Hypogeal geological survey in the “Grotta del Re Tiberio” natural cave (Apennines, Italy): a valid tool for reconstructing the structural setting     

Alice Ghiselli  Marzio Merazzi  Andrea Strini  Roberto Margutti  Michele Mercuriali 《Central European Journal of Geosciences》2011,3(2):155-168

As karst systems are natural windows to the underground, speleology, combined with geological surveys, can be useful tools for helping understand the geological evolution of karst areas. In order to enhance the reconstruction of the structural setting in a gypsum karst area (Vena del Gesso, Romagna Apennines), a detailed analysis has been carried out on hypogeal data. Structural features (faults, fractures, tectonic foliations, bedding) have been mapped in the ”Grotta del Re Tiberio” cave, in the nearby gypsum quarry tunnels and open pit benches. Five fracture systems and six fault systems have been identified. The fault systems have been further analyzed through stereographic projections and geometric-kinematic evaluations in order to reconstruct the relative chronology of these structures. This analysis led to the detection of two deformation phases. The results permitted linking of the hypogeal data with the surface data both at a local and regional scale. At the local scale, fracture data collected in the underground have been compared with previous authors’ surface data coming from the quarry area. The two data sets show a very good correspondence, as every underground fracture system matches with one of the surface fracture system. Moreover, in the cave, a larger number of fractures belonging to each system could be mapped. At the regional scale, the two deformation phases detected can be integrated in the structural setting of the study area, thereby enhancing the tectonic interpretation of the area (e.g., structures belonging to a new deformation phase, not reported before, have been identified underground). The structural detailed hypogeal survey has, thus, provided very useful data, both by integrating the existing information and revealing new data not detected at the surface. In particular, some small structures (e.g., displacement markers and short fractures) are better preserved in the hypogeal environment than on the surface where the outcropping gypsum is more exposed to dissolution and recrystallization. The hypogeal geological survey, therefore, can be considered a powerful tool for integrating the surface and log data in order to enhance the reconstruction of the deformational history and to get a three-dimensional model of the bedrock in karst areas.  相似文献   

Erratum to: Central European Journal of Geosciences, volume 3, number 2     

János Kovács  Szabolcs Á. Fábián  Gábor Varga  Karoly Németh  Corina Risso  Francisco Nullo  Gabor Kereszturi  Titusz Bugya  Szabolcs Á. Fábián  Noémi L. Görcs  István P. Kovács  Bertalan Radvánszky  Gabriella Barta  Rudolf Musil  Alice Ghiselli  Marzio Merazzi  Andrea Strini  Roberto Margutti  Michele Mercuriali  Rauf Gardashov  Daria Gushchina  Boris Dewitte  Martin Michálek  Marián Putiš  Christoph A. Hauzenberger  Jindřich Šancer  Martin Štrejbar  Aneta Maleňáková  George Migiros  George D. Bathrellos  Hariklia D. Skilodimou  Theodoros Karamousalis 《Central European Journal of Geosciences》2011,3(2):229-229

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Addressing non-uniqueness in linearized multichannel surface wave inversion   总被引：1，自引：0，他引：1  

Michele Cercato 《Geophysical Prospecting》2009,57(1):27-47

The multichannel analysis of the surface waves method is based on the inversion of observed Rayleigh-wave phase-velocity dispersion curves to estimate the shear-wave velocity profile of the site under investigation. This inverse problem is nonlinear and it is often solved using 'local' or linearized inversion strategies. Among linearized inversion algorithms, least-squares methods are widely used in research and prevailing in commercial software; the main drawback of this class of methods is their limited capability to explore the model parameter space. The possibility for the estimated solution to be trapped in local minima of the objective function strongly depends on the degree of nonuniqueness of the problem, which can be reduced by an adequate model parameterization and/or imposing constraints on the solution.
In this article, a linearized algorithm based on inequality constraints is introduced for the inversion of observed dispersion curves; this provides a flexible way to insert a priori information as well as physical constraints into the inversion process. As linearized inversion methods are strongly dependent on the choice of the initial model and on the accuracy of partial derivative calculations, these factors are carefully reviewed. Attention is also focused on the appraisal of the inverted solution, using resolution analysis and uncertainty estimation together with a posteriori effective-velocity modelling. Efficiency and stability of the proposed approach are demonstrated using both synthetic and real data; in the latter case, cross-hole S-wave velocity measurements are blind-compared with the results of the inversion process.  相似文献   

Transient processes in Stromboli’s shallow basaltic system inferred from dolerite and magmatic breccia blocks erupted during the 5 April 2003 paroxysm     

Alberto?RenzulliEmail author  Stefano?Del?Moro  Michele?Menna  Patrizia?Landi  Marco?Piermattei 《Bulletin of Volcanology》2009,71(7):795-813

We describe the mineralogy, geochemistry, and mesomicrostructure of fresh subvolcanic blocks erupted during the 5 April 2003 paroxysm of Stromboli (Aeolian Islands, Italy). These blocks represent ∼50 vol.% of the total erupted ejecta and consist of fine- to medium-grained basaltic lithotypes ranging from relatively homogeneous dolerites to strongly or poorly welded magmatic breccias. The breccia components are represented by angular fragments of dolerites entrapped in a matrix of vesiculated (lava-like to scoriae) crystal-rich (CR) basalt. All of the studied blocks are cognates with the CR basalt of the normal Strombolian activity or lavas and they are often coated by a few-centimeter thick layer of crystal-poor (CP) basaltic pumice erupted during the paroxysm. We suggest that they result from the rapid increase of pressure and related subvolcanic rock failure that occurred shortly before the 5 April 2003 explosion, when the uppermost portion of the edifice inflated and suffered brecciation as the result of the sudden rise of the gas-rich CP basalt that triggered the eruption. Dolerites and magmatic matrix of the breccias show major and trace element compositions that match those of the CR basalts erupted during normal Strombolian activity and effusive events at Stromboli volcano. Dolerites consist of (a) phenocrysts normally found in the CR basalts and (b) late-stage magmatic minerals such as sanidine, An_60-28 plagioclase, Fe–Mn-rich olivines (Fo_68-48), phlogopite, apatite, and opaque mineral pairs (magnetite and ilmenite), most of which are never found both in lava flows and scoriae erupted during the persistent explosive activity that characterizes typical Strombolian behavior. Subvolcanic crystallization of the Stromboli CR magma, leading to slowly cooled equivalents of basalts, could result from transient drainage of the magma from the summit craters to lower levels. Fingering and engulfing of the material that collapsed from the summit crater floor into the shallow basaltic system during the late evening of 28 December 2002 coupled with the short break in the summit persistent explosions between December 2002 and March 2003 permitted the CR magma pockets to solidify as dolerites, which were confined to the uppermost portion of the system and thus not involved in the ongoing flank effusive activity. Crystal size distribution of the basaltic blocks and crystallization of the finer-grained (<0.1 mm) mafic minerals of the dolerites over a time interval of ∼100 days closely agrees with the above interpretation. Vesicle filling (miarolitic cavities) locally found in some dolerites, with minerals deposited as vapor-phase crystallization is a result of continuous gas percolation through the rocks of the uppermost portion of the volcanic system. Poorly welded magmatic breccias formed during syn-eruptive processes of 5 April 2003, when the paroxysm strongly shattered the shallow subvolcanic system and many dolerite fragments were entrapped in the CR magma. In contrast, the high degree of welding between the dolerite clasts and the CR basaltic matrix in the strongly welded magmatic breccias provides a snapshot of subvolcanic intrusions of the CR basalt into the dolerite when, after a 2-month break in activity, CR magmas started to rise again to the summit craters. Blocks similar to these subvolcanic ejecta of 5 April 2003 were also erupted during previous paroxysms (e.g., 1930) suggesting that changes in the usual Strombolian activity (e.g., short breaks in the persistent mild explosions and/or flank effusive activity) lead to transient crystallization of dolerites in the shallow plumbing system.  相似文献   

Spatial and diurnal distribution of invertebrate and fish fauna of a Zostera marina bed and nearby unvegetated sediments in Damariscotta River, Maine (USA)     

Johanna Mattila  Glen Chaplin  Michele R. Eilers  Kenneth L. Heck Jr.  Jonathan P. O'Neal  John F. Valentine 《Journal of Sea Research》1999,41(4):209

Fish, epibenthos and macroinfauna were collected in a Zostera marina bed and nearby unvegetated sediments in the estuary of the Damariscotta River, on the mid-coast of Maine. Samples of epibenthic fauna and fish were collected at low tides both during day and night, and samples of infauna at low tides during the day. The mean density of Zostera shoots in the study area was 335 m⁻². Abundance and species number of fish were greater at night than during the day and greater in eelgrass beds (Z. marina) than in unvegetated habitats. Daytime fish collections were dominated by Atlantic silversides (Medinia medinia), while juvenile winter flounder (Pseudopleuronectes americanus) dominated night collections. Also Zostera-associated epifaunal abundances and number of species were significantly higher at night than during the day. Mysis stenolepis, Idotea balthica and Littorina obtusata were dominant species in the epifauna samples. Of the total of 37 invertebrate species encountered, only five occurred both in the infaunal and epifaunal samples. Nineteen different taxa were collected from the benthic core samples. The most abundant invertebrate infaunal taxa were sipunculids, the polychaete Nereis virens, and oligochaetes. Infaunal invertebrate abundances and species diversity were significantly higher in eelgrass beds than in unvegetated sediments. The abundance and number of species of benthic invertebrates were also positively correlated to seagrass biomass. Community diversity values (H′) were relatively low but fit well in the general pattern of decreasing diversity towards northern latitudes.  相似文献   

Deformation history of the ophiolite sequence from the Balagne Nappe,northern Corsica: insights in the tectonic evolution of Alpine Corsica     

M. Marroni  L. Pandolfi 《Geological Journal》2003,38(1):67-83

In Alpine Corsica, the Jurassic ophiolites represent remnants of oceanic lithosphere belonging to the Ligure‐Piemontese Basin located between the Europe/Corsica and Adria continental margins. In the Balagne area, a Jurassic ophiolitic sequence topped by a Late Jurassic–Late Cretaceous sedimentary cover crops out at the top of the nappe pile. The whole ophiolitic succession is affected by polyphase deformation developed under very low‐grade orogenic metamorphic conditions. The original palaeogeographic location and the emplacement mechanisms for the Balagne ophiolites are still a matter of debate and different interpretations for its history have been proposed. The deformation features of the Balagne ophiolites are outlined in order to provide constraints on their history in the framework of the geodynamic evolution of Alpine Corsica. The deformation history reconstructed for the Balagne Nappe includes five different deformation phases, from D1 to D5. The D1 phase was connected with the latest Cretaceous/Palaeocene accretion into the accretionary wedge related to an east‐dipping subduction zone followed by a Late Eocene D2 phase related to emplacement onto the Europe/Corsica continental margin. The subsequent D3 phase was characterized by sinistral strike‐slip faults and related deformations of Late Eocene–Early Oligocene age. The D4 and D5 phases were developed during the Early Oligocene–Late Miocene extensional processes connected with the collapse of the Alpine belt. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Long‐term sediment yield from a small catchment in southern Brazil affected by land use and soil management changes          下载免费PDF全文

Jean P.G. Minella  Gustavo H. Merten  Claúdia A.P. Barros  Rafael Ramon  Alexandre Schlesner  Robin T. Clarke  Michele Moro  Leandro Dalbianco 《水文研究》2018,32(2):200-211

Sediments produced from eroding cultivated land can cause on‐site and off‐site effects that cause considerable economic and social impacts. Despite the importance of soil conservation practices (SCP) for the control of soil erosion and improvements in soil hydrological functions, limited information is available regarding the effects of SCP on sediment yield (SY) at the catchment scale. This study aimed to investigate the long‐term relationships between SY and land use, soil management, and rainfall in a small catchment. To determine the effects of anthropogenic and climatic factors on SY, rainfall, streamflow, and suspended sediment concentration were monitored at 10‐min intervals for 14 years (2002–2016), and the land use and soil management changes were surveyed annually. Using a statistical procedure to separate the SY effects of climate, land use, and soil management, we observed pronounced temporal effects of land use and soil management changes on SY. During the first 2 years (2002–2004), the land was predominantly cultivated with tobacco under a traditional tillage system (no cover crops and ploughed soil) using animal traction. In that period, the SY reached approximately 400 t·km^?2·year^?1. From 2005 to 2009, a soil conservation programme introduced conservation tillage and winter cover crops in the catchment area, which lowered the SY to 50 t·km^?2·year^?1. In the final period (2010–2016), the SCP were partially abandoned by farmers, and reforested areas increased, resulting in an SY of 150 t·km^?2·year^?1. This study also discusses the factors associated with the failure to continue using SCP, including structural support and farmer attitudes.  相似文献   

On the correction of spectra by a displacement reduction factor in direct displacement-based seismic design and assessment     

Gian Michele Calvi 《地震工程与结构动力学》2019,48(6):678-685

The application of some design and assessment approaches, such as the direct displacement-based design (DDBD) and the capacity spectrum methods, requires the modification of elastic design spectra by some displacement reduction factor, to account for the appropriate energy dissipation capacity of different structures. While several equations to correlate dissipation and hysteresis cycles are available, once the displacement reduction factor has been obtained, the correction of the spectra is operated reducing the displacement demand accordingly and conserving the period of vibration at each point. This procedure is here discussed and proved to be conceptually inappropriate, because the spectral acceleration rather than the period should be kept at each point. The application of this alternative procedure may result in increased shear strength demand in design and in larger required displacement capacity for the same level of strength in assessment, if all other factors are not modified. However, the calibration of the reduction factors applied in DDBD has been extensive, and the method has proved to be effective in predicting displacement demands consistent with those resulting from refined nonlinear time history analysis; therefore, a possible introduction of the proposed correction will require equally extensive studies and possibly compensating corrections in the calculation of the equivalent damping. On the contrary, an appropriate calibration of the factors to be used in the application of the “capacity spectrum” method is still being developed, and the consideration of a constant acceleration may facilitate the derivation of effective equations.  相似文献   

Evaluation of force-based and displacement-based out-of-plane seismic assessment methods for unreinforced masonry walls through refined model simulations     

Michele Godio  Katrin Beyer 《地震工程与结构动力学》2019,48(4):454-475

The performance of force-based and displacement-based seismic assessment methods for the life-safety limit state check of out-of-plane loaded unreinforced masonry walls is evaluated on the basis of refined numerical simulations. For this purpose, a discrete element model of a vertically spanning wall is built and validated against experimental results from static and dynamic test conditions. The model is then analysed for a large range of wall configurations. For each configuration, a static pushover analysis and a series of incremental dynamic analyses are run, the latter permitting to determine the capacity of the wall under dynamic loading. The accuracy of the assessment methods in predicting the acceleration at which the walls collapse is evaluated. It is found that the displacement-based method is more accurate, robust, and safe than the force-based method. The comparison also shows that for walls characterised by a relatively high ratio of axial load to Euler's critical load, both assessment methods lead to an overestimation of the wall capacity. As a remedy, a modification to the methods based on a recently developed mechanical model is put forward and tested. For the force-based method, it is additionally suggested to set for walls with relatively high overburden ratios the behaviour factor equal to 1. To ensure reproducibility of this study, all input and output files of the numerical simulations are made publicly available.  相似文献   

A bar signature and central disc in the gaseous and stellar velocity fields of NGC 5448     

Kambiz Fathi  Glenn van de Ven  Reynier F. Peletier  Eric Emsellem  Jesús Falcón-Barroso  Michele Cappellari  Tim de Zeeuw 《Monthly notices of the Royal Astronomical Society》2005,364(3):773-782

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