# Geophysical Study of a Large Landslide Affecting the Urban Area of Albuuuelas (S Spain)
## 7 Conclusions  
A combination of geological, geomorphological and geophysical techniques has been applied here to reconstruct the architecture and the failure mechanism of a large landslide affecting the town of Albufuuelas in southern Spain. Among these techniques, a particular role was played by seismic passive methods. An intensive and extensive usage of ambient noise allowed for the provision of a reliable seismic characterization of the area. The surveys of ambient noise measurements, carried out in this study, provided a general assessment of the fundamental resonance frequency and the thickness of the sedimentary layer, estimating the lateral extent of the landslide and the depth to the failure surface. The seismic passive methods are especially suitable thanks to their ability to identify physical properties of the subsoil, including its thickness and shear-wave velocity. The measure of these parameters can then be used to depict the size of the land mass. Advantages of these surface methods are mainly related to their non-invasive nature. They can be performed more rapidly than borehole methods and are less expensive than the one required for drilling. Furthermore, in sites that are difficult to examine, the surface methods may be the only choice for geotechnical investigations. Another important aspect of the surface methods is related to the volume of soil involved in the survey, wider than borehole methods. For all these reasons, the passive seismic measurements have been significantly growing in importance in the recent few years for the dynamic characterization of soil and landslide investigations. Furthermore, a strict synergy between geologic surveys, borehole and seismic surveys allow for the further reduction in relevant uncertainties during the data inversion. The obtained results have allowed for the building of three cross-sections, showing the internal structure of this landslide. It is a rotational slide divided into several blocks with different degrees of displacement (rotation). The basal failure surface is found at more than 60 m in the upper parts of slide and about 50 m in its middle section, becoming shallower towards the toe. This study shows the importance of the river incision and erosion of the sedimentary fill of the basin, where an important part of it has been removed by river erosion, contributing to the destabilization of non-eroded parts of slope. Additionally, the results show that the general structure of the area, with materials dipping towards free face  
Figure 10: Estimated geometry of the valley slope before landslide occurrence for Section A–A’. Pink line: estimated position of top of red silt unites from average thickness of this unit in stable areas (Figure 7) and position of basement; orange line: estimated position of top of reef sandstone and calcarenite. Arrows mark the position of scarps in landslide body. of slope, also contributes to the landslide occurrence. Future evolution of this landslide will be controlled by the ability of the Saleres River to erode the bottom of the valley and by the materials found on it, which may lead to a different evolution of the western part, where soft materials exist in the bottom of the valley, with respect to the eastern part, where hard materials are found according to our results. This research work constitutes the first step for future projects focused on understanding the behavior of this landslide due to different triggering factors (scenarios of intense rain periods, river undercut or severe seismic shaking). M.M. : Fieldwork, data integration and interpretation, and wrote the paper. J.J.G.-M.: Data interpretation and integration, and revised the manuscript. J.G. : Fieldwork, data integration and revised the manuscript. L.L. : Conceptualization of work, fieldwork and revised the manuscript. S.M. : Conceptualization of work, fieldwork, supervised interpretation and revised the manuscript. J.P.: Fieldwork, data interpretation and revised the manuscript. J.A.P. : Fieldwork, data integration and revised the manuscript.