, will be of little value from an interpretive point of view. A significant increase in vertical resolution of the seismic section, resulting from Q-filtering application, makes the sequence of reflections on the PreSTM section similar to those occurring on the VSP corridor sum. A noticeable effect of the increase in vertical resolution is usually the separation of some reflections (marked as X in Figures 8, 9 and 11), which is best seen in the central part of the section from Figure 11, along the projection of the borehole profile. At this location, we observed a \"channel\" (probably a channel of a former river) of Miocene formations, which is revealed by an increase in the number and amplitude of reflections. In addition, as a result of the increase in the dominant frequency of the seismic signal, low-amplitude reflections are revealed in places where they did not occur before--this is basically the case along the entire section, and especially in its lower part. In the higher frequency range, the IQF procedure improves the link of the synthetic  
Figure 11: Upper Panel (**a**): Seismic section after processing without application of the IQF. Left panel shows well log data with lithological interpretation, middle section is the processed zero offset VSP, right panel, seismic section as shown in Figure 9 for wider range of CDPs (600 CDP). Lower Panel (**b**) Seismic section after processing application of the IQF. Left panel shows well log data with lithological interpretation, middle section is the processed zero offset VSP, right panel, seismic section as shown in Figure 9 for wider range of CDPs (600 CDP). Point X shows example of the vertical resolution increase resulting in the separation in whole or in part of some reflections and a noticeably better fit of the seismic image to the attached VSP result. seismogram to the seismic record; even subtle seismic reflections of small amplitudes created after IQF are reflected in the synthetic seismogram. Using IQF as a method to increase data resolution has its limitations. One of the criteria for the correctness of the solution is the analysis of the frequency spectrum. It seems optimal to obtain as flat of a spectrum as possible over the entire useful frequency range (Figure 10 right panel). Unfortunately, due to the nonlinear increase in the magnitude of the amplitudes for higher frequencies in the IQF process, we have to deal with the so-called overboosting of the upper frequency band. As a result, the seismic section becomes uninterpretable. A parameter that allows a certain degree of control over this effect is the so-called gain limit (expressed in dB), described earlier in Section 4.2. The principle of this procedure is shown in Figure 4.  
Correct selection of the mentioned gain is very important. This can be clearly seen in Figure 8 panel C where, for the same values of Q-factors, we observed very large differences in the seismic image, depending on the used amplitude limit. Conceptualization, T.M. and M.S. ; methodology A.P.L. and M.M. ; validation, A.P.L. and M.M. ; formal analysis, A.P.L. and M.M. ; data curation, A.P.L., A.C. and A.W.-P.; writing--original draft preparation, A.P.L., M.M. and A.W.-P.; writing--review and editing, A.P.L., M.M., A.W.-P. and A.C; visualization, A.P.L. and A.W.-P.; supervision, T.M. and M.S. ; project administration, A.W.-P. All authors have read and agreed to the published version of the manuscript. This research was funded by project No. POIR.04.01.01-00-0046/19. Not applicable.