# The Contribution of Near-Surface Geophysics for the Site Characterization of Seismological Stations
## 5 Results and Discussion
The revealed subsurface geophysical structure, corresponding to resistivity values greater than 7000 Ohm.m and _Vp_ greater than 1700 m/s, could be interpreted as the extension in depth of the same carbonate formation. At the _MDRA_ station, a geoelectrical formation of 1000 Ohm.m has also been revealed, probably due to the water saturation of the formation. Likewise, the ERT and SRT results at the _ATAL_ station (Figure 17) seem to reveal the subsurface existence of the compact bedrock of Jurassic limestones and dolomites (_Ji-m kD_). The corresponding resistivity and _Vp_ values are 8000 Ohm.m and 2700 m/s, which are similar to those of the _MDRA_ station. The relatively lower value of P-wave velocity at the _VILL_ station is assumed to be caused by the possible karsification of the carbonate rocks present in the area. The fact that the solid, hard carbonate formations (_TRm and Ji-m kD_) are almost up to the surface at the station sites of _MDRA_, _VILL_, and _ATAL_, affected both the MASW and the HVSR techniques. The inability to record the high-frequency content of the surface waves is the reason the 1D velocity models, derived by the MASW technique, are reliable from a certain depth, which seems to be 12 m for the _MDRA_ and _ATAL_ stations (Figures A2 and A5) and 8 m for the _VILL_ station (Figure A3). Thus, the Vs average values of the low-thickness sediments at these sites were estimated by converting the _Vp_ values (SRT technique), based on the relationship _Vp_ = 1.7 \(\cdot\)_Vs_. The H/V curves at the prementioned sites were complicated, with multiple low amplitudes and no clear peaks. More specifically, the H/V curves at the _MDRA_ station (Figure 4) show two close frequency peaks at 2.3 and 2.7 Hz, which could be an indication of the lateral irregularities inside the carbonate bedrock, possibly caused by the existence of the karst bauxite formation. At frequencies greater than 5.5 Hz, the H/V curves seem to be around an amplitude equal to 1.0, indicating the presence of the carbonate seismic bedrock. Therefore, no peak could be selected as the fundamental frequency peak at the _MDRA_ station. According to the H/V curves at the _ATAL_ station (Figure 16), no frequency peak could also be selected as the fundamental one, while the total form of the curves is the result of the presence of the carbonate hard rock formation almost at the surface. Regarding the H/V curves at the _VILL_ station (Figure 7), a high-frequency peak at 10.4 Hz was identified after the replacement of the recording instrument, which was interpreted as the fundamental frequency peak of the site (Table 5). With an average _Vs_ value of 530 m/s of the overlying sediments, converted from the _Vp_ value of 900 m/s, the depth of the seismic bedrock was calculated equal to 13.0 m. This outcome is consistent with the results of the SRT and ERT techniques but also with the local geology. The relatively low _Vp_ values (1700-2000 m/s) and high resistivity values (>7000 Ohm.m) can be related to the karsification of the carbonate formation, which justifies that the compact seismic bedrock may be present at depths greater than 13.0 m.  
Given the fact that the geophysical results at the _LOUT_ seismological station reveal relatively low values of elastic-wave velocities and resistivity (Figure 11), it is assumed that the maximum depth of investigation was not enough to overcome the thickness of the old talus cones and scree formation and, consequently, did not reach the inferred bedrock of the Middle Jurassic limestone formation (_Jm.k_). Regarding the MASW technique, a broadband frequency spectrum was recorded, extending the investigation depth down to 40 m (Figure A4). The H/V curves for this site (Figure 10) show two clear peaks at 2.7 and 5.1 Hz, with the lower frequency peak being interpreted as the fundamental one. With an average calculated shear-wave velocity equal to 320 m/s for the overlying sediments, the corresponding depths of the 2.7 and 5.1 Hz peaks were estimated equal to 30.0 and 16.0 m, respectively.