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41.
Geomorphology and GIS analysis for mapping gully erosion susceptibility in the Turbolo stream catchment (Northern Calabria, Italy) 总被引:8,自引:0,他引:8
Massimo Conforti Pietro P. C. Aucelli Gaetano Robustelli Fabio Scarciglia 《Natural Hazards》2011,56(3):881-898
This work summarizes the results of a geomorphological and bivariate statistical approach to gully erosion susceptibility
mapping in the Turbolo stream catchment (northern Calabria, Italy). An inventory map of gully erosion landforms of the area
has been obtained by detailed field survey and air photograph interpretation. Lithology, land use, slope, aspect, plan curvature,
stream power index, topographical wetness index and length-slope factor were assumed as gully erosion predisposing factors.
In order to estimate and validate gully erosion susceptibility, the mapped gully areas were divided in two groups using a
random partitions strategy. One group (training set) was used to prepare the susceptibility map, using a bivariate statistical
analysis (Information Value method) in GIS environment, while the second group (validation set) to validate the susceptibility
map, using the success and prediction rate curves. The validation results showed satisfactory agreement between the susceptibility map and the existing data on gully areas
locations; therefore, over 88% of the gullies of the validation set are correctly classified falling in high and very high
susceptibility areas. The susceptibility map, produced using a methodology that is easy to apply and to update, represents
a useful tool for sustainable planning, conservation and protection of land from gully processes. Therefore, this methodology
can be used to assess gully erosion susceptibility in other areas of Calabria, as well as in other regions, especially in
the Mediterranean area, that have similar morphoclimatic features and sensitivity to concentrated erosion. 相似文献
42.
43.
Pietro Passerini Marta Marcucci Giovanni Sguazzoni Leonardo Zan Abdourahman Omar Haga 《地学学报》1991,3(6):607-618
Slickenside studies in regions of crustal spreading such as Iceland and the Afar Depression, East Africa, reveal that a significant number of faults parallel and close to rift axes are strike-slip rather than normal. Therefore, the pattern of brittle deformation in these regions does not conform to the classic two-dimensional schemes of oceanic tectonics and pre-oceanic rifting. Dip-slip and strike-slip faulting presumably alternated along or in the vicinity of spreading axes, indicate a varying stress field and a combination of transverse and longitudinal movements. In Iceland, strike-slip faults parallel to rifts are observed both west and east of the rift system as well as in a median area between overlapping rifts; the mechanisms proposed for their origin include accommodation of oblique convergence or divergence of crustal sections due to variations of spreading directions along axis and the interaction of overlapping rifts. In the Afar Depression this kind of fault is recorded west of the rift of Asal and can be imputed to reflect an interaction among rifts in the vicinity of the Afar triple junction. Rift-parallel strike-slip faults cannot however be assumed to be a feature of all crustal spreading axes due to the peculiarity of the examined regions: both of them are hot-spot areas and the Afar Depression lies at a triple junction. 相似文献
44.
Pedro Corona-Chávez María del Sol Hernández-Bernal Pietro Vignola Rufino Lozano-Santacruz Juan Julio Morales-Contreras Margarita Reyes-Salas Jesús Solé-Viñas José F. Molina 《Chemie der Erde / Geochemistry》2018,78(2):248-253
We present the results of physical properties, petrography, bulk chemistry, mineral compositions, phase relations modelling and Noble gases study of the meteorite El Pozo. The petrography and mineral compositions indicate that the meteorite is an L5 chondrite with a low shock stage of S2-S3. Heterogenous weathering was preferentially along shock structures. Thermobarometric calculations indicate thermal equilibrium conditions between 768?°C and 925?°C at ~4 to 6?kb, which are substantially consistent with the petrological metamorphism type 5. A pseudosection phase diagram is relatively consistent with the mineral assemblage observed and PT conditions calculated. Temperature vs. fO2 diagram shows that plagioclase compositional stability is very sensitive to Tschermack substitution in orthopyroxene, clinopyroxene and XAn plagioclase during the high temperature metamorphic process. Based on noble gases He, Ne, Ar and K contents a cosmogenic exposure age CRE of 1.9?Myr was calculated. The 21Ne would be totally cosmogenic, with no primordial Ne. The 21Ne/22Ne value (0.97) is higher than solar value. According to the cosmogenic Ne content, we argue that El Pozo chondrite originally had a pre-atmospheric mass of 9–10?kg, which would have been produced by a later collision after the recognized collision of the L-chondrite parent body ~470?Ma ago. 相似文献
45.
Claudio di Prisco Luca Flessati Gabriele Frigerio Riccardo Castellanza Marco Caruso Andrea Galli Pietro Lunardi 《Acta Geotechnica》2018,13(3):651-670
In spite of the increasing diffusion of tunnel boring machines, conventional tunnelling is still preferred for economic reasons in case of short tunnels, unconventional cross sections or irregular tunnel trajectories. In conventional tunnelling, the mechanical response of the tunnel front is a main concern and, when tunnels are excavated in cohesive soils, this is dominated by the time factor, related to geometry, to the mean excavation rate and to the hydro-mechanical properties of the materials involved. This is particularly evident during excavation standstill: front displacements progressively increase with time and, in many cases, the system response under long-term conditions becomes unstable. In conventional tunnelling, a common technique employed to improve the system response (under both short- and long-term conditions) is the installation of fibreglass tubes within the advance core. In this paper, the mechanical response of both unreinforced and reinforced deep tunnel fronts in cohesive soils is experimentally analysed. In particular, the results of a series of 1 g small-scale tests, taking into account both the influence of the excavation rate (the unloading time) on the system response and the evolution with time of the tunnel face displacements, induced by a rapid reduction in the horizontal stress applied on the tunnel face, are reported. 相似文献
46.
Diana Salciarini Claudio Tamagnini Pietro Conversini Silvia Rapinesi 《Natural Hazards》2012,61(1):229-245
The evaluation of the combined influence of rainfall patterns (in terms of mean intensity and duration) and the geomorphological
and mechanical characteristics of hillslopes on their stability conditions is a major goal in the assessment of the shallow
landslide triggering processes. Geographic Information Systems (GIS) represent an important tool to develop models that combine
hydrological and geomechanical analyses for the evaluation of slope stability, as they allow to combine information concerning
rainfall characteristics with topographic and mechanical properties of the slopes over wide areas. In this paper, a GIS-based
code is developed to determine physically based intensity/duration rainfall thresholds at the local scale. Given the rainfall
duration and the local geometric, hydrological and mechanical characteristics of the slopes, the code evaluates the spatial
distribution of the minimum rainfall intensity that triggers shallow landslides and debris flows over a given area. The key
feature of the code is the capability of evaluating the time t
p
required to reach the peak pore pressure head on the failure surface and computing the corresponding critical intensity/duration
thresholds based on post-event peak pore pressures. The reliability of the model is tested using a set of one-dimensional
analyses, comparing the physically based thresholds obtained for three different slopes with some empirical rainfall thresholds.
In a log–log scale, the thresholds provided by the model decrease linearly with increased rainfall duration and they are bracketed
by the empirical thresholds considered. Finally, an example of application to a study area of the Umbria region in central
Italy is presented, describing the capability of the model of providing site-specific thresholds for different rainfall scenarios. 相似文献
47.
Vincenza Guarino Rogério Guitarrari Azzone Pietro Brotzu Celso de Barros Gomes Leone Melluso Lucio Morbidelli Excelso Ruberti Colombo Celso Gaeta Tassinari Mauro Brilli 《Mineralogy and Petrology》2012,104(1-2):43-61
The Ipanema alkaline-carbonatitic complex is part of the Meso-Cenozoic alkaline magmatism located within the southeastern part of the Brazilian Platform. Drill-core and field sampling have indicated the occurrence of glimmerites, with subordinate shonkinites (mela-syenites), clinopyroxene-bearing glimmerites, diorites and syenites. The glimmerites are cross-cut by lamprophyric dykes and calciocarbonatites. Fenitization has deeply affected the country rocks, originating dioritic and syenitic rocks. The Ipanema rocks show a distinct potassic affinity. The initial Sr-Nd- isotopic composition of the Ipanema rocks (87Sr/86Sr?=?0.70661–0.70754 and 143Nd/144Nd?=?0.51169–0.51181) is similar to that of tholeiitic and potassium-rich-alkaline rocks of the Eastern Paraguay. Stable isotope data for the Ipanema calciocarbonatite suggest interaction with fluids at temperatures typical of hydrothermal stages, as hypothesized for other carbonatite complexes from southeastern Brazil. The chemical differences between the lamprophyre, glimmerites, carbonatites, apatitites and magnetitites, and the absence of marked REE enrichment in the evolved lithologies, all indicate that fractional crystallization and accumulus of liquidus phases in a magma reservoir, likely coupled with liquid immiscibility processes, may have played an important role in the genesis of the Ipanema rocks. 相似文献
48.
49.
In this work, fossil molluscan assemblages are analyzed in order to reconstruct the evolution of the Northern Gulf of Thailand during the Holocene. The marine sediments (Bangkok Clay Formation) of the Lower Central Plain of Bangkok and the coastal plain of Phetchaburi were sampled at 16 localities, obtaining fossil shells and mangrove peat whose 14C ages range from 9000 to 2000 CYBP. A statistical treatment of abundance data returned four major groups, namely the Dendostrea rosacea association (intertidal mud), the Corbula fortisulcata–Mactra luzonica association (shallow infralittoral sandy mud), the Nuculana mauritiana–Timoclea scabra association (infralittoral sand spit) and the Timoclea scabra–Arcopagia pudica association (infralittoral mud). The data allowed both a stratigraphic correlation along two transects covering all of the Holocene basin and the creation of digitalized maps showing the presumable extension of the Thai paleogulf around the apex of Flandrian transgression event (about 5500 CYBP). 相似文献
50.
Land subsidence due to subsurface fluid (water, gas, oil) withdrawal is often predicted by either finite element or finite difference numerical models based on coupled poroelastic theory, where the soil is represented as a semi-infinite medium bounded by the traction-free (ground) surface. One of the variables playing a most important role on the final outcome is the flow condition used on the traction-free boundary, which may be assumed as either permeable or impermeable. Although occasionally justified, the assumption of no-flow surface seems to be in general rather unrealistic. A permeable boundary where the fluid pressure is fixed to the external atmospheric pressure appears to be more appropriate. This paper addresses the response, in terms of land subsidence, obtained with a coupled poroelastic finite element model that simulates a distributed pumping from a horizontal aquifer confined between two relatively impervious layers, and takes either a permeable boundary surface, i.e., constant hydraulic potential, or an impermeable boundary, i.e., a zero Neumann flow condition. The analysis reveals that land subsidence is rather sensitive to the flow condition implemented on the traction-free boundary. In general, the no-flow condition leads to an overestimate of the predicted ground surface settlement, which could even be 1 order of magnitude larger than that obtained with the permeable boundary. 相似文献