DInSAR analysis for slope instability monitoring due to Climate Change: CUZCO and Machu Picchu case study.

Andean plateau in Peru and its World Heritage sites are particularly affected by the impacts of climate change. The sacred Valley Archaeological Site around the city of Cuzco, a UNESCO World Heritage Site, is exposed to significant geological risks due to recurrent landslides induced and worsened by climate change effects that threaten its structural integrity, security and exploitation. The Machu Picchu Historic Sanctuary was built on Upper Permian-Lower Triassic (250–300 Ma) igneous rocks, primarily plutonic, which form the Vilcabamba Cordillera's backbone (from 2000m since 6000m a.s.l.) These intrusive formations, oriented ONO–ESE, constitute the elevated regions of the Eastern Cordillera. The area is dominated by a batholith composed mainly of granite and granodiorite, with medium-textured basic granite prominently outcropping within the citadel. The Machu Picchu site and all the sacred valley of Cuzco its surroundings are characterized by instability phenomena driven by complex geomorphological and structural/tectonic conditions worsened by the effects induced at altitude by the climate change (melting of the permafrost, heavy rainfall and increase in temperature). The above mentioned phenomena are exacerbated by the interplay of primary discontinuity families, resulting in recurring processes such as planar slides, rockfalls, topples, debris slides, debris flows, and avalanches. The present work shows the application of Differential Interferometric Synthetic Aperture Radar (DInSAR) technique to measure slow, non-catastrophic morphological changes with millimeter-scale precision. A previous interferometric satellite analysis work carried out in the early 2000s to test the general stability of the Inca Citadel has been resumed and updated. The analysis captures both long-term and seasonal processes triggered by diverse causative factors, enabling informed planning of mitigation strategies. Specifically, DInSAR data processing was conducted for the Machu Picchu archaeological area and for the wider Cusco area, complemented by direct field surveys to validate the results (November 2024). Multi-temporal SAR images from the Sentinel-1 constellation (C-band radar) were processed using advanced DInSAR techniques to generate ground displacement measurement points. The spatial distribution and correlation of these measurements with slope instability and structural damage were analyzed, revealing ground deformation trends from January 2020 to August 2024. Preliminary results indicate that the citadel exhibits average ground and structural displacement of less than 1 mm/year substantially negligible. However, localized analyses highlight distinct patterns of small-scale displacement in the Grupo de las Tres Puertas with slight brick detachment and in the Upper Plaza and Eastern Citadel sector showing relative subsidence compared to adjacent areas, suggesting potential movements of the eastern flank. Monitoring systems (remote and in situ) are recommended. The use of Sentinel-1 DInSAR data provided critical insights into the interaction between ground displacement and archaeological structures. It facilitated the identification of potentially unstable areas, detected anomalies, and traced ground displacement accelerations over time. Displacement anomalies and weather-climate anomalies over time, highlights the effects of the latter on the spatial-temporal increase of instability phenomena. These findings underscore the utility of DInSAR as a powerful tool for addressing preservation of intervention on CH threatened by slope instability, offering data-driven approaches for damage prevention and site management.