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51.
Structure of the lithosphere beneath the Eastern Alps (southern sector of the TRANSALP transect) 总被引：1，自引：0，他引：1
Alberto Castellarin Rinaldo Nicolich Roberto Fantoni Luigi Cantelli Mattia Sella Luigi Selli 《Tectonophysics》2006,414(1-4):259
The interpretation of the seismic Vibroseis and explosive TRANSALP profiles has examined the upper crustal structures according to the near-surface geological evidences and reconstructions which were extrapolated to depth. Only the southern sector of the TRANSALP transect has been discussed in details, but its relationship with the whole explored chain has been considered as well. The seismic images indicate that pre-collision and deep collision structures of the Alps are not easily recognizable. Conversely, good records of the Neo-Alpine to present architecture were provided by the seismic sections.Two general interpretation models (“Crocodile” and “Extrusion”) have been sketched by the TRANSALP Working Group [2002]. Both illustrate the continental collision producing strong mechanical interaction of the facing European and African margins, as documented by giant lithosphere wedging processes. Arguments consistent with the “Extrusion” model and with the indentation of Adriatic (Southalpine) lithosphere underneath the Tauern Window (TW) are:
- – According to the previous DSS reconstructions, the Bouguer anomalies and the Receiver Functions seismological data, the European Moho descends regularly attaining a zone south of the Periadriatic Lineament (PL). The Moho boundary and its geometry appear to be rather convincing from images of the seismic profile;
- – the Tauern Window intense uplift and exhumation is coherent with the strong compression regime, which acted at depth, thus originating the upward and lateral displacement of the mobile and ductile Penninic masses according to the “Extrusion” model;
- – the indentation of the Penninic mobile masses within the colder and more rigid Adriatic crust cannot be easily sustained. Wedging of the Adriatic stiffened lower crust, under high stresses and into the weaker Penninic domain, can be a more suitable hypothesis. Furthermore, the intrusion of the European Penninic crustal wedge underneath the Dolomites upper crust is not supported by any significant uplifting of the Dolomites. The total average uplift of the Dolomites during the Neogene appears to be 6−7 times smaller than that recognized in the TW. Markedly the northward dip of the PL, reaching a depth of approximately 20 km, is proposed in our interpretation;
- – finally, the Adriatic upper crustal evolution points to the late post-collision change in the tectonic grow-up of the Eastern Alps orogenic chain. The tectonic accretion of the northern frontal zone of the Eastern and Central Alps was interrupted from the Late Miocene (Serravallian–Tortonian) onward, as documented by the Molasse basin evolution. On the contrary, the structural nucleation along the S-vergent tectonic belt of the eastern Southern Alps (Montello–Friuli thrust belt) severely continued during the Messinian and the Plio–Pleistocene. This structural evolution can be considered to be consistent with the deep under-thrusting and wedge indentation of the Adriatic lithosphere underneath the southern side of the Eastern Alps thrust-and-fold belt.
52.
We propose and validate a new sampling method to assess the presence, abundance and distribution of macrophytes in circular-shaped lakes according to the requirements of the Water Framework Directive (WFD2000/60/EC). The results of the macrophyte survey, and in particular of macrophyte diversity, obtained using this method are also discussed.The sampling is based on randomly selected transects homogeneously distributed around the perimeter of the lake. The number of transects is proportional to the lake's size. The method was validated on six Italian volcanic lakes using computational resampling procedures on a total of 126 transects.Using resampling procedures, we show that the proposed approach identifies more than 75% of the overall species richness through a moderate sampling effort. According to our results, Charophytes dominate aquatic vegetation in Italian volcanic lakes. Species diversity is highest at shallow depths, whereas the most abundant species, such as Chara polyacantha, are located at an intermediate depth between the shoreline and the maximum growing depth. 相似文献
53.
Two‐dimensional nonlinear diffusive numerical simulation of geomorphic modifications to cinder cones
The temporal evolution of simple landforms such as cinder cones by nonlinear diffusive processes is studied through the use of a new 2D numerical model using well‐established and accurate numerical mathematics and high‐resolution digital elevation models (DEMs). Extending 1D (profile) nonlinear diffusion analyses used in cinder cone, hillslope and fault scarp evolution studies, we have implemented a 2D numerical model with a spatially and temporally varying sediment transport rate coefficient scaled nonlinearly by the ratio of local slope to critical slope. The high accuracy and efficient numerical implementation are documented in the paper and the MATLAB toolkit developed is used to solve for the developmentof an initial 2D cone form. First, we examine the nonlinear transport rule and suggest a refinement that accounts explicitly for flux at threshold slopes. We find that the maximum diffusion (necessarily introduced in the numerical model to avoid infinite rates) at the critical slope controls the final morphology, especially approaching steady state. Secondly, solving the landscape evolution problem in 2D enables a natural accounting for sediment flux convergence or divergence in the profile. Thirdly, the boundary behavior of a given landscape element controls much of what happens in that domain and so we allow for arbitrary flux magnitude or elevation boundary conditions. Fourthly, landscapes are heterogeneous in their surface cover and so we allow for spatially and temporally varying transport rate k and we permit an arbitrary vertical displacement field within the model domain. To test the new formulation for the nonlinear term, the effect of variable diffusivity k and the numerical schemes implemented, we apply the model to cinder cones built on the flanks of Mount Etna in 2001 and 2002–2003. We explore the effects of DEM resolution with data from the 2001 cone and the utility of spatially variable diffusivity to explain the variation in erosion measured by differencing repeat light detection and ranging (LIDAR) surveys gathered in 2004 and 2007 over the 2002–2003 cone complex. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
54.
Jan Blahut Ilaria Poretti Mattia De Amicis Simone Sterlacchini 《Natural Hazards》2012,60(3):1065-1083
This paper presents the results of a research concerning available historical information about natural hazards (landslides
and floods) and consequent disasters in the Consortium of Mountain Municipalities of Valtellina di Tirano, in Northern Italy.
A geo-referenced database, collecting information till 2008, was designed with the aim of using available data of historical
events for hazard estimation and the definition of risk scenarios as a basis for Civil Protection planning and emergency management
purposes. This database and related statistics about landslides and floods are shown, and a brief overview of historical disasters
caused by natural hazards in the study area is presented. A case study showing how useful the database can be to define a
simple but realistic scenario is described. Information availability and reliability is discussed and possible uncertainties
are underlined. The study shows that collecting and making use of historical information for the definition of hypothetical
scenarios and the evaluation of territorial threats is a fundamental source of knowledge to deal with future emergencies. 相似文献
55.
Accurate 3D surface measurement of mountain slopes through a fully automated image-based technique 总被引：1，自引：1，他引：0
In this paper an automated procedure for surface reconstruction that can be used for surveying and monitoring rock and ground slopes is presented. This method has been developed for geological and engineering applications, where accuracy and completeness are factors of primary importance for the final 3D model, which must provide a detailed metric survey and not only a visual reconstruction of the scene. The proposed procedure integrates two image matching techniques. The first one is used to automatically extract a set of tie points that are needed for computing the exterior orientation parameters of all images through a photogrammetric bundle adjustment. Such tie oints are also exploited to obtain a preliminary seed model that is then enriched based on Multi-photo Least Squares Matching. During this second stage, the surface model is improved in terms of point density and accuracy. Different strategies were implemented to successfully combine both techniques, along with some new improvements. The presented procedure has been tested in two different applications: geometric modelling of rock cliffs and evaluation of weathering of a ground slope. In both cases the obtained results presented accuracy sufficient for geological investigation. Moreover, outcomes were comparable to the ones from laser scanning surveying and other photogrammetric implementations. 相似文献