Tomography images derived from dispersion curves of the SW and those extracted from FGEs are shown in Figure 3. The images correspond to an average frequency of 24 Hz, whose vertical wavelength is proportional to the first 3 m depth (with Vs average of 300 m/s). Both images show velocity zones less than 200 m/s. However, Vs values less than 100 m/s are obtained by ANT, whose lateral extension indicates the areas of softer or highly saturated materials and prone to slip between geophones 24 and 42 (according to direct observations at the site). Velocity values greater than 300 m/s, which correspond to compact materials, are observed at the array center. The velocity structure described by these values is similar in both methods in the southern part of the array but differs in position in the northern part.
Differences in velocity values distribution are due to the nature of surface waves and the coverage lack in the northern part of the array. However, we note that Vp tomography (Figure 2b) also shows a high-velocity zone that coincides with that obtained from ANT. Furthermore, ambient noise tomographies for frequencies below 24 Hz (not shown here for brevity) corroborate the existence of such anomaly at greater depth.
The construction of a 3D model of Vs using ANT allows us to outline the extent of the materials prone to falling. This model emphasizes the zone defined by velocities larger than 350 m/s concerning those less than 200 m/s. The figure allows us to appreciate the irregularity and depth of the bedrock and the extension materials susceptible to sliding. So, we consider these two elements essential to understanding landslide behavior and taking the necessary mitigation measures.