Deep-seated gravitational slope deformations controlled by the structure of flysch nappe outliers: Insights from large-scale electrical resistivity tomography survey and LiDAR mapping

The flysch nappe outliers represent a structural setting prone to the development of deep-seated gravitational slope deformations (DSGSDs). The study area of the Palkovické hůrky hills represents an isolated outlier of the Carpathians flysch nappes, Czech Republic. Geomorphological mapping based on field surveys and interpretation of LiDAR data reveals the occurrence of various types of slope deformations, including two DSGSDs. With the aim of detecting the main controlling factors of the DSGSDs, a multiapproach investigation combining surface and underground studies has been performed. Structural measurement points to a brachysynclinal structure composed of jointed and lithologically diverse strata with step-like topography. High-resolution LiDAR data suggest strong tectonic disruption caused by conjugated transtensional and en echelon tectonic faults controlling the course of slope segments, river valleys and landslide scarps. Four specific localities have been subjected to geophysical surveying. Kilometre-scale electrical resistivity tomography (ERT) profiles that have depths of penetration reaching the limits of the method (>150 m) were acquired across the gravitationally deformed nappe outlier. The data show the overall structural conditions of the nappe outlier consisting of alternating lithological units affected by folds and fault zones. A local subordinate anticline within the central part of the brachysynclinal structure has controlled the origin of the most morphologically pronounced DSGSDs. Other large-scale DSGSDs related to the inherited fault system potentially affect the entire N/NW segment of the studied elevation. Data integration indicate that structural conditions, including lithological boundaries, tectonic disruption and local folding to be the main controlling factors of the DSGSDs evolution.