Lithological control on landslide detection and dynamics revealed by two-pass InSAR in the Northern Apennines of Italy

This study investigates active slow-moving landslides in the Northern Apennines of Italy, where Clay Shales, Flysch rocks, and young Pliocene overconsolidated Clays (OC Clays) are the most common outcropping lithotypes. We aim to detect active slope deformations, assess geological controls, and evaluate their evolution in relation to rainfall. Sentinel-1 SAR data (2015–2022; 720 images) from both orbits were processed to generate interferograms with temporal baselines ranging from 6 to 36 days. We selected interferograms based on coherence and visual inspection before stacking them over 1-month and 1-year time scales. Longer term stacks were analyzed together with geology, geomorphology, and aerial photos to detect deformation signals associated with active landsliding (IDS). Their abundance varies significantly across lithologies, with Clay Shales and OC clays exhibiting the highest spatial densities, while Flysch frequently reached displacement rates exceeding 100 mm/yr. However, landslide types could not be distinguished solely from the shape of the deformation signal. Shorter term stacks were used to produce raster maps of downslope-projected velocities, enabling comparative analysis of landslides displacement over time: Flysch showed episodic accelerations, OC clays displayed dynamic reactivations with extreme peaks (>300 mm/yr), and Clay Shales maintained consistent moderate activity. Correlation with rainfall revealed sustained deformation in clay-rich units, whereas Flysch responses were weaker and discontinuous. These findings improve the characterization of landsliding across lithologies and its dynamics in relation to rainfall. Interferometric stacking of short-baseline Sentinel-1 interferograms provides an effective approach for regional-scale investigation of slow-moving landslides, enabling the detection and monitoring of relatively rapid displacements even in moderately to densely vegetated terrain.