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41.
Emanuela De Beni Jan R. Wijbrans Stefano Branca Mauro Coltelli Gianluca Groppelli 《地学学报》2005,17(3):292-298
Recent geological studies performed at Etna allow reassessing the stratigraphic frame of the volcano where distinct evolutionary phases are defined. This stratigraphic reconstruction was chronologically constrained on the basis of a limited number of U–Th and K–Ar age determinations whose uncertainty margins are sometimes too wide. For this reason, we successfully adopted at Etna the 40Ar/39Ar technique that allowed obtaining more precise age determinations. The incremental heating technique also gives information on sample homogeneity, and potential problems of trapped argon. Five samples were collected from stratigraphically well-controlled volcanic units in order to chronologically define the transition between the fissure-type volcanism of the Timpe phase to the central volcanism of the Valle del Bove Centers. Isotopic ages with an uncertainty margin of 2–4% have been obtained emphasizing that this transition occurred (130–126 ka) without significant temporal hiatus. 相似文献
42.
Emanuela Bianchi Janetti Monica Riva Alberto Guadagnini 《Computational Geosciences》2016,20(3):555-565
We analyze three-phase flow of immiscible fluids taking place within an elementary capillary tube with circular cross-section under water- and oil-wet conditions. We account explicitly for momentum transfer between the moving phases, which leads to the phenomenon of viscous coupling, by imposing continuity of velocity and shear stress at fluid-fluid interfaces. The macroscopic flow model which describes the system at the Darcy scale includes three-phase effective relative permeabilities, K i j,r , accounting for the flux of the ith phase due to the presence of the jth phase. These effective parameters strongly depend on phase saturations, fluid viscosities, and wettability of the solid matrix. In the considered flow setting, K i j,r reduce to a set of nine scalar quantities, K i j,r . Our results show that K i j,r of the wetting phase is a function only of the fluid phase own saturation. Otherwise, K i j,r of the non-wetting phase depends on the saturation of all fluids in the system and on oil and water viscosities. Viscous coupling effects (encapsulated in K i j,r with i ≠ j) can be significantly relevant in both water- and oil-wet systems. Wettability conditions influence oil flow at a rate that increases linearly with viscosity ratio between oil and water phases. 相似文献
43.
M. Gabriella Carboni Luisa Bergamin Daniela Esu Emanuela Pisegna Cerone Vladimiro Verrubbi 《Quaternary Research》2010,74(2):265-128
Foraminifera and molluscs from the 90 m deep ENEA borehole (Versilian plain, central Italy) were studied for paleoenvironmental purposes. Palaeontological analyses, integrated with U/Th and radiocarbon data, helped to recognize late Quaternary sea-level changes and supplied results on tectonic mobility of the area. The study highlighted four sedimentary phases. The first phase consists of a shore environment attributed to MIS 7.1. A hiatus corresponding to MIS 6 is hypothesized at the top of this interval. Recognition of the paleo-shoreline of MIS 7.1 at − 72.8 m signifies a vertical displacement due to the extensional tectonics of the Apennine orogenesis. The second phase consists of a transgressive succession with evidence of warm temperatures, which was interpreted as part of the transgression leading to the MIS 5.5 highstand. The third phase includes sub-aerial and lacustrine deposits. Radiocarbon dates and palaeoecological reconstruction led us to attribute this interval to MIS 4, MIS 3 and MIS 2. The fourth phase begins with a lagoon environment attributable to Holocene sea-level rise and ends with marsh episodes, signifying the progradation of the alluvial plain. This reconstruction confirms the hypothesis of tectonic stability for the Versilian area during the Holocene. 相似文献
44.
Central Italy is an active tectonic area that has been recently studied by several regional mantle, Pn and SKS, studies which revealed the presence of a strong regional anisotropy. In this paper, we present the first petrophysical results on the only mantle xenoliths from Central Italy, which place new constraints on the upper mantle structures of this region. The Torre Alfina mantle xenoliths are very small in size, from few millimetres to about 1.5 cm. They are mainly dunites and harzburgites, with subordinate lherzolites and wehrlites. Since olivine and spinel are always present, they should have crystallised in the spinel-bearing lherzolite field. Their mineralogical composition is ol+spl±opx±cpx. Both olivines and pyroxenes are present as porphyroclasts and as neoblasts. The xenoliths show different degrees of recrystallization. Geothermobarometry on these xenoliths give a temperature range of 1040±40 °C and a pressure estimate of about 1.5 GPa, corresponding to 50 to 60 km depth. Previous seismic studies have estimated the Moho to be at 20 to 25 km in this region, hence the xenoliths come from a hot mantle, probably asthenospheric, below a lithosphere of about 25 to 40 km in thickness below the Moho. We measure the crystallographic preferred orientation (CPO) of olivines and pyroxenes using a SEM and the Electron Back Scattered Diffraction (EBSD) technique. The CPO shows all three axes of olivine are tightly clustered: [100] axis is typically more tightly clustered than [010] and [001] is the most widely distributed axis. The fabric strength expressed by the integral J index, varies from 4.5 to 25.9, and decreases with the degree of recrystallization. We use CPO data to calculate anisotropic seismic properties of the xenoliths. They are very homogenous and probably statistically representative of the mantle below the Torre Alfina area. Vp ranges from 8.4 to 9.1 km/s, Vs1 from 4.8 to 5.0 km/s. The seismic anisotropy is more variable; AVp ranges from 9.8% to 19.3% and AVs from 7.3% to 13.4%. The majority of the xenoliths display an orthorhombic seismic symmetry, but xenoliths with a transverse isotropic behaviour have also been observed.
We consider four geodynamic models for the source region of the xenoliths (extension, shear, upwelling, slab tilted), defined by different orientations of the structural reference frame, and we calculated for each model the variation of the seismic properties with temperature, pressure and volume fraction of orthopyroxene. After comparing this variation of calculated seismic parameters with seismic observations from the region, we form the hypothesis that the xenoliths come from either an extensional tectonic zone (lineation X and foliation plane XY horizontal) or transcurrent shear zone (lineation X horizontal and foliation plane XY vertical) and that the mantle beneath Torre Alfina is composed by 70% olivine and 30% orthopyroxene forming an anisotropic layer of about 160 or 110 km in thickness, respectively. 相似文献
45.
Paolo Riva Federico Perotti Emanuela Guidoboni Enzo Boschi 《Soil Dynamics and Earthquake Engineering》1998,17(7-8)
The existence of a valuable historical heritage of the Medieval age in Bologna has motivated a deeper study on the seismic behaviour of the Asinelli Tower, which, beyond being the town symbol, has a structural configuration prone to seismic damage. Accordingly, in the present paper, the seismicity of Bologna is reviewed and a synthesis of the damage observed in the urban area, based on an accurate historical research, is given, with the objective of evaluating the behavior of the Asinelli Tower within the framework of the effects localized in the municipality. An assessment of the tower's stability with respect to compatible seismic events, at least qualitatively, with the region seismicity is then carried out by means of a non-linear dynamic analysis on a simplified model. 相似文献
46.
Documentary Evidence on Climate in Sixteenth-Century Europe 总被引：2，自引：0，他引：2
47.
The 1631 Vesuvius eruption is one of its best known and most studied of its type. However, the historical approach performed within the framework of the Exploris project highlighted new evidence from previously unused or unknown historical sources. These consist of three treatises that were contemporary to the event; although written in Latin, they have been fully translated and analysed. To guarantee systematic use and open access to the large amount of information they contain, they have been provided as a small database. These treatises have provided new information on phenomena that preceded and accompanied the eruption of 1631, making possible the formation of a complex chronological profile, starting from around 6 months before the eruption. The anthropic impact is also outlined. The method applied has produced a chronology of “cold data”, which are not interpreted from the volcanological standpoint, but only derived directly from the analysed history and sequence of the texts. The analysis of the three treatises has not, however, solved all of the problems connected with the detailed knowledge of the event in 1631. Indeed, problems of two kinds persist: a) linguistic correspondence between the volcanological terms of today and those used in the texts; b) the lack of precision of the measures indicated. Here, the main results obtained from this analysis method are presented, along with a discussion of their limitations and some new perspectives. 相似文献
48.
49.
Francesco Panzera Sebastiano D’Amico Giuseppe Lombardo Emanuela Longo 《Journal of Seismology》2016,20(3):1001-1019
The Siracusa area, located in the southeastern coast of Sicily (Italy), is mainly characterized by the outcropping of a limestone formation. This lithotype, which is overlain by soft sediments such as sandy clays and detritus, can be considered as the local bedrock. Records of ambient noise, processed through spectral ratio techniques, were used to assess the dynamic properties of a sample survey of both reinforced concrete and masonry buildings. The results show that experimental periods of existing buildings are always lower than those proposed by the European seismic code. This disagreement could be related to the role played by stiff masonry infills, as well as the influence of adjacent buildings, especially in downtown Siracusa. Numerical modeling was also used to study the effect of local geology on the seismic site response of the Siracusa area. Seismic urban scenarios were simulated considering a moderate magnitude earthquake (December 13th, 1990) to assess the shaking level of the different outcropping formations. Spectral acceleration at different periods, peak ground acceleration, and velocity were obtained through a stochastic approach adopting an extended source model code. Seismic ground motion scenario highlighted that amplification mainly occurs in the sedimentary deposits that are widespread to the south of the study area as well as on some spot areas where coarse detritus and sandy clay outcrop. On the other hand, the level of shaking appears moderate in all zones with outcropping limestone and volcanics. 相似文献
50.
The relevant results of the study of more than 1700 Italian historical earthquakes from the year 1000 to 1982 are presented here. The research was carried out from 1983 to 1987 as part of a study promoted by ENEL (the National Electricity Board) for the seismic siting of nuclear power plants. A single coherent project has been developed, that involved 111 historical researchers who operated in 813 research centres in Italy and abroad. Problems such as the methods, research, analysis and interpretation of the numerous and various effects caused both by destructive and non-destructive earthquakes recorded in the historical sources, have been considered on a large scale for the first time. The earthquake records, collected in a data bank and interpreted according to a multi-disciplinary historical and seismological approach, have allowed the detailed reconstruction of the location and chronology of both individual and repeated events. This major research study has allowed us to evaluate the inexactness of the present Catalogue of Italian earthquakes in relation to the parameters of intensity, location and dating. From the synthesis of the results of the revision emerged sufficient information to value the reliability of the present Catalogue. TERRA Nova (1989) 1 , 151–162. 相似文献