## 5 Results
### HVSR Seismic Passive Technique  
The processing of the HVSR data has been carried out using the free software GEOPSY (www.geopsy.org, accessed on 10 January 2022), composing the records of the horizontal geophones (directions N-S and E-W) geometrically and applying the fast Fourier transform (FFT) on the time windows of 20 s established in the records once filtered [32].  
The analysis in the domain of the frequency of the spectral ratio \(H/V\) offers a result of a curve called ellipticity and is related to the surface waves, Rayleigh. In these curves, the maximum value or peak for the dominant frequency (\(f_{o}\)) is analyzed, which has an associated amplification \(A_{o}\) of the signal (spectral ratio \(H/V\)).  
The processing flow starts with filtering raw data to eliminate the transients. The time window size, established in 20 s in this case, and its selection allows the data to be computed in each geophone record. Then, FFT was applied to every selected window before the geometrical combination of horizontal data. The GEOPSY software computes the H/V ratio and shows the spectral analysis in a frequency vs. H/V ratio (also called amplification of the signal, \(A_{o}\)) [32; 33].  
A single peak is usually shown in ellipticity curves, but some broad or multiple peaks can be obtained as well from processing. The graphics' different forms have the meaning of some basement geometry variations (an inclination, for example), as the SESAME project indicates [32].  
Figure 6 shows selected examples of HVSR processing results. The ellipticity curve in continuous black lines and its standard deviation (dashed black lines) are shown. The characteristic peaks for the \(f_{o}\) (in hertz) value are indicated at the center of the two gray bars of different shades (these bars show its standard deviation). The first two graphics are from control points (HS1 and HS3), and the other four are from different elevation points, used as examples of the other sixteen surveyed points.  
Results obtained in the HVSR technique single-station applied surveys are those shown in Table 2. The value of \(A_{o}\) is dimensionless since it represents the spectral ratio \(H/V\) of the horizontal components versus the vertical. The first five values, indicated with an S as a numbering prefix, would correspond to the parametric tests (performed in the same position as the VES surveys) to be used in the subsequent establishment of the empirical relationship.  
Figure 6: Example of six of the HRSV surveys processing, belonging to the proposed investigation. The two first are measured on control points (the same position as VES surveys). The gray vertical bars indicate the position of the fundamental frequency of each point, and the black dashed line shows the variation on the dispersion curve (continuous).  
Most of the graphical results show a broad peak type related to the SESAME project explanation of a high-angle inclination of the basement that could be present in this area. Otherwise, single, cleared peaks (as shown in HS1 point, see Figure 6) were obtained in several points.  
The _f\({}_{o}\)_ obtained values are comprised between the 57.67 and 0.25 Hz, with a 1.83 Hz average value (if we consider three higher values are excepted). For the amplification \(A_{o}\), the obtained values in the entire performed surveys are between 12.6 and 1.54 (see Table 2). As a simple explanation, a higher frequency value is related to a shallow position of the rocky basement, whereas lower values indicate a deeper compacted substratum [32].