1,721,076 research outputs found
Pattern of seismic deformation in the Western Mediterranean
No full textThe seismic deformation of the Western Mediterranean was studied with the aim of defining the strain pattern that characterizes the Africa-Eurasia plate boundary in this area. Within different sections along the boundary the cumulative moment tensor was computed over 90 years of seismological data. The results were compared with NUVELlA plate motion model and geodetic data. A stable agreement was found along Northern Africa to Sicily, where only Africa and Eurasia plates are involved. In this zone it is evident that changes in the strike of the boundary correspond to variations in the prevailing geometry of deformation, tectonic features and in the percentage of seismic with respect to total expected deformation. The geometry of deformation of periadriatic sections (Central to Southern Apennines, Eastern Alps and the Eastern Adriatic area) agrees well with VLBI measurements and with regional geological features. Seismicity seems to account for low rates, from 3% to 31%, of total expected deformation. Only in the Sicily Strait, characterized by extensional to strike slip deformation, does the ratio reach a higher value (79%). If the amount of deformation deduced from seismicity seems low, because 90 years are probably not representative of the recurrence seismic cycle of the Western Mediterranean, the strain pattern we obtain from cumulative moment tensors is more representative of the kinematics of this area than global plate motion models and better identifies lower scale geodynamic features.JCR Journalope
Longitudinal deformation of a lava flow: the influence of Bingham rheology
No full textThe behaviour of a lava flow is reproduced by a two-dimensional model of a Bingham liquid flowing down a slope. The liquid is described by two parameters, viscosity and yield stress, both strongly temperature dependent. Assuming liquidus temperature at the eruption vent, the temperature decrease due to the heat loss by radiation produces changes in the rheological parameters and, consequently, in velocity, strain and strain rate along the flow. Velocity, compressive strain, strain rate and stress along the flow direction are computed as functions of the distance from the vent and of time, for different kinds of lava flows (basic and acidic) and are compared with corresponding results for a Newtonian liquid. The model shows that, in connection with the pronounced velocity decrease occurring at a certain distance from the vent, the compressive strain, strain rate and stress also show a strong variation. A greater compressive strain is, in fact, induced in a Bingham flow cooling by radiation, than in a Newtonian flow. This behaviour may explain the presence of folds which are commonly observed at the surface of cooled lava flows
Longitudinal deformation of a lava flow: the influence of Bingham rheology
No full textThe behaviour of a lava flow is reproduced by a two-dimensional model of a Bingham liquid flowing down a slope. The liquid is described by two parameters, viscosity and yield stress, both strongly temperature dependent. Assuming liquidus temperature at the eruption vent, the temperature decrease due to the heat loss by radiation produces changes in the rheological parameters and, consequently, in velocity, strain and strain rate along the flow. Velocity, compressive strain, strain rate and stress along the flow direction are computed as functions of the distance from the vent and of time, for different kinds of lava flows (basic and acidic) and are compared with corresponding results for a Newtonian liquid. The model shows that, in connection with the pronounced velocity decrease occurring at a certain distance from the vent, the compressive strain, strain rate and stress also show a strong variation. A greater compressive strain is, in fact, induced in a Bingham flow cooling by radiation, than in a Newtonian flow. This behaviour may explain the presence of folds which are commonly observed at the surface of cooled lava flows
Depth of the brittle-ductile transition in a transcurrent boundary zone
No full textA model is proposed which describes the boundary zone between two transcurrent plates as a viscoelastic body, with rheological properties changing with depth. In this model, the brittle-ductile transition is defined as the depth at which the time derivative of shear stress changes from positive to negative values. Variations of this depth are studied as functions of geothermal gradient, rheological parameters and strain rate, using a "power law" rheology with exponent ranging from 1 to 4. Stress relaxation in the ductile zone is controlled by a local characteristic time, which depends on petrology, temperature and, in the case of non-Newtonian rheology, on strain rate. The composition and the hydration degree of crustal rocks may also sensibly influence the depth of the brittle-ductile transition. The model predictions are compared with observations regarding the San Andreas, Imperial Valley and North Anatolian Faults: it is found that values of n from 1 to 3 are more appropriate to reproduce the transition depth inferred by the seismicity distribution
European-mediterranean regional centroid moment tensor catalog: Solutions for years 2003 and 2004
No full textMonitoraggio di aree ad elevata instabilità e di aree urbane con metodologie integrate di rilevamento
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Seismic strain and stress field studies in Italy before and after the Umbria-Marche seismic sequence: a review
No full textThe seismic sequence that hit Umbria and Marche during 1997 and 1998 was particularly significant because it dramatically marked the evolution of analysis tools and the development of our geophysical knowledge of the region. Since September 1997, we have had a growing, coherent catalogue of source moment tensors that provides reliable information on earthquake sources in Italy and the surrounding regions. Together with borehole and other tectonic data, this has conspicuously improved our knowledge of the regional strain and stress fields. The main impact of these new data that include local information consists of the possibility to change the scale of the regional geodynamic frame. The simple description of extension tectonics that dominate the Apennines belt has evolved into the present-day maps of the strain and stress fields, where the active tectonics involve compression in the eastern Alps, extension and compression fronts in the northern Apennines, extension and strike-slip structures in the southern Apennines, and a compressional front along the southern Tyrrhenian Sea. This recent geodynamic evolution and the present-day seismotectonic sketch of the Italian peninsula are here described on the basis of the recognition of these tectonic features.Published319-3303.2. Tettonica attivaJCR Journalope
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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