Centrifuge models simulating magma emplacement during oblique rifting   总被引：1，自引：0，他引：1  

Giacomo Corti  Marco Bonini  Fabrizio Innocenti  Piero Manetti  Genene Mulugeta 《Journal of Geodynamics》2001,31(5)

A series of centrifuge analogue experiments have been performed to model the mechanics of continental oblique extension (in the range of 0° to 60°) in the presence of underplated magma at the base of the continental crust. The experiments reproduced the main characteristics of oblique rifting, such as (1) en-echelon arrangement of structures, (2) mean fault trends oblique to the extension vector, (3) strain partitioning between different sets of faults and (4) fault dips higher than in purely normal faults (e.g. Tron, V., Brun, J.-P., 1991. Experiments on oblique rifting in brittle-ductile systems. Tectonophysics 188, 71–84). The model results show that the pattern of deformation is strongly controlled by the angle of obliquity (α), which determines the ratio between the shearing and stretching components of movement. For α35°, the deformation is partitioned between oblique-slip and normal faults, whereas for α45° a strain partitioning arises between oblique-slip and strike-slip faults. The experimental results show that for α35°, there is a strong coupling between deformation and the underplated magma: the presence of magma determines a strain localisation and a reduced strain partitioning; deformation, in turn, focuses magma emplacement. Magmatic chambers form in the core of lower crust domes with an oblique trend to the initial magma reservoir and, in some cases, an en-echelon arrangement. Typically, intrusions show an elongated shape with a high length/width ratio. In nature, this pattern is expected to result in magmatic and volcanic belts oblique to the rift axis and arranged en-echelon, in agreement with some selected natural examples of continental rifts (i.e. Main Ethiopian Rift) and oceanic ridges (i.e. Mohns and Reykjanes Ridges).  相似文献   

Adaptive wavelet‐based finite‐difference modelling of SH‐wave propagation     

Stéphane Operto  Jean Virieux  Bernhard Hustedt  Fabrizio Malfanti 《Geophysical Journal International》2002,148(3):476-498

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Persisting effects of the Colfiorito (central Italy) Pleistocene paleo-landslide in the planning of land use: Upper Palaeolithic and proto-historical coexistence and Antique-Modern modifications     

F. Galadini  L. Colini  B. Giaccio  P. Messina  S. Salvi  A. Sposato 《Environmental Geology》2003,43(6):621-634

A huge late-Quaternary landslide (about 2᎒⁶ m³) dammed the Colfiorito basin in central Italy. This landslide was responsible for the formation of the present saddle, which divides the basin from the Chienti river valley. Landslide damming caused persisting lacustrine conditions during the Late Pleistocene-Holocene. High-standing lacustrine episodes are evidenced by two terraces located close to the top of the landslide dam, one of which can be related to the Last Glacial Maximum (LGM). During this period, the landslide dam was probably overtopped by the imponded lake. Before and during the LGM, the area of the landslide dam was affected by alluvial deposition. The landslide-induced lacustrine environment has played a key role in the history of land use at Colfiorito. The presence of water close to a strategic area located at the divide between the Adriatic and Tyrrhenian regions favored its frequentation and settlement during the Upper Palaeolithic (in particular Aurignacian-Early Gravettian), as shown by the numerous archaeological remains contained in the alluvial deposits close to the landslide accumulation. During the Iron Age, the lake represented a unique source of sustenance, as indicated by the presence of peri-lacustrine settlements. In contrast, the land use drastically changed during antiquity with the Roman domination of the region. The necessity to cultivate new lands and particularly the problem of providing a food supply for Rome are the causes of the drainage of the Colfiorito lake by means of a tunnel excavated through the landslide dam. Based on radiocarbon dating, the operation of the Roman tunnel ended during the 5th-7th centuries A.D. (dates related to the deposits filling the tunnel), but the continuation of agricultural vocations in the area did not fade, and a new tunnel, which operated until 2000, was built during the 15th century. Because of the damaged conditions of the 15th century hydraulic works, a third tunnel was built (between 1998 and 2000), which permits the drainage of the Colfiorito area and the continuation of the agricultural activities.  相似文献   

Fractal distribution of particle size in carbonate cataclastic rocks from the core of a regional strike-slip fault zone   总被引：2，自引：0，他引：2  

Andrea Billi  Fabrizio Storti 《Tectonophysics》2004,384(1-4):115-128

We present particle size data from 31 samples of carbonate cataclastic rocks collected across the 26 m thick fault core of the Mattinata Fault in the foreland of the Southern Apennines, Italy. Particle size distributions of incoherent samples were determined by a sieving-and-weighting technique. The number of weight-equivalent spherical particles by size is well fitted by a power-law function on a log–log space. Fractal dimensions (D) of particle size distributions are in the 2.091–2.932 range and cluster around the value of 2.5. High D-values pertain to gouge in shear bands reworking the bulk cataclastic rocks of the fault core. Low D-values characterise immature cataclastic breccias. Intermediate D-values are typical of the bulk fault core. Analysis of the ratio between corresponding equivalent particle numbers from differently evolved cataclastic rocks indicates that the development of particle size distributions with D>2.6–2.7 occurred by a preferential relative increase of fine particles rather than a selective decrement of coarse particles. This preferentially occurred in shear bands where intense comminution enhanced by slip localisation progressed by rolling of coarse particles whose consequent smoothing produced a large number of fine particles. Our data suggest that during the progression of cataclasis, the fragmentation mode changed from the Allègre et al.'s [Nature 297 (1982) 47] “pillar of strength” mechanism in the early evolutionary stages, to the Sammis et al.'s [Pure and Applied Geophysics 125 (1987) 777] “constrained comminution” mechanism in the subsequent stages of cataclasis. Eventually, localised shear bands developed mainly by abrasion of coarse particles.  相似文献   

Tectono-stratigraphic modelling of the North Sicily continental margin (southern Tyrrhenian Sea)     

Fabrizio Pepe  Giovanni Bertotti  Sierd Cloetingh 《Tectonophysics》2004,384(1-4):257-273

A two-dimensional numerical modelling that simulate the kinematic and thermal response of the lithosphere to thinning was used for the quantitative reconstruction of the late Neogene to Recent times tectonic and stratigraphic evolution of the North Sicily continental margin (southern Tyrrhenian Sea). The numerical study of the evolution of the North Sicily margin builds on the crustal image and kinematic interpretation of the margin obtained by Pepe et al. [Tectonics 19 (2000) 241] on the basis of seismic data and gravity modelling. Tectonic modeling indicate that different segments of the margin were undergoing different vertical movements, which are mainly expression of the rifting and thinning of the lithosphere occurred during tectonic evolution of the southern Tyrrhenian Sea. A prediction of the pre-rift basement topography and the Moho along the margin converges to a value of 6.5 km for the depth of necking and a temperature-dependent EET (500° isotherm). The model fails to reproduce the morphology of the Solunto High confirming its non-extensional origin. A polyphase evolution is required to reproduce the observed syn- and post-rift stratigraphy. During the first rifting stage (between 9 and 5 Ma), crustal thinning factors reach maximum values of 1.27 in the Cefalù basin. A similar value is predicted for the subcrustal thinning around 60 km NNE of the profile margin. Crustal thinning factors increase during the second rifting stage (from 4 to 2 Ma) and reach values of 2 and up to 3.5 in the Cefalù basin and in the continent–oceanic transition zone, respectively. Similarly, subcrustal lithospheric thinning factors reach values up to 2.5 in the distal sector of the margin. An uplift of more than 100 m is predicted for the North Sicily shelf and surrounding onshore areas during the post-rift stage. The evolution of thermal structure with time is very sensitive to the partial thinning factors describing the evolution of the thinning itself during time. The lithosphere preserved part of its strength during extension. The effective elastic thickness (EET) along the margin through time is 24 km at the onset of rifting and reaches values less to 8 km during the second rifting stage in the northeastern end of the margin.  相似文献   

The unlikely independence of Northern Italy     

Fabrizio Eva 《GeoJournal》1997,43(1):61-75

The past fifty years have seen several elements and factors leading to the current homogenization of Italian society: the internal migration from South to North, the development of a more and more industrial and affluent society, the increase of links with Europe/World culture and economy. Nevertheless in the last decade in Northern Italy emerged the political phenomenon of autonomist parties, in particular the most successful of them: the Lega Nord. This success happened in parallel with the loss of power by traditional government parties, also as a consequence of the trial against corruption held in Milan at the beginning of the '90. Italian politics is in turmoil and it is impossible to forecast the duration or even its end. The problem is to determine the most significant elements, and which factors have the greatest effect on the current reality, also to be able to venture a prediction regarding trends. The paper suggests some ethno-nationalism evaluation criteria, useful to assess the more or less successful geopolitical dynamics where there are separatist claims. According with those criteria the Northern Italian political situation has been briefly described and evaluated, with particular attention to electoral results of the Lega Nord party. These results show a well defined geographical distribution and hence the minority condition in the North of the separatist supporters. The actual political debate in Italy has the aim to change some parts of the Constitution in the sense of federalism; it can be a sufficient reply to secessionist claims and it can make the independence of Northern Italy unlikely.  相似文献   

Eruptive history and petrologic evolution of the Albano multiple maar (Alban Hills, Central Italy)     

Carmela Freda  Mario Gaeta  Daniel B. Karner  Fabrizio Marra  Paul R. Renne  Jacopo Taddeucci  Piergiorgio Scarlato  John N. Christensen  Luigi Dallai 《Bulletin of Volcanology》2006,69(1):115-115

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Using GB-SAR technique to monitor slow moving landslide   总被引：3，自引：0，他引：3  

Linhsia Noferini  Massimiliano Pieraccini  Daniele Mecatti  Giovanni Macaluso  Carlo Atzeni  Matteo Mantovani  Gianluca Marcato  Alessandro Pasuto  Sandro Silvano  Fabrizio Tagliavini 《Engineering Geology》2007,95(3-4):88-98

A Ground-Based SAR (GB-SAR) interferometer was employed to measure the surface displacements of a landslide occurring in the Carnian Alps, north-eastern Italy, which has affected a national road and seriously damaged a road tunnel still under construction. Moreover, since the landslide is located on the left bank of the Tagliamento River Valley, it is feared that this mass movement might dam the river, creating a basin that would increase natural hazard for the valley inhabitants. The data collected from December 2002 to July 2005 by a conventional monitoring system, consisting of a GPS network and boreholes equipped with inclinometric tubes, showed that the landslide was moving at a quasi-constant rate of about 3 cm per year. Due to the slow deformation rate of the landslide, a recently developed GB-SAR technique based on the analysis of a restricted ensemble of coherent points was used. Two surveys, each lasting two days, were planned in December 2004 and July 2005, in order to map and measure the surface displacements that occurred over time. The results from the radar were compared with the ones derived from the GPS monitoring network. An agreement was achieved among the data collected, showing the capability of the GB-SAR technique to measure displacements even within a time span of several months between the surveys.  相似文献   

Minerals at high pressure. Mechanics of compression from quantum mechanical calculations in a case study: the beryl (Al<Subscript>4</Subscript>Be<Subscript>6</Subscript>Si<Subscript>12</Subscript>O<Subscript>36</Subscript>)     

Mauro Prencipe  Fabrizio Nestola 《Physics and Chemistry of Minerals》2007,34(1):37-52

The Bader topological analysis has been applied to ab initio computed electron densities of beryl, in order to clarify its mechanism of compression. Full structural optimization and total energy (E) calculations were performed at different cell volumes (V _c). The pressure at each volume and the equation of state were estimated from the first and second derivatives of the resultant E(V _c) curve. The total (negative) potential energy of the crystal, sum of both attractive and repulsive electrostatic terms, was found to systematically decrease (i.e., it moved to more negative values) up to the highest pressure considered (28.4 GPa), indicating that interelectronic and internuclear repulsions are not the only terms controlling the compressibility, at least in the pressure range investigated. Electronic kinetic energy increases as the cell volume is reduced, leading to a parallel increase of the total energy. Both structure at equilibrium and compressibility are therefore due to the balance between the opposing kinetic and potential energy terms. The Bader theory has been used to identify the topological atoms within the structure and to calculate their properties, with particular attention to the forces driving the structural relaxation at high pressure. On a qualitative basis, the obtained results are expected to be transferable to the discussion of compressibility of other mineral phases.  相似文献   

Recharge estimation from discrete water-table datasets in a coastal shallow aquifer in a humid subtropical climate     

Fabrizio Rama  Konrad Miotlinski  Davide Franco  Henry X. Corseuil 《Hydrogeology Journal》2018,26(6):1887-1902

A time-series approach to the estimation of recharge rate in unconfined aquifers of highly variable water level is proposed. The approach, which is based on the water-table fluctuation method (WTF), utilizes discrete water-level measurements. Other similar techniques require continuous measurements, which makes them impossible to apply in cases where no data from automatic loggers are available. The procedure is deployed at the Ressacada Farm site, southern Brazil, on a coastal shallow aquifer located in a humid subtropical climate where diurnal water-level variations of up to 1 m can follow a precipitation event. The effect of tidal fluctuations on the groundwater levels is analyzed using a harmonic component builder, while a time-variable drainage term is evaluated through an independent analysis and included in the assessment. The estimated recharge values are compared with those obtained from the continuous measurements showing a good agreement with the approaches for discrete dataset intervals of up to 15 days. Subsequently, the estimated recharge rates are incorporated into a transient groundwater-flow model and the water levels are compared showing a good match. Henceforth, the approach extends the applicability of WTF to noncontinuous water-level datasets in groundwater recharge studies.  相似文献