Tectonic geomorphology and active strain of the Northern Apennines mountain front

The Northern Apennines (NA) chain is the expression of the active plate margin between Europe and Adria. Given the low convergence rates and the moderate seismic activity, ambiguities still occur in defining a seismotectonic framework and many different scenarios have been proposed for the mountain front evolution. Differently from older models that indicate the mountain front as an active thrust at the surface, a recently proposed scenario describes the latter as the frontal limb of a long-wavelength fold (> 150 km) formed by a thrust fault tipped around 17 km at depth, and considered as the active subduction boundary. East of Bologna, this frontal limb is remarkably very straight and its surface is riddled with small, but pervasive high- angle normal faults. However, west of Bologna, some recesses are visible along strike of the mountain front: these perturbations seem due to the presence of shorter wavelength (15 to 25 km along strike) structures showing both NE and NW-vergence. The Pleistocene activity of these structures was already suggested, but not quantitative reconstructions are available in literature. This research investigates the tectonic geomorphology of the NA mountain front with the specific aim to quantify active deformations and infer possible deep causes of both short- and long-wavelength structures. This study documents the presence of a network of active extensional faults, in the foothills south and east of Bologna. For these structures, the strain rate has been measured to find a constant throw-to-length relationship and the slip rates have been compared with measured rates of erosion. Fluvial geomorphology and quantitative analysis of the topography document in detail the active tectonics of two growing domal structures (Castelvetro - Vignola foothills and the Ghiardo plateau) embedded in the mountain front west of Bologna. Here, tilting and river incision rates (interpreted as that long-term uplift rates) have been measured respectively at the mountain front and in the Enza and Panaro valleys, using a well defined stratigraphy of Pleistocene to Holocene river terraces and alluvial fan deposits as growth strata, and seismic reflection profiles relationships. The geometry and uplift rates of the anticlines constrain a simple trishear fault propagation folding model that inverts for blind thrust ramp depth, dip, and slip. Topographic swath profiles and the steepness index of river longitudinal profiles that traverse the anti- clines are consistent with stratigraphy, structures, aquifer geometry, and seismic reflection profiles. Available focal mechanisms of earthquakes with magnitude between Mw 4.1 to 5.4, obtained from a dataset of the instrumental seismicity for the last 30 years, evidence a clear vertical separation at around 15 km between shallow extensional and deeper compressional hypocenters along the mountain front and adjacent foothills. In summary, the studied anticlines appear to grow at rates slower than the growing rate of the longer- wavelength structure that defines the mountain front of the NA. The domal structures show evidences of NW-verging deformation and reactivations of older (late Neogene) thrusts. The reconstructed river incision rates together with rates coming from several other rivers along a 250 km wide stretch of the NA mountain front and recently available in the literature, all indicate a general increase from Middle to Late Pleistocene. This suggests focusing of deformation along a deep structure, as confirmed by the deep compressional seismicity. The maximum rate is however not constant along the mountain front, but varies from 0.2 mm/yr in the west to more than 2.2 mm/yr in the eastern sector, suggesting a similar (eastward-increasing) trend of the apenninic subduction.

Abbandono del territorio e dissesto idrogeologico in Appennino bolognese: analisi delle dinamiche e degli interventi di gestione idraulico-forestale

The abandonment of less productive fields and agro-forest activities has occured in the last decades, interesting large mountain areas in all mediterranean basin. Until the fifties, agricultural practices dealt mainly with soil surface and surface runoff control systems. However, the apparent sustainability of soil use results often in contrast with historical documents, witnessing heavy hydrogeological instability, in naturally fragile areas. The research focused on the dynamics and effects of post-coltural land abandonment in a critical mountain area of the Reno River. The Reno River rappresents a typical Tuscan-Emilian Apennines Watershed where soil erosion occurs under very different conditions depending on interactions between land use, climate, geomorphology and lithology. Landslides are largely rappresented, due to the diffusion of clay hill slopes. Recent researches suggest that climatic variability will increase as a consequence of global climate change, resulting in greater frequency and intensity of extreme weather events, which could increase rates of erosion, landslides reactivations and diffusion of calanchive basins. As far as hill slopes are concerned, instability is today basically due to intrinsic factors, as the Apennine range is a rather young formation, in geological terms, and is mainly formed by sedimentary rocks with high occurrence of clays. Therefore landslides and rockfalls are very frequent, while surface soil erosion is generally low and anyway concentrated in the low Apennine, where intensive farming is still economically worth. The study, supported by GIS use, analyses the main fisical characteristics of the area and the historical changes of land use, and focalizes the dynamics of spontaneous reafforestation. Futhermore, the research studies the results of soil bioengineering and surface water control solutions for the restablishment of landslides occured in the last period. Infact soil bioengineering has been recently used in different situations in order to consolidate slopes and hillsides and prevent erosion; when applied, it gave good results, both in terms of engineering efficiency and vegetational development, expecially if combined with a good hydraulic control, thus proving to be an actual alternative to other techniques with heavier environmental impacts. Research into the specific site features and the use of proper plant species is vital to the success of bioengineering works.

Analisi climatica ad alta risoluzione delle precipitazioni sul nord Italia (1961-2005)

L’obiettivo di questo lavoro di tesi è di ottenere un’analisi climatica giornaliera ad alta risoluzione della precipitazione sul territorio del nord Italia realizzata con tecniche di controllo statistico, di analisi e di strumenti di descrizione dei risultati presentati nella recente letteratura. A tal fine, sono stati utilizzati i dati dell’Archivio ARCIS. In seguito alle fasi di controllo qualità, omogeneità e sincronicità i dati sono stati utilizzati per realizzare un’analisi giornaliera su grigliato regolare a 10 km di risoluzione utile alla rappresentazione della variabilità spazio-temporale della precipitazione sul Nord Italia per il periodo 1961-2005. I risultati di tale analisi mettono in evidenza dei valori medi di precipitazione annuale abbastanza intensi sulla parte centrale dell’arco Alpino, con massimi (oltre 2000 mm) sull’estremità orientale e sull’Appennino Ligure. Valori minimi (500 – 600 mm) sono osservati lungo le aree prospicienti il fiume Po, in Val d’Aosta ed in Alto Adige. La corrispondente analisi del trend temporale indica la presenza di lievi cali statisticamente significativi solo in aree limitate del territorio. In coerenza con questi risultati, la variazione nel tempo della precipitazione annuale mediata su tutto il territorio mette in evidenza un’intensa variabilità decennale, ma solo una lieve flessione lineare sull’intero periodo. Il numero annuo di giorni piovosi ed il 90° percentile della precipitazione giornaliera presentano invece trend lineari un po’ più pronunciati. In particolare, sul periodo considerato si nota un calo del numero di giorni piovosi su gran parte del territorio e solo su alcune aree del territorio un aumento dell’intensità del 90° percentile, sia a scala annuale che stagionale. Nell’ultima parte di questo lavoro è stato realizzato uno studio della relazione fra la forzante climatica e l’evoluzione della morfologia dell’Appennino Emiliano-Romagnolo. I risultati mostrano che a parità di quota, di pendenza e di litologia, la franosità è influenzata dalle precipitazioni.