Fattori geologico – geomorfologici per la definizione della suscettibilità da frana a cinematismo lento in aree ad alta sismicità: analisi e confronti di casi studio
Creators: name: Rivieccio, Mario
Publisher: name: Università degli Studi di Napoli Federico II
Year: 2013

description: Nowadays, the frequent natural disasters and the increasing impacts on man and his activities, along with the intensification of the anthropic development of the territory, highlight the conflictual relationship that exists between man and the dynamics of landscape systems. This has led in recent times both the scientific community and institutions operating in the territory to investigate the state of knowledge about the natural environment and to acquire new techniques aimed at both preventing risks and developing proper land management. This thesis is framed in the context just described, analyzing the theme regarding the slope dynamics in areas characterized by high seismicity. In particular, attention has been focused on landslides such as rotational/translational slides, flows and complex movements (slides evolving in flows) frequently encountered in land units dominated by terrigenous flysch formations, investigating the state of knowledge about the main geological and geomorphological factors that contribute in varying degrees to the instability of the slopes. From the methodological point of view the first part of the work has provided the focus of the investigation in an area of Campania where the high density of landslides is associated with the high frequency of seismic events, which is the upper valley of the Sele river. In such a case, analysis of multiscale topographic maps, multi-temporal photogrammetric observations and direct surveys have made possible the implementation of thematic maps useful for the purposes of the study. These products were developed in two different scales of reference: 1/25000 and 1/5000. In the first case, attention has been paid to the entire river basin and this allowed to reach a state of global knowledge, while, in the second case we considered three sample areas relating to the territories of Caposele, Senerchia and Oliveto Citra, to which have been addressed investigations at large scale to deepen the landslide triggering factors in normal and seismic conditions. At the scale 1/25000 the following maps were produced: 
1) a map of the geomorphological units, meaning the zonation of the study area on the basis of morphometric, morfoevolutive and litho-stratigraphic peculiarities;
2) a geolithological map, based on the grouping of the formational units of the geological map Carg in scale 1/50000 associated by similar lithology;
3) a slope map extrapolated from the DEM with a resolution of 20 m;
4) a map of the density of springs, based on the informations listed in the IGM topographic maps in scale 1/25000 and on the literature.
For what concerns the products developed for the three sample areas in scale 1/5000, the research included firstly the realization of a DEM with resolution of 5 m using as basis the topographic maps CTR in scale 1/5000. Therefore, the following steps were carried out:
1) a geomorphological map, in which the different forms of the landscape distinguished on the basis of the activities and morphogenetic processes were recognized;
2) a geolithological map, realized grouping the Carg formational units characterized by the same lithological characteristics, after a reworking of the geological map where it was marked the nature of the substrate located below the small debris quaternary covers;
3) a slope map, extrapolated using the software ArcGis and considering the DEM with resolution of 5 m for the calculation;
4) a map of the density of springs, where has been performed a zonation of areas with the highest incidence of springs using informations contained in the topographic maps IGM 1/25000, CTR 1/5000 and in the scientific publications consulted. 
The location of the landslides in the study area and their digitization on the topographic maps has been one of the principal operations in the development of the investigations. The landslide inventory started from the reorganization and the mapping at 1/25000 scale of the data obtained from the previous knowledges. This allowed the acquisition of  the location of slope movements and to differentiate normal phenomena by earthquake induced events. The integration of this data with direct observations allowed the elaboration of a more complete landslide inventory map at scale 1/25000. The subsequent analysis carried out on the three sample areas at 1/5000 scale was addressed to delineate more accurately the spatial disposition of the studied phenomena, and for each of them to recognize the detachment zone and the landslide body. Topographic sections made for each of the slope movements recognized allowed to make more exhaustive the morphological study.  In this phase of the work, in addition to the production of a landslide inventory map, the creation of a database containing all the descriptive information relating to the analyzed landslides was also provided. 
By overlying each level of analysis (i.e. the landslide inventory maps and the thematic maps) it was possible to extrapolate a series of information about the triggering factors of landslides in the upper Sele valley, with particular reference to the seismic induced events. 
The results obtained in this phase were then compared with the data derived from the analysis carried out on other cases of earthquake induced landslide present in Italy, in areas with geological features similar to the ones of the upper Sele valley. This new phase of the study based on a new bibliographic research carried out through the consultation of archives and scientific publications, addressing to the entire national context, in which were considered a sufficient number of cases with an adequate store of knowledge implemented, when was lacking, with additional data from direct analysis. After the observations made it was possible to reach the following conclusions:
a)	The comparison between the epicentral distance of the landslides with the intensity values of earthquakes that generated them confirmed that the probability of triggering of landslides is higher in the first 30-40 km from the epicenter, while, for progressively greater distances the possibility of triggering increases with increasing of the intensity of the earthquake;
b)	The complex movements and the slides have high percentages of activation following an earthquake, while the slow flows have low probability of occurrence in similar circumstances;
c)	Almost all of the landslides induced by earthquake analyzed is represented by reactivations of previously movements;
d)	The chronological analysis of the seismic induced movements has revealed that the probability of triggering is greater in the time from half an hour to eight hours after the earthquake;
e)	The set of the examined events develops frequently, from the geolithological point of view,  in the clayey formations, while, only the complex movements and slides have frequent activations also in the marly calcareous flysch;
f)	For what concerns the conditions of acclivity significant in terms of triggering of landslides was found the following range of grades (maximum and minimum) for each type of movement: 23 ° - 7 ° for complex movements, 24 ° - 8 ° for the slides, 24 ° - 10 ° for the flows;
g)	About the height of triggering of landslides has been observed that the complex movements tend easily to be active in the vicinity of the watershed, the slides tend to develop in both the high summit and in the lower zone of the slope, and finally, the flows not have a definite tendency to trigger in a given area of the slope;
h)	Most of the seismic induced events has developed in the autumn and winter season, generally as a result of prolonged periods of rain;
i)	Regarding the hydrogeology was observed a prevalence of triggers on slopes characterized by superficial levels of groundwater and soils in saturation conditions.