## 4 Results and Discussion
### Landslide Geological Structure  
The results obtained from the geophysical studies on the Guevejar landslide are integrated and synthesized with ground surface geology in order to build, for the first time, a model of the whole unstable mass (Figures 9 and 10). The landslide limits are based on data from boreholes and on the contrast in shear wave velocities found with depth. Superficial limits are based on field observations and on observations supplied by land owners. The results show that the whole area is characterized by a shallow layer with very low Vs velocity (average value of 251 m/s, ranging from 139 to 422 m/s). Its thickness varies irregularly (6.6 m on average, ranging from 1.1 up to 11.9 m), although the greater values are found in the central part of the slide area (thickness > 5 m), where a gentle slope exists (Figures 9 and 10). The obtained values are in agreement with those observed in the available borehole soil columns. This layer is found elsewhere, in both landslide and stable terrain areas. It is interpreted as a shallow layer of alteration due to several not exclusive possible causes (weathering, agricultural activities, fills or the deposition of debris in low areas). Figure 9: Longitudinal cross sections of the landslide. See Figure 3 for location of sections. The dashed red line shows the location of the failure surface. In the landslide area, below the shallow layer, a second layer exists exhibiting a complex pattern of velocities, depending on whether it is found in the earth flow or in the slide deposits. At the lower parts of the slope, corresponding with the area where the earth flow is, a layer with moderate Vs exists, averaging 375 m/s (ranging from 340 to 427 m/s), with thicknesses varying in the range of 16-25 m (Figure 9). Such thicknesses reduce towards the flanks of the instability, as is seen in some ravines that have partially eroded landslide mass. The observed Vs velocities may be related to the degree of disturbance of the materials involved in the landslide. The materials involved in the earth flow are characterized by a high degree of disturbance, and they are altered to a soil state. A significant reduction in Vs is expected with respect to the same undisturbed materials. In the zone occupied by slide deposits, this second layer may comprise several sublayers. Downhole tests show moderate Vs values (500-800 m/s; Figure 4) for these sublayers. Similar results are obtained at most of the sites where HVSR (Figure 7) or arrays (Figure 8) measurements were accomplished. The average Vs value of all sublayers is 710 m/s, markedly higher than the Vs of earth flow deposits. This may be explained by the lower degree of disturbance of the materials involved. Between all measurement sites, the sum of the thicknesses of all sublayers varies from 24 m up to 48 m (Figures 9 and 10). The lower limit of landslide, or failure surface, is attributed to a sudden increase in Vs with depth observed below the layer previously described, in accordance with results observed in the boreholes drilled and downhole tests. Below the earth flow area, Vs > 800 m/s, resulting in a high contrast with earth flow deposits (average increase in Vs > 100%). The resulting surface shows a gentle dip towards the base of the slope (Figure 9). Below the slide area, materials show an average Vs of 1060 m/s (ranging from 910 to 1100 m/s; average increase > 50%), and the failure surface is more irregular than in the earth flow area (Figures 9 and 10), with changes in relation to the secondary failures recognizable in the field (Figure 2). It is interesting to note that, for the in situ materials, lower values of Vs coincide with the spatial distribution of marks of the MU unit, while higher Vs values were found in areas where RSU and MLU materials crop out (Figures 3, 9 and 10). The resulting model of the landslide shows that its maximum thickness is approximately 56 m in the western part (site HV20; Figures 3 and 10). This value results from the sum of thicknesses of surficial layer and that below it.