**2. Study Area**

#### *2.1. Geological and Geomorphological Setting*

The study area is located in Central Italy within the northern sector of the Abruzzo Region, and it is strictly located in the Apennines Chain area, showing a high-relief mountainous landscape. The Central Apennines chain's morphology is characterized by the presence of a series of ridges trending from NW–SE to N–S (i.e., Gran Sasso Massif, 2912 m a.s.l.; Maiella Massif, 2793 m a.s.l.), separated by longitudinal and transversal valleys and broad intermontane basins (elevation 250–1000 m a.s.l.—i.e., Fucino Plain and Sulmona Basin) (Figure 1). The elevation abruptly drops down to the hilly piedmont area (ranging from ~800 m a.s.l. to the coastline), which features a mesa, cuesta, and plateau landscape [47–50]. The northeastern front of the asymmetric Abruzzo Apennines chain is characterized by a steep mountainside with large escarpments. The Gran Sasso Massif is the highest in the Central Apennines, with several peaks above 2500 m a.s.l. It features an

arched shape, trending from W–E to N–S, and drops down to lower elevations (>1000 m a.s.l.), defining a large and steep mountain escarpment.

The chain is composed of pre-orogenic lithological sequences that belong to different Meso–Cenozoic paleogeographic domains (carbonate ramp and platform limestones and slope-to-pelagic limestones). The Neogene deformation of these sequences, along NW–SE to N–S-oriented (W-dipping) thrusts, determined the emplacement of the main mountain ridges, also including the Gran Sasso one (Figure 2) [51–58].

**Figure 2.** Geological map of NE Abruzzo (modified from [59]). Legend: post-orogenic deposits—(1) fluvial deposits (Holocene) and (2) fluvial and alluvial fan deposits (Middle-Late Pleistocene); sin- and late-orogenic deposits—(3) hemipelagic sequences with conglomerate levels (Late Pliocene–Early Pleistocene) and (4) turbiditic foredeep sequences (Late Miocene–Early Pliocene); pre-orogenic deposits—(5) carbonate ramp facies (Early Miocene-Early Pliocene), (6) slope and pelagic basin sequences (Cretaceous–Miocene), and (7) carbonate platform sequences (Jurassic–Miocene); (8) major thrust (dashed if buried); (9) major normal fault (dashed if buried); and (10) major fault with strike-slip or reverse component (dashed if buried). Seismicity derived from the CPTI15 catalog [60]. The black line indicates the location of the study area.

This compressional phase was followed by extensional and strike-slip tectonics along mostly the NW–SE to NNW–SSE-oriented faults, which define the present-day landscape configuration [47,61,62]. The hilly piedmont and coastal areas are made up of sin- and late-orogenic deposits (i.e., sandy-pelitic turbiditic foredeep sequences), largely covered and unconformably overlaid by Pleistocene hemipelagic sequences. The post-orogenic

deposits mainly consist of fluvial and alluvial fan deposits, as well as glacial, travertine, slope, and eluvial–colluvial deposits (Figure 2).

The geomorphological framework is mainly related to mass wasting; gravity-induced (e.g., mostly rotational–translational slides, earth flows, rockfalls, and complex slides); and fluvial-related (e.g., debris flows, alluvial fans, etc.) processes. Ancient glacial processes are preserved as relict landforms [48,63–66].

According to the historical and instrumental data [67–69], Central Italy has been affected by many earthquakes, with recurrent seismic events of moderate-to-high intensity. The present-day regional tectonic setting is dominated by intense seismicity (up to Mw 7.0 [60]), with earthquakes mostly located in the chain sectors (i.e., 2009, L'Aquila and 2016–2017, Central Italy); moderate seismicity also affects the hilly piedmont and Adriatic areas.
