Earthquakes and rainfall accelerating deep-seated landslides toward failure: significance of combined use of InSAR and feature tracking in landslide analysis

Deep-seated landslides are found across various geological settings, with their velocity influenced by processes such as rainfall infiltration and earthquakes shaking, which alter pore pressure and shear stress at the landslide base. This paper examines the Borrano and Ponzano landslides in Abruzzo, central Italy, as representative examples of deep-seated landslides. Our analysis focuses on their geometry, mechanisms, and velocity changes using field, subsurface, and remote sensing. Both landslides, involving Laga Formation rocks, feature a concave basal sliding surface and exhibit rotational sliding with continuous movement since at least 2015. Displacement rates exceeded 10 mm/year between 2015 and 2022, with the Ponzano landslide moving 15 m in a few days during a slip event in February 2017. Time series analysis shows a substantial velocity change at both landslides following the August 24, 2016, earthquake and 2 months of above-average rainfall, with the Ponzano landslide slipping 15 m 6 months later. While our data does not provide a conclusive origin for this rapid slip event, the earlier changes suggest that earthquakes and rainfall can perturb landslide motion, possibly driving strain-induced material weakening and eventual failure.