Mathematical identification of diffuse and localized instabilities in fluid‐saturated sands     

Constance Mihalache  Giuseppe Buscarnera 《国际地质力学数值与分析法杂志》2014,38(2):111-141

The mathematical properties of diffuse and localized failure modes in fluid‐saturated sands are investigated. The granular medium is modeled as an elastoplastic solid, and a recently proposed set of scalar indices, here referred to as moduli of instability, is used to identify the onset of potential bifurcations of the incremental response. First, the analytical properties of these moduli are discussed, stressing their dependence on the kinematic constraints associated with the imposed deformation modes. Then, by using an elastoplastic model for sands, drained and undrained loading paths are simulated under axisymmetric, plane‐strain and simple shear conditions. For each deformation mode, the instability moduli are computed and monitored throughout the simulations, with the purpose of elucidating the consequences of changes in control conditions. In addition, it is illustrated that suitable linear transformations allow the same strategy to be used to perform drained or undrained shear band analyses and predict the interval of possible band inclinations. The final comparison against literature experiments on loose Hostun sand shows that the instability moduli are indicators of the loss of resistance against specific modes of deformation. As a result, they can be used to identify and explain a number of failure mechanisms that can be commonly observed in experiments. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

A Variable Slip Fault Model For the 1908 Messina Straits (Italy) Earthquake, By Inversion of Levelling Data   总被引：1，自引：0，他引：1  

Giuseppe De  Natale Folco Pingue 《Geophysical Journal International》1991,104(1):73-84

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The Campanian Ignimbrite (southern Italy) geochemical zoning: insight on the generation of a super-eruption from catastrophic differentiation and fast withdrawal   总被引：2，自引：2，他引：0  

Lucia Pappalardo  Luisa Ottolini  Giuseppe Mastrolorenzo 《Contributions to Mineralogy and Petrology》2008,156(1):1-26

More than ca 100 km³ of nearly homogeneous crystal-poor phonolite and ca 100 km³ of slightly zoned trachyte were erupted 39 ka during the Campanian Ignimbrite super eruption, the most powerful in the Neapolitan area. Partition coefficient calculations, equilibrium mineral assemblages, glass compositions and texture were used to reconstruct compositional, thermal and pressure gradients in the pre-eruptive reservoir as well as timing and mechanisms of evolution towards magma chamber overpressure and eruption. Our petrologic data indicate that a wide sill-like trachytic magma chamber was active under the Campanian Plain at 2.5 kbar before CI eruption. Thermal exchange between high liquidus (1199°C) trachytic sill and cool country rocks caused intense undercooling, driving a catastrophic and fast (10² years) in situ fractional crystallization and crustal assimilation that produced a water oversaturated phonolitic cap and an overpressure in the chamber that triggered the super eruption. This process culminated in an abrupt reservoir opening and in a fast single-step high decompression. Sanidine phenocrysts crystal size distributions reveal high differentiation rate, thus suggesting that such a sill-like magmatic system is capable of evolving in a very short time and erupting suddenly with only short-term warning.  相似文献   

New remains of Eremotherium laurillardi (Lund, 1842) (Megatheriidae, Xenarthra) from the coastal region of Ecuador     

Giuseppe Tito   《Journal of South American Earth Sciences》2008,26(4):424-434

New remains of Eremotherium were recovered from the Pacific coast of Ecuador’s Manabi province. The Machalilla fossiliferous locality records the northernmost presence of Eremotherium along the Pacific coast of South America. Most of the fossil remains belong to the same individual, mainly its posterior half, but other individuals are represented. Among the better-preserved specimens are skull fragments, most of the hind limb bones and a number of trunk and caudal centra. These remains were compared with samples collected during the 20th century along the southern coastal regions of Ecuador and northern Peru. Many characters of the long bones and tarsals testify to a possibly different lineage despite the closeness of other Eremotherium populations. Some metric and morphological aspects suggest a different space-temporal southern Caribbean provenance. Other Eremotherium specimens, coming from other Ecuadorian localities, were studied and compared with classic Eremotherium samples. Interesting morpho-functional aspects are pointed out with regard to the tail and its importance in the bipedal stance.  相似文献   

The role of spatial effects in the empirical analysis of regional concentration   总被引：13，自引：0，他引：13  

Giuseppe Arbia 《Journal of Geographical Systems》2001,3(3):271-281

 Economists have recently devoted an increasing attention to the issue of spatial concentration of economic activities. However, surprisingly enough, most of the empirical work is still based on the computation of very basic statistical measures in which the geographical characteristics of data play no role. By making use of a series of empirical examples we show that spatial concentration consists of two different features that are rarely kept as separate in the statistical analysis: an a-spatial concept of variability which is invariant to permutations, and the concept of polarization that refers to the geographical position of observations. Received: 8 August 2000 / Accepted: 20 June 2001  相似文献   

The structure of the Campanian Plain and the activity of the Neapolitan volcanoes (Italy)     

Roberto Scandone  Francesca Bellucci  Lucio Lirer  Giuseppe Rolandi 《Journal of Volcanology and Geothermal Research》1991,48(1-2)

The central Campanian Plain is dominated by the structural depression of Acerra whose origin is tectonic, but may have been enlarged and further depressed after the eruption of the Campanian Ignimbrite (42-25 ka). The deposits of the Campanian Ignimbrite are possibly the results of multiple eruptions with huge pyroclastic deposits that covered all the Campanian Plain.The more recent activity of Vesuvius, Campi Flegrei and Procida occurred on the borders of Acerra depression and resulted from a reactivation of regional faults after the Campanian Ignimbrite cycle. The activity of Vesuvius produced the building of a stratovolcano mostly by effusive and plinian explosive eruptions. The Campi Flegrei area, on the contrary, was dominated by the eruption of the Neapolitan Yellow Tuff at 12 ka that produced a caldera collapse of the Gulf of Pozzuoli. The caldera formation controlled the emplacement of the recent activity of Campi Flegrei and the new volcanoes were formed only within the caldera or along its rim.  相似文献   

Setting-up local “mapping geoids” with the aid of GPS/LEV traverses. Application to the geoids of Sardinia and Calabria     

Giuseppe Birardi  Domenico Santarsiero  Donato Tufillaro  Luciano Surace 《Journal of Geodesy》1995,70(1-2):98-109

The problem of fitting a pre-existing geoid on local GPS/LEV points is first taken into account, a possible way for its solution is proposed, based on techniques similar to the aerophotogrammetric absolute orientation.This approach is then used to compute themapping geoids of Sardinia and Calabria i.e. geoids with decimetric accuracy, needed for the heigthing of large scale maps. The pre-existing geoids EAGGI by Brennecke et al. (1983), and EGG2 by Denker et al (1993) are utilized, fitted on points of GPS/LEV traverses.The complete input-output data, the contour maps of both geoids, and a substantial checking on some Calabrian GPS/TRIG points of the entreprise IGM.95 are finally reported.  相似文献   

Trace elements in the shallow ground water of The Netherlands. A geochemical and statistical interpretation of the national monitoring network data     

Giuseppe Frapporti  Simon P. Vriend  Pauline F. M. Van Gaans 《Aquatic Geochemistry》1996,2(1):51-80

Concentration levels of the trace elements Al, As, B, Ba, Be, Cd, Co, Cr, Cu, Li, Mo, Ni, Pb, Sr, V, Y, and Zn in the shallow Dutch ground water were studied. Data were extracted from the data base of the Dutch National Ground Water Quality Monitoring Network, a network set up to monitor the diffuse contamination. The network contains over 350 sites at a low density of about 1 per 100 km². The sites are sampled once a year at two depths (approx. 10 and 25 m below surface). A two-step multivariate statistical approach was used, in which the major element chemistry was used to define water types. Within each water type, trace element behavior could be coupled to distinct geochemical processes: dilution, acidification and weathering, carbonate dissolution, oxidation/reduction, and ion exchange. In recently infiltrated acid rain water in low buffering capacity sands, the anthropogenic influence indirectly caused mobilization of Al (median 430 g/l), Cd (0.6 g/l), Co (14 g/l), Cu (2.7 g/l), Ni (16 g/l), Y (11 g/l), and Zn (50 mg/l). In carbonate bearing sediments the acidification is neutralized, and the mentioned trace elements remain immobile. Arsenic and Cr have higher concentrations levels in ground waters with a slightly reducing character and are possibly governed by the dissolution of iron-manganese hydroxides. Boron, Li, and Sr have high concentrations (respectively 875, 80, 2700 g/l) in the water type related to a seawater source. Strontium is related to carbonate dissolution in all other water types (medians ranging from 100 to 1000 g/l). Barium shows a complex behaviour. It is concluded that the high Al, Cd, Co, Cr, Ni, and Zn concentrations are anthropogenically induced. High Ba and Cr concentrations are inferred to be due to natural processes.  相似文献   

A microtremor survey to define the subsoil structure in a mud volcanoes area: the case study of Salinelle (Mt. Etna,Italy)     

Francesco Panzera  Simona Sicali  Giuseppe Lombardo  Sebastiano Imposa  Stefano Gresta  Sebastiano D’Amico 《Environmental Earth Sciences》2016,75(15):1140

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Petrology of parasitic and eccentric cones on the flanks and base of Somma-Vesuvius     

Ray Macdonald  Bogusław Bagiński  Giuseppe Rolandi  Benedetto De Vivo  Anna Kopczyńska 《Mineralogy and Petrology》2016,110(1):65-85

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