land Article Geomorphological Hazard in Active Tectonics Area: Study Cases from Sibillini Mountains Thrust System (Central Apennines) Domenico Aringoli 1,*, Piero Farabollini 1 , Gilberto Pambianchi 1, Marco Materazzi 1 , Margherita Bufalini 1 , Emy Fuffa 1 , Matteo Gentilucci 1 and Gianni Scalella 2 1 School of Sciences and Technology, Geology Division, University of Camerino, Viale Gentile III da Varano, 7, 62032 Camerino, Italy; [email protected] (P.F.); [email protected] (G.P.); [email protected] (M.M.); [email protected] (M.B.); [email protected] (E.F.); [email protected] (M.G.) 2 Office of the Extraordinary Commissary for Central Italy Earthquake 2016, via della Ferratella in Laterano, 51, 00184 Rome, Italy; [email protected] * Correspondence: [email protected] Abstract: In many areas of the Umbria-Marche Apennines, evident traces of huge landslides have been recognized; these probably occurred in the Upper Pleistocene and are conditioned by the tectonic-structural setting of the involved Meso-Cenozoic formations, in a sector of the Sibillini Mountains (central Italy). The present work aimed to focus on a geomorphological hazard in the tectonic-structural setting of a complex area that is the basis of several gravitational occurrences in different types and mechanisms, but nonetheless with very considerable extension and total Citation: Aringoli, D.; Farabollini, P.; destabilized volume. An aerophoto-geological analysis and geomorphological survey allowed Pambianchi, G.; Materazzi, M.; verification of how the main predisposing factor of these phenomena is connected with the presence Bufalini, M.; Fuffa, E.; Gentilucci, M.; in depth of an important tectonic-structural element: the plane of the Sibillini Mountains thrust, Scalella, G. Geomorphological which brings the pre-evaporitic member of the Laga Formation in contact with the Cretaceous-Eocene Hazard in Active Tectonics Area: limestone lithotypes (from the Maiolica to the Scaglia Rosata Formations) of the Umbria-Marche Study Cases from Sibillini Mountains sedimentary sequence. Another important element for the mass movements activation is the presence Thrust System (Central Apennines). of an important and vast water table and related aquifer, confined prevalently by the different Land 2021, 10, 510. https://doi.org/ structural elements and in particular by the thrust plane, which has acted and has continued to act, 10.3390/land10050510 weakening the rocky masses and the overlaying terrains. Academic Editor: Oren Ackermann Keywords: large-scale landslides; DSGSDs; normal faults and overthrusts; Sibillini Mts.; Received: 28 March 2021 Central Apennines Accepted: 7 May 2021 Published: 11 May 2021 Publisher’s Note: MDPI stays neutral 1. Introduction with regard to jurisdictional claims in The Central Apennines (Italy) is a young and tectonically active mountain range published maps and institutional affil- characterized by a high structural complexity. The single structures related to the different iations. tectonic phases interact with each other, favoring the reactivation of the old ones or leading to the segmentation of the recently formed ones. The result is a strong stress, both on the seismic characteristics of the area and on the geomorphological evolution of the Apennine reliefs, especially those characterized by the presence of important tectonic elements. In Copyright: © 2021 by the authors. general, it is accepted that tectonics can play a dual role in influencing the gravitational Licensee MDPI, Basel, Switzerland. evolution of the slopes: (i) a passive role, related to the influence on the structural setting of This article is an open access article the slopes, which can be inherited from a tectonic phase no longer active; and (ii) an active distributed under the terms and role, represented by the changes that it can determine on the slopes, producing increases in conditions of the Creative Commons the relief energy and tensional stress suffered by the rock volumes [1]. Attribution (CC BY) license (https:// In this perspective, a study was carried out on the southern slopes of the Sibillini creativecommons.org/licenses/by/ Mountains ridge in correspondence with the area most affected by the recent seismic 4.0/). Land 2021, 10, 510. https://doi.org/10.3390/land10050510 https://www.mdpi.com/journal/land Land 2021, 10, x FOR PEER REVIEW 2 of 22 Land 2021, 10, 510 In this perspective, a study was carried out on the southern slopes of the Sibillini2 of 21 Mountains ridge in correspondence with the area most affected by the recent seismic se- quence where, through detailed geological and geomorphological surveys, several large sequencelandslides where, and deep-seated through detailed gravitational geological slope and geomorphological deformations (DSGSDs) surveys, severalhave been large landslidesmapped. and deep-seated gravitational slope deformations (DSGSDs) have been mapped. Analyses andand kinematickinematic verificationsverifications allowallow us us to to hypothesize hypothesize an an important important correlation correla- bothtion both with with the the present present tectonic tectonic structures structures and and with with thethe hydrogeological characteristics characteristics of thethe rocky masses and the contained aquifers, aquifers, in in analogy analogy with with what what has has already already been been verifiedverified in other areas of the Alps and and of of th thee Apennines Apennines chain chain [1–10] [1–10 ]or or in in other other areas areas of of thethe Earth’sEarth’s surface on various various mountain mountain ridges, ridges, such such as as Bethic Bethic Belt, Belt, Carpathian Carpathian Belt, Belt, Tien Tien Shan Mountains, Pamir Mountains, and and Williams Williams Range Range in in Colorado Colorado [11–18]. [11–18]. The present present work work therefore therefore aims aims to highlight to highlight how how the combination the combination of the ofabove-men- the above- mentionedtioned factors factors is fundamental is fundamental in many in many gravitational gravitational processes processes ranging ranging from from large large mass mass movements to huge landslides and and to to DSGSD DSGSD sensu sensu [2], [2], as as well well as as in in more more superficial superficial phenomenaphenomena and in “classical” ones [19]. [19]. The relationship between active tectonics and and DSGSDs DSGSDs and/or and/or large large landslides landslides along along thethe tectonictectonic slopes of the Sibillini Mountains Mountains also also plays plays an an extremely extremely important important role role in in differentiating thethe riskrisk associatedassociated with with seismic seismic and/or and/or hydrogeologicalhydrogeological events events occurring occurring in thein the area. area. 2. Data and Methods 2.1. Geological and Structural Setting Setting In the area outcrops the the typical typical Umbria-Marche Umbria-Marche Succession, Succession, a a sedimentary sedimentary sequence sequence consistingconsisting of of a a stratified stratified sedimentary sedimentary succession succession of ofpelagic pelagic environment, environment, in which in which calcar- cal- careouseous and and marly-calcareous marly-calcareous lithotypes lithotypes alternate alternate with siliceous with siliceous ones (Figure ones (Figure1). This1 succes-). This successionsion is set on is massive set on massivelimestones, limestones, disjointed disjointed by an extensional by an extensional tectonic phase tectonic in the phaseMiddle in theLias. Middle This situation Lias. This gave situation rise both gave to the rise depo bothsition to the of a deposition complete succession, of a complete characterized succession, characterizedby considerable by thicknesses, considerable and thicknesses, to the depo andsition to the of reduced/condensed deposition of reduced/condensed succession, char- suc- cession,acterized characterized by considerable by considerable variations in variations thickness in and thickness with singular and with lithological singular lithological features features[20–22]. [20–22]. FigureFigure 1.1. Geological and structural sketch sketch of of the the Sibillini Sibillini Mountains Mountains area. area. The typicaltypical structuralstructural arrangementarrangement is is that that of of thrusts thrusts and and folds folds chain chain with with a prevalently a preva- easternlently eastern vergence, vergence, with with axes axes in approximately in approximately N–S N–S direction direction (Figure (Figure1 ).1). TheThe tectonic tectonic movement that gave rise to to the the relief relief has has produced produced a a series series of of overthrusts overthrusts and and inverse inverse faults,faults, very evident on the eastern flanks flanks of of the the anticlines, anticlines, which which caused caused the the shortening shortening and overlapping of older terms terms on on more more recent recent deposits. deposits. The The main main structural structural element element that that delimits to the east the carbonatic ridge is the Sibillini Mountains thrust, which extends southward until it joins the “Ancona-Anzio Line” [23–25]. The structure of the thrust front is characterized by a northeastern arched geometry and Adriatic convexity; in the northern part the trend is “apenninic” (NNW–SSE), while in the southern part it is approximately N–S. This regional tectonic style presents a complex Land 2021, 10, 510 3 of 21 articulation: in some areas it is realized through