Mapping and monitoring different types of landslides through InSAR in the Northern Apennines of Italy

Landslides in mountainous regions are a major concern due to their potential impact on infrastructure and human lives. Many deep-seated slope movements alternate between phases of sustained movement to phases of dormancy. Detecting and monitoring active movements over large territories can effectively support risk mitigation efforts. Satellite radar interferometry is widely used for such purposes, despite its poor coverage in uninhabited rural areas. Our study aims to overcome such limitations by using conventional two-pass interferometry. We use interferometric stacking to improve the signal-to-noise ratio and carefully select interferogram duration and coherence to enhance the ability to detect active slow-moving landslides. The current study focuses on five large catchments of the Northern Apennines, Italy. In the first phase of the study, yearly stacks from 2016 to 2023 were used to identify InSAR Deformation Signals likely related to slope deformation processes. More than 80 signals were detected in the study area, showing sustained deformation in multiple interferometric stacks either in ascending and/or descending geometry. This provides strong evidence for the effectiveness of our approach. We compare our results with geomorphological and geological information, as well as the landslide inventory, illustrating how active landslides are favored by weak lithologies and pre-existing slope instability. The analysis of the evolution of selected signals over time, representative of the pattern of landsliding in our study area, shows distinct trends for landslides involving fine-grained materials and arenaceous bedrock. Earthslides and earthflows show sustained downslope motion with seasonal velocity changes, while rockslides are subject to short-duration acceleration episodes. Time series analysis show that surface displacements can be observed throughout most part of the year, with exceptions during periods of snow cover and the summer peak of vegetation. These findings highlight the potential of standard InSAR for mapping and monitoring active landslides.