On 25 January 2016, an earthquake of magnitude Mw=6.4 occurred at the southern part of the Alboran Sea, between southern Spain and northern Morocco. This shock was preceded by a foreshock (Mw=5.1) ...and followed by a long aftershock sequence. Focal mechanism of main shock has been estimated from slip inversion of body waves at teleseismic distances. Solution corresponds to left-lateral strike-slip motion, showing a complex bilateral rupture, formed by two sub-events, with most energy propagating along a plane oriented N30°E plane dipping to the NW. Relocation of larger events of the aftershock series, show two alignments of epicentres in NE-SW and NNE-SSW direction that intersect at the epicentre of the main shock. We have estimated the focal mechanisms of the largest aftershocks from moment tensor inversion at regional distances. We have obtained two families of focal mechanisms corresponding to strike slip for the NNE-SSW alignment and thrusting motion for the NE-SW alignment. Among the faults present in the area the Al Idrisi fault (or fault zone) may be a good candidate for the source of this earthquake. The study of Coulomb Failure Stress shows that it is possible that the 2016 earthquake was triggered by the previous nearby earthquakes of 1994 (Mw=5.8) and 2004 (Mw=6.3). The possible seismic reactivation of the central part of the Ibero-Maghrebian region is an open question, but it is clear that the occurrence of the 2016 earthquake confirms that from 1994 the seismicity of central part of IMR is increasing and that focal mechanism of largest earthquakes in this central part correspond to complex ruptures (or zone of fault).
•Relocation of largest aftershocks show two alignment of epicentres in NE-SW and NNW-SSW direction.•Two families of focal mechanism corresponding to strike-slip and thrusting motion.•The Al Idrisi fault may be a good candidate for the source of this shock.•The CFS shows a possible trigger effect of the 1994 and 2004 earthquakes on the 2016 shock.
From October 2012 to October 2013, a seismic swarm released more than 7000 microearthquakes beneath the eastern Guadalquivir foreland basin. From double-difference relocations of 501 events (md>1.5), ...we can image the active structures associated with this swarm. Most of the events occurred along two ~N–S trending lineaments separated ~1km. Relocation places most events at 4–6.5km depth in the Iberian-massif basement below the basin. Moment tensor inversion yields strike-slip mechanisms consistent with the hypocenter alignments, attributing left-lateral motion to the N–S structures and right-lateral motion to the ESE–WNW ones, in compliance with the ~NNW direction of the main compressive stress field in the central Betics. These structures respond to a vertical-axis bend in the mountain front associated with the protrusion of Sierra Cazorla east of the epicentral area. This bend is mimicked by concordant, gentle bends in the foreland units, which are evident from the surface geology as well as through structural elements like strike-slip faults, crisscrossing joints. In this context, the right-lateral shear zone responsible for the Torreperogil sequence is taking up deformation in the western limb of the foreland bend.
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•A seismic swarm provides significant tectonic information for a low seismicity area.•Relocation and field data relate the swarm source with orocline bending.•We do not find evidence for the previously proposed triggering of the sequence.
The thermal decomposition process of calcite particles (0.45–3.60mm average diameter), made up of porous agglomerates of very small CaCO3 microcrystals, was studied in the 975–1216K temperature ...range. The experiments were carried out under isothermal conditions in air atmosphere, in CO2 atmosphere, as well as in a gas stream comprising different concentrations of air and CO2.
An equation is proposed that relates the calcite conversion degree to both reaction time and operating conditions. The equation satisfactorily fits to the experimental results obtained in the entire tested range of particle sizes and temperatures in all the studied carbon dioxide concentrations.
This paper presents a comparative study of three- and four-point bending tests and diametral compression (DC) tests, used to measure the mechanical strength of green pressed compacts. The study has ...been conducted on pressed ceramic test pieces, formed at different pressing conditions. It was found that Weibull statistics largely explained the differences in the results of the three-point and four-point bending tests. However, Weibull statistics could not explain the much lower mechanical strength obtained with the diametral compression tests. The study establishes a correlation between the bending and DC tests; however, this correlation depends on moisture content, which is directly related to the plasticity of the piece. This finding confirms that the types of mechanical tests studied do not have the same sensitivity to the factors that lead to fracture. The differences in mechanical strength between the bending and DC tests were explained using a suitable fracture criterion (based on maximum strain) and plastic deformation.
Most industrial porcelain tiles suffer changes in their curvature after firing: such process is known as delayed curvature. One of the hypotheses used to explain this phenomenon is based on the ...relaxation of residual stresses by creep. In this study two types of industrial glazed porcelain tiles have been studied. One of them displayed delayed curvature after firing, whereas the other one presented a stable curvature. The main objective was to determine if the delayed curvatures were caused by the residual stresses generated during rapid industrial cooling. Both types of existing residual stresses (thermal stresses, caused by thermal gradients inside the tile during cooling, and body–glaze fit stresses, due to the thermal expansion mismatch between body and glaze) were measured, as well as related samples properties (elastic modulus, creep behaviour, thermal expansion). The results demonstrated that the residual stresses are not the main cause of the delayed curvature phenomenon.
Inappropriate mechanical properties of spray-dried powder compacts lead to significant green product losses, entailing considerable costs in ceramic tile manufacture as well as serious environmental ...problems. In addition, green strength can be indicative of how well a ceramic processing system is working.
In this study, granules were prepared by spray drying a red clay slurry used in floor tile manufacture. The resulting granules were characterised and their porosity, morphology, and mechanical behaviour were determined.
The study analyses the fracture properties of green ceramic materials using Linear Elastic Fracture Mechanics (LEFM), which has been widely used for fired materials, but whose application to green compacts has drawn much less attention. Two types of tests for determining fracture parameters (fracture toughness, fracture energy, and crack size) in green materials are also critically examined. Finally, the fracture parameters have been correlated to the microstructural characteristics of the compacts, in particular to granule size and the topography of the fracture.
Industrially fast-dried ceramic tiles were used to determine the variation of dried tile mechanical strength with storage time in a moisture-free container. Dried tile mechanical strength rose with ...storage time under these conditions. Under the most favourable conditions, dry mechanical strength increased by up to 60% of the initial value. The reason for the rise in mechanical strength is attributed to the relaxation of stresses that develop during rapid industrial drying. A model was derived making the assumption that on exiting the dryer, the tile acts as a Maxwell linear viscoelastic system. The relation was determined between tile moisture content and mechanical strength, which was shown to be independent of whether tile moisture content was the result of drying wet tiles, or dried tile adsorption of ambient humidity. This relation and the stress relaxation model were used to derive a model that describes the evolution of dried tile mechanical strength during subsequent storage in ambient air very well.
El objetivo de este trabajo es estudiar el comportamiento a desgaste de distintos recubrimientos de WC sobre acero inoxidable mediante proyección por plasma atmosférico. Se proyectan dos tipos de ...polvos comerciales con base cobalto (12 %) y níquel (10 %), con el objeto de analizar la influencia de la matriz e incluso del espesor del recubrimiento. Los recubrimientos obtenidos se caracterizan microestructuralmente por microscopía electrónica de barrido y difracción de rayos X. La caracterización tribológica de los recubrimientos se realiza mediante ensayos pin-on-disc contra bolas cerámicas de alúmina (2.400 HV) y nitruro de silicio (1.600 HV), sin lubricación, obteniéndose las tasas de desgaste y la evolución del coeficiente de rozamiento. Las pistas de desgaste y los residuos generados se caracterizaron mediante Microscopía Electrónica de Barrido, MEB. Los resultados muestran diferentes mecanismos de desgaste en cada par de material ensayado en función de la matriz y de la naturaleza de la bola empleada en el ensayo, encontrándose mayores tasas de desgaste con bola de nitruro de silicio. En una segunda fase, se obtienen recubrimientos, con dos polvos base cobalto cuyos tamaños de partícula son micrométrico y nanométrico, respectivamente, con el objetivo de estudiar la influencia del tamaño de partícula inicial sobre las propiedades a desgaste del recubrimiento. Los resultados obtenidos ponen de manifiesto una mayor resistencia al desgaste de los recubrimientos obtenidos con polvos nanoestructurados, bajo condiciones de carga elevadas, mientras que para cargas bajas ambos recubrimientos presentan un comportamiento similar a pesar de las diferencias microestructurales apreciadas.
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