Attività tettonica, grandi frane in roccia ed evoluzione del reticolo idrografico nell'area epicentrale della sequenza sismica dell'Italia centrale 2016-2017

This PhD thesis is part of three different research activities, the main of which is related to relates to the analysis of geomorphological markers (mainly fluvial terraces) and to the geomorphometric elaborations of the earth's surface studies carried out by the research group of Geografia Fisica e Geomorfologia of Dipartimento di Scienze della Terra dell’Università La Sapienza di Roma. The other activities are carried out by the working groups by the Institute of Environmental Geology and Geoengineering of the CNR and interested: - geological and geophysical surveys for preparatory studies for seismic microzonation and evaluation of geomorphological hazard conditions in areas affected by cosismic instability; - palaeoseismological analyzes conducted on the fault system responsible for the main earthquakes that occurred in Central Italy in 2016. With this PhD thesis the various disciplines were integrated in order to use a multidisciplinary approach for the estimation of trends and rates of valley engraving in a tectonically active mountain landscape. The aim of the present work is to understand and define the complex interactions between the processes acting along the slopes linked to gravity and the fluvial morphodynamics in tectonically active areas. This problem, which is still open today, has been approached by numerous authors who propose different morfoevolutionary models of hydrographic networks in the main mountain ranges of the planet, explaining the role of valley incisions in high energy areas of the relief compared to rock slope instability (e.g. Korup, 2006a for the Swiss Alps and for the Southern Alps of New Zealand; Ouimet et al., 2007 and Larsen et al., 2010 for the Himalayan chain). The seismic sequence that struck Central Italy in 2016-2017 led to focus attention on the Apennine sector of the epicenter area, particularly in the upper valley of the Tronto River. This area falls into one of the tectonically active areas of the Apennines (D'Agostino et al., 2001a; Galli et al., 2008; 2017), and it is characterized by a well-developed hydrographic network and by the presence of important phenomena of instability of the rock slopes (Aringoli et al., 2010; Romeo et al., 2017; Martino et al., 2019a; 2019b). Within the identified area, quantitative analysis of landscape were applied through geomorphometric elaborations with GIS and Matlab software based on a Digital Terrain Model (DTM) with soil resolution equal to 5 m. The results of these analyzes were been integrated with the data obtained from the realization geomorphological surveys carried out ad hoc and geological and geophysical surveys, also useful for understanding the effects related to the mainshocks of the 2016-2017 seismic sequence, carried out following seismic events, also in the context of preliminary studies of seismic microzonation of the Municipalities involved. Paleoseismological studies have been carried out, in collaboration with researchers from the Civil Protection Department and the CNR-IGAG, in order to better define the behavior of the main tectonic structures in the study area: the Monte Gorzano fault and the Monte Vettore fault system, which in their southern portion cross the upper valley of the Tronto River. Quantitative analyzes were conducted on the longitudinal profile of the main channel of Tronto River, for the section concerned, through the study of the Area-Slope function and the application of the index for the identification, classification and interpretation of the main anomalies . Two different innovative techniques were also applied for the analysis of the style and timing of the morphological evolution of the hydrographic network, associated to the presence of large rock landslides and the presence of active faults: time-dependent hypsographic analysis (Demoulin 2011, 2012 and Demoulin et al., 2013, 2015) and the analysis of the spatial distribution of the parameter  (Perron and Royden, 2013). The time-dependent ipsographic analysis was performed using the study of the hypsometric curves, and the calculation of the relative integrals, by basin, hydrographic network and main channel of the Tronto River, according to the intervention proposed by Demoulin (2011; 2012) and subsequently perfected by Demoulin et al. (2013; 2015). Initially, the methodology proposed by Demoulin et al. (2015) was applied. This approach made it possible to identify two distinct series of data, one for the sector upstream of the basin in which it was not possible to estimate the timing of the last change in the basic erosion level and one for the downstream sector which on the contrary, it allowed us to estimate a significant change in the base level that occurred during the Holocene. The time-dependent analyzes were subsequently carried out for the main catchment areas of the Tronto River tributaries, appropriately selected in the preliminary phase based on their geometric characteristics. However, this second approach has highlighted some defects in the methodology linked to the poor reliability of the method in the presence of numerous phenomena of fluvial capture or, more generally, a remarkable reorganization of the lattice in agreement with what has already been partially highlighted in Della Seta et al. (2017). Eight catchment areas of tributaries of the Tronto River which are in the vicinity or which are crossed by the Monte Gorzano fault were subsequently isolated and analyzed. In this way it was possible to observe and quantify that the four basins in which the fault crosses the main channel have recorded a variation of the most recent base level compared to the other four that are almost entirely on the hanging wall of fault. The analyzes were then integrated with the analysis of the parameter  (Perron and Royden, 2013) to highlight the effects of the differential deformation along the direction of the Monte Gorzano fault. The map of the values of  made it possible to obtain useful information on the state of imbalance of the Tronto River hydrographic network generated by the presence of the fault. Comparing the data obtained at the points where the fault crosses the hydrographic network at different altitudes, with a new approach compared to the classical that compares the values of  values in correspondence of certain isoipses, and applying the methodology proposed by Peronace et al. (2018), it was therefore possible to hypothesize the throw trend along the structure. The results of this study made it possible to subdivide the structure analyzed into three sectors, two of which, the northern and the southern, would be active. In particular, the southern sector could be considered as the terminal part of the fault that continues and runs along the Campotosto lake, as already highlighted by Galadini and Messina (2001) and by Galadini and Galli (2003). Furthermore, the area of maximum rejection hypothesized for this sector corresponds to the point of maximum throw indicated by Boncio et al. (2004). Geomorphometric studies and studies through land surveying for the analysis of geomorphological markers. Numerous terraced surfaces of river origin have been identified in the upper basin of the Tronto River, with the spatial analysis of the slopes calculated starting from the digital model of the terrain and with the analysis of aerial photos and satellite images (available on Google® Earth). This studies was integrated with the survey campaign (some of the results achieved presented by Vignaroli et al., 2019; Mancini et al., 2019). The geometry of the terraced surfaces and the limited thickness of the deposits, provide important information about the erosion and the subsequent transport of sediments downstream by the river dynamics in this area. Furthermore, the correlation of the surfaces has allowed us to hypothesize the trend of the pre-Holocene longitudinal profile of the Tronto River. Furthermore, the arrangement of the numerous terraced surfaces indicates that the basin has recorded several variations in the base level of erosion, which have generated many regressive erosive waves that have spread upstream, the most recent of which could be witnessed by the presence of a knickzone today located downstream of the Pescara del Tronto village. To understand the behavior of the tectonic structure responsible for the 2016 seismic events, activities were carried out for the characterization of the Monte Vettore fault system, in collaboration with the CNR-IGAG working group (Galli et al., 2019). The results achieved by this study were used in the discussion of the present thesis work in order to evaluate the possible correlations with the morphological evolution of the hydrographic network, but the methodologies adopted, typical of geomorphological and paleoseismological studies, will not be treated. This activity made it possible to recognize six superficial faulting events, including that which occurred in 2016, which occurred in the last 9,000 years, with an average return period for earthquakes with MW ≥ 6.6 of 1.8 ± 0.3 kyr (Galli et al., 2019). The study carried out on the main tectonic structures of the study area did not allow to understand the role of the single structures on the fluvial morphodynamics of the area. This is caused by the superposition of the effects due to the presence of large slope instabilities due to gravity which have obliterated the effects linked to the variations of the local base level and consequently they prevent the reading of the effects of active tectonics on the spatial models of the longitudinal profile adopted. The integration of different types of analysis and the results obtained allowed us to understand the relationship between the evolution of the hydrographic network and the large rock landslides in the upper basin of the Tronto River. The most relevant innovation of the present work is represented by the application of a combined multidisciplinary approach for the study of the cause-effect relationships of canal- slopes systems in tectonically active and geologically complex areas characterized by medium-low relief energy values. In particular, the valley incision linked to the lifting of the chain in combination with the differential lifting of some active fault sectors has contributed significantly to the activation of mass rock creep phenomena on the slopes, which in some cases have evolved with phenomena of collapse (for example the slope near Pescara del Tronto) in other cases (slopes of Tino and Grisciano) have not yet reached the collapse phase. In conclusion, in tectonically active areas similar to the studied area, tectonics in general leads to the uplift, even differential of the area, but its direct effects on the hydrographic network are removed relatively quickly. Therefore, the morphometric analyzes of the hydrographic network make it possible to read with good approximation only the effects of the valley incision on the instability of the rock slopes and are indirectly the regional effects of tectonics.