1,720,973 research outputs found
Displacement-dependent microstructural and petrophysical properties of deformation bands and gouges in poorly lithified sandstone deformed at shallow burial depth (Crotone Basin, Italy)
Full text linkWe present the results of meso-and micro-structural analyses performed on fault-related soft-sediment deformation structures affecting poorly lithified, high-porosity siliciclastic sediments in the Crotone Basin, Southern Italy. The investigated extensional fault zone has a total displacement of ~90 m and juxtaposes marine clayish sediments in the hanging wall against arkosic to lithic arkosic sandstone in the footwall. In the footwall damage zone, deformation is achieved by a network of conjugate deformation bands, whereas the foliated fault core hosts cm-thick gouges. Deformation bands and black gouges accommodated displacement between 0.2 and 20 cm. Microstructural observations and quantitative image analysis pointed out that particulate flow operated during the early stages of faulting, followed by cataclasis after significant porosity loss. Mineralogy of clasts controlled grain-scale deformation mechanism: following this, feldspar experienced extensive intragranular crushing, while quartz grains were deformed mainly by splitting and abrasion. Permeability of pristine sandstone spans from 5.4 × 104 to 1.4 × 105 mD, while inside deformation bands is reduced by 1-2 orders of magnitude, reaching 3-4 orders of magnitude within fault gouges. Permeability drop inside the fault zone is related to the accommodated displacement along each deformation structure, potentially leading to hydraulic compartmentalization of high-porosity sandstone reservoir
Fingerprints and energy budget of the earthquake cycle in shallow sediments
No full textEarthquake cycle consists of alternating transient coseismic slip and long-lasting interseismic periods, covering a wide range of slip rates. Unveiling the deformational signature of earthquake cycles in major seismogenic fault systems is an essential component of seismic hazard evaluation. Here, we present a study combining field and microstructural data acquired from an extensional fault zone with ∼100 m displacement, developed in poorly lithified siliciclastic sediments of the Crotone Basin, South Italy. The maximum burial depth of faulted sediments did not exceed 500 m. Within the fault core a dense network of mutually cross-cutting dark gouges and deformation bands is hosted. Dark gouges and deformation bands display striking distinctive features (i.e., geometric arrangement, grain size distribution, displacement, fractal dimension and clast preferential orientation), suggesting their genesis occurred under different slip rates. Based on grain size distribution data, total surface energies required for dark gouge and deformation band development are in the order of 106 and 104 J/m2, respectively. These values are in accordance with literature fault scaling laws regarding moment magnitude-surface energy relationship. Our results support the genesis of deformation bands during inter-seismic, creeping fault activity periods, while dark gouges were produced during coseismic slip events
Cathodoluminescence, Raman and scanning electron microscopy with energy dispersion system mapping to unravel the mineralogy and texture of an altered Ca-Al-rich inclusion in Renazzo CR2 carbonaceous chondrite
Full text linkAn altered fluffy type A Ca-Al-rich inclusion in the CR2 Renazzo carbonaceous chondrite was examined by combined Raman, scanning electron microscopy with energy dispersion system (SEM-EDS) and cathodoluminescence (CL) mapping. Blue CL at 450 nm and orange emission at 600 nm were related to anorthite and calcite, respectively. Raman spectra were highly fluorescent, and only the stronger peaks of anorthite, clinopyroxene and calcite were observed. Raman-induced fluorescence emission was measured using the 632-nm Raman laser source, up to 850 nm, and used to chart the mineral phases. A fluorescence structured peak at 690 nm, split in three subpeaks at 678, 689 and 693 nm, was found; it is likely related to the fluorescence emission of Cr3+ from a fassaitic pyroxene in anorthite. Secondary pyroxene in the Wark–Lovering rim does not show the peak at 690 nm; the different fluorescence emission from the secondary rim and the pyroxene patches within anorthite could be a marker to spot the primary pyroxene. From combined imaging, the events in the altered chondrite could be sequenced. Starting from a pristine assemblage of spinel and melilite, with little fassaite, several alteration episodes occurred. Alteration in secondary anorthite, which could be mapped by the blue CL emission at 450 nm, was followed by alkalization, with rims of sodalite and nepheline, and subsequent formation of secondary clinopyroxene, encircling the inclusion. Widespread calcite alteration, present also in the matrix between chondrules, was the last recorded event
The influence of density on the fracture energy of AAC: From experimental investigation to the calibration of a cohesive law
Full text linkThe paper investigates cracking development in Autoclaved Aerated Concrete (AAC) elements, and clarifies the effect of density and porosity on material mechanical properties. To this purpose, 4 material densities are analyzed, ranging from 300 kg/m3 to 580 kg/m3, corresponding to a compressive strength interval approximately ranging from 1.90 MPa to 5.50 MPa. Fracture mechanics of AAC is analyzed by carrying out three-point bending tests on notched beams, similar to those commonly used for normal concrete elements. In these tests, the onset and development of crack pattern is studied by means of Digital Image Correlation technique. An almost linear dependence of fracture energy from density (and consequently from strength) is derived based on test results. Experimental results are used to calibrate a bi-linear cohesive law, whose parameters vary with material density, so allowing to differentiate fracture properties for structural (high density) and non-structural (low density) AAC elements in finite element analyses. The cohesive law parameters are calibrated by exploiting a neural network algorithm and interfacing MatLab with ABAQUS Finite Element package. The curves obtained for the 4 investigated densities, normalized with respect to material tensile strength, are almost superimposed on each other as if the stresses were scaled with porosity. The displacements corresponding to the knee of the curve are nearly coincident, independently from material density. The good agreement between experimental and numerical results proves the reliability of the proposed approach
Combined Effect of the Microstructure and Mechanical Behavior of Lateritic Soils in the Instability of a Road Cut Slope in Rwanda
No full textA very common hazard in Rwanda is represented by the instability of steep road cut slopes in lateritic soil. In its natural state, this material appears as a fine-grained weak and altered rock, generally in unsaturated conditions. Steep cut slopes made by this material could remain stable for a long time unless weathering weakens its mechanical behavior and heavy rainfall provokes a rapid landslide. This paper presents the results of an experimental investigation on the microstructural, petrophysical, and geotechnical properties of lateritic soil from a road cut slope located in Kabaya (Ngororero District—Rwanda), which was recently subjected to a landslide. The mechanical properties of the material are strictly related to the geological origin and history of the deposits, their formation environment, and weathering processes. These characteristics were revealed by peculiar microstructural features (micro-texture, porosity, and degree of alteration of original mineral paragenesis). The experimental investigations included identification and classification tests, direct shear tests on saturated samples, and swelling tests. This multidisciplinary approach provided insights into the relationship between geotechnical properties and the microstructural, petrophysical, and chemical characteristics of the altered rocks. This study showed how different levels of chemical alteration operated by weathering processes, in conjunction with brittle deformation related to the tectonic history, formed in the same site two shallow rock layers with similar macro-scale features and mechanical behaviors but markedly different microstructural and chemical properties. The innovative aspect of this research suggests an integrated multidisciplinary approach to considering microstructural aspects in addition to mechanical behavior in the slope stability analyses in lateritic soil. In particular, this study demonstrates the importance of such an approach since the failure mechanism is better explained if it is based on microstructural observations instead of considering the soil shear strength parameters only. This research helped to explain the formation of the landslide failure mechanism in a specific road cut slope, which could be assumed as representative of many other similar slopes subjected to landslides in Rwanda
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
Along- and across-strike variation of damage zone parameters in the Kornos-Aghios Ioannis normal fault, Lemnos Island, Greece
Full text linkThe Kornos-Aghios Ioannis Fault (KAIF) is an extensional fault system that deformed Lower Miocene volcanic rocks and Middle Eocene to Lower Miocene turbidite sandstones at shallow depth (<1 km). The fault system is exposed for about 10 km and consists of two major NW-SE-striking segments connected by an E-W-striking one. This structural architecture provides the opportunity to study the variation of damage zone parameters (i.e., damage zone width, fracture density, attitude of deformation structures, and fracture connectivity) in wall, tip and intersecting damage zones. The >122 m wide tip damage zone has a width greater than the wall and intersecting damage zones (72.6 and 50.9m, respectively) and exhibits the highest average fracture density recognized along the entire KAIF. In tip and intersecting damage zones, damage structures exhibit a larger azimuthal variability and hence a greater fracture connectivity (average number of connections per branch (CB) 1.60 and 1.53, respectively) compared to wall damage zones (average CB value 0.88). Accordingly, significant along-strike variations of damage zone parameters occur in the absence of a clear dependence on fault displacement. Particularly, fault intersections and tip regions represent areas of enhanced secondary permeability potentially controlling fluid circulation in the subsurface
Appropriate 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
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