Deep-seated landslides in tectonically active areas: insights from InSAR data and field evidence in the western Gulf of Corinth (Greece)

Mapping landslides in tectonically active regions using remote sensing is particularly uncertain where detailed geomorphological constraints are lacking, as measured ground displacements may reflect uplift, subsidence, active faulting, or other deformation processes rather than gravitational slope failure. However, when integrated with field-based geomorphological analysis, remote sensing provides a robust framework for disentangling complex deformation signals. This study investigates deep-seated landslides in a seismically active area 15 km east of Nafpaktos, within the western Gulf of Corinth (Greece), aiming to identify active gravitational processes and quantify their kinematic response to external forcing. A time-series clustering approach was applied to Sentinel-1 InSAR data (2019–2023) to classify ground displacement patterns based on their temporal evolution. Time series from the European Ground Motion Service (EGMS) Ortho product were partitioned to distinguish landslide-related motion from transient deformation associated with seismic activity and other non-gravitational processes. Five landslide sectors were identified and mapped through detailed geomorphological field surveys, allowing the reconstruction of their spatial distribution and temporal evolution. Landslide dynamics were analyzed using descending-orbit time series in relation to rainfall and seismic activity. Comparison of pre- and post-seismic periods reveals a heterogeneous kinematic response: the largest seismic sequence (late 2020–early 2021) did not produce uniform acceleration patterns, but instead modulated slope behavior in a strongly site-specific manner. Rainfall emerges as the primary driver of long-term post-failure displacement in deep-seated landslides, while seismic shaking induces localized, delayed, and prolonged acceleration phases, reflecting time-lagged responses controlled by structural and hydrogeological conditions.