Publication: Cálculo de magnitudes de esfuerzos mediante elementos finitos en el macizo de El Berrocal (Sistema Central Español)
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2005
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Instituto Geológico y Minero de España
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Abstract
Se ha analizado la distribución de las magnitudes de esfuerzos actuales mediante el método de los elementos finitos a lo largo de una sección NO-SE transversal al macizo granítico de El Berrocal (Sistema Central Español), en la que se incluye la superficie topográfica, las variaciones litológicas y las cargas tectónicas compresivas. La estructura geológica profunda se ha obtenido a partir de una modelización gravimétrica. En un modelo sencillo, con una reología media cortical y una topografía plana, se han establecido previamente las condiciones de contorno y las propiedades mecánicas de los materiales necesarias para reproducir estados de esfuerzos litostáticos y tectónicos con elementos finitos. Aplicando una carga vertical gravitacional y una carga horizontal litostática, sólo se obtienen esfuerzos verticales iguales a los horizontales si el coeficiente de Poisson es de 0,49. Cuando se incluye además una carga tectónica se consigue un estado de esfuerzos tectónicos en régimen compresivo. Sin embargo, al modelizar el caso real del macizo de El Berrocal, la carga topográfica produce una desviación de los esfuerzos respecto al estado litostático y para obtener un régimen compresivo hay que aplicar como mínimo un empuje tectónico de 13 MPa.
The orientation and magnitude of stresses along a NW-SE cross-section of the Southern Border of the Spanish Central System (the granitic massif of El Berrocal) has been calculated using the finite element technique. Topographic surface, lithological variations and the most recent compressional tectonic stresses have been considered. The geologic structure has been established by gravity modelling and geological data. Firstly, a finite element model with an average crustal rheology and a flat topography has been performed in order to evaluate the influence of boundary conditions, and rheologic properties in the lithostatic and tectonic stress states. Thus, when vertical and horizontal lithostatic loads are applied, only vertical and horizontal stresses are equal to the weight of the overburden when the Poisson’s ratio is 0.49. If a tectonic load is added, a tectonic stress states reproduces a compressive regime. However, the topographic load in the El Berrocal massif produces a stress deviation from the lithostatic state and to get a compressional regime it is necessary to include a minimum tectonic push of 13 MPa.
The orientation and magnitude of stresses along a NW-SE cross-section of the Southern Border of the Spanish Central System (the granitic massif of El Berrocal) has been calculated using the finite element technique. Topographic surface, lithological variations and the most recent compressional tectonic stresses have been considered. The geologic structure has been established by gravity modelling and geological data. Firstly, a finite element model with an average crustal rheology and a flat topography has been performed in order to evaluate the influence of boundary conditions, and rheologic properties in the lithostatic and tectonic stress states. Thus, when vertical and horizontal lithostatic loads are applied, only vertical and horizontal stresses are equal to the weight of the overburden when the Poisson’s ratio is 0.49. If a tectonic load is added, a tectonic stress states reproduces a compressive regime. However, the topographic load in the El Berrocal massif produces a stress deviation from the lithostatic state and to get a compressional regime it is necessary to include a minimum tectonic push of 13 MPa.