1,722,217 research outputs found
Rheological behaviour in continental and oceanic subduction: Inferences for the seismotectonics of the Aegean region
No full textWe reconstructed several rheological transects across the Aegean Region, comparing the behaviour in collisional versus subducting settings. We interpolated closely spaced 1D strength envelopes, realized through a dedicated MATLAB script, for determining the shallow lithospheric distribution of brittle and ductile layers. We mainly used literature data and geodynamic considerations to fix the parameters for the rheological modelling and took particular care in reproducing reliable thermal models. The results of the mechanical-rheological model highlighted the following features and differences between the northern continental collision and the southern oceanic subduction settings: i) a slightly shallower brittle-ductile transition (BDT) in the western sectors of the northern transects (~30–33 km) with respect to the southern ones (~40 km); ii) on the contrary, in the central-eastern sectors of the investigated area, corresponding to an extensional tectonic regime, the northern transects have a relatively deeper BDT (about 20–25 km) compared with the southern ones (about 15 km); iii) the occurrence of a thick, deeper brittle layer below the shallowest BDT, in the central-eastern sectors of the northern transects. We suggest that such regional differences are mainly related and attributable to the surface heat flow distribution (which directly affects the geothermal gradient) and to the tectonic and geodynamic context. The results of the rheological modelling in terms of depth extent of the brittle layer(s) have been compared with the depth distribution of available relocated seismicity, showing good agreement with the rheological layering proposed here. Finally, the depth of the shallowest BDT along the transects has been adopted as a constraint for the seismogenic layer thickness. Such information has been used to improve the seismotectonic characterization of selected crustal seismogenic sources crossing the transects, by estimating their maximum potential magnitudes on the basis of their geometrical features and consistency with the rheological layering
Sensitivity analysis for crustal rheological profiles: Examples from the Aegean region
No full textWe tested the validity of rheological profiles and their sensitivity to variations in the input parameters, with particular emphasis on the resulting BDT (brittle-ductile transition) depth and corresponding strength and temperature. For this purpose, we selected two test-sites from the Aegean Region, one in an extensional tectonic setting and the other in a strike-slip regime, and carefully realized the corresponding “reference” rheological profiles based on literature data and specific geological constraints. The reference envelopes have been then compared with a set of different profiles realized by varying the input parameters of the constitutive equations of the brittle and ductile behaviours within reasonable ranges. Firstly, tests were performed by changing the value of only one input parameter per time, with the aim of quantifying and comparing its influence on the BDT properties. The parameters exerting the greatest control are the activation energy, the power-law exponent and the surface heat flow (through its influence on the geothermal gradient), for the creep behaviour. As regards the brittle behaviour parameters, the friction coefficient and the pore fluid pressure could play a significant role especially in determining the maximum strength. In a second phase, we simultaneously varied all the input parameters in order to consider the possible synergistic effects on the resulting rheological profiles and to verify the likelihood and consistency of the reference models. For the statistical approach, one hundred thousand random combinations of the analysed parameters have been generated. The particular care spent on selecting the range of values of each parameter is reflected in the results of the statistical analyses, which show a good agreement with the reference profiles and allow estimating the overall uncertainties. Finally, the obtained strength envelopes have been compared with the accurately relocated depth distribution of recent seismic sequences that affected the two test areas. In both cases, the depth corresponding to the 95% of the total released energy nicely fits the BDT depth obtained from the rheological modelling, therefore confirming that this parameter could represent a reasonable and reliable approximation of the seismogenic layer thickness
Inference of a seismic gap from geological data: Thessaly ( Central Greece) as a case study
No full textAs a result of neotectonic, morphotectonic and seismotectonic research it is now possible to draw detailed maps of the major active faults affecting Thessaly, a large region of continental Greece. For many of these faults, where specific studies have been carried out, the degree of fault activity (i.e. the long-term slip-rate) has been also assigned ranging from 0.05 to 4 mm/yr-l. In the present work, the main morphotectonic features and seismotectonic characteristics of the more important faults are recalled from previous works, while the recent tectonic activity is compared with the seismic activity of the area. The occuuence of both large (M ?x2264; 6.0) and moderate (M ?x2265; 6.0) earthquakes during the present century is concentrated in the southern sector. Earthquakes have been virtually absent in the northern part of the region during the same period. In contrast, according to geological and geomorphological criteria, the recent (Late Quaternary) tectonic evolution of the region and the overall extensional rate do not seem to djffer significantly in the two sectors. Although palaeosejsmological trenches, geodetic surveying and the record of the microseismic activity may enhance our knowledge of this problem, on the basis of available geological (structural and morphological) data, it is likely that the northern sector of Thessaly represents a large seismic gap. The implications on seismic hazard in one of the more populated regions of Greece are also discussed.JCR Journalope
Seismological data versus rheological modelling: Comparisons across the Aegean Region for improving the seismic hazard assessment
No full textCompared analyses of the seismicity cutoff depth and the corresponding BDT (brittle-ductile transition) depth obtained from rheological modelling have been performed for numerous test sites all over the Aegean Region. The major goal of this research is to determine whether the rheological transition could be effectively correlated to the seismological one, so that both information can independently contribute in determining the seismogenic layer thickness and hence in constraining the maximum width of active faults affecting a region. As concerns the seismological data, only relocated events have been considered for the purpose of this paper, included either in seismic sequences associated with a mainshock, or in datasets of background seismicity. In the same areas, we carried out rheological modelling for reconstructing the local strength envelope, focusing our attention on the BDT depth. The systematic comparison at the investigated sites indicates that 90% of the relocated seismicity always occurs within the corresponding rheological transition. Moreover, for the datasets also providing magnitudes, 99% of the total seismic scalar moment is always released above the BDT depth. Such results are verified for different tectonic regimes and geological settings, both extensional, transcurrent and compressional. The achieved results confirm that the BDT depth based on accurate strength envelopes could be considered a reliable indicator for the thickness of the seismogenic layer, thus contributing to constrain the maximum widths for active faults affecting those regions. Based on these constraints, we also applied some empirical relationships to estimate the possible maximum magnitude for seismogenic sources in correspondence of the tested sites, thus potentially improving our seismic hazard assessment analyses for these areas
Environmental and energetic implications of the geothermal anomalies in the Eastern Po Plan
No full textThe present research is devoted to contributing on the characterization of the low-to-medium enthalpy geothermal resources existing in the broader Ferrara-Modena territory, Northern Italy. To achieve the goal, first, we analysed temperature data in selected deep boreholes to estimate the local thermophysical parameters of the underground. In order to discriminate the influence of the circulation fluids and then estimate the real temperature values of the surrounding rocks, we applied different methodological approaches. Secondly, different deep seismic reflection profiles for hydrocarbon exploration were analysed to evaluate the main lithological formation and tectonic assessment. Thirdly, we elaborated hydrochemical data obtained from borehole and temperature logs measurement to estimate the influence of the deep geothermal fluids on the shallow aquifer systems. Finally, the integrated analysis of all data allowed to infer both the horizontal and vertical temperature distributions, which are clearly strongly affected by the geological, hydrogeological and tectonic evolution of the eastern sector of the Po Plain, and especially to recognize the area with a highest geothermal potential within the region
The active Nea Anchialos Fault System (Central Greece): comparison of geological, morphotectonic, archaeological and seismological data
No full textThe Nea Anchialos Fault System has been studied integrating geological, morphological, structural, archaeological and seismic data. This fault system forms the northern boundary of the Almyros Basin which is one of the Neogene-Quaternary tectonic basins of Thessaly. Specific structural and geomorphological mapping were carried out and fault-slip data analysis allowed the Late Quaternary palaeo-stress field to be estimated. The resulting N-S trending purely extensional regime is consistent with the direction of the T-axes computed from the focal mechanisms of the summer 1980, Volos seismic sequence and the April 30, 1985 Almyros earthquake. A minor set of structural data indicates a WNW-ESE extension which has been interpreted as due to a local and second order stress field occurring during the N-S regional extension. Furthermore, new archaeological data, discovered by the author, have improved morphology and tectonics of the area also allowing a tentative estimate of the historic (III-IV century AD. to Present) fault slip rate. Several topographic profiles across the major E- W topographic escarpment as well as along the streams, have emphasised scarps and knick-points, further supporting the occurrence of very recent morphogenic activity. In the last section, the structural, morphological and archaeological data are compared with the already existing seismological data and their integrated analysis indicates that the Nea Anchialos Fault System has been active since Lower(?)-Middle Pleistocene.JCR Journalope
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
Some remarks on water resources degradation and ground fissures formation in Thessaly, Greece
No full text(i.e. low precipitations) affecting the Aegean Region and the huge increase of the cotton cultivation in large sectors of Thessaly, central Greece, forced people to search for new water resources to provide the needs. Accordingly, during the seventies and eighties, the synergy of the natural phenomenon with the inappropriate agricultural choice, was coupled with the drilling of an almost uncontrolled number of boreholes across the entire area. These water-wells that mainly exploit the alluvial multi-aquifer system of the Larissa Plain caused a significant downdrop of the piezometric level that critically exceeded the capacity to regenerate the underground natural hydraulic conditions. As a consequence, a quantitative and sometimes qualitative degradation of the water resources occurred. During the nineties, numerous ground fissures have been documented within the Larissa Plain. These superficial features have locally roduced important damages by creating open fractures in houses,
stores and infrastructures, dislocations and hollows across roads and even caused a road accident. The occurrence of the phenomenon more than once, the associated damages and the awareness of the general seismogenic character of Thessaly deeply frightened the inhabitants of the region and their Authorities. A common opinion is that the production of fissures is straightforwardly and directly elated to the general lowering of the piezometric level (Soulios, 1997). In the present research, we revised all available data in order to better understand the phenomenon and the cause-effect relationships
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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