# Geophysical Study of a Large Landslide Affecting the Urban Area of Albuuuelas (S Spain)
## 5 Results
### Stable Areas  
The first step in our study was verifying if the obtained results were congruent with the data gathered from outcrops of the same geological formations in this zone. For this purpose, we focused on the results obtained from sites not affected by landslides, for which a complete soil column is available. As it was previously mentioned in Section 2, observed outcrops presented a red silt unit approximately 60 m thick, together with reef sandstone and calcarenite units with highly variable thicknesses that do not exceed 55 m (10 m for reef sandstones and 45 m for calcarenites) [37, 38]. The results obtained at these sites on stable areas are presented in Figure 7. In this figure, we consider that the lower layer corresponds to the basement (marbles and schists), and according to the stratigraphy of the area, the units above represent the red silt, reef sandstone and calcarenite, red-orange conglomerates and silt, and continental conglomerates (only at sites N1 and N2), respectively. Finally, a thin layer of very low velocity is observed on the surface, which may be attributed to altered materials or artificial fills.  
Figure 6: Examples of S-wave profiles obtained by joint-inversion of H/V and dispersion curves at four different sites of the landslide: (**a,b,d**) Sites A4, A6 and A5 (west cross-section); (**c**) site A3 (central cross-section). On the left panel, the minimum misfit model (black) is shown together with the models comprising inside the minimum misfit + 10% (dark gray) and all the tested models (light gray). On the right panels, the mean value plus standard deviation bars of the experimental H/V curve (right bottom panel) and dispersion curve (right top panel) are shown in black together with the ellipticity/slowness curves associated with the best-fitting model (darkest gray), minimum misfit + 10% (dark gray) and all the other tested models (light gray). The minimum misfit value is shown above the right panels.  
The obtained results show that _Vs_ velocities in the basement are high, typically above 1000 m/s. Above the basement, the red silt layer is characterized by _Vs_ velocities in the range of 600-800 m/s. The thicknesses of this unit show some variability, with values varying from 42 m (site N13) up to a maximum value of 70 m (site N2). Figure 7 shows that sites located in the eastern part of the study zone show lower thicknesses and dispersion, but values obtained are similar to those estimated in the western part of the study zone. It is noticeable that these values agree with data known from outcrops, showing differences lower than 10 m with respect to outcrop data (average value of 52 m vs. 60 m).  
The results obtained for the reef sandstone and calcarenite unit (layer above red silt) (Figure 7) present _Vs_ velocities in the range of 400-600 m/s and thicknesses with notable differences depending on the considered sector. For sites located in the western part of the study zone, the thicknesses vary in the range of 33-37 m (average value of 35.4 m). On the contrary, this same material shows lower thicknesses in the eastern sector of the study zone, between 12 and 17 m (14.4 m in average). These data seem to point out that this layer diminishes its thickness towards the east in the study zone. From the outcrop data, it is important to remark that this unit shows high variability in thickness, so the values obtained are consistent with the data obtained from this formation.  
Figure 7: (**a**) _Vs_ profiles obtained at sites located outside of landslide areas. (**b**) Distribution of _Vs_ velocities for the red silt and sandstone units. Numbers show average thickness for each unit and zone. See Figure 3 for location of sites in this figure.