## 4 Results and Discussion
### The Gura Apelor Data  
At the Gura Apelor dam, the collected data yields reliable data up to a depth of approximately 4 m. Although migration was not carried out on this site, this depth estimation is derived from several attempts at fitting hyperbolas, and the images are presented with a depth scale that is calculated based on a velocity of 0.1 m/ns. Below this area, there do not seem to be any significant reflections. Across all of the profiles, a consistent feature is the presence of three distinct almost uninterrupted horizons (Figures 7 and 8) which span from one side of the dam to the other. In Figure 7, two profiles are shown: profile GA2 (Figure 7--up), which is closer to the middle of the dam, and profile number GA4 (Figure 7--down), which is closer to the edge of the dam facing the reservoir, 4 m apart in between. The first horizon (Figures 7 and 8) starts at 10 ns on the start of the profile and continues relatively horizontal and uninterrupted with few disturbances. The second horizon has a different character, as it starts to dip from a time depth about 10 ns to the start of the profile to 20 ns at the 200 m mark, with its lowest point at 25 ns at the 310 m mark, after which it continues in an uptick, ascending back to a time depth of 10 ns with a high point at the 410 m mark, and closer to the right side, it starts slightly to descend again. The third horizon appears to follow the same pattern as the second horizon. The appearance of the horizons marks a change in permittivity values, probably due to a change in material, and can probably be interpreted as different layers forming part of the road's foundation on the top of the dam and the sealants on the crest, which is also due to the fact that they appear on all of the four profiles and have a similar character. Even though these layers appear to be relatively constant in appearance from one side to the other, there are some areas with gaps more visible in Figure 9. These are called gaps just because the reflections are not as intense as the general pattern of the horizon from which they appear to belong. This character might be due to an increase in moisture content, which reduces the speed of the waves traveling through the medium, therefore reducing the intensity of what appears to be a linear anomaly, with higher intensities throughout the profile [43]. Another feature of interest is represented by the area marked by the lowering of the horizons (Figures 7 and 8) with a lowest point at approximately 320 m at 40 ns, which appears to have a distinct character compared to the surrounding area and looks less homogeneous with the third horizon (Figure 8), appearing as more distinct with a stronger reflection in that particular area. In the same area, there appear to be a multitude of well-contoured hyperbolas, which creates an inhomogeneous aspect, marking a change in subsurface parameters. Compared to the background trend, this area appearing with this combination of characteristics might represent a place of deformation consistent with subsidence. Another area of interest (Figure 7) appears as inhomogeneous, with the horizon no. 3 slightly higher in intensity, but less intense compared to the area marked as subsidence, with ripples underneath. Lastly, the area marked as uplift (Figure 7) highlights the area where all of the three horizons have their highest point after the drop appearing in the area marked as subsidence. Figure 7: Processed data from profiles GA2 (up) and GA4 (down) on the Guta Aelero dam. Area of interest marked with rectangles and horizons marked with arrows. Even though all of the features are constant throughout the four profiles at the Gura Apelor dam, it appears that the area marked as subsidence (Figures 7 and 8) has a more distinct character, described as a inhomogeneity, on the middle profiles (GA2 and GA3) compared to the profiles on the extremities (GA1 and GA4).