# Geophysical Study of a Large Landslide Affecting the Urban Area of Albuuuelas (S Spain)
## 5 Results
### Landslide Geological Structure  
The results obtained from the ambient noise measurements have been used in conjunction with the soil column information obtained from the borehole and the geological data (position of landslide scarps, material outcropping at ground surface, and dip and dip direction of beds in the landslide area) to model three cross-sections of the Albu\(\hat{\text{n}}\)uelas landslide (Figures 8 and 9). The location of these three sections is shown in Figure 3.  
Figure 8: Longitudinal cross-sections of the Albu\(\hat{\text{n}}\)uelas landslide showing the estimated position of the successive slides that constitute the landslide. Plot shows apparent dips used to build the model. Plot limits depth of the lowest layer to 625 m of elevation for clarity purposes. See Figure 3 for location of cross-sections. Arrows mark the position of scarps in landslide body.  
The results obtained in the stable areas (see Section 5.3) have been useful for identifying the zones in each cross-section where thicknesses of red silt and/or sandstone (ree sandstones and calcarenites) agrees with the average values observed in stable zones, or where they show thicknesses lower than the expected ones. In this last case, it was interpreted as due to the presence of a failure surface, which cuts such a unit, reducing its thickness. For constructing these plots, we also considered the relative angle between each cross-section and the bed's dip-direction, to use a geometrically consistent dip in the plots. The apparent dip was computed by Equation (3):  
\[tan\beta^{\prime}=cos\alpha\cdot tan\beta \tag{3}\]  
where \(\alpha\) is the angle between the line of the cross-section and dip direction of beds (approx. N285\({}^{\circ}\) E to N300\({}^{\circ}\) E, depending of the site), \(\beta\) is the real dip of beds, and \(\beta^{\prime}\) is the apparent dip of beds along the cross-section. Section A-A' (Figure 8) is approximately parallel to the dip direction of beds in the landslide area (\(\alpha=0^{\circ}\)), so units are presented with their real dip. Section B-B' forms an angle of approximately \(30^{\circ}\) with the dip direction of beds and units show a dip slightly lower than the measured one (24\({}^{\circ}\) vs. 28\({}^{\circ}\)). Finally, section C-C' is almost perpendicular to bed's dip direction (\(\alpha\approx 90^{\circ}\)), so materials were arranged horizontally in this cross-section (Figure 9).  
With the previous considerations, the obtained results show that upper limit of high velocity unit (basin basement) draws a surface dipping toward the south (right border of plots), where the Albufuuelas Fault is located, from approximately 750 m.a.s.l. in the northern part of sections to 650 m in the opposite side. Additionally, the sedimentary cover is thinner towards the southern part of sections, reaching the lowest values at the base of the valley where the basin basement should be found a few meters below ground surface in section B-B' (Figure 8, bottom). This agrees with the map prepared by [36], showing where it is very likely that recent sediments provided by the Saleres River buried the outcrop mapped by these authors. In the upper parts of the slope, sedimentary units also dip  
Figure 9: Transversal cross-section of the Albufuuelas landslide. Figure follows the same colors scale shown in Figure 8. See Figure 3 for location of cross-section. Arrows mark the position of scarps in landslide body.  
toward the south with the exception of section B-B', where a broad syncline exists in the top of the area (Figure 8).