Preliminary investigation of an urban landslide in evaporitic terrains detected by European Ground Motion Services in Monóvar, SE Spain

European Ground Motion Services (EGMS) provides Europe-wide SAR interferometry results, enabling the identification of previously unknown ground motion active areas. In Monóvar, a town in southeastern Spain, an active area has been identified with an approximate length of 450 m and a width of 650 m, affecting an urban area of approximately 6.5 ha. The site exhibits maximum east-west and vertical displacement rates of 23.8 and 64.6 mm/year, respectively, between 2019 and 2024. The geology of the area is characterized by Triassic evaporitic terrains composed of red sandy clays, silts, and marls with gypsum. The western sector of the active area, which is not urbanized, is predominantly marked by massive gypsum reliefs with smooth topography and maximum elevations of 393 m a.s.l. This sector also contains ancient gypsum quarries, exploited artisanally in the past, as well as some landfills. In contrast, the eastern sector, with a maximum elevation of 377 m a.s.l., is mostly urbanized. Borehole data indicate the presence of anthropogenic fill, used for grading and leveling the terrain, with thicknesses exceeding 6 m in certain locations of the eastern sector. The two sectors are separated by an urbanized ravine with a SE-NW orientation. Beneath the fill materials, the underlying strata consist of clays, limestones, and massive gypsum. To the north lies the CV-83 road, with elevations ranging from 375 to 358 m a.s.l. within the affected area, as well as the Charco barranco, a natural ravine crossing the north region from SE to NW. A field campaign conducted in the area identified widespread damage to roads, walls, and buildings. This damage is predominantly concentrated within the urban area, although some tension cracks have also been observed in the gypsum formations in the western sector. Several buildings in the urban area have been underpinned, repaired, or demolished due to ground movement. Based on the available data, the movement is associated with a very slow landslide, termed the Borrasca Landslide, which is divided into two main bodies by the urbanized ravine. The western body exhibits maximum eastward and vertical displacement rates of 14.7 and 64.6 mm/year, respectively, while the eastern body presents maximum rates of 23.8 and 45.5 mm/year, respectively. The failure surface of the landslide develops along the evaporitic terrains, causing significant damage to the urban area and the CV-83 road, including a bridge. Further investigations are needed to enhance understanding of the landslide (e.g., failure surface depth, triggering factors) to inform the local authorities and to develop appropriate corrective measures for its stabilization.

Acknowledgements

This project is funded by the ESA-MOST China DRAGON-6 project (Grant No. 95355) and by the funding scheme of the European Commission, Marie Skłodowska-Curie Actions Staff Exchanges in the frame of the project UPGRADE – GA 101131146.