1,721,018 research outputs found
Structure and mechanics of carbonate-hosted fault zones: insights from lab, field, and virtual outcrop models
Full text linkCarbonate-hosted fault zones have been extensively studied in the recent past, due to their high socio-economic importance. In fact, they often host seismic sequences characterized by destructive earthquakes with shallow hypocentres (< 10 km) and high magnitude (MW > 5). Studies dealing with carbonate-hosted faults can therefore help a better assessment of the seismic risk of regions where seismicity occurs within thick carbonate successions. Moreover, since more than the half of the current hydrocarbon reserves are held within carbonate reservoirs, carbonate-hosted faults play a key role in hydrocarbon migration and storage. Being intimately related to fault mechanics and fluid flow, fault zone structure has been studied at different scales and using different techniques. Segmentation and/or bending of faults at sub- regional scales (1-10 km) can have important consequences on seismic rupture propagation and arrest. The outcrop-scale (10 m – 1 km) structure has fundamental implications for the fluid flow and fault mechanics. On one hand, the fault core vs. damage zone arrangement, and particularly fracture distribution within the latter, define the fault permeability structure. On the other hand, the deformation style (i.e., localized or/and distributed) can offer insights on the frictional properties of the fault zone (i.e., strong or/and weak fault). Microstructures collected on the principal slip zones (mm-thick zones that accommodates most of the displacement in faults) can shed light on the deformation mechanisms accommodating slip on faults. Finally, natural microstructures in principal slip zones can be associated with a specific mechanical behaviour and physical-chemical conditions (e.g., normal stress, slip velocity, saturating fluid, temperature) leveraging on their comparison with structures observed in principal slip zones retrieved from friction experiments.
Although many studies focused on carbonate-hosted faults structure during the last two decades, there is still a lot of work to do in order to accomplish the complete characterization of their structure and mechanics. One of the most challenging goal is to understand factors controlling fault zone structure.
In this thesis I investigate the factors controlling the geometry, kinematics, mechanics, and distribution of various components of fault zones: principal slip zones (chapter 2), subsidiary faults (chapter 3), and fractures (chapter 4).
In chapter 2, “Strength evolution of simulated carbonate-bearing faults: The role of normal stress and slip velocity”, I present the results obtained from a series of rock mechanics experiments, conducted to evaluate the friction of simulated carbonate-bearing faults in water- saturated conditions and for a wide range of normal stresses (from 5 to 120 MPa) and slip velocities (from 0.3 to 100 μm/s). Since the coexistence of structures related to pressure dependent (i.e., cataclastic) and pressure independent deformation processes (i.e., pressure- solution and granular plasticity) is common within natural carbonate-hosted faults exhumed from shallow seismogenic depths (< 6 km), I simulated the slip nucleation on simulated carbonate-bearing faults in order to constrain the boundary conditions (normal stress and slip velocity) that are necessary to activate pressure independent processes. The comparison between the mechanical results and the obtained microstructures allowed me to evaluate the effect of the activation of pressure independent deformation processes on friction. At low normal stresses (σ" ≤ 20 MPa) the deformation is accommodated by localized cataclastic grain size reduction, and friction is high (μ = 0.64). Pressure independent processes, especially pressure-solution, increase their contribution in accommodating slip with increasing normal stress and decreasing slip velocity. The activation of such processes produces an anastomosed foliation, accompanied by cementation, grain indentations, grain folding, and the formation of striated surfaces coated with nanograins. Friction decreases with an increasing contribution of pressure independent processes, reaching very low values (μ = 0.47) at the highest normal stress (σ" = 120 MPa) and lowest slip velocity (v = 0.3 μm/s) tested conditions. The results suggest that the activation of fluid assisted diffusion mass transfer (i.e., pressure-solution) and grain plasticity can significantly reduce the frictional strength of carbonate-bearing faults, facilitating the onset of fault slip.
In chapters 3, “Complex geometry and kinematics of subsidiary faults within a carbonate- hosted relay ramp”, and 4, “Lithological and structural control on fracture distribution within a carbonate-hosted relay ramp”, I investigate an exceptional exposure of a portion of a carbonate- hosted relay ramp damage zone, pertaining to the Tre Monti normal fault in the Central Apennines (Italy). The studied outcrop is located immediately at the footwall of the front fault segment. The relay ramps are zones of slip transfer between overlapping normal faults and represent a very challenging and interesting case-study. In fact, the mechanical interaction between the two faults promotes an increase in damage, representing a potential preferential pathway for fluids. Moreover, relay ramps can represent zones of stress field rotation.
For both the chapters I leveraged on the integration of traditional field techniques and interpretation of virtual outcrops. Three-dimensional digital reconstructions of outcrops (VOM: Virtual Outcrop Models, or DOM: Digital Outcrop Models) can be obtained from terrestrial laser scanner and/or photogrammetric surveys. Virtual outcrops are increasingly used in structural geology because they enhance our ability to collect data, allowing the exploration of inaccessible portions of the outcrop and the collection high-precision georeferenced dataset.
In chapter 3, the geometry and the kinematics of the subsidiary faults have been investigated. Minor faults show complex geometry and kinematics, having multiple attitudes each one characterized by highly variable kinematics. The fault slip analysis highlights that minor faults geometry and kinematics are not compatible neither with the overall dip-slip kinematics of the Tre Monti fault nor with the active regional extension occurring in the central Apennines. Conversely, a local stress field, retrieved from the kinematic inversion of the locally occurring right lateral slickenlines on the front fault segment, is able to explain most of the minor faults geometry and kinematics. Such a stress field is likely caused by the mechanical interaction between the fault segments bordering the relay ramp. The results obtained in this chapter highlight that the local stress field plays a key-role in the complex minor faults geometry and kinematics. Further complexity can be provided by the local scale temporal interaction with other stress.
Finally, in chapter 4, the fracture distribution within the relay-ramp damage zone is imaged through the integration of classical field techniques (i.e., scanlines), fracture counting on oriented rock samples, and interpretation of a virtual outcrop derived from an aero- photogrammetric survey. Fracture density increases with distance from the front segment of the relay ramp. The results also highlight a control of carbonate facies on fracturing, with supratidal and intertidal facies showing higher fracture density than subtidal limestones. This apparent anomalous pattern of fracture density, that increases moving away from a main fault segment, is related to two main factors. (1) Since moving away from the front segment (i.e., toward the centre of the relay ramp), also the number of subsidiary faults increases, the damage is likely related to the activity of subsidiary faults accompanying the development of the relay ramp. (2) The supratidal/intertidal facies content increases toward the centre of the relay ramp leading to an increase in fracture density.
This thesis furtherly emphasizes the importance of friction experiments and virtual outcrops in structural geology studies dealing with fault zone structure and mechanics. Friction experiments allowed to establish the effect of pressure insensitive deformation processes on the carbonate- faults mechanics through a direct comparison between microstructures and the mechanical behaviour. The employment of virtual outcrops enabled a very detailed mapping of subsidiary faults and fracture density within a carbonate-hosted damage zone, allowing the investigation of the factors that controls subsidiary faults geometry and kinematics, and fracture distribution
Prima segnalazione di noduli monzonitici a Stromboli (Isole Eolie, Italia meridionale): caratterizzazione petrografica e geochimica.
No full text
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
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
A multi-criteria model for the security assessment of large-infrastructure construction sites
Full text linkThe construction of large infrastructures (e.g., railways, gas pipelines or power grids) is increasingly facing widespread and violent opposition of radical environmentalist and ideological groups. Therefore, it is necessary to consider also the risk related to violent opposition actions when selecting construction sites. However, the classical paradigm of risk considering probability and impact hardly applies in this context, especially because of the difficulty of assessing probabilities, due to the lack of historical and/or reliable data. This paper develops a novel framework to support the selection of construction sites for infrastructure development, considering the risk of attacks by radical or ideologically motivated groups. The main originality is that the risk of attacks is evaluated considering the attractiveness of the different locations for the attackers, based on several criteria. Specifically, a novel multi-criteria decision model is introduced, which involves fourteen criteria related to the effort required to the opponents for performing the attack and to the expected outcomes of the attack in terms of potential damage to the targeted infrastructures and visibility of the action; moreover, the lifespan of the construction site and its influence on the possibility of an attack are taken into account. The criteria have been selected by a pool of forty-four Subject Matter Experts (SMEs), i.e., security managers and experts from the academia, industry and law enforcement. With such criteria, it is possible to construct a holistic index of attractiveness and quantify it by the Sparse Analytic Hierarchy Process (SAHP), based on the evaluations of the criteria provided by the pool of SMEs. The proposed methodology is applied to support the localization of the construction sites for the cross-border section of the Turin–Lyon High Speed and High Capacity Railway, including a new base-tunnel. Indeed, such an 8.6 billion Euro project has experienced strong opposition in Italy and, hence, security has become one of the main issues to be considered. The proposed model constitutes a decision aid tool to support the selection of construction plans, considering attractiveness and impact of attack
Aumentata suscettibilità alla perossidazione delle VLDL e HDL di pazienti diabetici non insulino-dipendenti: una possibile correlazione con la composizione in acidi grassi
No full textAlteration in fatty acid composition and susceptibility to peroxidation of very low density lipoproteins during diabetes mellitus
No full textAppropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
