# Geophysical Study of a Large Landslide Affecting the Urban Area of Albuuuelas (S Spain)
## 2 Geological Setting  
The study zone is located in the Granada Basin (Figure 1). This is a Neogene intramountain basin in the boundary between the External and the Internal Zones of the Betic Cordillera. It is located in the central part of the cordillera, where seismicity is frequent and some destructive earthquakes have struck the area [28; 32; 33]. The basement of the Granada Basin is constituted by Mesozoic sedimentary rocks from the External Zones of the Cordillera to the north and west borders of the basin, and by Palaeozoic to Triassic metamorphic rocks from the Internal Zones in the south and east borders (Figure 1). The basin fill comprises sedimentary rocks from Burdigalian (Miocene) up to Quaternary [34; 35]. In the study zone, the basement is formed by marbles and schists of the Alpujarride Complex (Internal Zones of the Cordillera). They outcrop to the south of the study zone, limited by the Albufuuelas fault (Figure 1). According to [36], a very small  
Figure 2: (**a**) General view of Albufuuelas. It is noticeable that the escarpment is almost 50 m high and composed of calcarenite behind the town. (**b**) Zoomed view of the main scarp of the Albufuuelas landslide close to the main church. (**c**) Back-tilted conglomerates inside the Albufuuelas landslide mass. (**d**) Landslides affecting the slope in front of the town of Albufuuelas (south slope of the Albufuuelas valley) revealing a diffused rotational mechanism. (**e**–**g**) Examples of tilted houses. outcrop of these materials exists in the lower part of the valley, south of the town, in the vicinity of the Saleres River. Unfortunately, this outcrop could not be identified in the field work conducted for this study because the area was covered by recent sediments provided by the river. The stratigraphic record of the basin starts with continental red silts that have a thin layer of grayish blue clays on top, Serravallian in age, and are in direct contact with the basement. Above them, reef sandstone and calcarenite with abundant marine fauna (lower Tortonian) and red-orange conglomerates and silt, a poorly cemented and deposited in a marine environment (Upper Tortonian in age), are found. Finally, on top of all these materials, there are continental conglomerates, associated with the glacis that formed in the area during the Pliocene and Quaternary, in recent hillside deposits along slopes and alluvial sediments in the lower part of the valleys, deposited by the rivers that run through them. From measurements made in outcrops, red silts are about 60 m thick, reef sandstone and calcarenite have a highly variable average thickness, but it seems that they do not exceed 55 m as a whole (10 m for reef sandstones and 45 m for calcarenites), and red-orange conglomerates and silts have very variable thickness, with a maxima estimated at several hundreds of meters [37; 38]. The remaining units (recent materials) have very variable thickness, depending on size of outcrop and position on the slopes. This sedimentary sequence is folded and faulted [38; 39]. They show a general dip towards the south, where the so-called Albufuuelas fault constitutes the southern limit of the basin (Figure 1). Shear strength data of materials in this zone are scarce. [PERSON] [40] presented results obtained from undisturbed block samples of red silts unit, tested in triaxial shear box tests, resulting an average friction angle of 33\({}^{\circ}\) (\(\pm\)2\({}^{\circ}\)) and a cohesion of 40 kPa. [PERSON] et al. [41] compiled data of shear strength for marbles and schists in areas close to the study zone. According to these authors, average values of friction angle and cohesion are 36\({}^{\circ}\) and 13.7 kPa, respectively, but these values increase to \(>\)40\({}^{\circ}\) and \(>\)200 kPa when marbles are present. No data are available for other formations in the study zone. Landslides are common in the Granada Basin [42]. [PERSON] [43] studied this problem in the southeast border of this basin and inventoried several hundreds of landslides.